On 3 August 2015 at about 0410 Eastern Standard Time (EST), a Cessna 441 aircraft, registered VH-EQU, departed Scone Airport for a positioning flight to Illawarra Regional Airport (Wollongong Airport), New South Wales. The flight was to be conducted as a multi-crew operation with the pilot flying (PF) occupying the left seat, and the pilot monitoring (PM) occupying the right seat.
Prior to departure, the pilots conducted a pre-flight briefing noting that the weather forecast for the Wollongong area included a warning for severe turbulence below 8,000 ft. The departure and cruise were uneventful. After commencing descent into Wollongong, the PF briefed the PM for an area navigation (RNAV) instrument approach and landing to runway 16 (Figure 1). The approach was planned to be hand flown in darkness under clear skies with a westerly wind of 25–30 kt, reducing to a light breeze on the ground.
The aircraft arrived overhead position WOLND (Figure 1) at about 5,000 ft on descent to 3,700 ft. Due to the strong westerly wind, flying conditions were turbulent and the PF reported that it was quite difficult keeping the aircraft’s wings level. Approaching WOLNI, the PF levelled the aircraft and maintained 3,700 ft as planned. The aircraft was then slowed down to permit the extension of flap and landing gear.
Figure 1: Cessna 441, VH-EQU
Source: Aircraft owner, modified by the ATSB
In accordance with the approach, the PF recommenced descent at 2.2 NM prior to position WOLNF. Due to the steeper than normal approach path angle (3.7 degrees as opposed to the usual 3.0 degrees), the PF reported establishing a descent rate of about 1,000 feet per minute (fpm). The PM reported that they were expecting a descent rate of about 900 fpm. Air traffic control surveillance data showed the descent rate established was somewhere between 1,000 and 1,500 fpm.
Shortly before WOLNF and as the aircraft approached 2,700 ft, the PM called ‘two thousand seven hundred’ with the expectation that the PF would maintain that altitude until passing WOLNF. However, the descent continued and a few seconds later, the terrain alerting and warning system (TAWS)[1] generated visual and aural ‘CAUTION-TERRAIN’ alerts. These alerts were generated as the system detected that the flight path was projected to come within 300 ft of an obstacle or terrain.
Figure 2: Wollongong RNAV(GNSS) approach to RWY 16 showing approximate flight path profile (green/red dotted line) based on air traffic control surveillance data
Source: Airservices Australia, modified by the ATSB
Pilot flying comment
The PF’s company duties included aircraft charter pilot and flight instructor. The PF’s flying experience included 230 hours operating Cessna 441 aircraft (16 hours in the last 90 days) and 6,930 total flying hours.
The PF recalled working hard trying to keep the aircraft’s wings level, which may have distracted them from monitoring the descent profile adequately. The PF recalled thinking that they may have been slightly low on profile approaching WOLNF, but was startled when the terrain warning sounded. The PF had not participated in any TAWS training, even though they had flown the aircraft (fitted with TAWS equipment) for the previous 12 months.
Pilot monitoring comment
The PM company duties included aircraft charter pilot and flight instructor. The PM’s flying experience included 350 hours operating Cessna 441 aircraft and 3,400 total flying hours.
The PM believed that the when the TAWS alert activated, the aircraft was at an altitude somewhere between 2,600 ft and 2,500 ft and about 0.5 NM before WOLNF. The time between being below 2,700 ft, having the TWAS alert and an appropriate response was less than 10 seconds.
The PM reported having completed TAWS training with a previous employer. The PM believed that following the TAWS warning, they should have applied full power, climbed at maximum rate and conduct a missed approach in accordance with the operator’s procedures.
Fatigue management
Prior to the flight, both pilots had completed 2 days free of duty. They reported being well rested and obtaining about 8 hours sleep each night.
On the morning of the flight, the pilots reported waking up around 0300. They advised that they generally found it counterproductive to try and get to sleep early and therefore only received about 5 hours of sleep.
Despite the limited amount of sleep, both pilots reported being alert during all stages of the flight.
ATSB comment
The aircraft was fitted with a terrain awareness and warning system (TAWS) designed to reduce the risk of flight into terrain. While a TAWS was not required for the particular type of operation, the lack of TAWS training probably explains the nature of the PFs response to the terrain alert.
Pilots and operators of aircraft are encouraged to be appropriately trained in the use of all equipment fitted to their aircraft.
Safety action
Whether or not the ATSB identifies safety issues in the course of an investigation, relevant organisations may proactively initiate safety action in order to reduce their safety risk. The ATSB has been advised of the following proactive safety action in response to this occurrence.
Aircraft operator
As a result of this occurrence, the aircraft operator has advised the ATSB that all pilots now receive TAWS training.
Safety message
Due to the early start combined with inadequate sleep the night before, despite reporting otherwise, the pilots were likely fatigued. Pilots need to be aware that obtaining less than 7-8 hours sleep a night increases the risk of operating with a level of fatigue known to have a demonstrated effect on performance.
Pilots also need to consider the effect flying in the early hours of the morning has on their performance. Their body is in a circadian low period which could lead to periods of impaired alertness and delayed reaction times.
