Pilot information
The pilot’s logbook combined with the operator’s records showed a total flying experience of about 10,762 hours up until 30 December 2017. In the previous 90 and 30 days, the pilot had flown about 147 and 61 hours respectively. In the 72 hours before the day of the accident, he had flown 8.7 hours, all of which were in the Cessna 208 (amphibian). On 31 December, prior to the accident flight, he had flown about 2 hours,[5] all in VH-NOO (Table 1).
Pilot’s licence
The pilot commenced flying in Canada in 1997 and obtained his Canadian Commercial Pilot (Aeroplane) Licence in 1998. He also attained his multi-engine rating in 1998, floatplane endorsement and instrument ratings in 1999, and later his Air Transport Pilot (Aeroplane) Licence.
On 4 May 2012, the Civil Aviation Safety Authority (CASA) first issued the pilot with an Australian Commercial Pilot (Aeroplane) Licence. On return to Australia after working as a pilot overseas for about 3 years, CASA reissued the pilot with the licence on 21 March 2017, following a flight review and proficiency check. The pilot held the following ratings and endorsements:
- single and multi-engine aeroplane class ratings
- floatplane, manual propeller pitch control, gas turbine engine, and retractable undercarriage design feature endorsements
- multi‑engine instrument rating.
The pilot’s current CASA licence, found in the wreckage, was annotated indicating that he had conducted a single-engine aeroplane flight review on 29 June 2017, which was valid to 30 June 2019. The pilot held the appropriate licence, endorsements and ratings to conduct the flight.
The pilot held an Australian Class 1 Aviation Medical Certificate valid until 6 March 2018 and he was reported to have a high standard of health and fitness (refer to section titled Medical and pathological information).
At the time of the accident, the pilot also held valid Canadian and Republic of Maldives Airline Transport Pilot (Aeroplane) Licences.
Floatplane experience
The pilot’s logbook showed that the majority of his flying experience, at least 9,000 hours, was on floatplanes. He had experience on a number of float-equipped aircraft including the Cessna 172, 182, 185, 206 and 208, and the de Havilland Canada DHC-2 and DHC‑6. A summary of the pilot’s floatplane experience is below.
- From 2000 to 2002, commenced flying the Cessna 185 in Canada on a regular basis and conducted two flights in the DHC-2.
- In 2003, regularly flew the Cessna 206.
- Late-2004 to mid-2005, copilot on the DHC-6 in the Republic of Maldives.
- In 2007, returned to Canada flying the DHC-2 and Cessna 182. This included flying over high terrain, and operating to and from alpine lakes.
- From December 2011 to April 2014, with Sydney Seaplanes flying DHC-2 aircraft. The pilot accrued about 447 hours on VH-NOO and 351 hours on VH-AAM (the operator’s other DHC‑2).
- From mid-2014 to 2017, copilot and captain on the DHC-6 in the Republic of Maldives.
- In May 2017, recommenced with Sydney Seaplanes, accruing about 88 hours on VH‑NOO, 24 hours on VH-AAM, and about 269 hours on the Cessna 208 amphibious aircraft by the date of the accident (31 December 2017).
Training and checking
The operator was not required by the regulations to provide a training and checking organisation. However, after the cessation of their regular public transport service between Rose Bay and Newcastle, they maintained this approval and subsequently re-applied when it expired in October 2017. As a result, the operator’s training and checking regime included annual and biannual checks. The operator’s records indicated that, on his return to Australia in May 2017, the pilot successfully completed training and checks on the DHC-2 and Cessna 208 amphibious aircraft.
The operator’s records of checks conducted showed the pilot had completed the following.
Training and checks
- Pilot induction training, which included a theory and flight component.
- Engineering, data and performance questionnaires for each aircraft type, which assessed his knowledge of each aircraft, including the amphibious aspects of the Cessna 208.
- Operator proficiency check flight to a number of locations, including Cottage Point. The flight included emergency actions such as simulated engine failures after take-off and during cruise. The pilot was rated highly.
- Authorised landing area (ALA) authorisation check for various locations, including Cottage Point. This check assessed the pilot’s preparation for the flight; route knowledge; consideration for wires, water depths/channels, tidal effects; and awareness of en route facilities such as communications and emergency services. The check indicated a high standard of proficiency.
- Low-level manoeuvring proficiency check where the pilot was assessed as being at a high standard. This included:
- level steep turns in cruise configuration
- climbing steep turns in take-off configuration
- descending steep turns in landing configuration
- missed approach and go-around
- stall[7] and recovery in approach configuration
- manoeuvring at low-level after take-off and before landing.
- Non-technical skills training in communication, situational awareness, decision making and workload management.
- Civil Aviation Order 20.11 emergency procedures training on both the DHC-2 and Cessna 208.
Additional training
The pilot had completed a flight crew dangerous goods and non-dangerous goods course, engine compressor/turbine water wash course, fuel barge training, and a CASA alcohol and other drugs ‘managing risk’ training module. In addition, the pilot completed human factors flight operations refresher training in October 2017, which included subjects on information acquisition and processing; decision making; health, fatigue and stress; and operator incidents.
Carbon monoxide awareness
The CASA syllabus and standards for the obtainment of a Private Pilot (Aeroplane) Licence and Commercial Pilot (Aeroplane) Licence have long included the requirement for pilots to be aware of 'the sources, symptoms, effects and treatment of carbon monoxide poisoning'. Similarly, this was also a requirement by Transport Canada. Therefore, it was very likely that the pilot would have been aware of this hazard.
Cottage Point flight experience
According to the operator’s estimates, the pilot had significant experience operating at Cottage Point, having conducted at least 780 return flights there. The majority of these flights were in the DHC-2 aircraft. As such, the pilot was likely very familiar with the area and the routes between Cottage Point and Rose Bay.
On the day of the accident, the pilot had conducted seven flights in VH-NOO. This comprised two scenic flights over Sydney and five flights between Rose Bay and Cottage Point including one positioning flight without passengers (Table 1).
Table 1: Pilot's prior flights in VH-NOO on 31 December 2017
Departure time
|
Departure location
|
Route/destination
|
Flight time (minutes)
|
Persons on board
|
1000
|
Rose Bay
|
Sydney North
|
30
|
7
|
1100
|
Rose Bay
|
Sydney Highlights
|
15
|
7
|
1130
|
Rose Bay
|
Cottage Point
|
15
|
6
|
1200
|
Cottage Point
|
Rose Bay
|
15
|
3
|
1230
|
Rose Bay
|
Cottage Point
|
15
|
3
|
1300
|
Cottage Point
|
Rose Bay
|
15
|
1
|
1330
|
Rose Bay
|
Cottage Point
|
15
|
5
|
Source: Sydney Seaplanes
Operator observations of pilot’s approach to safety
The operator’s Chief Pilot stated that the pilot had good aircraft handling skills and was conservative with his decision-making. A previous Chief Pilot for the operator also indicated that, while he had not flown with the pilot, he was a reliable, steady operator who did not take risks, and had a very strong attitude to safety. The pilot was described by his work colleagues as being:
- very diligent and methodical
- very meticulous, always correcting small things
- a safe pilot who had all the experience behind him; he had no issues with grounding an aircraft and was safety ‘conscientious’.
72-hour history
The pilot’s specific personal routine in the 3 days prior to the accident was unknown as he lived in shared accommodation. However, a friend of the pilot reported that the pilot’s daily routine was regimented and consistent. The pilot exercised regularly, ate healthily, and would usually go to bed around 2100 on a work night. The friend further indicated that the pilot’s work schedule generally commenced between 0700 and 0800, and finished between 1700 and 1800. The pilot also attended the gym every 2-3 days.
Between 24 and 27 December, the pilot was rostered off work, but on the 27th he volunteered to fly to Proserpine, Queensland to pick up parts for the damaged Cessna 208 (refer to section titled Previous incident). He then flew in the 3 days leading up to the accident. His roster indicated that he had been on duty between 0800 and 1530 on 28 December, 0800 and 1330 on 29 December, and 1330 and 1830 on 30 December.
At about 0630 on the morning of the accident, the pilot phoned a long-term friend in Canada, whom he spoke to regularly. The friend reported that the conversation was normal and positive, and the pilot talked about his future personal and career plans.
On 31 December, the pilot was rostered for duty from 0900 to 1700, with his first flight scheduled for 1000. Work colleagues and persons at the Cottage Point restaurant and kiosk who conversed with the pilot prior to the accident flight and throughout the day reported that he appeared normal, up-beat and happy. This was consistent with comments received from passengers who flew with the pilot earlier and from photographs taken of the pilot throughout the day. The pilot was scheduled for another return flight to Cottage Point following the accident flight. That flight was scheduled to depart Cottage Point at 1600.
Previous incident
On the afternoon of 23 December 2017, the accident pilot was landing an amphibious Cessna 208 at Rose Bay when the aircraft encountered unexpected boat wake. The aircraft momentarily became airborne before impacting the water in a nose-low attitude. There were nil injuries, but the aircraft sustained damage to the landing gear and floats, rendering it unserviceable.
The operator’s internal review found that the incident was the result of ‘bad luck’. The area was busy with boat traffic, which limited the landing opportunities, and the choppy water conditions made it difficult to detect boat wake. While the incident was considered beyond the control of the pilot, a line check was conducted with the chief pilot on 28 December 2017. The Chief Pilot stated that the pilot operated and managed the flight to a high standard and complied with the relevant standard operating procedures, and approved him for a return to line flying. In addition, the operator distributed an email to all staff detailing the incident and providing additional guidance on operating in rough water conditions with significant boat traffic.
When discussing the incident with the operator, the pilot expressed disappointment and regret regarding the event and the associated damage sustained to the aircraft. However, the operator reported that they had emphasised to the pilot that the event could have occurred to any of their pilots and that there would not be any consequences. Further, the chief pilot and other company pilots all indicated that the incident did not appear to adversely affect the pilot. Similarly, the pilot's long-term friend, with whom he spoke to on the morning of the accident, also stated that they had discussed the incident and he did not believe that the pilot was concerned.
While there was some increase in the pressures for the operator having one aircraft out of service during the busiest time of the year, they managed this by re-scheduling, cancelling or moving passengers to other aircraft. They also had additional flights on their other C208 with ‘split’ shifts, having one pilot fly the aircraft in the morning and another in the afternoon. There was no evidence to indicate that this placed additional pressures on the pilot, or that it otherwise influenced the accident.
When interviewing the operator following the accident involving VH-NOO, they advised the ATSB about the above incident. It was established they had not initially reported the incident to the ATSB due to a misunderstanding in the reporting requirements for this particular event but recognised in hindsight that it should have been notified. However, it had been immediately reported to CASA. The ATSB noted that the reporting requirements, as detailed in the Transport Safety Investigation Regulations 2003, were included in their operations manual. Further, the operator had notified the ATSB of an event that occurred in 2019.
Aircraft information
General
VH-NOO was a float-equipped de Havilland DHC-2 Beaver, a predominantly all-metal high-wing aircraft manufactured in 1963 and first registered in Australia in 1964 (Figure 5). The DHC-2 was originally designed and manufactured by de Havilland Canada, but Viking Air Ltd has been the type certificate holder since 2006.The aircraft was powered by a Pratt & Whitney ‘Wasp Junior’ R-985 nine‑cylinder, single‑row, air‑cooled radial engine, which drove a Hartzell HC‑B3R30-4B three‑blade propeller.
Figure 5: de Havilland Canada DHC-2 Beaver floatplane, registered VH-NOO

Source: Sydney Seaplanes
The DHC-2 was designed and certified to carry one pilot and seven passengers in a three-row configuration. The front row seats were fitted with lap-sash seatbelts, where the lap portion attached to the seats and the shoulder (sash) belts attached to the aircraft structure through an inertia reel. The middle and rear seats were fitted with lap only seatbelts. The three lap belts on the middle row bench seat attached to the seat structure while the rear bench-seat lap belts attached to the aircraft floor structure.
The original undercarriage was removed and EDO model 679-4930 floats, auxiliary vertical fins and a water rudder steering system were fitted to the aircraft in 1999.
Ventilation to the VH-NOO cabin was via circular snap vents in both front fixed side windows, and by opening the pilot and front right sliding windows. The window position was secured by a friction lock mechanism. Two vents were installed in the rear cabin roof above the passenger seats (Figure 6). The aircraft was not fitted with ventilation louvres in the roof at the front of the cabin, which, according to Airag Aviation Services were standard fitment on DHC-2 aircraft. The aircraft did not have a cabin heating system.
Figure 6: VH-NOO cabin ventilation

Source: Sydney Seaplanes, annotated by the ATSB
Maintenance history
General maintenance
Apart from daily inspections, all maintenance was conducted by an external CASA approved maintenance organisation, Airag Aviation Services. The aircraft’s logbook statement indicated that it was maintained in accordance with the operator’s system of maintenance, approved by CASA. This program consisted of daily inspections; engine, airframe and float checks every 50 hours (‘A check’); engine and airframe ‘periodic’ inspections every 100 hours or 6 months (‘B check’); numerous other specialised inspections; and the requirement to comply with the appropriate airworthiness directives and Civil Aviation Orders.
A periodic inspection (100-hourly) of the aircraft was completed on 6 November 2017 and certified by a licensed aircraft maintenance engineer. At that time, other inspections and rectifications were carried out. To allow access for this work, the rudder, elevators and horizontal stabiliser were removed and subsequently refitted. A scheduled engine change was also carried out at this time and the corresponding inspection/s were certified by a licensed aircraft maintenance engineer. The replacement engine had been previously fitted to VH-AAM.
While fitted to VH-AAM, and with about 95 hours time‑in‑service since it was last overhauled, metal contamination was detected in the engine. The engine was disassembled, inspected and reassembled by an Federal Aviation Administration approved repair station in the United States (US) with nil defects evident. The repair station advised that insufficient cleaning of the engine at the last overhaul may have been the reason for the suspected metal contamination. The engine was test run satisfactorily before being returned and fitted to VH-NOO.
The current maintenance release was issued on 9 November 2017 at 21,786.6 hours total time‑in‑service.
On 11 December 2017, an ‘A Check’ was carried out and certified by a licensed aircraft maintenance engineer.at 21,835.9 hours total time-in-service. This check, conducted on the water, involved inspections of the engine including an oil change, airframe, floats and their associated components. Two minor additional maintenance items were carried out at this time, consisting of minor propeller leading edge repairs and rectification of a leak in the engine fuel primer system. The associated maintenance worksheets did not identify any further defects. At the time of the accident, the aircraft had flown 85.9 hours since the engine change and had a total time‑in‑service of 21,872.5 hours.
Engine exhaust system inspections
The DHC-2 engine exhaust system (collector ring) consisted of seven segments, each of which connected to the cylinder exhaust port on the engine by an integral elbow and flange. The segments terminated in a ‘Y’ piece, which connected to the exhaust ports of cylinders number 4 and 5, and to the exhaust tailpipe (Figure 7). Exhaust gases were expelled through this tailpipe on the lower, right side of the engine bay.
Each of the segments were joined using connecting sleeves (slip joints). These were a friction-fit join, which permit individual segment maintenance. They were designed to expand with heat when the exhaust system reaches operating temperature, effectively sealing the joints. A licensed aircraft maintenance engineer (LAME) from the maintenance organisation reported that the slip joints were generally not completely sealed.
Figure 7: DHC-2 exhaust collector ring

Source: Viking Air, annotated by the ATSB
The exhaust system for the DHC-2 was an ‘on-condition’ component and therefore its time‑in‑service was not tracked. The maintenance schedule for the aircraft required a periodic inspection of the entire exhaust system at the ‘B’ check or every 12 months. In addition to this, a scheduled inspection of the exhaust collector ring segments under the carburettor heater muff (cylinders number 6, 7, 8 and 9) was required under a CASA airworthiness directive (AD/DHC‑2/33) every 150 flight hours. According to the DHC-2 maintenance manual, minor cracks in the segments could be repaired by welding. However, if further cracking developed from these repair welds, the segment was to be replaced. It was also recommended that, if major breaks, cracks other than minor, or burning was detected, the segment should be replaced, and no attempt should be made to carry out the repair.
The maintenance organisation advised that this inspection was performed at every 100‑hourly, in conjunction with the ‘B’ check. The aircraft’s maintenance records indicated that this inspection was certified completed in November 2017 as part of the engine change. This included certification for:
- an overhaul of the exhaust system and heater muff assembly (as stated in the engine build‑up worksheets), which the maintenance organisation advised consisted of a thorough inspection
- fitment of new exhaust flange gaskets
- fitment of new exhaust ring and heater muff assembly locknuts.
The records did not indicate that any cracks had been identified, or repairs to the exhaust system were performed at that time. However, it was noted that the ‘Y’ section was replaced in June 2015, with one from another aircraft (history unknown).
Engine firewall and inspection
The firewall is a fireproof wall between the engine/accessory bay and aircraft cabin. The aircraft was fitted with both a main firewall between the accessory bay and cabin, and then an accessory firewall between the accessory and engine bays. The main firewall was fitted with two panels, to allow easy access to the magnetos from within the cabin under the instrument panel (Figure 8). This provided for adjustment and/or maintenance of the magnetos with the engine installed. A gasket was bonded to each panel, and the panel was to be secured to the main firewall using four hex-head AN3-3A[7] (AN3) bolts (as specified by Viking Air) into a self-locking metal nut plate. There was no requirement by the manufacturer for the bolts to be torqued to a specific value and therefore, they were to be assembled as per standard airframe practice using proper judgment to avoid a collapsed fitting, but to ensure a tight joint.
An inspection of the main firewall for cracks and structural damage was required to be completed at the ‘B’ check. The maintenance records indicated that this was completed in November 2017. The access panels may have been used during the engine change. However, the LAME reported that the magnetos were already fitted to the engine prior to it being re-installed. Also, there was no indication that the magnetos were adjusted at that time or up to the time of the accident. Further, the maintenance organisation reported that the panels were generally only used for magneto maintenance rather than during an engine change.
It was noted that the left magneto was replaced in April 2017 and the right magneto was replaced in November 2016. The LAME indicated that the left magneto panel disturbance was on 8-9 June 2017 as a report of rough running engine attributed to a left magneto issue. The LAME also commented that the magnetos were not always inspected at a ‘B’ check, unless an issue was reported by one of the operator’s pilots. Sydney Seaplanes reported that all magneto maintenance was performed by the maintenance organisation, Airag Aviation Services.
On 28 September 2020, in response to the draft report, Airag Aviation Services indicated that there were other openings in the main firewall including those for mechanical engine controls. The ATSB noted that the openings for mechanical controls in the main firewall used a fire seal to minimise gaps and prevent the ingress of gases into the cabin.
Figure 8 shows the location of the magneto access panels in an exposed main firewall and is not representative of a main firewall in use.
Figure 8: DHC-2 main firewall with magneto access panels removed

Source: Sydney Seaplanes, annotated by the ATSB
Carbon monoxide detector
While not required, the aircraft was fitted with a disposable carbon monoxide (CO) chemical spot detector (refer to section titled Carbon monoxide information). The detector was affixed to the instrument panel, to the left of the pilot, and below the suction gauge (Figure 9).
The detector had a shelf-life of 3 years when unopened, but once removed from its packaging it had a useful life of 12 months. The detector fitted to the aircraft had a use-by date of 1 April 2018, written on the reverse side of the card.
Figure 9: Carbon monoxide detector fitted to VH-NOO

Source: Previous passenger
The operator advised that their usual practice was to annotate the installation date on the face of the detector in permanent ink, in the space provided (‘date opened’). They further advised that this date was their reference to determine the detectors serviceability and they replaced them as recommended by the manufacturer, during a scheduled maintenance event before the 1 year expiry date. However, no other records of fitment or monitoring of the detector was used by the operator.
Previous accident
On 15 November 1996, the aircraft was involved in a fatal accident.[8] At that time, the aircraft was registered as VH-IDI and configured for aerial agriculture operations including a fixed undercarriage for land-based operations.
The aircraft was rebuilt in 1999, during which the floats were fitted, converting it from a landplane to a floatplane. A Certificate of Airworthiness was issued and the aircraft re-entered service in December 1999, initially as VH-IDI and then registered as VH-NOO, in February 2000. Sydney Seaplanes acquired the aircraft in 2006. There was nothing to indicate the previous accident or the rebuild of this airframe 18 years prior had any connection with this accident.
Aircraft system controls
The location of the key aircraft system controls in VH-NOO are detailed below (Figure 10).
- Engine controls: The propeller (left), throttle (middle) and mixture levers (right) were located in the engine control quadrant on the top of the pedestal. A friction control lock was located below each lever.
- Flight control system: The flight control system on the DHC-2 is conventionally operated by a control column and rudder pedals. VH-NOO was fitted with a single control column and dual rudder controls. The upper portion of the control column, including the hand wheel, could be positioned in front of either ththe balance of the aircraft e left (pilot) seat, or ‘thrown-over’ for use by a copilot in the right seat. This could be done during level cruising flight without disturbing the balance of the aircraft by unlatching the throw-over lock, which held it in position, and rotating the top portion of the control column from left to right. Rudder pedals were placed in front of the left and right forward seats, the left side having ‘toe pedals’ on the top for brake application (no longer required after float conversion) (Figure 11).
- Trim system: Trim tabs were fitted to the elevator and rudder, which could be adjusted through hand wheels on the cockpit roof.
- Flaps: The wing flap selector, UP and DOWN, and hydraulic hand pump were located between the front seats. Intermediate positions of the flaps were made by moving the selector to either the UP or DOWN position and then pumping the hand pump until the desired flap position (‘FULL’, ‘LAND’, ‘TOFF’ and ‘CLIMB’) was shown on an indicator located above the instrument panel.
- Fuel system: The aircraft was fitted with three fuel tanks (front, centre and rear) under the cabin floor. Fuel was fed to the engine from a single tank, with a selector located to the left of the instrument panel to control which tank fed fuel to the engine. The quantity in each tank was presented to the pilot on an indicator in the centre instrument panel. The aircraft was also fitted with optional ‘long range’ fuel tanks in each wingtip, which fed the forward tank under the action of gravity. The operator reported that they very rarely used the wingtip tanks.
Figure 10: VH-NOO cockpit showing the aircraft system controls

Source: Sydney Seaplanes, annotated by the ATSB
Figure 11: VH-NOO rudder and flap controls

Source: DHC-2 flight manual, annotated by the ATSB
Stalling
An aircraft’s wing is said to be ‘aerodynamically stalled’ when the airflow over the wing separates from the wing; that is, the airflow no longer follows the contour of the top surface of the wing. This results in a rapid loss of lift, which balances the weight of the aircraft, and the aircraft will rapidly descend. Unless the nose is held up, an aerodynamic stall will also normally result in the nose of the aircraft pitching down.
The characteristics of the aerodynamics of an aircraft wing are such that the airflow will separate and the wing stall when the angle of attack (the relative angle between the wing and the approaching airflow) reaches a critical value. Aerofoils of the type used on aircraft such as the DHC-2, typically stall at angles of attack of around 12-16°.
Most small aircraft do not have an instrument that indicates the aircraft’s angle of attack. However, the angle of attack at which the stall occurs may be referenced to an equivalent airspeed. The airspeed at which a stall will occur is not fixed to a single value, and varies depending upon the flap setting, aircraft weight and load factor.[9]The stall speeds for an aircraft are typically presented in the Aircraft Flight Manual. As the load factor increases with bank angle in a level turn,[10] the stall speeds are normally presented in relation to the bank angle.
The primary control for angle of attack is the aircraft’s elevator. Pulling back on the control column will increase the angle of attack and pushing forward will decrease the angle of attack. Recovery from a stall normally requires that the nose of the aircraft be lowered (pitched down) by reducing the back force on the control column and moving it forward.
The DHC-2 flight manual stated that the aircraft’s stall speed with nil and landing flaps selected was 60 mph (52 kt) and 45 mph (39 kt) respectively. The manual specifically stated that:
In tight turns, flight load factors may reach the limit loads, and may also increase the danger of an unintentional stall.
Figure 12 shows how the stall speed and load factor increase with the angle of bank with nil flap. The stall figures presented in ‘kt’ (in red) have been annotated by the ATSB.
Figure 12: Load factors and stall speed with increased angle of attack