The ATSB continues to be concerned about flight below minimum descent altitudes. When conducting an approach in instrument meteorological conditions, which includes darkness, pilots must ensure the approach is conducted in accordance with the prescribed procedure. In this case, the pilots were required to manage the vertical profile to ensure the aircraft remained at or above the minimum descent altitude, thereby ensuring clearance from terrain and obstacles.
Descent below the minimum descent altitude compromises the minimum terrain clearance requirements and increases the risk of controlled flight into terrain (CFIT).
Decisions regarding whether to conduct an investigation, and the scope of an investigation, are based on many factors, including the level of safety benefit likely to be obtained from an investigation. For this occurrence, a limited-scope, fact-gathering investigation was conducted in order to produce a short summary report, and allow for greater industry awareness of potential safety issues and possible safety actions.
Publishing information
Released in accordance with section 25 of the Transport Safety Investigation Act 2003
Ownership of intellectual property rights in this publication
Unless otherwise noted, copyright (and any other intellectual property rights, if any) in this report publication is owned by the Commonwealth of Australia.
Creative Commons licence
With the exception of the Coat of Arms, ATSB logo, and photos and graphics in which a third party holds copyright, this publication is licensed under a Creative Commons Attribution 3.0 Australia licence.
Creative Commons Attribution 3.0 Australia Licence is a standard form licence agreement that allows you to copy, distribute, transmit and adapt this publication provided that you attribute the work.
The ATSB’s preference is that you attribute this publication (and any material sourced from it) using the following wording: Source: Australian Transport Safety Bureau
Copyright in material obtained from other agencies, private individuals or organisations, belongs to those agencies, individuals or organisations. Where you wish to use their material, you will need to contact them directly.
On 8 August 2015 at about 0930 Western Standard Time (WST), a Cessna 208B, registered VHLNH, departed Kununurra, Western Australia, on a scenic flight to the Bungle Bungle Range. On board were the pilot and 12 passengers. The weather was fine and clear, with an easterly wind blowing at about 13 knots. The pilot conducted all normal pre-flight procedures, including an engine runup to confirm that the engine and other systems were functioning normally.
The flight departed from runway 12 and made a right turn to the south to follow the standard Kununurra to Bungles departure route. After levelling at about 700 ft above mean sea level (about 550 ft above ground level), the pilot reduced engine power and propeller RPM for a level segment of the departure. The pilot then commenced a commentary for the benefit of the passengers.
Soon after the pilot commenced the commentary, when the aircraft was about 1.5 NM south of the airport, engine oil appeared on the windscreen. The pilot turned back towards the airport but oil on the windscreen soon turned into an opaque film, substantially limiting forward visibility. Additionally, a number of engine instrument indications were abnormal and white smoke began to enter the cabin through cockpit vents. Although the smoke dissipated quickly, the pilot continued to monitor for any signs of a fire in the engine compartment.
The pilot made a MAYDAY[1] call on the Kununurra CTAF,[2] broadcasting that the engine had failed and that the aircraft was returning to land on runway 12. The pilot of another aircraft operating in the area at the time heard the MAYDAY call and relayed relevant information to Air Traffic Control (ATC) (located in Brisbane), who initiated an emergency response.
At around the same time that the pilot made the MAYDAY call, they also attempted to ascertain the extent of the engine malfunction. Advancing the power lever produced a change in engine sound and an increase in engine torque. Although the propeller was turning, there was no audible response and no apparent change in propeller RPM when the pilot advanced the propeller lever. The pilot also noted that the engine low oil pressure light was illuminated, and deduced that the propeller had probably feathered as a consequence of engine oil loss.
The pilot found that the engine/propeller were capable of providing a small amount of positive thrust (but not sufficient to maintain level flight), so established the aircraft in descent, holding a speed of about 85 to 95 knots. The pilot elected to leave the flaps set at 10 degrees, which was the same position that was set at the time the engine problem first became apparent. The pilot assessed that the aircraft could reach runway 12, but with little margin.
Another aircraft operated by the same company as the aircraft involved in the incident was about to depart Kununurra, and had lined up on runway 12. Upon hearing the MAYDAY call, the pilot of that aircraft vacated the runway. The incident pilot advised the pilot in the other aircraft (vacating the runway) of the nature of their predicament, particularly the extent to which forward visibility was affected, and sought their assistance. The incident pilot also advised the Airport Safety Officer on the CTAF that assistance may be required after landing,[3] and advised the passengers that an emergency landing at Kununurra was required.
With forward visibility substantially limited, the pilot maintained orientation using ground based navigation aids, GPS information and the view of landmarks from the side windows. The dark shape of a nearby waterway to the south of the airport was evident, but forward visibility was so poor that the pilot was unable to effectively identify roadways or cleared areas through the windscreen.
With some directional guidance from the pilot of the aircraft that had vacated the runway, and by reference to navigational instruments, the incident pilot was able to position the aircraft on final approach to runway 12. The turn onto final approach was made through about 100 degrees, at around 150 ft above ground level, and required about 50 degrees angle of bank. The pilot elected to leave the flap setting at 10 degrees throughout the approach and for the landing. The aircraft landed firmly, with the pilot unable to effectively judge flare height due to the restricted visibility.
After landing, the pilot found that forward visibility was obscured to the extent that they were unable to taxi safely. The Airport Safety Officer moved alongside the aircraft in a vehicle to guide the pilot to the next taxiway exit. When safely clear of the runway, the pilot contacted ATC and cancelled the MAYDAY.
The time from take-off to landing was about 2 minutes and 15 seconds. From the time the pilot broadcast a MAYDAY call to the time of landing was about 1 minute and 20 seconds. At its furthest point, the aircraft was about 2.3 NM south of the airport.
After exiting the runway and coming to a stop, the pilot completed the engine shut-down checks. No reaction was felt or heard when the pilot selected the propeller lever to the feather position as part of the shutdown procedure (normally, there was an audible change as the pitch of the propeller changed). After exiting the aircraft, the pilot found that the propeller was in the feather position, and had seized. The extent of oil loss was also apparent, with oil smeared over much of the forward fuselage, particularly the engine cowls and windscreen (Figure 1).
Figure 1: Photographs of VH-LNH after the aircraft had landed, with oil visible on the engine cowl and forward fuselage
Source: Aircraft operator
Aside from the apparent engine and propeller system problem, there was no damage to the aircraft and the pilot and passengers were uninjured.
Subsequent on-site inspection of the engine by engineering staff revealed that an oil leak had developed at a join between the oil transfer elbow and oil transfer tube at the forward end of the engine. This assembly was part of a larger assembly that transferred oil under pressure to the reduction gearbox at the front of the engine. One of the oil transfer elbow mounting lugs (that secured the elbow to engine assembly) was found to be fractured, allowing the oil transfer elbow to move and unseat the O-ring between the elbow and the tube (Figures 2 and 3).
Figure 2: Photograph (in situ) showing fractured oil transfer elbow mounting lug and the unseated O-ring seal
Source: Aircraft operator (annotations by the ATSB)
Figure 3: Oil transfer elbow assembly
Source: Engine manufacturer (annotations by the ATSB)
Technical follow-up
Following the incident, the operator submitted a Service Difficulty Report (SDR) to CASA. The engine was removed from the aircraft by the operator and dispatched to a repair and overhaul facility for further examination. The oil transfer elbow (with cracked mounting lug) was removed and sent to the engine manufacturer for detailed analysis. The results of those examinations are summarised in the following paragraphs.
Engine teardown
The engine teardown did not reveal any unrelated engine abnormalities that might have contributed to the oil transfer elbow mounting lug fracture. Among other things, the report noted that there was little or no engine oil remaining in the engine and that the reduction gearbox could only be turned with considerable force (more than the amount of force that would normally be required). The report also noted that the propeller shaft would not rotate.
Inspection of the engine confirmed that an oil transfer elbow mounting lug had fractured and the report noted that the ‘hardware holding it in place was loose’. The lug was found to have completely broken through, and it was noted that a segment of the lug was missing (Figure 4). The report also noted that the O-ring (see Figures 2 and 3) had moved.
Figure 4: Fractured lug (the figure on the right shows that a segment of the lug was missing)
Source: Pacific Turbine (left) and CASA (right)
Mounting lug fracture analysis
The manufacturer’s examination of the fractured oil transfer elbow mounting lug and associated securing assembly allowed them to draw a number of conclusions, including:
The fracture of the lug occurred due to fatigue originating from multiple locations on the side of the mounting lug that meets with the face of the mounting flange. The fatigue mode was found to be high-cycle, under unidirectional bending.
Wear and imprint marks on the securing assembly (bolt, nut and washer) and the fractured lug suggested that the bolt was sitting askew in the bore of the flange to which the elbow mounting lug was secured. The report commented that this wear pattern was consistent with a lack of pre-load on the bolt.
The lack of pre-load on the bolt that secured the mounting lug to the flange was considered to be the initiating factor that led to fracture of the mounting lug. The reason for the lack of preload on the bolt could not be ascertained.
Impact marks were identified on the oil transfer elbow, which may have been caused by interference from tooling used to conduct unrelated maintenance in the vicinity of the oil transfer elbow. This damage was found to be superficial which suggested that it played no part in fracture of the mounting lug.
CASA comments
At the time that this report was prepared, CASA was continuing to consider relevant information, including the manufacturer’s fracture analysis report. Notwithstanding their ongoing consideration of relevant information, CASA did not believe that there was any conclusive evidence of a lack of pre-load on the bolt. CASA commented to the effect that the typical signs of an incorrectly torqued fastener were not evident, and noted that the separated portion of the lug remained in place after the lug had fractured – that was unlikely if there was a lack of pre-load on the bolt. CASA also commented to the effect that incorrect installation of the oil transfer elbow (mounting lug), rather than incorrect installation of the mounting lug bolt, may have been the origin of the problem. CASA reported that this is a scenario that is known to have occurred in practise.
Engine teardown facility comments
Staff from the engine teardown facility suggested that the following may assist in preventing similar occurrences:
Paint-free lug and flange mating surfaces: Paint on the elbow mounting lug and/or the mating face of the flange to which the lug is secured may wear with working and vibration. This wear has the potential to loosen the fastener and amplify the effects of vibration on lug security.
Lug strengthening: The construction of the elbow transfer tube is such that the mounting lug itself is substantially narrower than the stem leading to the lug (see Figure 4). Added thickness/material depth would strengthen the lug.
Expanded and mandated inspection: Mandating inspection of the elbow mounting lug (see CASA Airworthiness Bulletin 72-004 below), and including oil transfer elbow mounting lug inspection as a specific task during relevant engine servicings.