Source: DHC-2 flight manual, annotated by the ATSB
Stall characteristics [11]
Under the controlled conditions of certification, the DHC-2 stall was described as being gentle. Specifically, the DHC-2 flight manual stated that:
The stall is gentle at all normal conditions of load and flap and may be anticipated by a slight vibration, which increases as flap is lowered. The aircraft will pitch if no yaw[12]is present. If yaw is permitted, the aircraft has a tendency to roll. Prompt corrective action must be initiated to prevent the roll from developing.
However, the stalling characteristics were more abrupt in a steep turn. Further, and similar to other aircraft, stalling under power in a steep turn could trigger an incipient spin with little to no indications of an impending stall (Transportation Safety Board of Canada, 2017). In addition, less than ideal conditions such as wind turbulence and unintended sideslip may aggravate the stall characteristics resulting in larger roll angles and increased altitude loss. Further, a pilot may not immediately recognise the condition if an aircraft is unintentionally stalled and an altitude loss of more than 100 ft may result (Transportation Safety Board of Canada, 2011).
A series of flight tests conducted in 1995 by Aeronautical Testing Service Inc. (reported by Transportation Safety Board of Canada, 2018) also found that the stall characteristics of the DHC‑2 were considered acceptable with a forward centre of gravity. However, with an aft centre of gravity, for a power-on stall, the characteristics were considered to be unacceptable by Aeronautical Testing Services. Similarly, the US Federal Aviation Administration also described the stall characteristics with a forward centre of gravity as being docile and predictable. Conversely, for an aft condition it was unstable and unpredictable, and often unrecoverable at low altitude.
The Transportation Safety Board (TSB) of Canada‘s investigation into a loss of control and collision with water involving a DHC-2 in November 2009 (A09P0397) discussed the stall characteristics of the aircraft. Specifically, they mentioned flight tests that had been conducted in 1992 and the results indicated that:
...When a wheel-equipped aircraft was stalled at a 30º bank angle, it pitched nose down and rolled both into and out of the turn. The maximum roll was 50º. The maximum altitude loss was 100 feet before a pilot, using the proper technique, regained controlled flight. The test pilot noted that the Beaver [DHC-2] displayed little or no pre-stall warning buffet.
The fact that the pre-stall buffet may not provide pilots with adequate warning of an impending stall was also highlighted in the TSB’s investigation into a DHC-2 floatplane accident in 2012 (A12O0071).
Stall warning
A stall warning system is independent of the pilot’s recognition of inherent aerodynamic qualities near the stall, such as buffeting, and provides a clear and distinguishable warning of an impending stall, aurally and/or visually.
During certification of the DHC-2 in the 1940s, a stall warning system was not included as it was considered that the aerodynamic buffeting near the stall was a clear and distinctive warning of an impending stall. As a result, the Canadian regulations (which referenced the British Civil Airworthiness Requirements) did not require an artificial stall warning system to be installed. However, current Canadian regulations, which apply only to newly designed aircraft, now require those aircraft to incorporate a stall warning system.
In relation to the stalling accident of a DHC-2 in British Columbia in 2016, the TSB (Transportation Safety Board of Canada, 2017) highlighted that:
To reduce the risk of losing control of the aircraft, the pilot must have an immediate, clear indication of an impending stall: immediate because it is urgent, and clear to prevent any possibility of mistaking the impending stall for another type of event…
Recommendations for fitment of a stall warning system
In 2008, following a 2007 DHC-2 accident in Alaska, the US Federal Aviation Administration recommended to Transport Canada (the certifying authority) the fitment of stall warning systems to all DHC-2 aircraft. While Transport Canada acknowledged the value of this recommendation, they indicated that these systems ‘were unlikely to be installed on existing DHC-2s without regulatory amendment’.
In mid-2014, Viking Air published a non-mandatory technical bulletin for the fitment of a stall warning system on DHC-2 aircraft. At the same time, Transport Canada issued a civil aviation safety alert (CASA 2014-02) providing information on the safety benefits of these systems. The alert also recommended that all owners and operators install artificial stall warning systems in those aircraft not originally equipped with such. However, in response, the system was installed on only four of the 223 commercially operated Canadian-registered DHC-2 aircraft (Transportation Safety Board of Canada, 2017).
Further, the TSB’s investigation (A15Q0120) into a 2015 DHC-2 accident highlighted the elevated risk of stalling at low altitude and recommended that Transport Canada require all commercially operated DHC-2 aircraft in Canada be equipped with a stall warning system (recommendation A17-01). Transport Canada agreed in principle with the recommendation and recognised that:
…stalls encountered during critical phases of flight often lead to disastrous consequences. Although the historical accident rate does not indicate that there is any particular stall-related problem with the DHC-2 Beaver when it is flown within its certified envelope, the installation of an Artificial Stall Warning System can enhance operational safety.
They further stated that:
Mandating the installation of a stall warning system on all commercially operated DHC-2 aircraft in Canada will require further study, evaluation, and justification by TC. In 2018, the department will initiate an in-depth examination of the issue, particularly to determine how many accidents would have been prevented by a functioning artificial stall warning system. Following this evaluation the department will determine the most effective means of addressing the risks underpinning this recommendation and then outline its plan and consult industry stakeholders.
By March 2019, Transport Canada had reviewed the TSB’s aviation occurrence database and identified 120 DHC-2 accidents between 2001 and 2016. Of these, 13 involved a stall in the accident sequence. In August 2019, a panel of experts in flight operations and flight testing was convened to examine the 13 accidents. From this, they identified only four where an artificial stall warning device may have been helpful in preventing the accident. They also noted that:
…the study demonstrated that in specific configurations, the DHC-2 provides little natural warning of an impending stall. In these configurations, even with a stall warning system installed, a stall occurs and gives the pilot little to no time to react and recover.
However, in the light of the panel's findings, Transport Canada 'determined that there is insufficient justification to proceed with mandating the installation of a stall warning system on all commercially-operated DHC-2 aircraft in Canada'. Although they will continue to recommend the voluntary installation of such systems as per Civil Aviation Safety Alert 2014-02.
At the time of the accident, VH-NOO was not fitted with a stall warning system and was not required to under Australian regulations.
Pre-flight checks – 31 December 2017
The majority of piston-engine aircraft have dual ignition systems, that is, two sets of spark plugs, where each set is supplied with electrical power from an associated magneto (normally designated ‘left’ or ‘right’). During ground testing prior to a flight, each magneto is switched off in turn to ascertain if either magneto is equally capable of sustaining ignition at typical in-flight power settings. For the DHC-2, the magneto drop when the engine operation on a single magneto (either left or right) is checked, should be no more than 100 revolutions per minute (rpm), with a maximum differential between the magnetos of 40 rpm in the case of the DHC-2.
The operator’s chief pilot reported that, when a magneto drop in excess of 100 rpm was experienced, it was common practice to run the engine at a moderate power setting for a few minutes and then re‑checked. If the drop was within limits, the flight could continue. However, if it remained in excess of the limits, maintenance personnel would be contacted. This was consistent with their operations manual, which indicated that pilots were not authorised to conduct maintenance on the magnetos, and was subsequently confirmed with the operator on 13 October 2020.
The operator’s pilots and a subject matter expert all mentioned that it was not uncommon for the DHC-2 to experience ‘wet’ magnetos from moisture such as rain, humidity or washing the aircraft. By running the engine as described by the chief pilot, the moisture would typically burn off and the magnetos would function as normal.
At 0954 on the morning of the accident, the accident pilot sent a text message to one of the dockhands indicating 'NOO left mag dropping 150'.[13]The chief pilot, who was not at work on that day, also had a missed call from the pilot, but he did not leave a message and there were no additional communications from the pilot regarding the issue. Further, maintenance personnel were not contacted. Therefore, there was no evidence to indicate that the issue had not been rectified by the pilot and operations from then on were considered to be normal. The pilot who flew the aircraft the day before, also recalled experiencing a minor magneto drop in excess of the allowable limit during his engine ground test. This was rectified by running the engine at a moderate power setting as described above.
Meteorological information
Bureau of Meteorology
The nearest Bureau of Meteorology automatic weather station (AWS) was located at Terrey Hills, about 11 km south-south-east of Jerusalem Bay.[14]Another AWS was located at Gosford about 22 km north-north-east of Jerusalem Bay.[15]At 1500 on the day of the accident, the Terrey Hills AWS recorded the wind at 13 km/h (about 7 kt) from the north-east and a temperature of 23.2 °C.
The Gosford station recorded the wind at 20 km/h (about 11 kt) from the east-north-east and a temperature of 23.8 °C. The Bureau of Meteorology analysed the meteorological conditions in the accident area and advised that:
- The forecast low-level winds at 1400 and 1700 showed that the winds near the surface were from the east, north-east at about 15 kt, moving around to the north.
- Weather radar imagery showed there was no rain in the area.
- Based on the height and orientation of the terrain in Jerusalem Bay, and the assumption that the wind flow was from the north-east at about 10-15 kt, the wind would have been flowing over the hills into the bay. Based on the wind strength, it was reasonable to assume that moderate turbulence due to orography would have been unlikely. However, light turbulence could not be discounted.
Bureau of Meteorology tidal recordings at the Ku-ring-gai Yacht Club (near Cottage Point), stated that it was low tide at 1400 indicating that the tide was in-coming (rising) at the time of the accident.
Other pilot observations
The pilot of VH-AAM, who departed Cottage Point shortly before VH-NOO, stated that the conditions were considered standard and estimated the wind was from the north-east at about 15‑20 kt, with an occasional gust. The water conditions were not choppy and no white caps were visible.
Interpretation of passenger photographs
The ATSB sought the opinion of several experienced floatplane pilots on the meteorological conditions based on the photographs taken by the passenger on board VH-NOO (Figure 1). Those pilots estimated that the conditions were:
- A 15-18 kt breeze on the water and was considered to be a standard day.
- The wind was 12-15 kt from the north, north-north-east. The wind was coming over the hills and onto the water, and you would expect some gusting and very minor windshear. The cloud was at 1,500 ft or higher.
- The wind was 10-15 kt, possibly up to 20 kt. There was overcast cloud,[16]probably at 3,000‑4,000 ft.
Witness observations
Witnesses in several locations (detailed below) provided varying accounts of the environmental conditions at the time of the accident, in particular, that relating to the wind conditions. It was possible that these differences were related to their position, local terrain-induced turbulence effects, boat wake, or possibly their experience on the water.
Cottage Point
Personnel at Cottage Point reported that the wind was ‘fairly strong’, about 15 kt from the north‑east. Another commented that it was not that windy and the aircraft were sitting comfortably on the pontoon outside the restaurant. A witness also at Cottage Point observed the aircraft take‑off and reported that the wind was ‘suddenly very gusty’.
Cowan Water
Witnesses positioned in more open waters (Cowan Water), reported some variability in the wind and water conditions. They described the wind ranging between gentle to very windy, and from the north-east at 10 kt to 25 kt. A witness positioned at Cottage Rock (Figure 3), reported that the
wind was from the east and there was a ‘strong blustery breeze’ at an estimated 20 kt gusting to 25 kt. He suggested that the aircraft could have been buffeted by the winds along the take-off path. The overall conditions were described as a sunny, warm day, with some cloud cover and good visibility.
With regard to the water conditions, some witnesses commented that it was reasonably calm while others reported that it was choppy and there were some whitecaps visible.
Jerusalem Bay
Witnesses positioned in Jerusalem Bay and Pinta Bay also indicated that it was a sunny, warm day, with some cloud cover and good visibility. The wind was from the north-east and was funnelling directly into Jerusalem Bay. This would have resulted in the aircraft experiencing a tailwind at the time it entered Jerusalem Bay.
The wind strength reported was variable, ranging from a ‘slight breeze’ to being ‘extremely windy’, and estimated to be between 5 kt and 22 kt. Some witnesses commented that the wind was constant, while others indicated that it was gusting, with one estimate of gusts up to 24-27 kt.
As Jerusalem Bay was more protected, the water conditions in the bay were calmer in comparison to Cowan Water.
Communications and radar data
It was common practice for the operator’s pilots to make radio broadcasts when departing Cottage Point, to alert other aircraft in the immediate vicinity of their presence and intentions.
A review of Airservices Australia audio recordings of the applicable air traffic control frequency between 1430 and the time of the accident did not identify any radio calls, either routine or emergency, broadcast by the pilot of VH-NOO. The first broadcast heard from the pilot of the operator’s other DHC-2 (VH-AAM), which departed Cottage Point about 10 minutes prior to VH‑NOO, was when he was in the Pittwater and northern beaches area. However, given the low altitude of the aircraft, any calls made while on the water, or while below the level of the surrounding terrain, would likely have been shielded by the local terrain and not picked up by the Airservices Australia receivers. Further, by the time VH‑NOO was taking-off, the pilot of VH‑AAM was on a different radio frequency and did not hear any radio calls from VH-NOO.
Within the cabin, all of the occupants wore headsets. The pilot wore a noise-cancelling headset[17] with a microphone so that he could make radio calls and talk to the passengers. The passenger headsets were not fitted with microphones; they could listen to the pilot, but could not communicate with him or broadcast externally. If the passengers wanted to communicate, they had to talk above the engine noise or tap the pilot on the shoulder to gain his attention.
A review of the Airservices surveillance data did not identify any radar returns in the vicinity, most likely due to terrain shielding. The lowest radar return observed in that area at other times was 700 ft. Airservices advised that there was nil notice to airmen[18] relevant to the area of operation leading up to, and on the day of the accident.
Recorded information
On board recording devices
Recording devices on VH-NOO
VH-NOO, which had a maximum take-off weight of 2,309 kg, was not equipped with either a cockpit voice recorder (CVR) or a flight data recorder (FDR), nor was it required to be. Further, there was no video equipment fitted to the aircraft, which may have been used to record the passengers’ experience of the flight.
Regulatory requirements
International Civil Aviation Organization (ICAO) Annex 6 Operation of aircraft[19] has recommendations and standards for the fitment of recorders to small aeroplanes (maximum take‑off weight less than 5,700 kg) used for commercial air transport. These, however, apply only to turbine-engine powered aircraft and those certificated after January 2016. Amendments to Annex 6 since 2012 have included additional provisions for the fitment of lightweight flight recorders including airborne image recording systems. Although ICAO has not recommended the fitment of lightweight recorders to commercial small aeroplanes without turbine engines, guidance in Annex 6 is that lightweight recorders can be used to fulfil this purpose.
The CASA requirements[20] for the fitment of recorders to small aircraft similarly only applies to turbine‑powered aircraft. They did not require the fitment of an FDR to any aircraft with a maximum take-off weight less than 5,700 kg, and required the fitment of a CVR to aircraft below 5,700 kg only if they were:
- pressurised; and
- turbine-powered by more than one engine; and
- of a type certificated in its country of manufacture for operation with more than 11 places (seats); and
- issued with its initial Australian Certificate of Airworthiness after 1 January 1988.
As none of these applied to VH-NOO, the aircraft was not required to be fitted with recording devices.
Historical perspective
On 10 June 1960, a Fokker F-27 aircraft, registered VH-TFB and operated by Trans Australia Airlines, was on a scheduled passenger service from Brisbane to Mackay in Queensland. When at Mackay, the crew attempted two approaches, but these were aborted due to low visibility conditions. However, on the third attempt to land, air traffic control advised the crew that they were cleared for a visual approach, but no further communications were received from the crew. About 5 hours later, aircraft wreckage was found floating on the ocean about 9 km from the airport. All 29 occupants were fatally injured.
The subsequent board of inquiry was unable to come to any definite conclusions as to what had contributed to the accident. However, they recommended that all aircraft the size of the F-27 and larger be fitted with flight data recorders. The Federal Government implemented this recommendation the following year. Australia was one of the first countries to introduce this requirement.
The benefits of onboard recording devices have long been recognised internationally as an invaluable tool for investigators in identifying the factors behind an accident and assisting with the identification of important safety issues.
Standards, practices and specifications for lightweight recorders
The retrofit of traditional crash protected flight recorders to lighter aircraft (below 5,700 kg) is costly and technically difficult. The Transportation Safety Board (TSB) of Canada noted in its investigation report (A11W0048) into a 2011 accident involving a de Havilland DHC-3 Otter:
Commercially operated aircraft weighing less than 5700 kg are usually not fitted at manufacture with the system infrastructure required to support an FDR, and conventional FDRs would require expensive modifications in order to be installed in this category of aircraft. Several affordable, stand-alone, lightweight flight recording systems that can record combined cockpit image, cockpit audio, aircraft parametric data, and/or data-link messages, and that require minimal modification to the aircraft to install, are currently being manufactured…
To address this, ICAO has developed guidance for lightweight recorders[21]in Annex 6 as an alternative to traditional FDR and CVR in smaller aircraft. ICAO refers to the specifications applicable to lightweight flight recorders in the European Organisation for Civil Aviation Equipment (or EUROCAE) document, Minimum Operational Performance Specifications for Flight Recording Systems (ED 155). This document defines:
….. the minimum specification to be met for aircraft required to carry lightweight flight recording systems [in Annex 6] which may record aircraft data, cockpit audio, airborne images or data-link messages in a robust recording medium primarily for the purposes of the investigation of an occurrence (accident or incident). It is applicable to robust on-board recording systems, ancillary equipment and their installation in aircraft.
…a combination of audio, data and cockpit image recordings will provide air safety investigators with the necessary information to better define the facts, conditions and circumstances of an occurrence, and to broaden the scope of the vitally important human factor aspects of investigations. Additionally, image recordings can capture other cockpit information that would otherwise be impractical or impossible to record.
Recent technological advancements have meant that airborne image recorders with additional capabilities are available on the market requiring only aircraft power to be connected. Devices with a compact high-resolution camera and microphone can be fitted under the cockpit ceiling. These devices can also contain a GPS receiver, electronic gyroscopes and accelerometers. The audio, video, location, attitude and acceleration information is recorded in a crash resistant memory and replicated on a removable memory card.
In addition to ICAO Annex 6 and EUROCAE ED-155, CASA also allowed operators to fit a lightweight recording device. Advisory circular AC 21-46, Airworthiness approval of avionic equipment, provided guidance and information on the fitment of this type of ‘required’ and ‘non‑required’ equipment, which included the ED-155 specifications.
Relevant ATSB investigations
A number of accident investigations undertaken by the ATSB, including a loss of control, controlled flight into terrain, and impact with water, have resulted in undetermined findings. This is generally the result of no physical evidence indicating a technical problem with the aircraft combined with the lack of witness and recorded data evidence. The availability of recorded data would have likely provided information about the events that led to the development of these accidents, and thereby possibly allowed for timely and appropriate safety action. Summaries of these are provided in Appendix C – On board recording devices. However, more recently, the ATSB’s investigation into a collision with terrain involving a Cessna 441 aircraft, near Renmark, South Australia in 2017 (ATSB investigation AO-2017-057) stated that:
The limited recorded flight information available to the investigation prevented a full analysis of the handling aspects and cockpit communications, This in turn restricted the extent to which the factors contributing to the accident could be analysed and the potential for identification of safety issues and areas for safety improvement.
Similarly, the TSB have also commented that there were ‘numerous [Canadian] examples of accident investigations involving small aircraft that were hampered by the lack of flight recorder data’.[22]However, there have been recent examples of investigations where the use of recording devices, although not crash protected, have greatly assisted in determining the contributing safety factors and ultimately the identification of safety issues. Examples have included a GoPro, mobile phone and camera. These accidents involved an aircraft structural failure, engine power loss and main rotor speed decay, and are summarised in Appendix C – On board recording devices.
Recommendations for the fitment of lightweight recording devices
On 28 July 2004, a Piper PA-31T Cheyenne aircraft, registered VH-TNP, with one pilot and five passengers, on a private, instrument flight rules flight from Bankstown, NSW to Benalla, Victoria collided with terrain 34 km south-east of Benalla. All occupants were fatally injured and the aircraft was destroyed (ATSB investigation AO-2008-050).
The experienced pilot was familiar with the aircraft and its navigation and autoflight systems, and had flown this route at least once a week. Despite this, the flight did not follow the usual route, but diverted south along the coast before tracking inland.
The ATSB noted that this investigation was severely hampered by the extent of destruction of the aircraft and the lack of recorded or other evidence. In particular, the investigation could not reconcile how a pilot would continue navigation by GPS with the alerts and warnings provided by the GPS receiver and the instrument indications.
The aircraft’s allowable take-off weight was 4,082 kg and it was not required to be fitted with an onboard recording device. However, the investigation noted that:
Australian regulations requiring the carriage of an FDR and/or a CVR have not changed since 1988. During the interim period, advances in technology have resulted in solid-state recorders that are smaller, lighter, use less power and require less maintenance than those manufactured before 1988. In that time there has been considerable change to US and European requirements for the carriage of recording devices and the US National Transportation Safety Board (NTSB) has included improved recorder systems on its ‘Most Wanted’ list for many years. At least one large US general aviation aircraft manufacturer has indicated that it may incorporate recording devices in its aircraft as standard equipment.
The report also cited a number of previous ATSB accident investigations involving multi-engine aircraft that were limited by a lack of factual information that onboard recording devices would have otherwise provided. These investigations involved a Beech 200, VH-FMN (200105769 – although the aircraft was fitted with a CVR); a Beech 200, VH-SKC (200003771); and a Piper Chieftain, VH‑MZK (200002157).
Therefore, on 02 Feb 2006 as a result of the Benalla accident, the ATSB recommended that CASA ‘review the requirements for the carriage of on-board recording devices in Australian registered aircraft as a consequence of technological developments’ (R20060004). The CASA response to the recommendation on 23 November 2008 advised.
As you would be aware, there has been extensive liaison between CASA and the ATSB on this matter over the last twelve months. I can now advise that CASA has completed its cost benefit analysis (CBA). The CBA results confirm CASA's initial view that there is no justification to mandate the carriage of recording devices in smaller aircraft. The analysis considered 7 categories of small aeroplane operations, from Low Capacity RPT and Charter, down to aerial work, business and private operations and did not find fitment justified on safety grounds.
CASA believes that the safety regulator's focus should be on passenger carrying operations and preventing accidents by fitment of new generation technologies such as Airborne Collision Avoidance:Systems, Terrain Avoidance and Warning Systems and Automatic Dependent Surveillance Broadcast equipment, rather than mandating fitment of OBR devices to assist in determining the cause of an accident.
The CBA determined that the industry was unlikely to make this investment on its own accord. The use of quick access recorders by larger airlines provides considerable economic and business benefits which outweigh the costs involved. With the recent emergence of low cost and light weight recorders for small aircraft it is expected that the take up of recorders may gather momentum over the next couple of years once suppliers become more active in the market and prices come down. In the interim, CASA will be monitoring voluntary fitment of OBRs.
The need for onboard recording devices in other than large aircraft has also been recognised by other investigation agencies, who have made various recommendations for these devices to be fitted. These agencies have included the US National Transportation Safety Board, Transportation Safety Board of Canada, United Kingdom (UK) Air Accidents Investigation Branch (AAIB), European Union Aviation Safety Agency and New Zealand Transport Accident Investigation Commission. Appendix C – On board recording devices details the reasoning for, and a summary of these recommendations.
Passenger camera
During the aircraft wreckage examination, a Canon EOS 40D digital single-lens reflex camera (DSLR) containing a compact flash (CF) memory card was found inside the cabin (Figure 13). The camera with an intact strap was found embedded in the mud on the ceiling of the inverted cabin. The camera was identified as belonging to the front right seat passenger.
Figure 13: Passenger camera as found in the aircraft (left) and CF card removal (right)

Source: ATSB
The memory card was cleaned and dried before X‑ray examination. Corrosion was identified and the card was unable to be read. The memory and controller chips were transplanted onto a donor memory card circuit board and successfully downloaded. The memory card contained 412 images.
The images included several taken before leaving Rose Bay, but did not include any photographs from the flight from Rose Bay to Cottage Point. Photographs were also taken while the passengers were at Cottage Point and when boarding the aircraft for the return flight.
The last series of photographs on the memory card were consistent with having been taken from the front right passenger seat. This contained 22 photographs taken during the taxi, take-off and initial climb, through either the front windscreen or the front right passenger window. Nine of those photos were taken while airborne over a period of 39 seconds.[23]
The last three photographs on the memory card were through the front windscreen with the aircraft in a right bank. The final photograph was when the aircraft was over Cowan Water and heading south towards Cowan Bay.
ATSB assessment of passenger photograph locations
The recovered passenger photographs were analysed by the ATSB using commercial camera tracking software[24] to estimate the position and altitude of the aircraft when each photograph was taken (Figure 14). The timing and location of the images was consistent with the two photographs taken by a witness on the river (Figure 2). The image positions were similar to NSW Police Force (the police) forensic imaging estimates[25] with the exception of the final photograph (412). The ATSB estimated that this photograph was taken at a more southerly position more towards Cowan Bay.
In addition, the images indicated that the aircraft initially climbed to an altitude of about 135 ft, but by the time of the last photograph, the aircraft had descended to about 98 ft.
Figure 14: Images taken by the front right seat passenger following take-off from Cottage Point during the accident flight, and used in the flightpath estimation