Related background information
Similar occurrences
ATSB investigations AO-2010-005, AO-2008-005 and AO-2010-003 identified the failure of the same oil transfer elbow fitting that fractured in the case of this occurrence. In two cases (AO2008005 and AO-2010-005), the investigations found that oil transfer elbow mounting lug failures were a consequence of other unrelated engine problems (compressor turbine blade failures). In one case (AO-2010-003), both oil transfer elbow mounting lugs were fractured, but the cause of those fractures could not be conclusively determined.
Advice from the engine manufacturer suggested that there have been a number of oil transfer elbow mounting lug failures reported over the past 15 years, including those investigated by the ATSB. In most cases, either a vibration source or mechanically induced damage was found to be a contributor. The manufacturer identified the possibility that tooling could interfere with the elbow fitting during removal and installation of nearby engine components.
Possible sources of oil transfer elbow damage – manufacturer comments
During the course of the investigation (but aside from the specific nature of the mounting lug fracture in this case), the engine manufacturer highlighted possible sources of oil transfer elbow damage that could ultimately lead to mounting lug fracture. While these comments may not be specifically relevant in this case, they are noteworthy and warrant the attention of organisations involved in the logistics of transporting and/or maintenance of PT6A114A and similar engines:[4]
Pratt and Whitney Canada Service Information Letter. In 2008, the manufacturer issued a Service Information Letter (SIL Gen PT6A026 applicable to all PT6A engines) to remind operators of the precautions to be taken when installing, removing and performing maintenance on external engine tubes, lines and fittings. The letter pointed out that:
Investigations of incidents in service (including in-flight shut downs) have determined that mishandling tubes and fittings during normal maintenance activities can subject these components to distortion or stresses beyond normal utilisation, leading to fracture during subsequent operation.
Reduction gearbox chip detector removal/installation. The engine manufacturer commented that the proximity of the oil cooler and reduction gearbox magnetic chip detector may be a factor if tooling used to install or remove those components is allowed to interfere with the oil transfer elbow, and induce mechanical stress on the mounting lug. To that end, the reduction gearbox maintenance manual (in the areas dealing with removal and installation of the magnetic chip detector) included the following caution:
AVOID FORCING OR CONTACT WITH THE OIL PRESSURE TRANSFER ELBOW WHEN YOU REMOVE THE CHIP DETECTOR. DAMAGE TO THE ELBOW MOUNTING LUGS CAN OCCUR RESULTING IN LOSS OF ELBOW RETENTION AND OIL LEAKAGE.
CASA Airworthiness Bulletin 72-004
In 2010, CASA released an Airworthiness Bulletin (AWB) AWB 72004 which identified a possible link between the incorrect installation of an engine mount bracket assembly (vibration isolator), and fatigue cracking in the oil transfer elbow fitting. The AWB identified the possibility that fatigue failure of the oil transfer elbow fitting may be linked to unusual vibration caused by incorrect installation of the engine upper vibration isolator. The AWB went on to recommend that operators inspect the relevant vibration isolators for correct installation, and inspect oil transfer elbow fittings for any signs of cracking.
Safety action
Whether or not the ATSB identifies safety issues in the course of an investigation, relevant organisations may proactively initiate safety action in order to reduce safety risk. The ATSB understands that the following safety actions are being considered in response to this occurrence.
Engine manufacturer
After reviewing the circumstances surrounding this incident (and noting concerns that the oil transfer elbow may be interfered with or damaged during unrelated engine maintenance in the area of the elbow), the engine manufacturer is considering adding information in relevant publications and issuing a Service Information Letter. Publication amendments are likely to draw attention to the need to refer to relevant instructions if the oil transfer elbow is removed/replaced during fuel nozzle replacement. The Service Information Letter is likely to provide information and warnings with respect to the possibility of damage to the oil transfer elbow during engine maintenance. The Service Information Letter is also likely to include information and warnings related to removal and installation (or other disturbance) of the oil transfer elbow.
Civil Aviation Safety Authority
At the time this report was written, CASA was continuing to consider relevant information, which may lead to a re-issue of AWB-72004.
Operator
Prior to this incident, the operator was already in the practice of periodically inspecting the area of the fractured lug (although those inspections did not alert the operator to the problem in this case), In response to this incident, the operator intends to expand the periodic inspection to include removal of the bolt and an inspection of the internal radius of the mounting lug for signs of crack development.
Safety message
The manner in which the pilot handled a very difficult set of circumstances provides some positive examples for other pilots to consider.
The pilot maintained positive control of the aircraft, despite the challenging circumstances. The adage ‘aviate-navigate-communicate’ continues to prove a fundamentally effective prioritisation guide for pilots.
The pilot used available resources including other pilots, ATC, and the Airport Safety Officer, to assist in dealing with the circumstances. The combined efforts of those involved clearly contributed to a favourable outcome. The principles of effective crew resource management extend to all operations, including single pilot operations.
The pilot conducted a pre-flight emergency self-briefing. Even though it may be impractical to consider all possible emergency scenarios during a pre-flight emergency self-briefing, having a general plan in mind may be important, particularly when confronted with a time-critical and stressful situation.