Source: Passenger camera, annotated by the ATSB
Table 2 details the timing and respective camera setting for each photograph taken by the passenger, and the estimated location of the aircraft (latitude, longitude and altitude).
Table 2: Camera setting, photograph direction, timing, location and altitude for comparison photographs
#.jpg
|
Time hhmm:ss[26]
|
Focal length[27][2]
|
Photo direction
|
Estimated latitude
|
Estimated longitude
|
Estimated altitude
|
404
|
1511:45
|
17 mm
|
Forward
|
33.600098°S
|
151.216291°E
|
38 ft
|
405
|
1511:45
|
17 mm
|
Forward
|
33.599865°S
|
151.216371°E
|
38 ft
|
406
|
1511:52
|
17 mm
|
Forward
|
33.598033°S
|
151.216926°E
|
67 ft
|
407
|
1512:02
|
17 mm
|
Right side
|
33.595773°S
|
151.220259°E
|
135 ft
|
408
|
1512:08
|
41 mm
|
Right side
|
33.594933°S
|
151.221451°E
|
131 ft
|
409
|
1512:08
|
41 mm
|
Right side
|
33.594791°S
|
151.221605°E
|
134 ft
|
410
|
1512:18
|
41 mm
|
Forward
|
33.594835°S
|
151.224664°E
|
104 ft
|
411
|
1512:18
|
41 mm
|
Forward
|
33.594873°S
|
151.224782°E
|
112 ft
|
412
|
1512:24
|
41 mm
|
Forward
|
33.597227°S
|
151.225413°E
|
98 ft
|
Source: ATSB
Using the information in Table 2, an approximate flight path was developed for the portion of the flight where camera images were available (Figure 15).
Figure 15: Estimated flight path derived from passenger images

Source: Google earth, annotated by the ATSB
Pilot and passengers’ mobile phones
The pilot’s mobile phone was found in the aircraft cabin, but the information on this phone was unable to be downloaded due to the extent of damage. A mobile phone belonging to a middle row passenger and one belonging to a rear seat passenger were recovered from the riverbed at the initial impact location. Data was able to be extracted from those passenger’s phones. Images
taken at Rose Bay just prior to boarding VH-NOO were correlated with the operator’s closed‑circuit television footage from the Rose Bay terminal and the front seat passenger’s DSLR camera. This established the timings of events from the DSLR camera. Photographs taken of the passengers on board the aircraft at 1502 were used to identify their seating positions. No photographs were taken on the phones during the accident flight.
Images of the pilot’s door ajar while engine operating
Examination of photographs taken by passengers on earlier flights at 1041 and 1202 (Figure 16) showed the aircraft with the pilot’s door ajar and window closed while the engine was operating when the aircraft was just commencing taxi. Closed-circuit television footage that captured the aircraft for a ten second period heading south during the 27 minute taxi along Cowan Creek immediately prior to the accident flight similarly showed the pilot’s window closed and door ajar (Figure 16). There were no images from the accident flight that indicated the position of the pilot’s door during the taxi.
Other company DHC-2 pilots advised that their routine was to open their sliding window rather than having the door ajar when ventilation in the cabin was required before take-off. Sydney Seaplanes indicated that taxiing with the door ajar was common practice in light non-airconditioned aircraft, especially in summer.
Figure 16: Pilot’s door ajar and window closed during previous flights and extended taxi just prior to accident flight

Source: VH-NOO passengers and resident of Cottage Point, annotated by the ATSB
Images of passenger door while engine operating
Examination of photographs taken by the passenger on the accident flight during the taxi and when airborne showed the aircraft with the passenger door and side window closed. Similarly, an 11 second segment of the closed-circuit television footage of the aircraft during the 27 minute taxi north along Cowan Creek immediately prior to the accident flight showed the passenger’s door and window closed.
Wreckage and impact information
Wreckage distribution
Witnesses observed the aircraft impact the water banked to the right in a nose-down attitude. The right wing tip and both float tips impacted the water first. The left wing and float tips separated from the fuselage and the aircraft became inverted. The left wing, shattered windscreen, mobile phones and float tips were found on the river bed about 95 m from the northern shoreline of Jerusalem Bay, indicating that this was likely close to the initial impact location. The right wing tip fuel tank and right front passenger door separated on impact and were recovered from the river surface.
The right wing and remainder of the floats remained with the inverted and partially submerged main fuselage, attached only by the control cables and strut structure. During the period when the main wreckage was floating, it drifted<[28]about 75 m west into Jerusalem Bay before sinking near the entrance to Pinta Bay.
Figure 17: Location of the initial impact (circled) with the windscreen/left wing (1) and fuselage/tail/right wing floats (2) locations on the riverbed

Source: Google earth, annotated by the ATSB
Aircraft recovery
The aircraft came to rest on the floor of Jerusalem Bay. The main wreckage, comprising the cabin, tail, engine, floats and right wing was located near the entrance to Pinta Bay, 120 m from the northern shoreline at a depth of about 14 m and had been marked with a buoy by first responders. A significant quantity of fuel leaked from the aircraft and was observed in the water (Figure 18).
Figure 18: VH-NOO accident location in Jerusalem Bay (image taken 30 minutes after the accident)

Source: NSW Police Force, annotated by the ATSB
On 4 January 2018, the aircraft was recovered from the river during three ‘secure and lift’ operations under the supervision of the ATSB. These operations, undertaken by the police diving unit and a barge operated crane crew, retrieved:
- the main sections of both aircraft floats and the right wing
- the main fuselage including the engine, propeller, cabin and tail section
- the left wing.
The police conducted further diving operations at the initial impact location to retrieve the remaining aircraft debris and items on‑board.
Aircraft wreckage
The aircraft was transported to secure facilities at Bankstown Airport for further examination by the ATSB. A representative from the aircraft type certificate holder also attended. Examination of the aircraft wreckage indicated that (Figure 19):
- all major sections of the aircraft structures were recovered
- the front of the aircraft and float tips had been significantly damaged by upward and backward impact deformation
- both wings and the floats had separated from the fuselage
- both wing front spars had fractured in overload
- the right wing tip was substantially more damaged than the left wing tip and was consistent with contacting the water first
- the outboard section of the right wing had significant leading edge compression and upward bending deformation
- flight control continuity[29] was established, indicating no evidence of flight control disconnection issues prior to impact
- the throw-over control column was positioned on the left (pilot’s) side
- while the engine control quadrant was distorted, the throttle lever was found in the full aft ‘closed’ position, although it could not be discounted that this occurred during the impact sequence
- the fuel was selected to the centre tank and all fuel filler caps were found secured
- the oil filler cap in the cabin was not found in the wreckage,[31]there was no evidence of oil residue in the immediate vicinity, and the oil pressure gauge needle showed evidence of being in the normal range at impact
- the right front passenger door had separated
- the left front pilot door window snap vent was found in the partially open position
- the aircraft cabin was fitted with a disposable CO chemical spot detector affixed to the instrument panel; there was no ‘date opened’ annotated on the front of the detector
- there was no evidence of a birdstrike or collision with an object prior to take-off or in-flight
- there was no evidence of an in-flight break-up or pre-impact structural damage
- no foreign objects were found obstructing the rudder pedals or the control column.
Figure 19: Wreckage examination

Source: ATSB
Aircraft attitude at impact
The damage to the aircraft suggested that the aircraft entered the water with the aircraft body at a high angle of attack[1] relative to the direction of travel (Figure 20).
Figure 20: Aircraft descending with a high angle of attack

Source: CASA (2016), annotated by the ATSB
This high angle of attack was consistent with an aerodynamic stall and was evident by:
- Deformation of the nose area indicated that the engine and forward fuselage was deformed upward by about 13° (Figure 21). Wrinkling in the fuselage skins around the rear doors and windows also indicated significant upward bending of the forward fuselage (Figure 21).
Figure 21: Engine and forward fuselage deformation post-accident (top) with pre‑accident nose to rear fuselage angle (bottom)

Source: ATSB (upper) and image provided by previous passenger (lower)
- The right wing tip leading edge impact damage indicated a considerable upward pressure relative to the wing chord on impact. The wing tip indicated deformation of approximately 23° upwards (Figure 22).[32]
Figure 22: Right wing tip leading edge deformation (view from outboard)

Source: ATSB
- Wrinkles seen in the right wing skins indicated an upwards force was applied to the outboard wing at impact.
- Deformation of the inboard right wing leading edge and spar failure indicated a large pressure generated at the wing/fuselage intersection consistent with an aircraft sideslip at impact.
Aircraft configuration
The examination found that the flap actuator was extended to 13.375 inches (Figure 23), which was consistent with ‘climb’ flap of 15° (Figure 23 and Table 3) and the amount of flap visible in the witness photographs (Figure 2). The flap setting noted during the initial climb on a previous flight matched the setting observed in the witness photographs.
The rudder trim was selected to the right, indicative of normal operations in this aircraft type.[33] The elevator trim was in a neutral position, consistent with normal operations for the aircraft near the maximum take-off weight.[34]
Figure 23: Flap actuator

Source: ATSB
Table 3: Flap actuator measurements and corresponding flap settings
Wing flap setting
|
Degrees
|
Measurement (inches)
|
Cruise
|
0
|
12.5
|
Climb
|
15
|
13.45
|
Take-off
|
35
|
15.35
|
Landing
|
50
|
16.5
|
Full Flap
|
58
|
Measurement not provided<[35]
|
Source: Viking Air
Engine and propeller examinations
The engine and propeller examinations were conducted at separate maintenance facilities under ATSB supervision. The organisation that carried out the repairs/overhaul of the engine (Covington Aircraft) also attended the engine examination. These examinations did not identify any pre‑existing damage or conditions that may have contributed to the accident. Specifically, the examinations identified that:
- damage to the front of the engine casing was consistent with the aircraft impacting the water in a nose-down attitude
- an engine crank case crack (Figure 24) was consistent with impact damage
- some of the supercharger section impeller intermediate drive gear teeth had sheared in overload, which was consistent with the engine producing power at the time of the collision with water
- examination of the magnetos found damage consistent with immersion in salt water, which precluded function tests from being conducted; however, there was no evidence of any pre‑existing defects
- one propeller blade had slight forward bending at the tip, then mid-span rearward bending, which was typically consistent with the engine driving the propeller at impact
- one propeller blade had damage to the leading edge that corresponded with impact damage to the forward portion of one of the engine cylinders (Figure 24) and was rotated in such a manner that suggested a broken pitch link; this indicated that the propeller was being driven by the engine at the time of impact.
Advice received from the propeller manufacturer indicated that the damage observed was consistent with the propeller rotating under power at the time of impact, but at a ‘lower power condition’. They further indicated that this may not necessarily represent the power condition when the aircraft departed controlled flight as it could not be discounted that the throttle had been manipulated after this time. The exact power setting on impact was unable to be quantified.
Figure 24: Damage to the engine and propeller, oriented upside down

Source: ATSB
Examination of engine exhaust system
Following advice from the NSW State Coroner concerning CO exposure of the aircraft occupants in March 2020 (refer to section titled Medical and pathological information), the engine exhaust system was removed from the aircraft and examined at the ATSB’s technical facilities in Canberra. A summary of the main findings from the examination is provided below, for full details refer to Appendix D – Engine exhaust system (manifold) materials examination report.
The scope of the examination included a visual inspection of the exhaust system (manifold) to identify any areas of cracking, fracture or other defects. In addition, selected exhaust sections were sectioned and microscopically examined to determine if any cracking existed prior to the accident.
The visual examination identified that some of the exhaust segments, particularly from cylinders number 3 through to 5, were significantly deformed as a result of the impact. Four cracks or partial fractures were identified on these segments and selected for more detailed examination. There was one partial fracture away from this area, adjacent to the welded flange connection to the number 7 cylinder exhaust port, which was also further examined. The identified fractures are labelled A to E in Figure 25.
Figure 25: VH-NOO exhaust segments and location of exhaust tailpipe on aircraft (inset)

Note: Image includes carburettor heat muff. Cylinders numbered clockwise. Labels A through E shows location of fractures examined.
Source: ATSB and passenger, annotated by the ATSB
The Y-segment (D) had been repaired or re-manufactured, but the extent to which the repairs may have influenced the observed cracking could not be determined. Further, it was worth noting that the extent of the exhaust deformation meant that all of the cracks identified were wider (more ‘open’) than they would have been pre-accident.
The exhaust segments were sectioned and fractured in the ATSB laboratory to allow the identified fracture surfaces to be microscopically examined. Most of the fracture surfaces had two visibly‑distinct regions, where one region exhibited significantly more surface contamination or oxidation. The newer fracture region was considered to have occurred during the impact sequence, while the more contaminated fracture surface represented a crack that existed prior to the accident.
All of the cracks had emanated from corrosion adjacent to welded locations, likely due to sensitisation of the steel during normal operations. At least one of these cracks, at the number 7 cylinder exhaust flange, resulted in exhaust gases leaking into the engine bay. This was evident by the discolouration of the area adjacent to the crack and through chemical analysis of the fracture surface contamination, which was consistent with fuel combustion by-product (Figure 26).
While it was assessed that cracks were present, which pre-dated the accident, the age of the cracks or the speed at which they developed was not able to be determined.
In addition, there did not appear to be any obvious exhaust gas (CO) leakage at the slip joints, however, the examination was limited by the corroded and/or discoloured condition of the exhaust segments.
Figure 26: Cylinder 7 exhaust flange (detail E)

Source: ATSB
Examination of the magneto access panels
The engine main firewall was examined and the two magneto access panels were identified as a potential pathway for CO to enter the cabin. Both panels were found to be installed in the main firewall. The left panel had minor impact damage, while the right panel had significant distortion and impact damage (Figure 27).
Each panel was found to only have two of their four bolts installed, which resulted in four 3/16 inch (4.76 mm) diameter holes in the main firewall. The number of bolts fitted to the panels was further confirmed with photographs of the main firewall taken in January 2018 during the initial aircraft examination. This showed four bolts were missing from the panels at that time.
The nutplate at the 9 o‘clock position on the right panel was missing, but was later found on the cabin floor with the threaded portion of a bolt/screw in situ. The distortion to this panel and adjacent main firewall at this position was indicative of the bolt having been installed at the time of impact. Therefore, it was determined that the right panel had only one bolt missing at the time of the impact.
The number, condition and type of hardware securing the panels to the main firewall is discussed below.
Figure 27: VH-NOO main firewall to aircraft cabin with magneto access panels highlighted

Source: ATSB and Viking Air, annotated by the ATSB
Left (pilot’s) magneto access panel
Two bolts were installed at the 4 and 10 o’clock positions (when viewed from the cabin looking forward) in the left access panel, while the other two bolts were missing. One bolt (10 o’clock) was consistent with an AN3 bolt, but fitted with a ‘butterfly’ modification welded to the hex head. The other bolt (4 o’clock) was an unidentified wing-head screw, with a narrowed (necked) shank (Figure 28). The gasket was present and bonded to the panel but was noted to be in a deteriorated condition.
The installed bolts were tested in the missing bolt nutplates. They were able to be screwed all the way down by hand, however, there was little or no friction torque present in the nut. A new AN3 bolt was also tested and was able to be wound in by several threads before the resistance required the use of a spanner to be correctly tightened. Based on this, it was reasonable to conclude that the installed bolts were worn and the nutplates for the missing bolts were functional.
On 28 September 2020, in response to the draft report, Airag Aviation Services advised the ATSB that the left magneto access panel was positioned with the cut-out[36]in the incorrect orientation (Figure 27). They further stated that the panel ‘would never have been installed in such manner by itself’. However, a LAME from the maintenance organisation reported that a panel installed upside down would still ‘sit flat’.
Right side magneto access panel
Two bolts were installed at the 3 and 6 o’clock positions in the right access panel and two other bolts were missing from the 9 and 12 o’clock positions. As discussed above, it was established that only the bolt in the 12 o’clock position was missing at the time of the impact. The bolt in the 3 o’clock position was consistent with an AN3 bolt, with a ‘butterfly’ modification welded to the head. The other bolt (6 o’clock) was a stainless steel Phillips-head screw, similar to those used on the aircraft’s instrument panel. The gasket was installed, however, it was in a deteriorated condition.
The installed bolts and a new AN3 bolt were tested in the missing bolt nutplate, with the same result as identified for the left panel.
Figure 28: Magneto access panels, attaching hardware and gaskets

Source: ATSB
Magneto access panel bolt modifications
A LAME from Airag Aviation Services advised that the Phillips-head screw was fitted to the right magneto access panel when the aircraft was at Rose Bay to ‘fill a hole’ and that they had intended to replace this at a later stage.The LAME reported that, when they needed to replace the bolts, they would source them from surplus bolts in their toolbox. They further stated that AN3 bolts were available in stock.
The LAME also advised that the maintenance organisation utilised AN3 bolts, but had added the ‘butterfly’ head to assist with the fitment and removal of the bolts in the magneto access panels. Specifically, these bolts were used so they only had one item in their hand at any time, which minimised the possibility of losing the spanner in a confined space. They would then either tighten the bolt by hand or use a spanner for the final ‘nip up’ (torque). This modification was reportedly quite prevalent on aircraft used in the aerial agricultural industry. Viking Air advised they are ‘not aware of a situation where a “Wing Head” [‘butterfly’] bolt may be used in substitution for an AN-3 hex bolt’.
A modified AN3 bolt was tested to determine if a standard 3/8” spanner could be utilised for the final torque. The spanner could be used to tighten the bolt on two of the three sides, but it did not fit onto the third due to the modification (Figure 29).
Figure 29: Spanner accessibility on AN3 modified bolt

Source: ATSB
Magneto access panel bolts on other aircraft
The magneto access panels of three other DHC-2 aircraft currently, or most recently maintained by the same maintenance organisation as VH-NOO, were inspected on an opportunity basis in 2020. Through direct observation and from photographic evidence, the ATSB found that:
- One aircraft had one bolt missing and one loose on the left access panel, while all the bolts were in place on the right panel. The bolts in situ for both panels were unmodified AN3 bolts. At the time the aircraft was observed by the ATSB, it had flown about 36 hours since the last maintenance inspection was conducted. That inspection included replacing the left magneto.
- For the second aircraft, the ATSB only observed the left panel on the aircraft and noted that one bolt was missing. The remaining bolts had all been modified.
- While the third aircraft had been sold and transported to Canada, it was reported that nil maintenance had been performed in the intervening period. Photographic evidence showed that the panels were fitted with a combination of unmodified AN3 bolts and one machine screw. Further, one bolt was missing from each panel and one screw was broken.
Figure 30: Magneto access panel on exemplar DHC-2 aircraft with two 4.76 mm diameter holes (circled) following bolt removal

Source ATSB
Fuel testing
Fuel samples were collected by the police from the operator’s refuelling point at Rose Bay. The fuel was tested by the ATSB for the presence of water, with nil indications found. A visual inspection did not identify any particulate matter in the fuel. In addition, there were no reports of fuel quality concerns with the operator’s other DHC-2 aircraft utilising the same fuel source.
Witness observations
A number of witnesses were interviewed by the ATSB and the police, including two who were positioned in Cowan Creek, nine in Cowan Water, 11 in Pinta Bay and 13 in Jerusalem Bay. Figure 31 shows the approximate locations of these witnesses and the following provides a description of those observations. Note that these observations may have been influenced by the physical location of the witness, the environmental conditions, the short time frame within which the accident occurred, and their knowledge of aircraft operations.
Figure 31: Approximate location of witnesses

Note: In some circumstances, multiple witnesses were positioned at each point annotated on the map.
Source: Google earth, annotated by the ATSB
Aircraft stability
Cowan Creek and Cowan Water
Of the nine witnesses located on Cowan Water, two did not observe the turn, but four reported that it was performed smoothly, and the aircraft appeared normal and in control. Similarly, the two witnesses in Cowan Creek also reported that the aircraft appeared to be in a stable condition. Some of these witnesses relied on their previous observations of floatplanes for comparison. However, the three remaining witnesses on Cowan Water described the aircraft as:
- When the witness first saw the aircraft it was just south of Little Jerusalem Bay, it was a ‘little bit shaky’, which he considered normal as it was very windy. However, when the aircraft went overhead, it was flying smoothly.
- The witness observed the aircraft flying towards him from the direction of Jerusalem Bay and it appeared normal. However, when the aircraft was near Cowan Point, it conducted a near vertical manoeuvre, likened to a stunt aircraft. The aircraft appeared to lose airspeed, rolled right, came down and then levelled off at about 10 m above the water. The aircraft then continued into Jerusalem Bay and appeared normal. In the distance, he observed the aircraft conduct a similar turn, before impacting the water.
- While moving west in a small vessel, the witness observed the aircraft flying up from Cottage Point. Shortly after, he saw the aircraft conduct a ‘sharp’, ‘hasty’ right turn, which he believed was not normal from his previous observations. The turn was described as being aggressive and a bit turbulent rather than smooth or gentle. The witness considered that maybe the winds conditions had affected the aircraft. It then flew into Jerusalem Bay and ‘looked fine’.
Variation between witness reports is common and expected, and is affected by several factors (such as the angle of observation, opportunity to observe, focus of attention, familiarity with aviation operations, expectations, and elapsed time before reporting among other reasons). As such, it was likely that the normal turn reported by the majority of witnesses was most accurate.
Jerusalem Bay
In Jerusalem Bay, 6 of the 13 witnesses observed the aircraft flying along the bay while only 2 of the 11 witnesses in Pinta Bay saw the aircraft just prior to the steep turn was commenced. All of these witnesses reported that the aircraft appeared normal and in control. Specifically, the aircraft was described as:
- Being reasonably level and there did not appear to be anything unusual, there were no abrupt movements and it appeared to be in control.
- Flying in a straight line, and there was nothing unusual.
- Appearing normal and in trim.
- Multiple witnesses stated that it was being manoeuvred smoothly and there were no sudden movements.
- There were no indications suggesting that the aircraft was experiencing difficulties.
- Looking normal until it made the turn, it was flying relatively straight.
- Level and did not appear to be landing; it was not all over the place and there were no indications to suggest that there were any issues.
One witness was positioned on the northern side of Jerusalem Bay, but to the east of the accident location. That witness reported that, from his previous floatplane observations, the aircraft appeared normal, and there was nothing untoward. It was in control and was ‘perfectly stable’. He thought that the aircraft was intending to fly over the terrain at the end of the bay, although it did not appear to climb any higher. Several other witnesses had also considered that the aircraft was intending to climb above the terrain at the end of the bay.
Aircraft flight path
After the turn in Cowan Water was conducted, 13 witnesses saw the aircraft entering and flying along Jerusalem Bay, of which eight reported that it was maintaining straight‑and‑level. Two witnesses specifically stated that the aircraft was not climbing, while one witness believed it was either level or slightly descending. Two other witnesses who were travelling north up from the Cottage Point area observed the aircraft tracking to the west from Cowan Point into Jerusalem Bay. They both had an unobstructed side-on view of the aircraft and reported that it was descending at a slow steady angle, as if there was an intention to land.
Of those witnesses who observed the aircraft flying along Jerusalem Bay, 10 were able to comment on where the aircraft was positioned in the bay. From this, seven witnesses indicated that it was positioned on the southern side of the bay. Two witnesses reported that it was in the middle, while one stated it was on the northern side.
Height above the water
There was some disparity in the witness observations regarding the height of the aircraft above the water.[37] Of all the witnesses interviewed, 22 were able to provide an estimate of the aircraft’s height. Eleven stated that the aircraft was between 10 and 50 m (33-164 ft) above the water, while three indicated it was 100 m or more (above 328 ft). Where witnesses referenced the surrounding
terrain, six stated that the aircraft was between half-way and up to the top of the terrain, while two mentioned that it was either at, or above the terrain height.[38]
One witness was positioned on the northern side of Jerusalem Bay, and slightly west of Pinta Bay. Using their knowledge of the height of similar terrain in the area, the witness estimated that the aircraft was 30-50 m above the water. The witness further stated that the aircraft remained level or descended slightly. When it reached Pinta Bay, there was a yacht in the bay with a 15 m mast, and the aircraft was only slightly higher than that, about 25 m off the water.
The two witnesses who had an unobstructed side-on view of the aircraft flying west while they were travelling north from Cottage Point reported that the aircraft was 10-15 m above the water or half-way up Shark Rock Point (Figure 4).
Engine sound
Two witnesses in Cowan Water, and 15 in Jerusalem and Pinta Bays heard the aircraft and indicated that the engine sound was loud, it was revving hard, but it remained constant. It was not misfiring, fluctuating or spluttering and there were no indications to suggest that the aircraft was in trouble. Witnesses who had previously observed floatplanes also indicated that the sound was normal.
An eyewitness on a vessel not hear anything due to the wind. However, a family member on the nearby shore commented that she heard the aircraft and then the engine stopped, and 1‑2 seconds later, she heard the impact. Another witness also mentioned that for a split second before the impact it went quiet.
Steep turn in Jerusalem Bay
Of the 24 witnesses located in Jerusalem and Pinta Bays, nine did not observe the aircraft conduct the steep turn, three did not describe the extent of the turn, but the remaining 12 reported that it was a sudden steep turn, with a bank angle up to 80-90°.[39] Of those 12 witnesses, seven were in a suitable location to indicate that the aircraft had flown at least half-way through the turn before the nose dropped. Specifically, they described their observations as:
- Could see the underneath of the aircraft and it appeared shaped like a red cross.
- During the turn, the nose of the aircraft 'looked pretty level'. The aircraft then became obscured by the headland, at which time the wing tips were straight up and down, and the aircraft was about halfway through the turn.
- The aircraft banked 'hard', about 90° and could only see the floats and wings.
- The witnesses initially heard an aircraft and then turned to observe the underside of the aircraft; it was horizontal and in a 90° turn.
- When the aircraft was abeam Pinta Bay, it suddenly banked steeply right at an angle of about 80° and commenced a U-turn. When about half-way through the turn, the aircraft began to lose height and the turn appeared to tighten slightly. The aircraft then appeared to ‘slide out of the air’. When about 130-140° through the turn, the right wing impacted the water.
- The wings were initially in a near vertical position and then half-way through the turn, the nose lowered, at which point he realised the aircraft was in trouble.
Medical and pathological information
Pilot-related information
Aviation medical examinations
The pilot’s aviation medical records were provided by Transport Canada for the period 2008 to 2014. Overall, these examinations found that the pilot’s respiratory, cardiovascular and neurological systems were all normal, and that he was fit and healthy. Further, the records indicated that there was no family history of cardiovascular disease or hypertension.
The pilot’s Australian medical records were provided by CASA for the issue of his Class 1 Aviation Medical Certificate in 2012, 2013, 2014 and 2017. This also included a medical assessment from the Republic of Maldives. Similar to the above, the pilot was assessed as being fit and healthy, and there was no family history of heart disease under the age of 60 years. The records further stated that the pilot had:
- never experienced chest pain, palpitations or high blood pressure
- not been diagnosed with ischaemic[40]or coronary heart disease
- never experienced symptoms of shortness of breath or coughing up blood
- never had frequent severe headaches, head injury, unconsciousness, fits, faints, blackouts, funny turns, dizziness, tremors or weakness of the limbs.
Electrocardiograms
As part of the pilot’s annual medical examinations, he was required to have specialist tests dependent on his age. For example, on initial issue for a Class 1 medical, CASA required the pilot to have audio and eye examinations, an electrocardiogram (ECG),[41]and serum lipids (cholesterol) and blood glucose testing. Thereafter, an ECG was required at 25, 30, 32, 34, 36 and 38 years of age. Between 40-80 years an ECG was required yearly.
Most of the ECGs performed showed that the pilot had sinus bradycardia, which was a slower than normal heart rate typically resulting from good physical fitness, taking medications, or from a heart blockage. Hafeez et al. (2020) stated that sinus bradycardia was an ‘incidental finding’ in many healthy adults and was commonly found in athletes. Similarly, the Harvard Medical School (2019) also indicated that, bradycardia:
…even as low as 50 beats per minute, can be normal in athletes and other people who are physically active. In these people, regular exercise improves the heart’s ability to pump blood efficiently, so fewer heart contractions are required to supply the body’s needs.
However, it was also noted that bradycardia can also be a form of heart-rate abnormality. Those who do experience symptoms may present with fatigue, exercise intolerance, light headedness, dizziness, syncope (fainting or sudden temporary loss of consciousness) or presyncope (a feeling of light headedness), worsening of anginal symptoms, worsening of heart failure or cognitive slowing. However, the majority of individuals with sinus bradycardia do not experience symptoms (Hafeez et al., 2020).
Several of the pilot’s ECG tracings were reported with a range of abnormalities. This is usually due to the nature of embedded algorithms in ECG recording devices designed to generate automated ECG reports. Subsequent reviews of these reported ‘abnormalities’ by cardiologists deemed these ECG tracings to be within normal limits (and therefore acceptable for medical
certification to fly). In addition, in 2016, the pilot underwent an echocardiogram,[42] a stress test[43] and magnetic resonance imaging (MRI)[44]of the heart. The results of these were examined by a specialist who determined that the pilot was fit for all types of duties and training.
The ATSB engaged an aviation medical specialist who reviewed the above records and considered them to be unremarkable.[4] He also concluded that there was nothing identifiable in the pilot’s family history that raised any concerns about the pilot’s medical fitness.
General health
A review of some of the pilot’s personal medical records determined there was nothing of significance and there were no indications that he was taking any prescription medications. It was further established that the pilot exercised regularly, attended the gym every 2-3 days, and was considered to be very fit.
With regard to drinking and eating on the day of the accident, the pilot was observed in the morning filling up his water bottle. Further, after returning to Cottage Point at about 1400, the pilot went to the kiosk and purchased a coffee and food. A muesli bar wrapper was also found on the pilot. There was no evidence to indicate any concerns with regard to the pilot’s general health.
Post-mortem and toxicology results
A full post-mortem examination and toxicological analysis was performed on the pilot.[46] That examination established that he received fatal injuries sustained during the impact sequence. There was no evidence found to indicate that he had suffered from any pre-existing medical condition that would have contributed to the accident. Further, the initial toxicology results did not identify any substance that could have impaired the pilot’s performance (refer to section titled Supplemental toxicological testing for carbon monoxide exposure).
The ATSB’s aviation medical specialist reviewed the post-mortem findings and determined that the neuropathological and histological examinations of the pilot’s vital organs (including the heart and brain) did not identify any natural disease that could have caused or contributed to the accident.
The specialist also noted that there were no fractures to the pilot’s upper and lower extremities such as the hands and feet. However, the specialist could not say with certainty if this suggested that the pilot did not have his hands and feet on the controls at the time of the impact. Further, the nature of the injuries suggested that the pilot was alive at the time of the impact, although it was not possible to determine if he was conscious or unconscious. There were also indications that the pilot was wearing a lap-sash style seatbelt.
The examination further identified that the pilot had a thyroid condition. However, the pilot’s family were not aware of him having had any indicators of such a condition and he had never mentioned displaying any of the symptoms.
The results of the examination also suggested that the pilot possibly had mild dehydration, however, the clinical significance of this was uncertain.
In addition, when compared with the front seat passenger, the aviation medical specialist stated that the pilot’s injuries were more severe, possibly due to his proximity to the control column.
Cardiologist review
After reviewing the pilot’s aviation medical records, post-mortem and initial toxicology results, the ATSB’s aviation medical specialist concluded that there were no indications of a pre‑existing condition that could have caused or contributed to the accident. However, he was of the opinion that sudden cardiac death or cardiac incapacitation remained a possibility. Consequently, the ATSB engaged a specialist cardiologist to examine the pilot’s aviation medical records, ECGs, and post-mortem results.
The cardiologist concluded that, although the pilot’s ECGs showed an incomplete right bundle branch block,[47] this was quite a common finding in healthy people. Further, a number of cardiac conditions were able to be excluded from the ECG results, and overall, the ECGs and the medical records were considered to be those of a healthy individual. In addition, although the echocardiogram conducted in 2016 suggested mild right ventricular dilatation, the subsequent MRI did not show any abnormalities with the right ventricle. The exercise stress test, echocardiogram and MRI findings were all considered normal.
The cardiologist reviewed the pilot’s post-mortem and found no abnormalities with the heart to suggest a sudden incapacity.
In an attempt to identify any genetic patterns known to be associated with sudden cardiac death, analysis of the pilot’s post-mortem DNA was conducted. The results of that genetic analysis were negative and the cardiologist indicated that they were not useful in deciding or diagnosing any pathological condition causing sudden cardiac death.
Passenger-related information
Post-mortem and toxicology results
Limited post-mortem examinations were performed on the passengers along with toxicological analysis. The post-mortem examinations of the passengers established that they had succumbed to either the injuries sustained during the impact, or a combination of the injuries and subsequent immersion. The initial toxicology results for all the passengers were insignificant (refer to section titled Supplemental toxicological testing for carbon monoxide exposure).
There were indications that the front seat passenger was wearing a lap-sash seat belt at the time of the impact. As mentioned above, the ATSB’s aviation medical specialist also noted that this passenger had received lesser injuries when compared with the pilot.
There were no visible indications on both the middle row passengers regarding the presence of seatbelts (refer to section titled Seatbelt positions). The middle row left seat passenger had also sustained a significant skull fracture during the impact. The ATSB’s aviation medical specialist indicated that this most likely resulted from being restrained by a lap belt only and subsequent hyperflexion into the pilot’s seat or possibly the pilot during the initial stages of the impact sequence. The right seat passenger did not sustain similar injuries.
The injuries received by the rear seat passengers were consistent with wearing lap-style seat belts.
Medical history
A review of the passengers’ medical histories was conducted based on medical records obtained by the police and information provided by the next-of-kin. The eldest passenger was a diabetic, and was taking medication for this, and for cholesterol and blood pressure. Otherwise, this passenger was considered to be in good health. Overall, there were no apparent pre‑existing conditions that could have been expected to result in an in-flight medical event with the passengers.
In addition, the next-of-kin advised that one of the passengers was a regular smoker. Another passenger was also considered a social smoker, but it was very unlikely that this passenger would have smoked while at the restaurant.
Supplemental toxicological testing for carbon monoxide exposure
Test results
The ATSB was of the understanding that testing for carbon monoxide (CO) exposure was conducted as part of the initial toxicology examinations performed on the aircraft’s occupants. However, during the internal review process of the draft investigation report, the ATSB’s aviation medical specialist recommended that this be confirmed with NSW Health Pathology on behalf of the NSW State Coroner. The ATSB were subsequently advised that CO testing was not part of the standard toxicological testing. As such, testing of the occupants retained blood samples was conducted and the results provided in March 2020. Those results found that the pilot, and the youngest and eldest passengers had 11, 10 and 9 per cent respectively of carboxyhaemoglobin (COHb) in their blood. The other three passengers each had 4 per cent COHb.
The levels of COHb detected in relation to the occupants’ seating position within the aircraft cabin are shown in Figure 32. The significance of these results is discussed further in the section titled Physical symptoms and cognitive performance effects of carbon monoxide exposure.
Figure 32: Occupant seating positions and associated COHb levels

Source: ATSB
Regarding the levels identified in the two passengers, the forensic pathologist assisting the NSW Coroner indicated that children have a higher metabolic rate and breathe at a faster rate. Therefore, the youngest occupant would have likely taken more breaths in the same period of time as the adults. Similarly, the eldest occupant may have also been breathing at a faster rate for medical reasons or was less conditioned. In which case, this passenger would have likely been more affected by CO at lower levels than an otherwise healthy adult.
Reliability and validity of the testing
As the testing was conducted about 2 years after the accident, the reliability and validity of the blood samples and subsequent results were considered. The ATSB engaged a forensic and aviation pathology specialist to review the results of the CO testing, referred to forensic toxicology senior scientists at NSW Health Pathology, and received correspondence from the police who consulted their forensic pharmacologist.
NSW Health Pathology advised that they had used sodium dithionite to treat the post-mortem blood samples prior to the CO testing, to avoid potential methaemoglobin interference.[48] The police pharmacologist also stated that, given that sodium dithionate was used and the samples contained preservatives to reduce bacterial contamination effects, any changes to the blood CO levels were likely minimal. The ATSB’s forensic specialist also concluded that the test results were very likely accurate, given the preservation of the samples and the stability of COHb.
Further, NSW Health Pathology also noted that there has been many international studies on the stability of CO in clinical and post-mortem blood samples. The results of those studies have indicated that there is an insignificant change in CO concentration over 2 years, regardless of the preservation or storage method used (Ghanem et al., 2012; Kunsman et al., 2000).
In addition, NSW Health Pathology conducted an internal validation of their testing equipment and determined a measurement of uncertainty of CO analysis in blood of up to 5 per cent. For a COHb of 10 per cent, this would result in a maximum error of 0.5 per cent COHb. That is, 10 per cent COHb ± 0.5 per cent. The COHb levels detected in the occupants and associated measurement of uncertainty is shown in Table 4.
Table 4: Occupant COHb levels, error values, and adjusted levels
Occupant COHb level (%)
|
Error (%)
|
Adjusted occupant COHb level (%)
|
11
|
0.55
|
10.45-11.55
|
10
|
0.5
|
9.5-10.5
|
9
|
0.45
|
8.55-9.45
|
4
|
0.2
|
3.8-4.2
|
Source: ATSB
Medical specialist reviews
ATSB’s forensic and aviation pathology specialist
The ATSB’s forensic and aviation pathology specialist reviewed the results of the CO testing and amended post-mortem reports. Taking into account the circumstances of the accident, the specialist concluded that:
- Given the elevated levels of COHb found in the pilot (11 per cent) and two of the passengers (10 and 9 per cent), it was very likely that CO was present in the aircraft cabin.
- The physical symptoms and cognitive effects of CO exposure generally start to occur at COHb levels of around 10 per cent. This includes headaches, nausea, dizziness, confusion, and disorientation. These will become more severe with increasing COHb levels and duration. In this case, the pilot was almost certainly experiencing some, if not all of these.
- The passengers with 9 and 10 per cent COHb saturation levels were are also likely experiencing symptoms, possibly distracting the pilot.
- While the elevated levels were not fatal, they were certainly capable of resulting in pilot incapacitation[49] in the form of headaches, nausea, confusion, disorientation, and visual disturbance.
- There were no other medical factors identified that would have resulted in pilot incapacitation.
- The pathological findings indicated that the pilot was alive at the time of impact, but not necessarily conscious.
- The passengers with 4 per cent COHb saturation levels were unlikely to have been experiencing any physical symptoms.
- The finding of 4 per cent COHb found in the smoker was of less significance as they may usually have had elevated levels similar to this. However, it was also possible that this was due to CO exposure from within the cabin.
- The observed difference in COHb levels for the six occupants may have been related to their seating positions with regard to the source of CO and airflow patterns within the cabin, as well as their smoking history.
NSW Police forensic pharmacologist
As part of the police investigation into the accident, they consulted their forensic pharmacologist regarding the CO levels detected in the occupants. The pharmacologist concluded that, at a COHb concentration up to about 11 per cent, the potential physical symptoms could include headache, breathlessness, weakness and confusion. However, it was likely that the pilot would not have displayed any obvious symptoms, although it could not be completely discounted that some confusion and impairment of complex psychomotor skills would have been experienced. It was also possible that the pilot may have had adverse effects such as decreased vigilance, impaired visual perception and manual dexterity.
The pharmacologist further noted that the CO levels of the occupants may have differed due to their seating positions in relation to the source of CO and the individual’s susceptibility to CO, which can vary depending on their health.
Observations of previous passengers
The passengers who last flew with the pilot arrived at Cottage Point at about 1353. Those passengers reported that there was no indication that the pilot was experiencing any obvious symptoms or effects of CO exposure. They specifically stated that the pilot was articulate and animated when talking about his flying experiences. In addition, they also indicated that they did not experience any of the common physical symptoms associated with CO exposure such as nausea, dizziness, headaches and shortness of breath.
Observations of pilots who recently flew VH-NOO
A company pilot who flew the aircraft in the days leading up to the accident reported that he did not notice anything out of the ordinary. Similarly, another pilot indicated that he did not believe he experienced any of the typical symptoms or effects associated with CO exposure.
Survivability
The ATSB’s aviation medical specialist concluded that, given the extent of the impact forces and injuries sustained, it was very likely that the pilot and passengers would have been rendered unconscious as a result of the impact. This, combined with the severity of their injuries, meant that an underwater escape would not have been possible.
Survivability aspects
Pre-flight passenger brief
Closed-circuit television footage (video only) showed that, prior to boarding VH-NOO at Rose Bay, the passengers received a pre-flight safety briefing at the aircraft boarding pontoon. The operator stipulated that the following was to be included in the briefing:
- Seatbelts: Instructions on how to fasten, adjust, and release the seat belt, and that they were to be worn at all times throughout the flight while seated.
- Emergency exits: The location of the emergency exits, which in the DHC-2 was the two doors at the front of the aircraft and two in the middle row. The brief would also detail the location and use of the door handles. Specifically, that the middle row exit door handles were located behind the seats. Noting they would have to reach behind and alongside the seat to access the handle, also accessible to the rear seat passengers. Once passengers were seated inside the aircraft, the importance of locating the door handle was emphasised.
- Life jackets: A demonstration on how to correctly wear the life jacket, for it to be fastened around the waist over the seat belt, and to be worn at all times. The brief also discussed how to operate the life jacket in the event of an emergency and not to inflate the jacket until outside the aircraft.
- Single-pilot operations: Detail the requirement of the passenger occupying the front (copilot) seat not to interfere with the controls during the flight.
- Safety briefing cards: Safety briefing cards were located in the seat pockets, and described the location and operation of safety equipment.
- Other safety equipment and considerations: The location of motion sickness bags, first aid kits, fire extinguishers and survival equipment. Passengers were to be advised that headsets were provided for noise protection, electronic devices were permitted for use during the flight, the proper stowage of hand luggage under the seats, and smoking was not permitted.
Search and rescue response
The aircraft collided with the water just before 1514,[50]came to rest inverted and was partially submerged, with the tail and floats remaining visible above the waterline. Witnesses on nearby vessels immediately responded to render assistance. A number of those people dived into the water to access the cabin. However, they indicated that the aircraft was too deep, visibility was poor, and there did not appear to be any movement inside the aircraft.
A number of witnesses contacted the emergency services, who were en route to the accident within 10 minutes. In the meantime, as the aircraft was sinking, witnesses attached a buoy and rope to the tail to mark the accident location. The aircraft became completely submerged at 1526.
At 1532, the water police arrived, followed shortly after by Marine Rescue, and the rescue helicopter at 1541. A police dive team reached the accident site at 1636 and subsequently located the aircraft at a depth of 13.7 m. All occupants were recovered from the aircraft by early evening on the day of the accident.
Seatbelt positions and life jackets
One passenger was located in the front right seat next to the pilot, two passengers were on the bench seat in the middle row and two passengers in the rear bench seat.
The police divers found the pilot in his seat, but he was recovered without having to release his seatbelt. The front passenger, two passengers in the rear seat, and the passenger in the middle row left seat were found with their seatbelt clasps fastened. The police were uncertain if the middle row right passenger had his seatbelt fastened.
The ATSB reviewed the police dive video in an attempt to establish the state of the middle row right passenger’s seatbelt before the removal of the occupants from the cabin. The video showed that, when the divers first arrived at the aircraft, an unfastened seatbelt (buckle end) was observed moving freely in the water near the right cabin door. This seatbelt was associated with the middle row seat. As the left seat passenger’s seatbelt was still fastened, this seatbelt was either from the middle or right seat. However, the ATSB’s wreckage examination established that the seatbelt for the middle seat was not long enough to reach the right cabin door. Therefore, the unfastened seatbelt observed was that from the middle row right seat.
All occupants had their life jackets fitted and none had been inflated.
Crashworthiness
Survival of occupants in an aircraft accident requires tolerable deceleration forces, the continued existence of a liveable space inside the cabin, a restraint system to prevent injuries, and a means of escape and subsequent rescue for the occupants.
Impact severity
Impact severity increases with both impact speed and impact angle. Witnesses reported a steep flight path angle following the nose drop during the steep turn.
The US National Transportation Safety Board’s (NTSB) general aviation crashworthiness project provided guidance on the factors affecting the impact forces and indicated that differences in speed during an impact had a direct effect on the survivability of the impact. The guidance stated that the upper limit speed for survivable accidents was 60‑70 feet per second (fps).
Although it can be difficult to accurately estimate the bank angle of an aircraft by observation only, if the lower limit of the bank angle during the turn was 60° and the aircraft was configured with climb flaps, the aircraft had an airspeed that was at least the stall speed of the aircraft. This would provide a lower limit on the potential impact speed.
The stall speed decreases with the use of flaps. The flight manual did not list the stall speed for the aircraft configured with climb flaps, but did for a 1g stall with landing flaps. The 1g stall speed with landing flaps at maximum gross weight was listed as 45 mph, which was 75 per cent of the flaps up stall speed of 60 mph (52 kt). Using this same proportion for a 60° bank angle stall speed of 105 mph (refer Figure 12), the stalling speed at 60° bank angle when configured with landing flaps was estimated to be 0.75 x 105 = 79 mph (115 fps, 69 kt). Thus, the speed at impact was likely to be at least 115 fps. From Table 3, the climb and landing flap configurations are 15° and 50° flap deflection, respectively. Thus, the stall speed with climb flaps would be closer to the flap up stall speed than the landing flap stall speed, indicating that the speed at impact was likely to be even higher than the landing flap estimate.
Therefore, the accident impact speed was in the order of twice that considered to be a survivable impact, and hence, this accident was not considered to have been survivable.
Occupant restraint system
The pilot and front row passenger seats were both fitted with lap and shoulder restraints (three‑point lap‑sash seatbelts). The remaining six passenger seats were fitted with lap belts only. There was no regulatory requirement for the fitment of upper body restraints to other than the front row of seats for aircraft built before December 1986.[51]The passenger seats and seat attachment fittings had last been inspected on 6 November 2017 as per the requirements of CASA airworthiness directive AD/DHC-2/26 Amendment 1.
The ATSB’s examination of the occupant restraint system found:
- Front row: Both front row seats had broken away from their floor attachment points and the shoulder harness upper attachment points had failed in overload. The seatbacks were significantly deformed in a forward direction, indicative of contact from both middle row seat occupants.
- Middle row: The lap belts in the middle row were relatively undamaged and remained attached to the seat. The bench seat had separated from the floor as a result of overload of the seat‑to‑floor attachment points. The damage was indicative of a progressive failure from left to right (Figure 33). Damage to the seat indicated that, on the left side, the seat had collapsed vertically then forward, consistent with the seat being occupied. The seat collapse and subsequent twisting would have resulted in the feet separating from all three floor attachment points on the left side. The right seat support structure did not display evidence of collapsing in a vertical direction.
- Rear row: The rear row seat base support tube had broken and the attachment points for the seatbelts being used had failed in overload.
The occupants’ seat attachment and restraint overload failures indicated that the impact forces had exceeded the design limitations. These failures meant that the occupants would not have been sufficiently restrained during the final stages of the impact sequence.
Figure 33: Middle row seats showing structural damage and seatbelts