The incident highlights also the importance of care and attention to detail when conducting maintenance on aircraft engines and accessories. This is particularly important where critical components are known to be susceptible to damage through interference from tooling or mishandling. Manufacturers, regulatory authorities, operators and aircraft maintenance organisations all have fundamentally important roles to play in maintenance of the highest practicable standards of airworthiness.
Decisions regarding whether to conduct an investigation, and the scope of an investigation, are based on many factors, including the level of safety benefit likely to be obtained from an investigation. For this occurrence, a limited-scope, fact-gathering investigation was conducted in order to produce a short summary report, and allow for greater industry awareness of potential safety issues and possible safety actions.
Publishing information
Released in accordance with section 25 of the Transport Safety Investigation Act 2003
Ownership of intellectual property rights in this publication
Unless otherwise noted, copyright (and any other intellectual property rights, if any) in this report publication is owned by the Commonwealth of Australia.
Creative Commons licence
With the exception of the Coat of Arms, ATSB logo, and photos and graphics in which a third party holds copyright, this publication is licensed under a Creative Commons Attribution 3.0 Australia licence.
Creative Commons Attribution 3.0 Australia Licence is a standard form licence agreement that allows you to copy, distribute, transmit and adapt this publication provided that you attribute the work.
The ATSB’s preference is that you attribute this publication (and any material sourced from it) using the following wording: Source: Australian Transport Safety Bureau
Copyright in material obtained from other agencies, private individuals or organisations, belongs to those agencies, individuals or organisations. Where you wish to use their material, you will need to contact them directly.
On 7 January 2015, a Pacific Aerospace Limited 750XL aeroplane, registered ZK-SDT and involved in commercial skydiving operations, departed Taupo aerodrome, New Zealand, with the pilot and 12 passengers on board. On climb through about 2,000 ft above ground level after take off, the single Pratt & Whitney Canada PT6A-34 turboprop engine failed suddenly. The six tandem pairs of skydivers and the pilot parachuted from the aeroplane, landing without injury. The unoccupied aeroplane crashed into the lake.
On 17 July 2015, the New Zealand Transport Accident Investigation Commission (TAIC) requested Australian Transport Safety Bureau (ATSB) assistance with a number of Australian aspects to their investigation. In accordance with paragraph 5.23 of Annex 13 to the Convention on International Civil Aviation Aircraft Accident and Incident Investigation, the ATSB appointed an accredited representative (ATSB investigator) to the TAIC investigation. The investigator assisted TAIC with its engine examination as part of an External Investigation under the provisions of the Australian Transport Safety Investigation Act 2003.
The ATSB has finalised its support of this investigation. TAIC is responsible for the release of the final investigation report into this accident. Any enquiries in respect of the ongoing TAIC investigation or release of the investigation report should, in the first instance, be directed to the:
Transport Accident Investigation Commission Level 16 80 The Terrace PO Box 10-323 Wellington, 6143 New Zealand
________________
The information contained in this web update is released in accordance with section 25 of the Transport Safety Investigation Act 2003.
On the evening of 9 May 2015, a Boeing B737-8FE aircraft, registered VH-YID and operated by Virgin Australia Airlines Pty. Ltd. (Virgin), was on a scheduled passenger service from Sydney, New South Wales to Adelaide, South Australia. During a high-speed descent, the crew responded to aircraft indications that they were approaching airspeeds greater than desired by extending the speed brakes. While the speed brakes were still extended, the airspeed continued to increase towards the aircraft’s maximum speed, the result of which would have been an overspeed. In an effort to prevent an overspeed, the first officer overrode the autopilot by pulling back on the control column until the autopilot entered a secondary mode known as control wheel steering‑pitch mode. This was followed immediately by an abrupt release of the control column, after which one cabin crew member sustained a minor injury.
What the ATSB found
The ATSB found that the crew selected a descent speed of 320 kt, which they routinely used for air traffic control-initiated high-speed descents. However, the increased risk of an overspeed in changing wind conditions had not been adequately considered by the crew.
The ATSB also found that, whereas Virgin’s training included a focus on the management of overspeeds, the crew had not yet completed this training. This increased the risk that the guidance provided through other sources would not be followed correctly.
Additionally, the flight crew had initiated the cabin preparation for landing earlier than usual due to the expectation of turbulence later in the descent. This likely reduced the risk of more serious injury to the cabin crew as they were in the final stages of securing the cabin than had they commenced preparations for landing at the normal time.
What's been done as a result
Prior to this occurrence, Virgin had implemented improved crew training and guidance on managing overspeeds. This included the addition of a cyclic simulator training session that focused on overspeed management on descent.
Safety message
This occurrence highlights the increased risk of overspeed when conducting high-speed descents in conditions of varying winds and any associated turbulence. Identifying and discussing the risks associated with high-speed descent increases the likelihood that crew will select a lower descent speed and/or consider the best way to deal with an impending aircraft overspeed before the descent is initiated.
The occurrence
On the evening of 9 May 2015, a Boeing B737-8FE aircraft, registered VH-YID and operated by Virgin Australia Airlines Pty. Ltd. (Virgin) as ‘Velocity 436’, was on a scheduled passenger service from Sydney, New South Wales to Adelaide, South Australia. The first officer (FO) was the pilot flying.[1]
At about 1915 Central Standard Time[2], the flight crew conducted an approach briefing in preparation for the descent. The crew discussed the ‘fairly strong’ westerly wind forecast in the area that would affect their descent, and decided they would instruct the cabin crew to prepare the cabin for landing at about flight level (FL) 270[3]. This was reported slightly earlier than usual and was intended to reduce the risk of turbulence-related injuries. Soon after, air traffic control (ATC) requested the crew to conduct a high-speed descent into Adelaide, which the crew accepted. The FO changed the planned descent speed from 280 kt to 320 kt, which was reported by the crew to be routinely used during ATC-initiated high-speed descents.
The descent was commenced about 4 minutes later and, passing about FL 270, the captain made the public address ‘cabin crew prepare for landing’. This was the cue for the cabin crew to commence the cabin preparation procedure by securing all loose cabin equipment, ensuring passengers were in their seats with seatbelts fastened and then securing themselves in their jump seats. Seven minutes later the flight crew switched the seatbelt signs on, as a cue to the cabin crew to finalise this procedure and take their seats.
During the descent the FO controlled the aircraft’s vertical profile using various autopilot descent modes. Passing through FL 250, the FO selected the VNAV PATH mode (see the section titled VNAV PATH descent mode).
As the aircraft passed through 10,000 ft, the airspeed started to increase above 320 kt and at 8,400 ft the message ‘drag required’ displayed on the flight management computer (FMC) scratchpad as per system design. In response, the FO extended the speed brake, making an effort to do so slowly and smoothly. The captain observed this action, initially concerned that the FO may extend the speed brake too quickly. However, the captain was satisfied that the speed brake was appropriately extended and that the increasing airspeed trend was being managed. The captain’s attention was then turned to other tasks. Over the next 6 seconds the airspeed continued to increase, and the FO recalled seeing the speed trend vector on the primary flight display (PFD) extend beyond the aircraft’s maximum certified speed (VMO).[4]
In an effort to avoid an overspeed, the FO pulled back forcibly on the control column in order to raise the nose, overriding the autopilot and activating the control wheel steering – pitch (CWS-P). This technique was routinely used to manage overspeeds on descent. On this occasion the FO reported feeling greater than usual resistance when raising the nose due to the already low pitch angle. The FO then recalled feeling a ‘pinch’ as the autopilot reverted to CWS-P, along with a sudden pitch change and a high g loading[5] on the aircraft. In response, the FO abruptly released the back pressure on the control column, rapidly unloading the g loading. At that moment, the cabin crew had almost completed securing the cabin and were about to take their seats. They reported experiencing what they thought to be turbulence, and two cabin crew in the rear galley lost their footing. This resulted in one of the cabin crew impacting the galley floor heavily, sustaining an injury to their knee.
The FO stowed the speed brake, selected the LVL CHG (level change) descent mode and reduced the selected speed to 250 kt. The captain checked the status of the cabin crew and was informed of the injury to the crew member.
The sequence of events during the descent is highlighted in Figure 1.
Figure 1: Sequence of events on descent, including the flight and cabin crew actions plotted against altitude and time
Source: ATSB
Personnel information
The flight crew signed on for duty in Sydney at 0900 Eastern Standard Time[6] and had been on duty for 11 hours at the time of the occurrence.
The captain held an Air Transport Pilot (Aeroplane) Licence and had a total flying experience of 13,500 hours, of which about 8,750 were on the B737 aircraft. The captain commenced flying with Virgin in 2003 and held a valid Class 1 Aviation Medical Certificate.
The FO held an Air Transport Pilot (Aeroplane) Licence and had a total flying experience of about 7,500 hours, of which about 5,000 were on the B737 aircraft. The FO commenced flying with Virgin in 2007 and held a valid Class 1 Aviation Medical Certificate. Although the FO reported feeling tired at the time of the occurrence, there was no additional evidence to indicate a level of fatigue known to affect performance beyond what would reasonably be experienced at the end of the day.
Aircraft information
VNAVPATH descent mode
VNAV PATH is an automated descent mode primarily designed to keep the aircraft on a predetermined descent path using aircraft pitch. During descents in this mode, airspeed is controlled using thrust or displaying messages to the flight crew to increase drag as required. The VNAV PATH mode allows for minor airspeed excursions while prioritising keeping the aircraft on path. If airspeed increases to 10 kt above the selected speed, the message ‘drag required’ appears on the FMC scratchpad. In response, crew extend the speed brake to arrest further speed increases.
Control wheel steering – pitch (CWS-P)
Pushing a CWS engage switch on the mode control panel engages the autopilot (A/P) pitch and roll axes in the CWS mode. At the time of the occurrence, CWS‑P could also be engaged by applying 40 lb back pressure to the control column to manually override the A/P. By doing so, a desired pitch attitude could be set. The ability to manually engage CWS‑P and override the A/P was later removed from the flight control computer’s software to avoid inadvertent and undetected reversion from a descent mode to CWS‑P. With CWS‑P engaged, the A/P manoeuvres the aircraft in response to control pressures applied by either pilot. The control pressure is similar to that required for manual flight. When control pressure is released, the A/P holds the existing attitude.
While the FO’s routine use of CWS-P as a means to manage overspeeds was not part of Virgin training, it was reported used by the FO and other pilots. This was because it was an effective way to handle an overspeed on descent without disconnecting the A/P, particularly when changing weather conditions meant that an overspeed could occur with little time for the crew to react.