Source: ATSB
Organisational and management information
Sydney Seaplanes
Sydney Seaplanes had been operating since 2005. Based out of Rose Bay, they conduct scenic flights around the Sydney area, and fly to numerous restaurants and accommodation in the region, with approximately 27,000 passengers travelling per year. At the time of the accident, they had five aircraft: two DHC-2, two Cessna 208’s, and one Cessna 206.
Air operator’s certificate
A CASA air operator’s certificate (AOC) was re-issued to the operator on 25 June 2015, valid until 30 June 2018. The AOC schedule stipulated that the operator was authorised to conduct charter operations in the Cessna 208 and single-engine piston aircraft with a maximum take-off weight less than 5,700 kg, such as the DHC-2. In addition, for operations conducted in the authorised aircraft types above, the operator was permitted to conduct amphibious operations and operate aircraft fitted with float alighting gear.
Subsequent to the accident, the operator’s AOC was re-issued on 19 June 2018, valid until 30 June 2021, with the same provisions stipulated above.
CASA surveillance
On 19 September 2017, CASA had conducted an on-site audit of the operator, which included an examination of both airworthiness and flying operations, and an observation flight on the DHC‑2. The Civil Aviation Safety Authority found the operator to be compliant with the regulations and the activities observed were very efficiently conducted in a professional and confident manner. No safety concerns were raised by CASA as a result of their surveillance.
Airag Aviation Services
Airag Aviation Services (previous known as Aerial Agriculture Pty. Ltd.) has been operating since the 1950s and have been maintaining DHC-2 aircraft since that time. They held a valid CASA Certificate of Approval. Based at Bankstown Airport, their work primarily consisted of maintenance inspections, modifications, repairs, and restorations.
On 18 October 2017, CASA conducted an on-site audit of Airag Aviation Services. While the primary purpose of the audit was to introduce new CASA personnel, no findings were issued at that time.
Civil Aviation Safety Authority post-accident regulatory and safety review
Following the accident, CASA conducted a regulatory and safety review. The review found no evidence to suggest that the operator and maintenance provider were non‑compliant with the provisions of their respective AOC and Certificate of Approval. The review did not identify any immediate action that CASA considered in the interests of aviation safety.
Passenger information
VH-NOO passengers
The passengers were international visitors from the UK. Family members provided the police with a summary of the passengers’ background and character. From this, it was apparent that they were well-educated, highly respected individuals and were a close-knit family. Staff at the restaurant at Cottage Point also reported that there was nothing untoward in the passengers’ behaviour, and they were well-mannered, quiet and happy customers. This was consistent with photographs of the passengers taken while at Cottage Point. Further, a family member who regularly flew gliders reported that the male passengers had not shown any particular interest in flying.
Passenger route deviation requests
The operating pilots reported that any requests from passengers to deviate off their standard flight path were predominately from locals wanting to see their house rather than international passengers. Further, the pilots stated that they would be accommodating if it was along the flight path, but they would not deviate too far off track.
With regard to the accident pilot, the operator indicated that it would have been uncharacteristic for the pilot to deviate off track at the request of a passenger. They specifically noted that, several
weeks prior to the accident, the pilot had conducted a flight with one of the operator’s owners. The owner had requested that the pilot deviate from the standard flight path, however, he declined and continued with the flight as scheduled.
Pilot-passenger area
The operator’s pilots and other DHC-2 pilots reported that they had never been physically interfered with by a passenger, either intentionally or accidentally, sufficient to affect the operation of the aircraft. They also indicated that there was sufficient room in the cockpit for the pilot to operate the aircraft without issue. While it was noted that a pilot had to reach down in between the seats to manipulate the flap selector and hydraulic hand pump, there was adequate room to do this. A reconstruction flight carried out by the police (refer to section titled Steep turns) also identified that there was sufficient space between the pilot and front seat passenger to operate without interference.
General passenger conduct and medical events
The operator’s pilots indicated that they generally had no issues with the conduct of passengers, particularly from Cottage Point and they had never observed any aggressive behaviour.
Regarding in-flight medical events, if a passenger had motion sickness, they would consider landing. If a passenger experienced a serious medical issue, they would continue to a location such as Palm Beach or even Rose Bay where emergency services were more readily available.
Operational information
Cottage Point departure
Cottage Point is located at the junction of Cowan Creek, and Coal and Candle Creek in the Ku‑ring-gai Chase National Park, about 26 km north of Sydney Harbour. Cottage Point was considered one of the operator’s most popular destinations, which was about a 20 minute flight from Rose Bay.
The operator’s authorised landing area (ALA) register provided their pilots with details on each of the locations they operated to, including Cottage Point. This included information such as the recommended approach, go‑around and departure paths; environmental considerations; passenger facilities; and any limitations or potential hazards such as weather, wires, water depths/channels, tidal effects etc. The purpose of the register was to supplement a thorough inspection and assessment of the alighting area by the pilot prior to landing or departing.
Figure 34 shows the recommended flight paths for Cottage Point from the operator’s ALA register. The blue hatching and crossed‑lines represent the take-off area and departure paths respectively, while the approach paths and landing areas are shown in red. Specifically relating to the accident flight, the recommended take-off area was to the north-east of Cottage Point. After take-off, the initial departure path was to follow the river to the north-east passing Cowan Point.
Figure 34: Cottage Point diagram of the recommended initial departure paths from the ALA register

Source: Sydney Seaplanes, annotated by the ATSB (blue labels)
There was no specified route from Cottage Point to Rose Bay, but operating pilots indicated that there were several common routes used (Figure 35):
- One option was to continue tracking east along Cowan Water to the coast and then head south.
- Another, depending on the aircraft’s climb performance, was to continue east along Cowan Water to Refuge and America Bay, and then track to the south-east over the terrain.
- An alternative was to conduct a reversal turn in Cowan Water and follow the waterway back towards Cottage Point and depart via Coal and Candle Creek.
Company pilots that had conducted the reversal turn indicated that, to ensure that the required terrain clearance was achieved, they only did this when the aircraft’s weight was low or there were no passengers on board. They would also typically conduct the turn when in the vicinity of Fishermans or Hallets Beach. One of the company pilot's also reported previously observing the accident pilot conduct a right reversal turn in Little Jerusalem Bay and a left turn near Hallets Beach.
Another floatplane operator, who was not flying on the day, reported that he had performed this turn to the east of Jerusalem Bay near Little Shark Rock Point. On the day of the accident, Airservices Australia surveillance data showed that the pilot of VH-AAM (once) and the pilot of VH-NOO (twice) had returned via Coal and Candle Creek.[52] Photographs and video footage taken by passengers on one of these flights earlier in the day showed that the pilot of VH-NOO had conducted a reversal turn over Cowan Creek near Yeomans Bay. The second flight was a positioning flight without passengers from Cottage Point to Rose Bay.
There were no departure routes via Jerusalem Bay.
Figure 35: Cottage Point reported common departure paths to the north-east

Source: Google earth, annotated by the ATSB
The ALA register noted that there was limited VHF (very high frequency) radio communications in the Cottage Point area due to terrain shielding and that a relay of broadcasts may be possible using overflying aircraft. In addition, if the wind conditions exceeded 30 kt, the ALA was considered unusable.
Jerusalem Bay
General description
Jerusalem Bay is part of the Cowan Water, Hawkesbury River waterway (Figure 36). The bay is surrounded by the Ku-ring-gai Chase National Park and is popular with recreational boaters. It is about 2.3 km long, 600 m wide at its entrance, and progressively narrows with the terrain rising steeply to an elevation above 200 m (650 ft). On both the northern and southern banks, the terrain rises steeply with peaks of 200 m (650 ft). The distance from the accident site to the end of Jerusalem Bay at water level was about 1.2 km.
Figure 36: Jerusalem Bay topographic map (top) and image taken from drone footage looking west to the end of Jerusalem Bay (bottom)

Source: NSW Government Spatial Services, annotated by the ATSB (upper) and NSW Police Force (lower)
About 1 km into the bay on the southern shore is Pinta Bay. The elevation along the southern escarpment between Cowan Creek and Pinta Bay ranged from 54 m (177 ft) in the vicinity of Shark Rock Point to 67 m (220 ft) towards Pinta Bay (Figure 37).
Figure 37: Elevation profile of southern escarpment along Jerusalem Bay

Flying in Jerusalem Bay
Sydney Seaplanes personnel indicated that there was no operational need for the aircraft to be in the bay. The bay was not on their standard flight path and the terrain rose faster than the aircraft could climb. In addition, there was nothing in Jerusalem Bay from a sightseeing perspective.
The pilot’s work colleagues stated that the pilot was well aware of the bay and that it was a ‘dead end’ with high terrain. They further indicated that, if for some reason they flew into the bay, even with the tailwind, the conditions were suitable for landing. The chief pilot also advised that the DHC-2 only required about 200 m within which to land.
In terms of activity in the bay, one pilot reported that he had landed in the bay once before on a private flight. He further indicated that the only time he would fly down the bay was when coming from Berowra Waters to Cottage Point, where he would descend from the west into the bay and then land south in the Cottage Point area. He did note having previously seen a private ultralight floatplane in Jerusalem Bay.
Similarly, another floatplane operator indicated that he had landed and taken off in the bay possibly 4‑5 times dropping off/picking up people from a boat. However, he also stated that there was no operational reason to be flying in the bay when operating from Cottage Point.
Multiple witnesses who were familiar with floatplane operations in the area reported they had never observed an aircraft in Jerusalem Bay before. Some specifically stated that they had:
- seen aircraft flying above the terrain
- observed an aircraft drop people off in Pinta Bay
- seen aircraft normally track east toward the ocean
- not seen them flying that low before.
Vessel traffic in Jerusalem Bay
Witness reports and images taken as they approached the aircraft indicated that there were no vessels or obstructions in the main waterway. Vessels in Jerusalem Bay were either anchored on the northern shoreline, at the far end of the bay, or in Pinta Bay.
Weight and balance
Weight and balance for the flight
In accordance with the operator’s booking procedures, the passengers provided their individual weights at the time of booking the flight, about 4 weeks prior to the accident, which totalled 452 kg. The operator’s records showed that these weights were used by the pilot on the day of the flight to determine the pre-flight weight and balance. The pilot’s calculations indicated that the aircraft was below the maximum take-off weight of 2,309 kg when departing Cottage Point. The operator and ATSB independently calculated the aircraft’s take-off weight using the passenger supplied weights, and by estimating the fuel on board and baggage weights. The seating positions were ascertained from a review of the passenger photographs. Both confirmed that the calculated aircraft weight was below the maximum take-off weight and within the centre of gravity limits.
As part of the post-mortem process, the occupants were weighed. These weights were greater than those volunteered by the passengers. The forensic pathologist assisting the NSW State Coroner advised the ATSB that variations such as wet clothing, the life jacket, and the effects of immersion in water could account for no more than 5 kg additional per occupant. Taking this into consideration, the combined passenger weights for the flight (totalling 478 kg) were underestimated by at least 26 kg. It was noted that the difference between the pilot’s weight used for the pre-flight weight and balance calculation, and the post-mortem weight was 3kg. However, for consistency, the 5 kg was taken into account. Based on these revised occupant weights, the aircraft was found to be just below the maximum take-off weight when departing Cottage Point and the centre of gravity was at 283.5 kg.mm/1,000, which was within the forward (72 kg.mm/1,000) and aft (360 kg.mm/1,000) limits.
Volunteered passenger weights
The Civil Aviation Safety Authority’s Civil Aviation Advisory Publication (CAAP) 235-1(1), Standard passenger and baggage weights, provided guidance on the use of standard passenger weights (refer to section titled Standard passenger weights below) or actual weights obtained by weighing all the occupants. Further, the publication advised the use of actual rather than standard passenger weights in aircraft with less than seven seats to avoid overloading.
Other regulatory authorities allowed alternative means regarding the determination of passenger weights. For example, the Civil Aviation Authority of New Zealand (2011) required operators to establish a passenger’s weight by one of three methods: actual weights, standard weights pre-determined by the operator, or by ‘a weight that has been declared by the passenger plus an additional allowance of 4 kg’.
The US Federal Aviation Administration (2019) indicated that an operator may determine actual weights by weighing each passenger on a scale prior to the flight or asking each passenger for their weight and adding at least 10 lbs (4.5 kg) to account for clothing. They further stipulated that this allowance may further be increased dependant on the route or during certain seasons, such as winter.
Similarly, Transport Canada (2019) defined ‘actual weight’ as the weight derived by actually weighing a passenger just prior to boarding the flight. However, under certain circumstances, ‘volunteered’ or ‘estimated’ weights could be used. These were defined as:
(ii) Volunteered Weight: means weight obtained by asking the passenger for their weight, adding 4.5 kg (10 lb) to the disclosed weight then adding the allowances for personal clothing and carry-on baggage and using the resultant value as the passenger’s weight; or
(iii) Estimated Weight: means where actual weight is not available and volunteered weight is either not provided or is deemed to be understated; the operator may make a reasonable estimate of the passenger’s weight, then add the allowances of personal clothing and carry-on baggage and use the resultant value as the passenger’s weight.
As the DHC-2 had a seating capacity of eight, standard weights could have been used based on the Civil Aviation Advisory Publication guidance; however, the operator elected to use a more representative measure of weights, those supplied (volunteered) by the passengers. The operator did not routinely weigh the passengers prior to a flight. However, staff would conduct a visual assessment of a passenger’s weight during check-in and if they had any doubt, they would then weigh them using scales available at their Rose Bay terminal. For the accident flight, the volunteered passenger weights totalled 452 kg. If a minimum allowance of 4‑4.5 kg per passenger was applied, this would have resulted in a total weight of 472-474.5 kg.
The operator reported that they believed the use of volunteered passenger weights was common practice in the charter industry.
Standard passenger weights
When discussing the purpose of standard passenger weights, CASA’s advice stated that:
The use of the standard passenger weights will, in most cases, ensure that the gross weight of the aircraft does not exceed the maximum take-off weight or the maximum landing weight of the aircraft.
‘To keep the probability of overloading within acceptable limits’, CASA provided a sliding scale of standard passenger weights based on the general Australian population (Figure 38). This scale was grouped by an aircraft’s maximum seating capacity (including the crew) and differentiated between men and women. With regard to the most recent population weights, the Australian Bureau of Statistics (2018) National Health Survey found that the Australian adult male and female had average weights of 87 kg and 72 kg respectively. These weights were similar to the standard weights specified by CASA for an aircraft with a capacity of 7-9 seats (highlighted in
Figure 38). However, as the number of seats increased, the standard weights became more underestimated when compared with the survey.
Figure 38: CASA standard passenger weights

Source: CASA
If the operator had elected to use these standard weights for the accident flight (highlighted weights in Figure 38), the total passenger weight would have been 373 kg. This was 79 kg less than the weights volunteered by the passengers, and 105 kg less than the actual weights from weighing.
Aircraft performance calculations
Using an indicated airspeed consistent with a normal climb flap configuration, and taking into account the wind conditions, the ATSB estimated the groundspeed from during the turn in Cowan Water, entering Jerusalem Bay, and to the final turn. This was then used to estimate the time interval between these points as the:
- time from when the last passenger photograph was taken to entering Jerusalem Bay was about 23 seconds
- time from entering the bay until the commencement of the steep turn was about 24 seconds.
Therefore, the total time from the last passenger photograph to the commencement of the steep turn in Jerusalem Bay was about 47 seconds.
From the photographs taken by the passenger in the front seat and altitude estimates established by the ATSB and police (refer to section titled ATSB assessment of passenger photograph locations ), the ATSB determined that the aircraft’s average rate‑of‑climb was between 200-240 feet per minute (fpm). Using this, and the time estimates above, if the aircraft had continued to climb after the initial turn in Cowan Water, it should have been about 390-430 ft (119-131 m) above the water at the commencement of the steep turn in Jerusalem Bay. This would have been above the highest point along the southern escarpment, which was 220 ft (67 m).
Radius of turn estimates
At the position where the initial turn in Cowan Water was conducted there was a width of about 760 m available in which to turn the aircraft over water (Figure 39). The ATSB estimated that for the 380 m radius turn, at an indicated airspeed of 70-80 kt, the minimum angle of bank required was 20-25°. Witness photographs of the aircraft early in the turn indicated that the angle of bank at that time was about 15-20°.
At the location of the steep turn in Jerusalem Bay, there was a width of about 320 m available in which to manoeuvre over water (Figure 39). This 160 m radius turn would have required a minimum angle of bank of 41-49° to complete the turn at 70-80 kt. If the aircraft’s speed was higher, the angle of bank required would have also increased.
Of note, the ATSB were advised by an experienced pilot that, following the accident involving VH‑NOO, they had completed a turn in a DHC‑2 with two occupants, under controlled conditions[53] in the vicinity of Pinta Bay without incident.
Figure 39: Radius of turn in Jerusalem Bay (left) and Cowan Water (right)

Source: Google earth, annotated by the ATSB
Steep turns
When an aeroplane is flying straight-and-level, the total lift is directed vertically up and balances the weight of the aeroplane, which is directed towards the Earth (Figure 40 left). However, when an aeroplane is banked in a level turn, lift produced by the wing needs to balance both the weight and provide the force to turn the aeroplane. The lift produced by the wings acts perpendicular to the wing, so when banked, the vertical component needs to balance the weight of the aeroplane and the horizontal component turns the aeroplane, balancing the centrifugal force (Figure 40 right). As the weight of the aeroplane does not change, the vertical component remains constant, requiring the total lift to be greater than the amount for straight‑and‑level flight. If the lift is not increased, the aeroplane will turn due to the horizontal component, but the aeroplane will descend as the vertical component does not balance the weight of the aeroplane. As the angle of bank increases, the lift required to maintain a constant altitude also increases, requiring the pilot to apply back pressure on the elevator control.
Figure 40: Basic loads on an aeroplane during a level turn