Maximum operating indicated airspeed
The maximum operating indicated airspeed (VMO) represents the maximum certified limiting speed of the aircraft. VMO for the B737-8FE is 340 kt. An overspeed warning sounds if the aircraft exceeds VMO.
Airspeed trend vector on the primary flight display
The primary flight display (PFD) presents a dynamic colour display of the parameters necessary for flight path control. This includes (Figure 2):
the manually-selected airspeed
a green speed trend vector, which indicates predicted airspeed in 10 seconds time
the VMO.
Figure 2: B737 PFD, showing the manually-selected airspeed (number 1), the green speed trend vector (number 2) and VMO (number 4). Note VMO gradually reduces below 340kt with increasing altitude above approximately FL250. In this graphic, the representation shows the aircraft at FL380 (38,000 ft), explaining the reduced VMO
Source: B737 Flight Crew Operations Manual and Wikipedia, modified by the ATSB
Effect of g loading
G loading refers to the aircraft occupant experiencing an apparent acceleration equal to the load factor times the acceleration due to gravity. For example, when the pilot performs a pull up with a load factor of two, loose objects fall to the floor at twice the normal acceleration of gravity. A g loading less than one results in feelings of reduced weight and, eventually, loose objects floating upwards once the g loading reduces below zero.
Meteorological information
The forecast meteorological information that was available to the crew included:
an Aerodrome Forecast for arrival into Adelaide that predicted a light south‑westerly wind and showers of rain with intermittent periods of less than 30 minutes of south-westerly winds at 20 kt, gusting up to 30 kt
winds from 264 °M at 54 kt at FL 350, from 250 °M at 38 kt at FL 250, from 258°M at 40 kt at FL 150 and from 270° at 41 kt at 5,000ft.
Recorded data
The flight data was examined to derive the aircraft’s computed airspeed (CAS) and the wind affecting the descent as they pertain to the crew’s actions. This examination showed the following:
By 10,468 ft in the descent the aircraft reached the selected descent speed of 320 kt. Over the next 30 seconds, as the aircraft descended to 8,136 ft (when the speed brake was extended) the headwind increased from 30 to 39 kt, and the airspeed increased from 320 to 333 kt.
Over the next 5 seconds, as the aircraft descended from 8,136 ft to 7,790 ft, the headwind increased from 39 to 48 kt, and the airspeed increased from 333 to a peak of 339 kt. At this point the back pressure on the FO’s control column was recorded as 41.5 lb, and CWS-P engaged with a peak g loading of 2.14 g.
One second later the back pressure on the FO’s control column reduced to 2 lb, consistent with a release of the back pressure, with a minimum g loading of 0.066.
The speed brake was stowed about 10 seconds later at 7,492 ft.
Training and guidance in overspeed management
The following overspeed management training and guidance was provided to flight crew:
B737-NGFlight Crew Training Manual content. ‘Crews routinely climbing or descending in windshear conditions may wish to consider a 5 to 10 knot reduction in climb or descent speeds to reduce overspeed occurrences…During climb or descent, if VNAV or LVL CHG pitch control is not correcting the overspeed satisfactorily, switching to the V/S [vertical speed] mode temporarily may be helpful in controlling speed.’ The cruise section of the manual also stated that ‘there have been reports of passenger injuries due to over‑controlling the airplane during high altitude, high airspeed flight when overriding the control column with the autopilot engaged…’.
High- and low-speed briefing document(valid from February to July 2015). ‘High speed descents need to be managed carefully when operating near areas of steep wind gradients or expected turbulence…Reducing speed prior to entering areas of large wind change is the best technique...It is preferable to accept a temporary overspeed (provided it is not excessive or sustained) rather than a breach of altitude or large abrupt control inputs at high altitude...’. The document also recommended ‘the momentary use of V/S if other modes are not correcting the overspeed.’ and that ‘CWS P may be required but must be applied smoothly with small inputs at high altitude. Speed brake use is also recommended to assist recovery in the cruise.’
Recurrent simulator training program on overspeed events. Guidance to crew for the simulator session on overspeed events stated that ‘use of VNAV PATH with high descent speeds…is not recommended in turbulent conditions or areas of steep wind velocity changes’. This simulator session had not been completed by either flight crew member at the time of the occurrence.
Procedures for FMC updates – wind data, QNH and temperature deviations
The B737 Flight Management Computer System Reference Manual (2015) stated that‘the descent forecasts page [on the FMC] enables the pilot to enter descent wind data to more accurately define the descent path and allow for varying conditions’. It also outlined that ‘ISA DEV’ (the temperature deviation from the international standard atmosphere standard (ISA)[8]) and QNH[9] can be manually entered. The ability to enter QNH and temperature deviation is designed to increase the accuracy of the VNAV PATH construction by the FMC, as it allows the FMC to compensate for deviations from ISA QNH and temperature values at sea level.
Virgin’s Flight Crew Operating Manual documented that during the pre-flight procedure, pilots enter ‘initial data’ and ‘navigation data’ into the FMC. This included entering three of the four available predicted descent winds from the flight plan. These four winds included at FL 350, FL 250 and FL 150 and 5,000 ft. The three selected winds were entered into the descent forecast page.