Source: Federal Aviation Administration (2016)
When a pilot deflects the ailerons to bank the aeroplane, both lift and drag are increased on the raised wing and decreased on the lower wing. As a result, the aeroplane will yaw opposite to the direction of turn. To counter this, rudder (through manipulating the rudder pedals) and aileron inputs (rotating the control column wheel left or right) are applied simultaneously in the direction of turn, thereby producing a coordinated turn.
Steep turns are typically performed at bank angles between 45° and 60°, and require the appropriate application of engine power and increasing elevator back pressure (aft movement of the control column) to maintain altitude and airspeed during the turn. This was consistent with the comments provided by the operator’s pilots regarding steep turns in the DHC-2. They further emphasised the importance of ensuring that the aircraft was coordinated. Some also indicated that they did not believe the DHC-2 could maintain an 80-90° angle of bank turn.
Another experienced DHC-2 pilot reported that steep turns were very docile and the aircraft was relatively stable. However, it would require a significant amount of aft control pressure to maintain altitude. If aft control pressure was not applied, the aircraft would descend through the turn. Any turn above 45° angle of bank would require an increase in engine power, possibly climb power and above up to maximum continuous power to maintain airspeed and altitude.
Viking Air also indicated that, if aft movement on the control column was released during a turn, the aircraft would lose altitude. This was demonstrated in a reconstruction flight conducted by the police in VH-AAM. In that flight, the chief pilot was flying the aircraft and commenced a 60° angle of bank right turn. The chief pilot then removed his hands from the control column and the aircraft very quickly went into a nose down attitude and descended.
In addition, several experienced DHC-2 pilots specifically mentioned the amount and coordinated use of rudder when banking the DHC-2. One noted that it, in a turn, it was ‘almost impossible to fly the DHC‑2 accurately and safely without using the rudder’. He also stated that it would be possible to fly the aircraft without using the rudder, but the aircraft would become ‘terribly’ uncoordinated and would get close to a stall-spin situation.
Stalling
Stall accident statistics
The US Aircraft Owners and Pilots Association Air Safety Institute (2017) reviewed 2,015 stalling accidents that occurred in the US between 2000 and 2014, and found that ‘unintended stalls continue to be among the most common triggers of fatal accidents in light airplanes’. Specifically, the research found that, while pilots are taught to recognise, avoid and recover from a stall, they accounted for almost 25 per cent of the fatal accidents over the reporting period. An ‘overwhelming majority’ of unintended stalls involved personal flights, while they accounted for only 7 per cent of all commercial accidents. However, the study found that the number of stall accidents had reduced over the 15-year period.
With regard to survivability, the research found that aircraft altitude was known with reasonable certainty in 545 of the accidents. Of those accidents where the stall occurred at or below 50 ft, about 15 per cent resulted in fatalities. However, between 50 and 100 ft, about 50 per cent resulted in fatalities.
DHC-2 stall related occurrences
A search of the ATSB’s database since 2003 found nil stall-related DHC-2 occurrences similar to the circumstances of the accident flight involving VH-NOO. However, TSB Canada had previously investigated numerous DHC-2 accidents where a stall had been involved in the accident sequence.[54] A summary of those accidents are contained in Appendix B – Transportation Safety Board of Canada investigated DHC-2 stall occurrences. Two particular accidents with similar characteristics to this accident were identified.
In October 2016, a DHC-2 was being operated on a flight in British Columbia, Canada with a pilot and four passengers on board. About 24 minutes into the flight, the aircraft collided with terrain. The TSB’s investigation (A16P0186) found that the pilot had commenced a turn away from the hillside and as the angle of bank increased, the stall speed also increased and the aircraft subsequently stalled. The aircraft was not equipped with a stall warning system. That investigation also cited a number of other stall-related DHC-2 accidents between 1998 and 2015 where a stall warning system was not fitted.
In a 2015 accident (A15Q0120) a DHC-2 was on a 20 minute sightseeing flight with the pilot and five passengers. When on the return trip at 110 ft above ground level, the aircraft stalled in a steep turn. The aircraft descended vertically and collided with terrain. A review of the GPS data found that the increase in the aircraft’s angle of bank reduced the turn radius from 400 ft (122 m) to 275 ft (84 m), and the airspeed increased from 73 mph (63 kt) to 85 mph (74 kt) during the turn. When at an angle of bank of about 50° mid-turn, the airspeed reduced to 60 mph (52 kt), the aircraft had climbed to 175 ft and then it stalled.
Control of the aircraft from the front right seat
The aircraft was configured such that the aircraft could be controlled by a copilot from the front right seat. Normally, to operate from the front right seat requires that the upper portion of the control column, including the hand wheel, be placed in front of the right seat using the throw-over mechanism. However, the ATSB examined what level of control a front right seat occupant may have without the control column being moved from in front of the pilot.
The operator’s pilots reported that it was relatively easy for a person in the front right seat to manipulate the pilot’s controls to roll the aircraft left and right. However, it would be more challenging for that person to apply forward and aft movements on the control to change the aircraft’s pitch attitude.
Another experienced floatplane pilot commented that a strong person could manipulate the controls from the front right seat. Similarly, a person in the middle row of seats could reach over and manipulate the controls. That pilot also stated that, if the aircraft was appropriately trimmed, someone could possibly fly the aircraft in a straight-and-level position.
Carbon monoxide information
What is carbon monoxide?
Carbon monoxide is a colourless, odourless and tasteless gas. It is the by-product of the incomplete combustion of carbon containing materials, but is often associated with other gases
that do have an odour or colour. The Agency for Toxic Substances and Disease Registry (2012) stated that CO is produced from both human-made and natural sources, including from:
- the exhaust gases from vehicles, recreational watercraft and boats
- gas appliances, furnaces, wood burning stoves and fireplaces
- tobacco smoke, whether as a smoker or through passive smoking
- fuel-powered small engines and tools.
When inhaled, CO is absorbed into the bloodstream where it readily binds with the haemoglobin to form carboxyhaemoglobin or COHb. The binding affinity of CO for haemoglobin is 200-300 times more stronger than that for oxygen. Therefore, CO reduces the oxygen carrying capacity of the blood. In turn, this decreases the release of oxygen to the tissues, directly affecting those parts of the human physiology that rely on oxygen to function properly, such as the heart, brain and central nervous system.
An individual’s COHb levels increase as the duration and intensity of the CO exposure increases. Carbon monoxide has a half-life of 5-6 hours when at normal oxygen concentrations and 30-90 minutes when 100 per cent oxygen is administered (Kunsman et al., 2000). Baselt (2014) also indicated that the half-life for a resting adult at sea level was 4-5 hours, but this may be reduced to about 80 minutes with the administration of pure oxygen.
The amount of CO present can be determined by measuring either the CO levels in the ambient air or the COHb concentration in blood. The measuring devices available for aviation use and the significance of the COHb concentrations are discussed below (refer to sections titled Carbon monoxide detectors and Physical symptoms and cognitive performance effects of carbon monoxide exposure respectively).
Carbon monoxide in aircraft
In aviation, the most common source of CO is from the exhaust gases of piston-engine aircraft. While these engines produce the highest concentration of CO, turbine engines also contain CO (European Union Aviation Safety Agency, 2020).
In 2009, the results of a comprehensive study conducted by the Wichita State University on behalf of the US Federal Aviation Administration (FAA) regarding the detection and prevention of CO exposure in general aviation aircraft was published (Hossein Cheraghi et al., 2009). The purpose of the research was to identify protocols to alert users to the presence of elevated levels of CO in an aircraft cabin, and to evaluate the inspection methods and maintenance practices with consideration of CO.
The study interrogated the NTSB’s safety database to identify occurrences related to CO exposure. Of the 71,712 accidents recorded between 1962 and 2007, 62 accidents (0.09 per cent) were directly related. The source of the CO exposure could be determined in 63 per cent of these, which were attributed to the muffler,[55] exhaust or heater systems, or a combination of these, although the muffler system was the most prevalent. In addition, the data revealed that a similar number of accidents occurred across the seasons throughout the year. While muffler and heater system-related cases were more prevalent in the colder seasons, the source of a large number of cases in summer were undetermined.
Overall, it was recognised that a significant hazard could result when there was a failure in the exhaust system of a piston engine. Similarly, Slusher (1964) as cited in Lacefield (1982), indicated that, ‘although engine exhaust failures in general aviation aircraft were not frequent, in 70 per cent of the failures, a CO hazard was created in the cabin atmosphere’.
Engine exhaust system failures
While the design of piston-engine exhaust systems can differ between aircraft manufacturers and models, there are a large number of connections that are fundamentally common, which can potentially become fatigued or fail. These include welded joints, and bolts or clamps that connect tubes.
The FAA (Hossein Cheraghi et al., 2009) noted that there were several factors that can lead to the deterioration of an exhaust system: piston-engines operate at varying revolutions per minutes, from idle to maximum take-off power, which can result in vibration-type fatigue; and the high temperature and corrosive effect of piston-engine exhaust can result in thermal fatigue or corrosion. In turn, these can result in the fatigue of welded and clamp joints, or failure of exhaust system components.
Engine exhaust system inspections
A manufacturer’s instructions for continued airworthiness requires routine maintenance inspections of exhaust systems. For general aviation aircraft, this is commonly performed through a visual inspection. However, as highlighted by the Civil Aviation Safety Authority (2020), the useable life of the exhaust system is typically ‘centred on an “on condition” maintenance inspection philosophy and as such requires increased vigilance with ageing exhaust components’.
The NTSB has previously expressed concerns regarding the number of CO-related fatal accidents that occurred soon after routine maintenance inspections had been performed. However, it was recognised that it can be difficult to visually detect cracks or subtle imperfections, particularly at welded joints. The design of an exhaust may also make it challenging to visually inspect the interior for corrosion and cracks, without having to disassemble the system. Further, a crowded engine bay can make it difficult to conduct a thorough inspection without having to remove engine components (Hossein Cheraghi et al., 2009).
The FAA’s research (Hossein Cheraghi et al., 2009) found that inadequate maintenance and inspections of engine exhaust systems (and mufflers) were associated with a considerable number of CO-related accidents. The NTSB also cited a number of service difficulty reports where exhaust system failures were identified after being disassembled and pressure tested, even though they had been recently inspected. This supports the notion that, visual inspections alone may be difficult and may not necessarily detect pre-existing imperfections. However, it is also important to recognise that (Hossein Cheraghi et al., 2009):
Even if the exhaust system is intact without leaks during an inspection, it is possible that a crack or failure simply occurs soon after inspection.
Of note, the FAA (Federal Aviation Administration, 1972) and Transport Canada (2019) have also indicated that it is good practice to supplement these regular inspections with functional testing using a CO detector, both on the ground and in-flight. This was considered a reliable test that could be accomplished without having to disassemble aircraft components, and would provide an indication as to the extent of CO contamination. In particular, this could enhance the effectiveness of maintenance activities by ensuring that any repairs or modifications performed involving the firewall, and/or exhaust or heating systems, has been appropriately actioned and not introduced damage that could increase the risk of CO exposure.
Ingress into the aircraft cabin
The CO produced by a piston engine is dispersed into the atmosphere, away from the aircraft, through the exhaust system. However, cracks, holes or poorly fitted components in this system can result in exhaust gases, including CO, leaking into the engine bay. As most piston-engine aircraft cabins are heated by air that has been circulated around the exhaust system, this can result in CO rich exhaust gases entering the cabin through the heating system. The highest risk is in winter, when the use of the cabin heating system is more frequent, and the windows and vents are closed.
Likewise, inadequately sealed firewalls, and poor sealing of the cabin and other critical areas of the fuselage such as degraded door and window seals, also provide potential pathways for CO to enter the aircraft cabin. Further, it is crucial that any modifications and access panels installed on engine firewalls for maintenance purposes, be re‑sealed and secured correctly following any maintenance activities (Civil Aviation Safety Authority, 2020).
In addition to breaches in the firewall, anecdotal reports suggest that having the door ajar while on the ground is another potential pathway, including:
- In 2019, the ‘FLYER’ magazine (a UK magazine for general aviation pilots) tested four digital CO detectors using a Cessna 182 aircraft, at altitude and on the ground. While ground testing, they noted:
It’s worth noting that while we were doing the exterior exhaust test, while the rest of the units were located on the passenger seat in the cabin with the door ajar, it was evident the CO level increased as slipstream pushed exhaust into the cabin…
- Similarly, in a reply to the US Aircraft Owners and Pilots Association (2014) article on CO, a pilot discussed the digital CO detector fitted to their aircraft and made the following comment:
It’s amazing how sensitive it is, and how much CO I find I’m sucking when taxiing my Bonanza with the door ajar.
As part of the FAA’s study into the detection and prevention of CO exposure (Hossein Cheraghi et al., 2009), the ambient CO levels of several single-engine aircraft used for training purposes were monitored over a 12 month period. The aircraft were fitted with several digital detectors, which were placed in locations based on the potential pathways for CO to enter the cabin. The measurements were downloaded on a weekly basis, at which time the detectors were recalibrated. In addition, the pilots were required to complete a questionnaire for each flight, which captured the nature and duration of the flight, if the heating system and fresh air vents were used, if the windows were open and for what duration, and time taken to complete each ‘flight procedure’ (e.g. taxiing to the run-up area, conducting the run-up checks, taxiing to the runway etc.). The results of those tests indicated that:
Monitoring ambient levels of CO during flights of GA [general aviation] aircraft indicated the presence of CO in the cabin when the aircraft was on the ground as well as in the air. Examining the procedures carried out before aircraft takeoff showed that most of the ground CO exposure events happened during taxiing before takeoff and after landing, particularly when the windows were open.
Normal levels of carbon monoxide
Hampson et al. (2007) indicated that there were differing views regarding the correlation between COHb levels and a patient's presenting clinical picture, citing various publications. For example, Piantadosi wrote '…the correlation between clinical deficits and measured COHb level is quite weak'. In contrast, Ilano et al. identified that, '…in general, the severity of the observed symptoms correlates roughly with the observed levels of COHb…'. Similarly, The Merck Manual Professional Edition stated that 'Symptoms tend to correlate well with the patient's peak blood carboxyhemoglobin levels'.
Further, when comparing the COHb levels detected in individuals, Rathore & Rein (2016) highlighted that it was important to note that ‘both the concentration and length of time are key distinguishing factors. It is vital to note however that individuals exposed to the same source simultaneously can exhibit differing levels of COHb’. Taking this into consideration, when discussing the normal levels of CO contained in an individual’s blood, the ATSB’s forensic and aviation pathology specialist stated that:
Normal levels of carbon monoxide in non-smokers are less than 2-3%. Smokers may have elevated levels around 3-5% or even as high as 9%, depending on number of cigarettes smoked and time since last cigarette smoked.
The police forensic pharmacologist reported similar levels, where a non-smoker’s maximum COHb level would be around 5 per cent, while smokers could have levels up to 10 per cent and up to 16 per cent for heavy smokers. Multiple medical studies were also cited, including:
- A study of deaths in NSW, which found a CO range of 1-10 per cent, with most cases between 3-6 per cent.
- A study of banked blood reported the average COHb level was 0.78 per cent. Of those samples, 10.3 per cent had COHb levels of 1.5 per cent or more, and the highest level was 12 per cent.
- Another study found that 45 per cent of non-smoking blood donors had COHb levels more than 1.5 per cent, up to 6.9 per cent depending on their location.
- Busch (2015) investigated the extent of CO exposure on Norwegian Sea King rescue pilots who were frequently subjected to engine exhaust. The crew were monitored for exposure to exhaust fumes and clinical symptoms of CO over 2 weeks. The study found that 64 per cent of the crews experienced subjective exposure to engine exhaust. Clinical symptoms of CO was reported in 8.6 per cent of cases, which included exhaustion, headache and nausea.
Although toxic levels of COHb were not reached, about one-third of the post-flight levels were outside the normal range (greater than 4 per cent), with a maximum of 7 per cent. The study also concluded that exposure to engine fumes was more common during open cargo door operations.
Other medical and aviation sources discussed the typical levels of CO expected in individuals. While there was some variability in the levels considered normal, the COHb levels for non‑smokers are generally less than 3 per cent, but up to about 10 per cent for smokers. Specifically, these included:
- The Agency for Toxic Substances and Disease Registry (2012) stated that all individuals are exposed to CO at varying levels through the inhalation of air and the typical COHb level for a non‑smoker is 0.5-1.5 per cent. They also noted that urban locations with high automobile usage tend to have greater atmospheric levels of CO when compared with rural or remote areas.
- Carel (1998), cited by Science Direct, indicated that normal urban dwellers may have up to 0.5 per cent COHb, but smokers may have 5-10 per cent.
- According to Hawkins (1993), as a baseline, a non-smoker has about 1-3 per cent COHb in the blood, while a smoker has about 4‑10 per cent, depending on how much they smoke.
- Ghanem et al. (2012) stated that the 'Measurement of COHb level is necessary as it is believed to be the only established marker for proper diagnosis of CO poisoning. Confirmation is done by reporting elevated COHb level more than 2% for non-smokers and more than 10% in smokers’.
- Safe Work Australia (n.d.) discussed the distribution of CO in the environment and COHb in the general population. They indicated that the typical COHb saturation levels without occupational exposure was 0.4-0.7 per cent for endogenous production;[56] 5-6 per cent for smokers consuming one packet per day, increasing up 20 per cent for cigar smokers; up to 5 per cent for commuters on urban highways (in the US); and 3‑5 per cent when exposed to a certain amount of methylene chloride.[57]
- Baselt (2014), citing Stewart et al. (1974), indicated that the COHb average in urban non‑smokers was 1-2 per cent and 5-6 per cent for smokers. It was also noted that atmospheric conditions of 50, 100 and 200 parts per million (ppm) equated to 8, 16 and 30 per cent COHb levels respectively.
- Elevated COHb levels are used to confirm a clinical diagnosis of CO exposure, and in some instances, assess the severity of poisoning. Hampson et al. (2007) stated that elevated levels of COHb, greater than 2 per cent and 9 per cent for non-smokers and smokers respectively, 'strongly suggests exposure to exogenous CO and supports a clinical diagnosis of CO poisoning'.
Carbon monoxide concentrations
The concentration of CO in the air is represented as parts per million (ppm). According to Safe Work Australia (n.d.), the maximum recommended exposure to CO over an 8 hour period is 30 ppm. Short-term excursions above this are permitted to 60 ppm for no more than 60 minutes total exposure, 100 ppm for 30 minutes, and 200 ppm for 15 minutes. However, short-term excursions should never exceed 400 ppm.
There are several graphical representations showing the relationship between COHb levels, exposure time and CO concentration (ppm) (Figure 41). While there is a noticeable disparity between the two graphs, the results indicate that, to attain a COHb level of 11 per cent (as found in the pilot) in about 30 minutes (the minimum exposure time for the pilot accounting for the 27 minute taxi prior to, and the taxi on the accident flight), this required a CO concentration of at least 500 ppm. According to the Occupational Safety and Health Administration as cited in Lacefield et al. (1982), exposure to concentrations between 500‑1,000 ppm could result in ‘the development of headache, tachypnea (rapid breathing), nausea, weakness, dizziness, mental confusion and in some instances, hallucinations, and may result in brain damage’. The ATSB recognised that the pilot may have been exposed to CO on previous flights that day for up to 200 minutes when the engine was running. A cumulative CO exposure time would require lower CO concentration levels to achieve the same COHb.
Figure 41: Relationship between COHb levels, CO exposure time and concentration

Source: Peterson and Stewart (1975) as cited by the Agency for Toxic Substances and Disease Registry (2012) (left) and Thakur (2019) (right), modified by the ATSB to represent possible exposure time for the pilot and passengers and COHb levels detected.
Physical symptoms and cognitive performance effects of carbon monoxide exposure
Typical effects experienced
It is well recognised that ‘the reaction to a given blood level of COHb is extremely variable’ and will result in differing physiological effects (World Health Organization, 1999; Lacefield et al., 1982). These effects may also vary depending on the length of exposure and concentration of CO in the environment; that is, rapid high exposure or prolonged at a lesser amount. Baselt (2014) noted that, if the COHb ‘concentrations are attained rapidly by exposure to high levels of CO, the resulting physiological effects are not as intense as if the concentrations are attained gradually’. Further, the UK Civil Aviation Authority (2020) stated that:
The physiological effects of CO poisoning are cumulative and take a very long time to disperse. Even a low level of CO ingestion, below the level that causes immediate physical symptoms, will cause a progressive reduction in blood oxygen levels which will reduce pilot performance and potentially cause permanent damage to the brain, heart and nervous system. It is therefore a mistake to assume that a cockpit contaminated with very low levels of CO is acceptable.
Irrespective, most researchers are willing to accept that some level of deterioration in psychomotor function will occur at COHb levels from about 3 per cent (Hawkins, 1993).
The police forensic pharmacologist indicated that while there are generally ‘no symptoms of toxicity’ at COHb levels below 10 per cent, studies have shown that COHb concentrations at or below 10 per cent can adversely affect an individual’s ability to perform complex tasks, such as operating an aircraft. Specifically, COHb levels between 5-7.6 per cent can produce significant decrements in vigilance, while levels between 5-17 per cent can impair visual perception, manual dexterity, ability to learn and the performance of complex sensorimotor tasks. The adverse health effects of corresponding COHb levels have been shown simply by the Agency for Toxic Substances and Disease Registry in Figure 42.
Figure 42: Adverse health effects of CO

Source: Agency for Toxic Substances and Disease Registry, annotated by the ATSB
There is a significant amount of literature on CO and the effects at varying COHb levels. The following references indicate that the occupants of VH-NOO with the most elevated levels (11, 10 and 9 per cent) would have experienced physical symptoms and cognitive performance effects with adverse consequences, these include:
- Numerous studies have shown the adverse effects of CO exposure on the functioning of the central nervous system. Referring to multiple sources, Hawkins (1993) noted that a decrease in vigilance task performance can occur at COHb levels of 2‑4 per cent, and it has been shown experimentally that there are reductions in visual discrimination and the judgement of time intervals with 4-5 per cent.
- Safe Work Australia (n.d.) mentioned that the World Health Organization, US National Institute for Occupational Safety and Health, and the Swedish National Board of Occupational Safety
- and Health all agreed that at COHb levels between 5-10 per cent, behavioural effects have been found on the performance of tasks requiring vigilance, and on reaction time.
- The World Health Organization (1999) indicated that COHb levels below 10 per cent were not usually associated with symptoms. However, between a broad range of 10-30 per cent, neurological symptoms may be experienced, such as headaches, dizziness, weakness, nausea, confusion, disorientation and visual disturbances.
- Research reported by Lacefield et al. (1982) has shown that COHb levels less than 12 per cent had no effect on psychomotor performance, but detrimental effects on visual perception were observed. Further, behavioural testing suggested that time discrimination, visual vigilance, choice response tests, visual evoked responses, and visual discrimination thresholds may be altered at COHb levels below 5 per cent.
- Citing previous research, Baselt (2014) stated that a number of studies have shown that COHb levels less than 10 per cent can adversely affect a person's ability to perform complex tasks. Levels between 15-25 per cent often result in dizziness and nausea.
According to the Federal Aviation Administration (n.d.) and Safe Work Australia (n.d.), the physical symptoms for the COHb levels observed in the pilot and passengers (9-11 per cent) may typically include tightness across the forehead and a slight headache. However, given that these are relatively mild in nature, occupants may disregard these symptoms and not necessarily associate them with CO exposure.
The terms ‘symptom’ and ‘effects’ are often used interchangeably to describe the consequences of CO exposure. However, the authoritative literature considers these to be two distinct categories: observable physical symptoms and cognitive functions (Table 5).
Table 5: Adverse cognitive effects and observable physical symptoms from CO exposure
Cognitive effects
|
ability to learn
|
performance of complex sensorimotor tasks
|
confusion
|
reaction times
|
disorientation
|
time discrimination
|
judgement
|
vigilance
|
manual dexterity
|
visual disturbances
|
neurological impairment
|
|
Observable physical symptoms
|
decreased exercise stamina
|
nausea
|
dizziness
|
weakness
|
headaches
|
|
Comparison with altitude hypoxia
Hawkins (1993) compared the effects of oxygen deprivation from smoking-induced CO exposure (anaemic hypoxia) to that of altitude hypoxia. By definition, anaemic hypoxia is the result of a decrease in the oxygen-carrying capacity of the blood, while altitude hypoxia is a reduction in the oxygen tension (partial pressure) in the arterial blood. While it is noted that there are slight variations in these two types of hypoxia, hypoxia can be generally defined as decreased amounts of oxygen in organs and tissues, less than the physiologically ‘normal’ amount (International Civil Aviation Organization, 2012).
Based on Figure 43 (McFarlane (1953) as cited in Hawkins (1993)), a COHb of 11 per cent at sea level is the equivalent of a physiological altitude of about 12,000 ft. To put this into context, the effects typically experienced at 10,000 ft and 12,000 ft as a result of altitude hypoxia are (International Civil Aviation Organization, 2012):
10 000 ft: The atmosphere provides a blood oxygen saturation of approximately 89 per cent. After a period of time at this level, the more complex cerebral functions such as making mathematical computations begin to suffer. Flight crew members must use oxygen when the cabin pressure altitudes exceed this level.
12 000 ft: The blood oxygen saturation falls to approximately 87 per cent and in addition to some arithmetical computation difficulties, short-term memory begins to be impaired and errors of omission increase with extended exposure.
Figure 43: Effects of CO on altitude tolerance

Source: McFarland (1953) as cited in Hawkins (1993), modified by the ATSB
Tests and research
Following notification to ATSB in March 2020 that the occupants had elevated levels of CO, a further inspection of the stored aircraft was conducted to determine the likely source and ingress of CO into the cabin. This included a detailed examination of the engine exhaust system (collector ring assembly) and firewall, including the two magneto access panels. In addition, the CO detector fitted to the aircraft was also examined for serviceability and specific CO testing was carried out using an exemplar DHC-2 aircraft.
Examination of VH-NOO carbon monoxide detector
On the type of disposable CO chemical spot detector fitted to VH-NOO, the chemical spot sensor of a serviceable detector is the same colour as the outer ring, in this case, orange (Figure 44 – middle right). When exposed to CO, the sensor darkens to grey/black (Figure 44 – lower right). A lighter-coloured sensor relative to the outer ring indicates that the sensor is sun bleached (refer to section titled Limitations of disposable chemical spot detectors.
The detector fitted to VH-NOO was examined after the accident and was found to be a light beige colour; lighter than the comparative orange outer ring (Figure 44 ‑ top right). It was noted that the detector had been immersed in fuel‑contaminated saltwater for 4 days following the accident, which may have influenced its condition.
However, photographs taken by passengers earlier in the day (at 1116, 1202 and 1330) showed that the detector was the same colour as that observed post-accident, with the spot a lighter colour than the outer ring (Figure 44). The last image of the detector taken at 1330, although not of a high quality, showed the same. A darkened spot to indicate the presence of CO was not evident at that time.
In addition, both the ATSB’s examination and the review of the passenger photographs noted that the ‘date opened’ was not annotated on the front of the detector. In order to establish when the detector was fitted to the aircraft, the operator examined photographs previously taken by their company pilots. From this, it was estimated that the detector was fitted in April 2017.
The operator advised that, although the CO detector had been fitted to the aircraft for 8 months, it had been inside a hangar for half this time (July – November 2017) and reportedly not subjected to sunlight. In addition, the operator indicated they were following the manufacturer’s instructions for use and did not expose the detector to any cleaning chemicals They were also aware that it could be used for 12 months after opening.
Figure 44: VH-NOO CO detector during the earlier flights on the accident day (time 1116, 1202 and 1330) and post‑accident (top right), compared with a new detector (middle right) and a detector exposed to CO (lower right)

Source: ATSB and passengers, annotated by the ATSB
Carbon monoxide testing on an exemplar DHC-2
In May 2020, the operator offered the ATSB the use of a DHC-2 aircraft at Moruya Airport, NSW to conduct testing of CO levels in the cabin. The key purpose of the test was to establish if an exhaust leak combined with a breach in the main firewall could result in CO entering the aircraft cabin, and if variations in ventilation conditions could exacerbate this. The intent was not to replicate the exact conditions of the accident flight. A summary of that testing is provided below and for full details refer to Appendix E – Report on carbon monoxide testing on an exemplar DHC-2.
A number of scenarios were performed to progressively and safely introduce deviations from the normal baseline CO levels. These included a combination of removing bolts from the magneto access panels in the main firewall; introducing smoke (using a smoke generator), followed by exhaust gases into the engine and accessory bays;[58]and configuring the pilot’s door, snap vent[59] and window. The front passenger door and window remained closed during the tests.
The aircraft was towed to an open grass area on the airport and orientated to provide a right quartering headwind,[60] similar to the prevailing wind conditions during the taxi of the accident flight. The aircraft remained stationary on a trailer during the testing, with the engine generally being run at idle power and the propeller at 500-700 rpm.
The CO levels were measured from within the cabin using several calibrated electronic CO detectors. To ensure a safe working environment for participants with regard to CO exposure during the tests, detector alarms were set to the occupational exposure limits stipulated by Safe Work Australia (n.d.). When the CO levels approached the 15 minute exposure limit of 200 ppm, the testing was discontinued.
Baseline
A baseline CO level in the cabin was determined with all magneto access bolts in place, no breaches in the firewalls, and the pilot’s door, window and vent closed. As there was evidence to indicate that the pilot would tend to have the door ajar rather than the window open when the engine was running prior to take-off, the window open CO readings are not discussed.
The engine was initially run at 500 rpm (idle) and the detector alarmed soon after the engine start (at 30 ppm), but the CO level then stabilised at 10 ppm. When the pilot’s window, vent or door was opened, or the engine speed was increased, there was a minimal change in the CO levels, which remained below the alarm level (Table 6 first column).
In preparation for a simulated exhaust leak, a smoke test was conducted using the baseline conditions described above to provide a visual indication of airflow in the cabin. A smoke generator[61] was held inside the gap in the engine cowling and the CO level in the cabin peaked at 55 ppm. Some smoke was visible in the cabin when the smoke generator was held on the left side of the engine. The highest CO readings were in the front seats, with decreasing levels toward the rear of the cabin.
Table 6: Results of the CO testing
Primary condition Engine at idle speed
|
Position of pilot’s door, window vent
|
CO concentration (ppm)
|
CO levels at pilot’s seat
|
Baseline Access panel bolts in place
|
Door and vent closed
|
10
|
Steady state ppm
|
Door closed with vent open
|
18
|
Door ajar
|
8
|
Access panel bolts removed Nil exhaust leak
|
Door and vent closed
|
30
|
Maximum ppm
|
Door closed with vent open
|
34
|
Door ajar
|
15
|
Access panel bolts removed
Exhaust leak into engine bay
|
Door closed
|
60
|
Door ajar
|
>100
|
Access panel bolts removed Exhaust leak into accessory bay
|
Door closed
|
144
|
Door ajar
|
<144
|
Access panel bolts in place
Exhaust leak into accessory bay
|
Door closed
|
28
|
Door ajar
|
<28
|
Source: ATSB
Access panel bolts removed
After establishing a baseline, the next test involved assessing how much CO would enter the cabin if two bolts on each magneto access panel were removed. When removed, the CO readings with the door and vent closed, and then the door closed but the vent open, increased above the baseline levels reaching a maximum value of 34 ppm. However, with only the door ajar, the level was similar to the baseline (Table 6).
A second smoke generator test was then carried out with the door closed and vent open. The amount of smoke in the cabin was noticeably higher than the first test. Having the pilot’s door ajar drew even more smoke into the cabin through the bolt holes in the access panel.
Exhaust leak simulation
An engine exhaust leak was then simulated by feeding a small diameter hose from the exhaust tailpipe, initially into the engine bay and then into the accessory bay (Figure 45). The CO concentration level measured at the outlet of the simulated exhaust leak exceeded 500 ppm.
With the magneto access panel bolts removed and the simulated exhaust leak in the engine bay, the detector reached the second alarm level (60 ppm) with the door closed. This then increased quickly above 100 ppm when the pilot’s door was ajar (Table 6). The levels were highest in the pilot’s footwell adjacent to the holes in the firewall, and were less in the middle and rear rows. With the simulated exhaust leak in the accessory bay, the CO level quickly increased to 144 ppm, again highest in the pilot’s footwell. The CO levels reduced slightly with the pilot’s door ajar (Table 6). When the magneto access panel bolts were reinstalled with the simulated exhaust leak remaining in the accessory bay, the CO concentration level dropped considerably to 28 ppm with the pilot’s door closed. With the door ajar the CO levels reduced slightly (Table 6).
Figure 45: Simulated exhaust leak into the engine bay (left) and the accessory bay (right)

Source: ATSB
This testing demonstrated that either the simulated exhaust leak or missing magneto access panel bolts did not result in high levels of CO in the cabin in isolation. However, the simulated exhaust leak in combination with missing magneto access panel bolts resulted in elevated CO levels in the cabin. The CO was more evident at the pilot’s position and was exacerbated when the pilot’s door was ajar with a simulated exhaust leak source in the engine bay. The CO levels reduced markedly in the cabin (by more than 80 per cent) when the access panel bolts were reinstalled with the exhaust leak remaining. The door position in this configuration did not adversely affect the CO levels.
Carbon monoxide detectors
Due to the characteristics of CO, it has no inherent warning properties and is therefore, generally very difficult to detect. Aircraft occupants are often unaware that they have been exposed, and that their physical and mental functions have been degraded (Transport Canada, 2019). While the initial aircraft design and continuing airworthiness requirements are the foundations for preventing CO exposure, they are not always effective, so a third barrier is needed to alert pilots to the presence of CO in cabin (Air Accidents Investigation Branch, 2020).
Types of detectors available for aviation use
The FAA (Hossein Cheraghi et al., 2009) conducted an extensive literature review and assessment of CO detector technology available for aviation use. This research identified that CO detectors generally fall into five categories based on the sensor type. These are:
- Disposable chemical spot detectors: The most common detector used in general aviation is the disposable CO chemical spot detector. These devices are small, widely-available, and are inexpensive. They are normally mounted on a card that can be attached to the instrument panel without the need to be professionally installed, or can be worn by the pilot on an identification badge or neck-lanyard (Civil Aviation Authority, 2013). The sensor mimics the effect of CO on haemoglobin and changes colour to black in the presence of CO by (Downunder Pilotshop, n.d.):
These simple detectors are pieces of cardboard with a small orange-colored circle in the middle. If there is a high-level of carbon monoxide in the vicinity, the circle changes color from orange to black. This happens as a direct result of chemistry. The detector circle is gritty and sand-like; it is silica gel impregnated with a catalyst made from chemicals that include palladium and molybdenum salts…
When carbon monoxide touches the detector, it's oxidized by the chemical salts on the strip and turns into carbon dioxide. The chemicals on the strip are simultaneously reduced and change color to black. The strip also contains a chemical salt made from a transition metal such as iron, nickel or copper. Once the carbon monoxide is removed, this metal salt steals some oxygen from the air and changes the catalyst back to its original chemical form—so the detector spot changes color back to orange again...
Spot detectors have a number of limitations (refer to section titled Limitations of disposable chemical spot detectors below). Further, spot detectors merely provide a qualitative warning and have no mechanism for actively alerting the pilot to the presence of the CO in the aircraft cabin. As such, they offer the lowest level of protection against CO exposure.
- Electrochemical detectors: Electrochemical detectors use the principles of a fuel cell. When CO is present, a chemical reaction is measured within the sensor, which creates an electrical output that is directly related to the amount of CO in the immediate environment. This will trigger an alarm at certain CO concentrations and time periods. These types of detectors are considered the most accurate and reliable devices for detecting elevated levels of CO. They are generally small and portable, have a low power consumption, are single‑gas units, and can be used over a wide range of temperatures. However, cross-sensitivity with other gases may occur and potentially result in inaccurate readings of CO exposure.
- Biomimetic detectors: Similar to the chemical spot detector, the biomimetic sensor mimics the effects of CO on haemoglobin. If CO is present, the gel-coated disc changes colour (darkens). When the light sensor detects this change in colour, an alarm activates. Again, comparable to the spot detector, they are simple to use, are cost effective and are portable due to their low power consumption. However, they can be easily contaminated by the ambient conditions, and the time between obtaining data from the sensor to displaying it on the detector is generally slow. In reverse, this means that the sensor takes a reasonable amount of time to re-set, even up to 48 hours.
- Infrared detectors: Infrared sensors measure the specific wavelength of CO. When CO is present, resistance in the circuit is increased, which triggers an alarm. These detectors are generally manufactured for portable and fixed-use, require less frequent calibration compared with other sensors, may operate in environments where no oxygen is present, and provide high levels of sensitivity and accuracy. However, the sensor units are typically made to detect several types of gases and single-gas units are uncommon.
- Semiconductor detectors: Semiconductor sensors use an electrically powered sensing element and a thin layer of tin oxide placed over a ceramic base. The presence of CO reduces the electrical resistance and the circuit closes. An integrated circuit monitors this change and will trigger an alarm. While they have a long useful life, they also have a number of limitations that reduces the reliability, accuracy and portability of this type of detector. They can be adversely affected by the ambient conditions, they require sufficient oxygen to operate, power consumption is high reducing portability, and stability and repeatability is poor.
To be most effective, an appropriate CO detector should provide reliable, early warning of elevated levels of CO in the cabin. The purpose of an alerting system is to direct the pilot’s attention to a non‑normal operating condition that requires their awareness. This allows a pilot to respond appropriately and in a timely manner (Federal Aviation Administration, 2010). According to Parasuraman, (1987) as cited in Tsang et al. (2003):
Alarms and alerts are pervasive and, if not heeded appropriately, can lead to adverse situations. Such alarms have been installed in aircraft because humans are not very good at monitoring infrequently occurring events because of declines in vigilance…
The disposable CO chemical spot detector, as fitted to VH-NOO on the accident flight, was a passive device that relied on the pilot regularly monitoring the changing colour of the detector to show elevated levels of CO. In contrast, electronic active CO detectors are designed to attract the pilot’s attention through auditory and/or visual alerts when CO levels are elevated, so pilots are more likely to notice an elevated CO level. These are now inexpensive and readily available. This was recently recognised by the Civil Aviation Safety Authority and highlighted in Coronial proceedings for a mid-air collision between Cessna 152 aircraft and Guimbal Cabri G2 helicopter in the UK in 2017 (refer to section titled Civil Aviation Authority of New Zealand occurrences (2018).
Finally, the fitment of placards designed to change colour when exposed to CO may not necessarily provide adequate warning to the pilot and passengers of the elevated levels of CO within the cabin. More modern devices which include audible and improved visual warnings are more suited to detect and warn cabin occupants of the elevated levels of CO….small electronic personal devices are available at relatively affordable prices, these devices allow for continual monitoring of CO levels with audible and visual warnings when escalated CO levels are detected…(Civil Aviation Safety Authority, 2020).
There are a range of active CO detectors available that use audible, visible or vibration warnings when pre-determined CO levels are exceeded. These have the notable advantage of actively engaging the pilot’s attention and are accordingly more likely to be more effective than the ‘spot-type indicators (Buckinghamshire Council Coroner’s Service, 2019).
Limitations of disposable chemical spot detectors
The manufacturers of disposable chemical spot detectors are openly transparent about the limitations of these types of devices. For example, the ATSB purchased the same detector that was fitted to VH‑NOO at the time of the accident and noted that the back of the detector and the associated packaging detailed the limitations as (Figure 46):
- the shelf life for the unopened package is 3 years; a use by date is also provided on the packaging
- do not remove the detector from the packaging until ready for use and replace after 12 months
- the reaction time is slightly faster when damp and slightly slower when dry
- if the spot gradually turns darker or bleaches out over time, the detector should be replaced; harsh direct sunlight will tend to bleach out the indicator spot and shorten the useful life
- the detector will be damaged by the presence of halogens, ammoniac, chlorine, cleansers, solvents, sewer gas, cat litter boxes, and diesel engines
- not intended as a life-saving device
- recommended as a supplemental detector in combination with an electronic alarm for household use.
Aside from highlighting the useful life of the detector, none of the above limitations were specified on the front of the detector for pilot awareness when the detector has been attached to the aircraft cabin.
Figure 46: Exemplar disposable CO chemical spot detector

Source: ATSB
The Civil Aviation Safety Authority, Federal Aviation Administration, and pilot shops that sell the detectors also publicly recognised the limitations of disposable chemical spot detectors as:
… Spot detector manufacturers indicate the useful life of a spot detector to range between 30 and 60 days, and thus necessitate replacement on a frequent basis…spot detectors merely change color in the presence of CO and are not capable of actively alerting the pilot of the presence of CO in the cabin. Manual visual inspection is necessary to determine if the sensor indicates the presence of CO; however, CO exposure determination is subject to pilot interpretation (Hossein Cheraghi et al., 2009).
…If the aircraft is only fitted with the placard type CO indicator, the operator should ensure the placard is placed in the field of view of the pilot, is regularly checked to ensure that the placard is not time expired and that the indicator is not faded from ultraviolet exposure or contamination (Civil Aviation Safety Authority, 2020).
It appears that many pilots of GA [general aviation] aircraft use spot detectors due to their low absolute cost on an individual sensor basis...However, spot detectors provide slow reaction (i.e., slow, gradual change in color) when exposed to CO and are easily contaminated by aromatic cleaners, solvents, and other chemicals that are routinely used in aircraft maintenance. Once contaminated, it is difficult to distinguish whether the change in color is due to contamination or to actual CO exposure. Also, spot detectors cannot distinguish between acute and chronic exposures to CO, as a change in color simply signifies that CO is present, with no regard to dose…Different dose levels may warrant different actions (e.g., high acute exposure levels may require immediate attention, while low-level chronic exposure may allow more time to react)…spot detectors are also susceptible to discoloration over time, thus providing the potential for false positive readings (Hossein Cheraghi et al., 2009).
There are available, in general aviation, paper discs, impregnated with a chemical that reacts and changes color in relation to the concentration of carbon monoxide. The color may be compared to a printed scale. Under strict laboratory conditions this system is capable of detecting hazardous levels of carbon monoxide but when used to monitor cabin air it has proven unreliable because of interference from sunlight, varying humidity, other gases and cigarette smoke (Federal Aviation Administration, 1972).
The disadvantage is that these detectors don't sound an alarm: you have to keep looking at them to notice that the color has changed. These strip detectors have to be replaced every 3-6 months depending on the environment you’re using them in; an expiration date is on every package (Downunder Pilotshop, n.d.).
Similarly, the Civil Aviation Authority of New Zealand, Avweb, the (US) Aircraft Owners and Pilots Association and Guardian Avionics have all published articles exploring the advantages and limitations of the varying types of CO detectors available for aviation use. Specifically, they made the following comments when discussing the disposable chemical spot detector:
…Though they are better than nothing, most pilots don’t realize that these have a useful life of only 30 to 60 days – so whether you fly the aircraft or not, you have to change these cards 6-12 times a year! (Guardian Avionics, 2018).
These cards do have a downside, in that all of the currently available products have a limited life in service. While the chemical reaction that causes the spot to darken is nominally reversible, in practice most units discolour over time. The instructions that come with the unit will state the in-service life of the particular product. They typically range from one to 18 months, depending on the cost of the unit… towards the end of the stated inservice life, most of these detectors start to show significant darkening or discoloration. This could pose a dilemma to the pilot who isn’t sure whether the colour observed is due to the age of the detector, or is a result of the presence of CO. It therefore pays to replace the units whenever discoloration is apparent, or the stated life, whichever comes first (Civil Aviation Authority of New Zealand, 2004).
…chemical spots are extremely vulnerable to contamination from all sorts of aromatic cleaners, solvents, and other chemicals that are routinely used in aircraft maintenance. Read the fine print on these things, and you’ll learn that the detectors will be inactivated and damaged by the presence of ammonia, chlorine, iodine, bromine, and nitrous gases. It doesn’t take much, either. One brand of spot detector actually warns that the ammonia produced by the presence of a cat litter box in the home may render the detector unusable! What’s worse, there’s not necessarily any warning that the detector has been contaminated. The bottom line is that you might easily be flying around with an inoperative detector (because it’s too old or contaminated) and not know it. In some ways, that’s worse than not having a detector at all (Busch, 2003 (Avweb)).
These things often remain stuck on the instrument panel for years, providing a dangerous false sense of security. What’s worse, there’s no warning that the detector is outdated or has been contaminated—in some ways, that’s worse than not having a detector at all (Aircraft Owners and Pilots Association, 2014).
Another advantage these units [electronic detectors] have over the spot type is that they generally have a shorter reaction time, and they can indicate the presence of CO much more quickly than the spot type. They can also show when the ambient CO level has decreased (eg, from turning off the heater), while the spot type take some time to return to the original colour (Civil Aviation Authority of New Zealand, 2004).
…Even when fresh, chemical spot detectors are incapable of detecting low levels of CO. They’ll start turning color at 100ppm, but so slowly and subtly that you’ll never notice it. For all practical purposes, you’ll get no warning until concentrations rise to the 200 to 400 ppm range, by which time you’re likely to be too impaired to notice the color change (Aircraft Owners and Pilots Association, 2014).
But even more dangerous, these chemical detectors are incapable of detecting low levels of CO, which when exposed to for longer durations, can cause major symptoms (Guardian Avionics, 2018).
These units are also passive, which means they won’t explicitly warn you about CO – you have to look at them. This means that they have to be part of your regular cycle of instrument scan or airmanship checks. The unit should also be located in the cockpit in an easily seen, prominent location. The expiry date of the unit should be clearly marked on it (Civil Aviation Authority of New Zealand, 2004).
In consideration of the popularity of disposable CO chemical spot detectors in general aviation and the above limitations, the ATSB issued a safety advisory notice (AO-2017-118-SAN-002) on 3 July 2020. The purpose of the notice was to strongly encourage operators and owners of piston‑engine aircraft to install a CO monoxide detector with an active warning to alert pilots to the presence of elevated levels of CO in the cabin. If not provided, pilots were encouraged to carry a personal CO detection and alerting device.
Location of detectors in the aircraft cabin
The UK AAIB investigation into a fatal accident in January 2019 involving a Piper Malibu aircraft registered N264DB concluded that the pilot was probably affected by CO poisoning (refer to section titled Aircraft Owners and Pilots Association (2020). While it established that the aircraft was not fitted with an active CO detector, it was possible that a spot detector was being carried,[62] although it would have been out-of-date. Despite this, the investigation determined that the position of the detector in front of the right (copilot) seat would have been of little use in alerting the pilot in the left seat to the presence of elevated levels of CO in the cabin, particularly when flying at night. This was also emphasised by Hossein Cheraghi et al. (2009), who not only indicated that it was essential to place the detector in a position that allowed for the early and consistent detection of CO, but also in the pilot’s field of view so that they could be alerted to the presence of CO.
Regulatory requirements for carbon monoxide detectors
Civil Aviation Safety Authority Civil Aviation Order 20.18 details the minimum instrumentation and equipment requirements for aircraft, in this case, for charter aircraft being operated under visual flight rules. In addition to other instruments and indicators specified in the aircraft flight manual, this included instruments such as airspeed, altimeter, direct reading magnetic compass or remote indicating compass and a standby, accurate timepiece, turn and slip, and outside air temperature indicators. The Civil Aviation Order also mentioned other instruments such as recording equipment, automatic dependent surveillance broadcast systems and mode-S transponders. However, there was no requirement to carry a CO detector.
This was also recognised by CASA in the issue of airworthiness bulletin 02-064 Issue 1, on 3 July 2020, and 02-064 Issue 2 on 19 October 2020. The purpose of this bulletin was to advise owners, operators and aircraft engineers of the dangers of potential CO poisoning via leaking exhaust systems and breaches in engine firewalls. Specifically, it was noted that:
CASA strongly recommends pilots wear personal CO detectors. As not all aircraft are required to have CO detectors fitted, small electronic personal devices are readily available at affordable prices. These devices allow for continual monitoring of CO levels with audible and visual warnings when escalated CO levels are detected.
The absence of a regulatory requirement for the carriage of CO detectors was also highlighted by the UK AAIB investigation into a fatal accident in January 2019 involving a Piper Malibu aircraft registered N264DB (refer to section titled Aircraft Owners and Pilots Association (2020). The investigation report stated that:
…there is no requirement for GA [general aviation] aircraft to be fitted with a CO detector. Instead, it is the owner’s/pilot’s discretion as to whether they fit or carry a detector in the aircraft.
…many manufacturers have chosen to fit detectors to new aircraft. However, this is not a mandatory requirement and will not address the large fleet of ageing piston engine aircraft.
The CAA [UK Civil Aviation Authority], EASA [European Union Aviation Safety Agency] and the FAA have all produced a specification for CO detectors and EASA has introduced a standard modification to make it easier for pilots to fit them to their aircraft; however, there is no requirement for pilots to do so.
As a result of this accident, the AAIB made safety recommendations to the UK, US and European Union aviation regulators mandating the carriage of active CO detectors. Likewise, the French Bureau d’Enquêtes et d’Analyses pour la Sécurité de l’Aviation Civile (BEA) and US NTSB have previously made similar recommendations to their respective regulators. However, to-date, these recommendations have not been accepted. A summary of these recommendations and the regulators response is detailed in Table 7.
Table 7: Investigation recommendations for the carriage of CO detectors
Agency
|
Year
|
Safety recommendation
|
Regulator response
|
AAIB
|
2020
|
That the FAA, the European Union Aviation Safety Agency, and CAA [Civil Aviation Authority] require piston-engine aircraft, which may have a risk of CO poisoning to have a CO detector with an active warning to alert pilots to the presence of elevated levels of CO.
|
The safety recommendation remains open awaiting further work by the authorities.
|
NTSB
|
2004
|
To the FAA: Require the installation of CO detectors meeting the standards developed as a result of Safety Recommendation A‑04‑27 in all single-engine reciprocating‑powered aircraft with forward-mounted engines and enclosed cockpits that are already equipped with any aircraft system needed for the operation of such a CO detector.
|
The FAA responded that, as the proper inspection and maintenance of mufflers and exhaust system components is the primary method of preventing CO contamination, they considered that installing a CO detector was not necessary to correct an unsafe condition…
|
BEA
|
2002
|
The BEA recommended that the DGAC [Direction générale de l'aviation civile] require the presence of a CO on general aviation aircraft.
|
This recommendation was addressed through the European Union Aviation Safety Agency, who indicated that, although the safety risk from CO ingress into the cabin of general aviation aircraft existed, the number of accidents where CO poisoning was determined as the root cause remained low compared to other root causes categories. CO detectors were also available on the market and as such many operators already make use of them, even though there was no rule requiring the installation of CO detectors. The Agency considered that this issue may be treated by other means than by the creation of a new rule…
|
AAIB
|
2002
|
In the absence of it being mandatory for all piston-engine aircraft to carry a CO detector, the Civil Aviation Authority [CAA] should vigorously promote that all such aircraft should have a current CO detector fitted to facilitate an early warning of the presence of the gas.
|
This recommendation was accepted by the CAA.
|
AAIB
|
2002
|
The Civil Aviation Authority [CAA] should develop an appropriate recognised performance specification against which CO detectors can be assessed and approved, with the eventual aim of mandating their use on all piston engine aircraft.
|
The CAA undertook a feasibility study to determine whether an appropriate airworthiness specification could be developed that would allow for a practicable and cost-effective CO detector for aviation use. The study proposed an update to the standard that addressed the use of CO detectors.
|
Of note, the Civil Aviation Authority of New Zealand Civil Aviation Rules (section 91.509) stated that a powered aircraft with an airworthiness certificate (other than a powered glider), must be equipped with a means for 'indicating the presence of carbon monoxide in the cabin if the aircraft is fitted with an exhaust manifold cabin heater or a combustion cabin heater'. While this was only related to aircraft fitted with cabin heating systems, it is recognition of the significant risk that CO exposure can have on aircraft occupants.
The marine experience
In addition to the aircraft cabin, the potential dangers of CO exposure have also been recognised in other enclosed spaces such as caravans, boat cabins and even tents. Of particular note, in 2016, two people onboard a yacht in Sydney were exposed to CO from a stove that was used to keep them warm. One of the occupants received fatal injuries, with a COHb level of 60 per cent. The subsequent NSW State Coroner's inquest recognised the challenges with establishing the prevalence of CO-related events, but noted that 'it is clear that there is a large potential risk in the leisure industry'. A such, the Coroner made the following recommendation to the Minister for Roads, Maritime and Freight:
It became clear during the course of the inquest that the potential danger of carbon monoxide poisoning is somewhat unknown or under-estimated in the recreational boating field. There is no requirement for carbon monoxide alarms in cabins and clear warning stickers attached to appliances are not mandatory.
Urgent consideration of the introduction of legislation to mandate carbon monoxide alarms in all recreational and leisure craft and vehicles with sealable cabins, including sailing and motor vessels, caravans and motor homes, that have potential carbon monoxide sources such as fuel burning heating and cooking appliances. These alarms should conform to an appropriately developed minimum standard…
Interestingly, the inquest noted legislative changes in Minnesota (US) in 2016 in response to the fatality of a child on a family boat. The state introduced mandatory hard-wired, marine-certified CO detectors in boats with enclosed cabins.
Similar occurrences
Exposure to elevated levels of CO has been identified as a contributing factor in numerous aviation accidents involving piston-engine aircraft. The FAA Civil Aeromedical Institute (Lacefield et al., 1982) conducted a toxicological study of samples from 4,072 pilots that were fatally injured in a general aviation accident. The results of that study found that only 0.5 per cent of the accidents were the result of pilot incapacitation from CO exposure. Similarly, as previously mentioned, an FAA study into the detection and prevention of CO exposure in general aviation aircraft found that only 62 of the 71,712 accidents (about 0.09 per cent) in the NTSB’s safety database, between 1962 and 2007, were directly related to CO exposure.
While these statistics show that a fatal accident involving CO is rare, the AAIB (2020) highlighted that it was possible there may be more occurrences, but these have gone undetected for several reasons. These include: toxicological testing was not conducted, evidence of CO exposure was masked by a post-impact fire, or mechanical evidence was destroyed during the accident sequence.
Further, as noted by Lacefield et al. (1982), ‘not all in-flight exposures to CO result in accidents’. Pilots may overlook or dismiss the onset of symptoms and not even consider an association to CO exposure, a hazard that is very difficult to detect (NTSB, 2017a). Likewise, Hampson et al. (2007) indicated that, as the signs and symptoms of CO exposure were non-specific, it was likely that many more cases were unsuspected or attributed to other causes, and therefore, have gone undiagnosed. It is also challenging to establish how often exhaust systems are repaired or replaced, or breaches in firewalls are detected. While the prevalence of these types of occurrences will never be accurately known, the following summaries provide insight into the nature of these types of events. It is acknowledged that, although the aircraft involved in the events below may be fitted with varying heating and ventilation systems, the potential for CO exposure in any piston-engine aircraft still exists. Of note, a search of the ATSB’s safety occurrence database did not identify any reports involving DHC-2 aircraft.
Australian occurrences
On 23 September 2020, the pilot of a Piper PA-28 aircraft departed Moree, NSW for a private ferry flight to Tamworth. Shortly after take-off, the pilot started to experience dizziness, breathlessness and a warm feeling in the chest. The pilot conducted a visual scan and observed that the CO chemical spot detector was gradually getting darker.
The pilot opened the air vents and storm window, and returned to Moree. A subsequent medical examination determined that the pilot had a COHb level of 1 per cent. The investigation is ongoing.
CASA defect report (Piper PA-28)
On 01 September 2020, during the taxi and run-ups in a Piper PA-28 aircraft, the smell of exhaust fumes were observed in the cockpit and the CO detector was darker than usual. An examination of the aircraft's exhaust system and firewall was conducted, with nil defects founds. In addition, it was determined that the CO detector fitted to the aircraft was in a 'poor condition' and was subsequently replaced.
Post-flight testing using an electronic CO detector during engine run-ups confirmed the presence of 'excessive CO' in the cabin. Interestingly, when the aircraft was stationary and positioned into wind, less than 10 ppm was observed on the detector. However, when the wind was at 90° to the aircraft, the CO levels within the cabin increased to 40 ppm. The wing and fuselage lower air vents were subsequently sealed and another CO test performed, with nil detection observed at various power settings and wind directions.
CASA defect report (Victa Airtourer 115)
On 26 August 2020, the owner of a Victa Airtourer 115 had asked their maintenance organisation to install a CO detector. Subsequent to this, on departure, the pilot reported that the CO detector alarmed. A post-flight inspection using a hand held CO detector established an 'unacceptable' CO level of 125 ppm in the cabin. The engine muffler, and boots/seals fitted to the throttle push pull rod in the firewall, and flaperon and centre flap were all replaced. After this, the CO level was deemed acceptable.
On 22 December 2019, while carrying out aerial work in the region of Sellicks Beach, South Australia, the pilot and two crew members of the Cessna 172 aircraft became ill, with symptoms including vomiting, light-headedness, dizziness, and loss of feeling in limbs. At that time, the flight had been conducted for about 4 hours through smoke from bushfires in the region.
The pilot observed that the aircraft’s disposable CO chemical spot detector was displaying two black dots, indicating exposure to CO. The pilot subsequently landed the aircraft safely at Parafield. The crew underwent a medical examination and blood samples were taken about 3 hours after the initial symptoms were experienced. The results of those tests showed two crew members having 1.2 per cent COHb levels and the third with 1 per cent. This was reported to be mildly elevated, above the normal expected range of 0.4-0.7 per cent. The investigation is ongoing.
ATSB occurrence (201600006)
During the cruise, the pilot of a Cessna 210 aircraft, reported feeling ‘a bit disorientated’. This continued for the remainder of the flight, although the pilot was aware of the aircraft’s location with reference to the GPS. After landing, the pilot opened the window and door, after which the pilot’s head started to clear and became ‘less brain foggy’. The pilot reported still feeling unwell in the stomach. At the suggestion of the aircraft owner and engineer, the pilot was checked for CO exposure. The tests revealed that the pilot had a ‘small amount of CO poisoning’. It was reported
that the potential source of CO was a loose exhaust manifold. The aircraft was not fitted with a CO detector.
ATSB occurrence (200001850)
During the climb after take-off, the pilot in command of a Mooney M20J aircraft, smelt a trace of exhaust fumes in the cabin. The aircraft heater was confirmed off and full cabin fresh air was selected. The pilot in command and pilot under training felt nauseous and developed a headache. The crew elected to return to Bankstown and landed without further incident.
The source of the crew discomfort was moderate CO poisoning. The aircraft's CO detector had indicated the presence of CO and the pilot in command had undertaken a blood test after the flight, which confirmed the presence of CO in the pilot's bloodstream. Company engineers could not establish how the engine exhaust fumes entered the cabin. Furthermore, company engineers were unable to find any faults with the aircraft. The aircraft was re-equipped with multiple CO detectors and the problem had not re-occurred since the engineering examination.
ATSB investigation (199601955)
The pilot of a Cessna 172 aircraft departed Orange, NSW at 0620 for a flight to Charleville, Queensland, and climbed to 6,500 ft. The weather was fine and sunny, but very cold so the pilot pulled the heater control to full on. After passing Bollon, 120 NM (222 km) south-east of Charleville, the pilot tuned to the Charleville non-directional beacon[63] and noted that the needle rotated to indicate straight ahead.
The pilot recalled passing a strip about 25-30 NM (46-56 km) from Charleville and made a mental note that they could land there if the weather deteriorated. The pilot then started to think about the descent and turning the heater down. It appeared that the pilot then lost consciousness. The pilot regained consciousness and observed the aircraft descending through 1,000 ft, at a rate of about 1,000 ft per minute.
The pilot reported pulling back on the control yoke and saw the horizon come into view. The pilot banked the aircraft hard left, and the engine coughed. The pilot then noticed what looked like a very long airstrip ahead and landed. After landing, the pilot noticed the time was 1230 and realised that the estimated time of arrival for Charleville had been about 1100. The pilot reported feeling cold and nauseous, and having an aching head.
The pilot eventually fixed his position about 150 NM (278 km) north-west of Charleville. After repairing the aircraft radio, the pilot was able make contact with an overflying jet aircraft late the next day and was rescued.
Examination of the aircraft’s cabin heating system revealed a large amount of exhaust build-up in the scat hose leading to the cabin heat selector valve. The muffler was badly cracked around the outlet port and had a white soot stain around it. It was concluded that the pilot may have been affected by CO, which entered the cabin via the cracked outlet port of the muffler.
ATSB occurrence (199101931)
While returning to Bankstown from a training flight in a Piper PA-28-181 aircraft, the pilot’s vision became blurred and started feeling nauseous. The pilot was unable to comply with air traffic control instructions, but landed safely. It was determined that the pilot had experienced CO poisoning. The aircraft was examined and a tear was found in an air vent hose.
ATSB occurrence (198803648)
The pilot of a Cessna 172 aircraft reported experiencing severe headaches and nausea during the flight. The aircraft had recently been painted and the 100-hourly maintenance inspection
conducted. However, a sealing boot on the nose wheel steering rod had failed, allowing CO gases to enter the aircraft cabin.
ATSB occurrence (198404934)
The pilot of a Piper PA-32 aircraft reported feeling discomfort and sickness. It was determined that an unauthorised modification to the aircraft’s ventilation/heating system allowed CO to enter the aircraft cabin.
International occurrences
Aircraft Owners and Pilots Association (2020)
In June 2020, an article was published by an instructor recalling his experience with CO exposure during an instrument training flight. During the flight, the instructor reported that the strong and gusty winds were occasionally pushing exhaust fumes into the cabin and he noticed a 'breeze' in the cabin despite the doors and vents being closed.
The training included turns, which the instructor reported students would often become dizzy and be exacerbated by turbulence. While conducting the exercises, the student mentioned that he was feeling a 'little dizzy' and asked to take a break. The instructor had considered CO, even though the chemical spot detector positioned on the instrument panel in plain view was normal. Despite this, they opened the window and overhead vent. As the instructor also felt a little dizzy, they elected to return to the airport.
On the return flight, the student mentioned that he was 'feeling off and was struggling to find the runway'. The CO detector, which was new, still showed no change. The instructor landed the aircraft and taxied off the runway; the student then taxied to the hangar. The instructor reported feeling more dizzy. After shutting down the aircraft, the student stumbled while exiting and was wobbling. The instructor placed the student onto his back, who started to shake lightly. The instructor also reported that his own feet were numb from the ankles down, and his hands and lips felt the same. He also developed a headache, which lasted all night. The student later told the instructor that he was struggling to understand the instruments on the return flight and could not recall taxiing back to the hangar or shutting down.
Testing established that the instructor and student had 19 and 26 per cent COHb levels respectively. The source of the CO was a hole in the muffler. The instructor specifically stated that:
This wasn't easy to recognize, especially with a brand-new carbon monoxide detector saying we were safe…If you smell fumes and you are dizzy, get back to the airport. It took 15 minutes from the time the dizziness started to the point where one of us couldn’t function. Another 10 minutes, and we both would have been unconscious on our way back to the airport.
AAIB investigation (AAR 1/2020)
On 21 January 2019, the pilot and passenger departed Nantes Airport, France in a Piper PA-46 Malibu aircraft, for a commercial flight to Cardiff Airport, UK. The flight was conducted under visual flight rules and the planned route would fly overhead Guernsey.
When about 13 NM (24 km) south of Guernsey, the pilot asked air traffic control for a clearance to descend to remain in visual meteorological conditions. About 10 minutes later, the pilot asked for a further clearance to descend. The aircraft’s last secondary radar return was observed about 4 minutes after this call. No further radio calls were made by the pilot. A subsequent search for the aircraft was commenced and the main wreckage was located in the water at a depth of 68 m, about 22 NM (41 km) north-north-west of Guernsey.
The passenger was recovered from the wreckage, but the pilot could not be located. The post‑mortem results of the passenger showed a COHb level of 58 per cent. However, as the passenger and pilot were sitting in the same cabin, it was considered likely that the pilot would have also been exposed to similar levels of CO. This would have likely impaired the pilot’s ability to control the aircraft during the later stages of flight.
The AAIB’s investigation report also referred to another fatal accident involving a Piper PA-28 aircraft, where the toxicology results of the four occupants ‘showed that individual levels of COHb can vary between individuals occupying a compartment contaminated with CO’.
It was reported by the person who managed the aircraft that it was fitted with a ‘strip detector’ located on the right side of the instrument panel in front of the right seat. However, the investigation noted that there were no aircraft records to substantiate this.
Barriers for reducing carbon monoxide exposure
When discussing the measures for reducing the risk to CO poisoning, the AIIB noted that regulators mandate two barriers for preventing CO exposure: ‘initial design’ and ‘regular in‑service inspections’. While many aircraft manufacturers are installing CO detectors in new aircraft, it was not mandatory. The AAIB recognised that:
There is considerable evidence that the second barrier, regular inspections, is not entirely effective. Not only is it difficult to carry out a thorough inspection of all the exhaust components in the crowded engine compartment, it is possible that a mechanic will miss a small crack or subtle signs of a leak. This was noted in Service Difficulty Reports where exhaust systems passed a visual inspection but then failed a pressure test. Moreover, corrosion and erosion occur from the inside of the exhaust system and can be difficult to detect without first dismantling the system.
…It would be difficult for regulators to mandate detailed inspections for the wide range of GA [general aviation] aircraft and exhaust systems currently in service. Moreover, it has been seen from other events that cracks and faults can initiate at any time. While periodic inspections can help reduce the risk, they will not catch every event.
As the existing two barriers to prevent CO poisoning (design and inspections) are not always effective, there is a need for a third barrier to alert pilots to the presence of CO in the cabin in time to take effective action. Low cost warning devices are readily available, and their carriage is actively encouraged by the regulators.
NTSB investigation (WPR19FA022)
On 9 November 2018, a private pilot, student pilot and two passengers of a Piper PA-28-236 aircraft, departed Le Mars, Iowa, US on a cross-country flight to Osceola. The purpose of the flight was for the private pilot to transport the other occupants for a hunting trip.
When about 40 NM (74 km) west of Des Moines International Airport, air traffic control observed the aircraft squawking the emergency transponder code of ‘7700’. Air traffic control established contact with the student pilot on board the aircraft, who reported that they were diverting as the pilot was having a ‘heart attack’. Other pilots in the vicinity were also in contact with the student pilot who indicated that they were intending to land at Guthrie Regional Airport. However, the aircraft did not land as expected and an alert notice was issued. The wreckage was located the following morning, south of the airport. The four occupants received fatal injuries and the aircraft was destroyed.
Examination of the wreckage identified a 2 inch-long crack in the engines aft exhaust muffler. Further, the inner surface of the muffler heat shroud was coated in sooty tan and grey coloured deposits. Similar deposits were also detected on the inner surface of the cabin heat hose that ducted air from the shroud to the cabin heat distributor box assembly.
Toxicology testing of the occupants revealed elevated levels of COHb.
Civil Aviation Authority of New Zealand occurrences (2018)
While conducting an instrument flight rules flight, the instructor and student pilot of a Diamond DA 40 aircraft, observed the CO detector illuminate four times. This was cross-checked with the standby detector, which had not discoloured. Both crew reported experiencing light headedness, and a reduction in cognition and coordination. In accordance with the Quick Reference Handbook, the crew turned the cabin heat off, and opened the air vents and emergency windows. The
indication continued to occur multiple times during the flight. With the assistance of air traffic control, the aircraft was landed safely.
The subsequent maintenance inspection identified a hole in the scat ducting, linking the exhaust shroud to the heater valve box. While not confirmed, this was considered the possible source of the CO exposure.
On 17 November 2017, while conducting training flights near Waddesdon, Buckinghamshire, UK, a Cessna 152 aircraft and Guimbal Cabri G2 helicopter collided mid-air. All four occupants received fatal injuries. The post-mortem results noted that the instructor of the Cessna 152 had an elevated level of COHb of 24 per cent, while the student had less than 5 per cent COHb. The investigation concluded that:
Exposure prior to flight is considered unlikely given the probable elapse of at least several hours since exposure, together with the rate of half-life decay of 4 to 5 hours. These factors would require the COHb to have been at a level considered to be incapacitating and clearly discernible to self or others in the period leading up to the accident flight. Also, there is no evidence to suggest an incapacitating exposure to CO in the one hour before the accident flight as the effects would have been apparent prior to commencement of that flight. It is more likely therefore that the exposure was as a result of a short survival period post-accident, as concluded in the toxicological report.
The subsequent Coronial proceedings (Buckinghamshire Council Coroner’s Service, 2019) into the accident not only raised concerns with the see-and-avoid procedure, but also considered the requirement for carrying CO detectors:
Although it could not be demonstrated that exposure to Carbon Monoxide prior to or during flight played a part in the implementation of “See and Avoid” or the collision, evidence demonstrated that it is not mandatory for light aircraft such as were involved in this collision to carry any Carbon Monoxide monitors or warning devices, notwithstanding their potential availability.
Given the regular service requirements for such craft and the possible limitations in identifying hairline cracks or hidden defects in aircraft exhaust and heating systems, there remains a risk that pilots and passengers may be exposed to Carbon Monoxide in such craft which might directly put them at risk of death or might put the craft at risk of collision or accident carrying with that the inherent risk of death.
In response to the Coroner’s concern, the Civil Aviation Authority (n.d.) (CAA) indicated that the potential for CO contamination in small aircraft was addressed through the regulations that related to aircraft design, manufacture and operation. Specifically:
- Aircraft design: The European Union Aviation Safety Agency promulgated design requirements specific to cockpit contamination measures. These also addressed the required levels for ventilation, the maximum acceptable CO concentration allowed in the cabin, and the design of heating systems with a view to preventing CO contamination. The code did not require CO detectors to be fitted.
- Maintenance: The continuing airworthiness requirements and recommendations require exhaust systems to be inspected in accordance with the manufacturer’s instructions. These inspections varied from a physical inspection, to a physical inspection with partial disassembly, internal inspection and pressure testing. The CAA noted that they have released publications that provide guidance on this topic.
- Operation: The CAA also noted that the CO detectors could be fitted to UK-registered aircraft as ‘standard’ changes’, which removed the need for ‘direct authority involvement’, and allowed detectors to be fitted without the associated time and cost. Essentially, CO detectors were not mandatory, but could be used at the pilot/owner’s discretion. However, the CAA noted that, while aircraft certification requirements should minimise the likelihood of CO contamination, the maintenance of sometimes notably high-utilised aircraft means that contamination may occur.
Notwithstanding the above, the CAA indicated to the Coroner that this was an opportunity for them to review the available guidance material for the prevention of CO contamination.
NTSB investigation (CEN17LA101)
On 2 February 2017, the pilot of a Mooney M20C, reported using the aircraft’s heater throughout the day, and having experienced a headache and stomach ‘butterflies’ at the end of the first flight. The headache subsided for the second flight, but returned after landing. Before the third flight, the pilot expedited his time on the ground, started the engine and sat in the aircraft while completing pre-flight preparations. While taxiing to the runway, the pilot still had a headache and experienced another episode of ‘butterflies’. The symptoms were more intense than previously experienced, but subsided. By the time they reached the runway, the pilot felt ‘good’ and ‘hyper focussed’. The pilot performed the engine run-up and take-off checklist three to four times, before air traffic control ‘snapped’ the pilot out of repeating the checklist.
The flight departed and the pilot experienced more ‘butterflies’ during the climb out. The last action the pilot remembered was receiving a clearance from air traffic control to climb to 6,000 ft on a heading of 240°. The pilot attempted to contact air traffic control twice after this, but on the wrong frequency. Radar data showed the aircraft climbing above 12,000 ft and off course. The aircraft continued to fly until it ran out of fuel and collided with terrain. The pilot survived the accident and regained consciousness afterwards. After exiting the aircraft, the pilot reported feeling very weak and had difficulties walking.
The examination of the aircraft found that the cabin heat was on. Further, the exhaust muffler had several cracks, one of which contained soot/exhaust deposits on the fracture surface, indicating it was pre-existing. This crack allowed exhaust gases to enter the cabin.
The morning following the accident, the pilot’s blood was drawn for CO testing. The results indicated, at that time the pilot had a COHb level of 13.8 per cent. Taking into account the half-life of CO of about 4‑5 hours, with a patient breathing ambient air at sea level, the pilot’s level at the time of the accident was at least 28 per cent.
Civil Aviation Authority of New Zealand (2007)
A New Zealand Civil Aviation Authority article detailed an incident involving an instructor and student pilot on a cross-country flight in winter. During the flight, the instructor elected to turn back to the north due to adverse weather conditions ahead. After completing the turn, the instructor performed a routine check, which involved scanning the instrument panel. When doing so, the instructor noticed that the 'dot' on the CO detector had turned grey since the last check was performed about 15 minutes prior, when it was the normal 'yellowish hue'. In response, the cabin air and heat controls were shut off and upper vents opened.
As the surrounding area was covered in snow, an immediate landing could not be conducted. The instructor monitored his and the student's condition for symptoms of CO exposure, with none apparent. The aircraft was subsequently landed without incident. A post-flight inspection found that the exhaust shroud had come loose and chafed through the exhaust pipe. This resulted in exhaust gases entering the cabin through the heating system. The article specifically noted that:
The cockpit CO detector had worked as intended, but it was the instructor’s vigilance that saved the day. By including the CO detector in his scan (it was positioned close to the ammeter), he noticed the problem within 15 minutes, and his prompt corrective actions and subsequent monitoring of both crew for symptoms quite possibly averted a major accident.
New Zealand Transport Accident Investigation Commission (97-012)
On 11 June 1997, a Beechcraft BE58 Baron twin-engine aircraft, registered ZK-KVL, was being operated on a night freight flight from Palmerston North, New Zealand to Christchurch. The aircraft disappeared from air traffic services radar and the wreckage was located in the Tararua Ranges. The pilot, who was the sole occupant, was fatally injured.
During the cruise and while maintaining 10,000 ft, the radar data showed the aircraft initially remained on track for a short period, before veering to the left. This amended track was maintained for about 1 minute, before the aircraft veered further left. Again, this track was maintained briefly before turning sharply to the right. The aircraft's altitude and ground speed began to decrease and the turn steepened. Shortly after, the aircraft spiralled toward the ground at a high rate of descent before the radar return was lost. The investigation determined that the aircraft had probably encountered severe in-flight icing at 10,000 ft, in the area of a convective cell, resulting in a loss of control.
Toxicology testing during the post-mortem examination found:
…an unexpected level of a carboxy haemoglobin (carbon monoxide) of 14%...The expected level for a person not exposed to carbon monoxide is significantly less than 1%.
The pilot was a non-smoker, and no evidence of exposure to carbon monoxide prior to the flight could be established, such as fumes from the exhaust system of his car. A blood carboxy haemoglobin level of 14% is consistent with an inspired air carbon monoxide concentration of at least 3000 parts per million, whereas under normal circumstances the carbon monoxide concentration in inspired air is infinitesimal.
Based on the established sequence of events and toxicology results, the investigation concluded that:
Another explanation for the aircraft drifting off track, considered likely given the results of the post‑mortem toxicological tests, was the impaired cognitive functioning of the pilot due to the presence and narcotic effects of carbon monoxide. The pilot probably experienced significant mental impairment in the last five to ten minutes of the flight, due to inhalation of carbon monoxide which had entered the cabin of the aircraft and caused a significant rise in the carbon monoxide concentration. This may have caused drowsiness, confusion and loss of situational awareness, of variable but progressive intensity. The pilot was unlikely to have suffered total incapacitation or been rendered unconscious by the carbon monoxide, during the early stages of its onset, and it is probable that he remained conscious at least until the aircraft departed from normal flight. The presence of carbon monoxide, and its symptoms, would probably have been unrecognised by the pilot.
Having eliminated other possible causes it was most likely that the source of inspired carbon monoxide was cabin air contaminated by fumes from a defective combustion type cabin heater. Such a defect could have included combustion tube failure (of the type covered by the AD) or exhaust erosion.
…The potential carbon monoxide affects may have contributed to mistakes of: flying outside the design requirements of the aircraft; continuing in conditions conducive to icing; electing not to use escape options available.
As a result of this accident, the Commission recommended that the Director of Civil Aviation (of the Civil Aviation Authority):
Review the likely safety benefits of the installation of suitable carbon monoxide detection devices in the cabins of aircraft which have potential for an ingress of carbon monoxide, with a view to making the installation of such devices mandatory in appropriate circumstances.
In response, the Civil Aviation Authority accepted the recommendation and indicated that this would be included in the rule making process for the next amendment to the relevant rule.
Historical occurrences
A carbon monoxide experience
The New Zealand Civil Aviation Authority (1997) cited an incident that was published by the UK CAA in 1996. The article recounted the experience of a pilot who was on a private flight with his wife in their Mooney aircraft, when they experienced CO exposure. Prior to this flight, the pilot had reported that the cabin air ducts were not delivering fresh air and, although turned off, the heater was providing warmth. This was to be fixed at a later stage.
On the evening of the incident, the occupants were conducting a test flight after having some maintenance performed on the engine. During the flight, they felt 'much greater heat than before, with a smell of engine'. The pilot elected to return to Shobdon airfield, but soon realised that he was having 'serious difficulties' and his wife was 'clearly in trouble'.
While the pilot was aware of the effects of CO exposure, he indicated that experiencing them first hand was 'another matter'. The pilot was a psychologist, and following the incident, documented his mental processes during the event as follows:
Firstly, I felt distant to operations, and nauseous, and I began to have doubts whether I was really in the plane or was only dreaming. Part of me just wanted to sleep more than anything else in the world, but at the same time a little voice inside told me we were dying of CO poisoning, but I could not quite remember why.
But all I wanted to do was sleep and carry on dreaming. I began to try to determine whether it really was a dream or was this real — and frankly got more and more confused — and I became obsessed with this problem… I gave up on this and decided that I would carry on with the scenario whether it was real or not — nothing worried me by then, my thoughts came from a long way off.
So Shobdon [airport] was in sight, tried the radio but it was after closing, and somehow I prepared for a direct join on long final. Here routine took over and the right things got done without thinking — which was now almost impossible.
There was a 15 knot crosswind and somehow I knew things did not look right... Without thinking I went around, did a circuit on automatic, fighting extreme nausea, and this time made a good touchdown. I do not remember the taxi back and can only pick up the thread when we were fully stopped, neatly parked at engineering. My wife could not stand and looked awful, and I was unable to exit the plane for some time. We recovered enough to get home three hours later.
A subsequent engineering inspection found that the source of CO was from two cracks in the aircraft's engine exhaust system, 'which were not able to be seen with the naked eye'. The pilot also reflected on his experience and concluded that:
Its effect removes urgency, and one just is unable to assimilate reality. One experiences what could be described as an altered state of conscious awareness, rapidly moving to coma.
… Original thinking and problem solving is impossible.
So we all read about human performance, but words in books cannot ever have the impact of experience. This is a problem that can happen to most aircraft at any time. I guess that quite a few unexplained accidents could be put down to this. Be prepared.
By the detector [CO detector], place a check list of procedure should this deadly gas be detected. If you are overcome, you will not be able to remember what to do.
While the CO saturation levels of the occupants was unknown, the pilot's recollection of events provided invaluable insight regarding the adverse effects of CO exposure on cognitive functions.
Carbon monoxide, silent killer
In 2014, the Aircraft Owners and Pilots Association (US) published an article titled ‘Carbon monoxide, silent killer’. The article listed a number of fatal accidents and close calls, where CO was either a known contributing factor or was suspect. Some of these included:
- January 1999: A Cessna 206, operated by the US Customs Service, collided with water on a night training flight. The pilot survived, but had no recollection of what occurred. There was sufficient COHb found in the pilot’s blood that Customs considered CO poisoning as a contributing factor. As a result, Customs purchased industrial electronic CO detectors for their single‑engine Cessna fleet. They subsequently discovered that many of the aircraft had issues with CO in the cabin.
- Mid-December 1997: The pilot of a new Cessna 182 was ferrying the aircraft from the factory to a buyer in Germany. During the flight, the pilot fell ill and suspected CO poisoning. The pilot successfully landed and an examination of the aircraft found that the exhaust muffler had been manufactured with defective welds. Subsequent pressure testing by Cessna identified that 20 per cent of the new 172 and 182 mufflers in inventory had leaky welds.
- 6 December 1997: The pilot of a Piper Comanche 400 fell asleep at the controls. The aircraft continued for another 250 NM (463 km), before running out of fuel. The aircraft glided for a soft wings‑level collision with terrain. The pilot survived the accident. Toxicological testing identified that the pilot had a COHb level of 27 per cent. It was considered almost certain that this level was higher at the time of the accident.
- 17 January 1997: The experienced pilot and mother, who was a low-time private pilot, departed on a 2 hour flight in a Piper Dakota. While en route, the mother contacted air traffic control to advise that the pilot had passed out. Air traffic control attempted to provide assistance, however, the mother also lost consciousness. The aircraft subsequently collided with terrain and both occupants received fatal injuries. Toxicological tests revealed that the pilot and mother had 43 per cent and 69 per cent COHb levels respectively.
- October 1994: The student pilot of a Cessna 150 returned from a solo cross-country flight complaining of headache, nausea and difficulties walking. The pilot was hospitalised and testing revealed elevated levels of CO, which required 5 1/2 hours of oxygen therapy. An inspection of the aircraft identified a crack in an improperly repaired muffler.
- April 1994: About 15 minutes after take-off, the Cessna 182 was observed deviating from headings, altitudes and air traffic control instructions. The pilot reported blurred vision, headaches, nausea, laboured breathing, and difficulties staying awake. The aircraft subsequently collided with terrain, but the pilot survived. The aircraft examination found numerous small leaks in the exhaust system. The pilot also tested positive to CO after 11 hours of oxygen therapy.
- July 1991: The student pilot and passenger were conducting a pleasure flight when the aircraft was observed to turn into a valley, into an area of mountainous terrain. The aircraft collided with the terrain and both occupants were fatally injured. The pilot had a COHb level of 20 per cent.
- August 1990: About 15 minutes into the flight, a Cessna 150 collided with water. Toxicological tests established that the pilot had a COHb level of 21 per cent.
- February 1984: The pilot of a Beech Musketeer aircraft reported to air traffic control that they were unsure of their position. Air traffic control attempted to assist, but a passenger reported that the pilot was unconscious. The aircraft subsequently collided with terrain and all four occupants were fatally injured. Toxicological testing identified that they had COHb levels of 24, 22, 35 and 44 per cent.
- March 1983: After levelling off at 9,600 ft, the right front seat passenger of a Piper PA-220-150 aircraft became nauseous, vomited and fell asleep. The pilot also began to feel sleepy and lost consciousness. A passenger in the back seat attempted to take control of the aircraft. During the emergency landing, the aircraft hit a fence, but none of the occupants were injured. Multiple cracks and leaks were found in the exhaust muffler. The NTSB concluded that the pilot had become incapacitated due to CO poisoning.
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