If an aircraft is fitted with an aircraft communications addressing and reporting system (ACARS), wind data can be automatically uploaded into the FMC once the flight plan has been loaded during pre-flight duties. This also facilitates receipt of updated descent wind information if requested. At the time of the occurrence, Virgin’s procedures did not include updating descent winds in flight or a requirement to enter the temperature deviation and QNH. The captain reported that if there is a ‘really strong’ head or tailwind at the top of descent, the crew may decide to amend the FMC top of descent point (either earlier or later) and use the VNAV SPD vertical mode[10].
In this occurrence, the flight plan wind information was generated 3 hours and 10 minutes before the scheduled arrival time. The aircraft was fitted with ACARS, however updated descent wind data was not requested and the temperature deviation and QNH were not entered before approaching Adelaide. This was not inconsistent with the then Virgin procedures.
Procedures for securing the cabin before landing
The procedures for securing the cabin on descent were documented in the Virgin Flight Crew Operating Manual and Standard Operating Procedures. The following is a summary of those procedures:
Not below FL 200, the pilot monitoring (PM) makes the public address ‘cabin crew prepare for landing.’ In response, the cabin crew commence the ‘galley secure’ actions including stowing all galley items, switching off equipment such as ovens and securing all latches. About 10 minutes is provided for cabin crew to complete these actions.
Around transition (10,000 ft), flight crew select the fasten seatbelt sign ON, which triggers cabin crew to complete the ‘cabin procedure’ actions. This includes ensuring that all passengers have their seatbelts fastened, their seat backs upright and that any cabin baggage is stowed. These actions take about 1 minute.
Related occurrences
Overspeed occurrences on descent
Between 2012 and 2015, 51 occurrence reports were submitted to the ATSB that involved an overspeed in a B737 aircraft on descent. Of these, two occurred during high-speed descents. Of the other occurrences, three reported the use of CWS-P This included investigation AO‑2012‑138 below.
The crew of a Boeing 737-800 aircraft was conducting a flight from Adelaide, South Australia to Canberra, Australian Capital Territory. Just prior to commencing descent, ATC cleared the aircraft to conduct a high-speed descent. The aircraft descended below the 7,000 ft altitude clearance limit and, after being alerted to this by ATC, the flight crew climbed the aircraft back to 7,000 ft and continued the approach to land. The ATSB found that the combination of auto-flight system mode changes (including inadvertent use of CWS‑P) and the management of the airspeed during the descent resulted in a high workload environment. This occurrence highlighted the need to continually monitor descent profiles and airspace limitations in relation to the aircraft’s position.
As part of their consideration of the effect of the ‘fairly strong’ winds on the approach, the flight crew discussed the possible effect of turbulence on cabin safety. Similarly, the crew considered the aircraft’s turbulence penetration speed when accepting the high-speed descent. However, the captain recalled that whilst they were aware of changing wind conditions, there was no forecast of severe turbulence, and therefore a descent at 320 kt was considered by the crew to be appropriate. Although likely influenced by the routine use of 320 kt for high-speed descents, the descent at that speed, when the maximum certified limiting speed was 340 kt, increased the risk of an overspeed.
In considering the influences on crew decision making, Orasanu (2010) stated:
What constitutes an appropriate course of action depends on the affordances of the situation. Sometimes a single response is prescribed in company manuals or procedures. At other times, multiple options exist from which one must be selected.
Poor decisions may…arise when a flight crew is aware of conditions that require a decision, but underestimates the level of risk associated with the conditions…Another arises from pilots’ routine experience. If similar…situations have been encountered in the past and a particular course of action has succeeded, the crew will expect to succeed the next time with the same response.
Likewise, Sitkin (1992) as cited in Orasanu (2010) stated that uniformly positive experiences provide no baseline by which to determine when a situation is becoming more dangerous.
The crew reported that selecting 320 kt for a high-speed descent was routine, indicating that this course of action was expected to be successful. Therefore, the likelihood that the crew would consider the risks of an overspeed in this case were harder to identify.
The Flight Safety Foundation (2014) recommended that the pilot monitoring role should include monitoring the aircraft’s flight path and immediately bringing any concern to the pilot flying’s attention. In this case, the captain was monitoring the aircraft’s speed, before focussing on the first officer (FO) as he extended the speed brake and then other operational tasks associated with the descent. Whilst this precluded the captain’s ability to detect the FO’s reaction to an increasing speed trend vector, it was reasonable that the captain felt that the situation was under control.
Orasanu (2010) outlined that the development of expertise contributes to decision making in different ways. This included the development of ‘stored condition-action patterns’, where decision makers interpret a cue pattern as being of a particular type and match it with an action according to a routine (Klein, 1989 and 1993 cited in Orasanu 2010).
In this case, the FO identified an immediate need to prevent an overspeed, and did so by pulling back on the control column and activating control wheel steering-pitch (CWS-P). This had previously been successful for the FO in addressing an impending overspeed, but the difference in this case was that the force required was larger than experienced by the FO in past situations. The flight data recorded a 41 lb back pressure on the FO’s control column with a resulting 2.14 g loading on reversion to CWS‑P. Given the altitude at the time, reversion to CWS-P was considered contrary to Virgin Australia Pty Ltd’s (Virgin) guidance and training in overspeed management. However, the use of the CWS-P mode was reported common among some pilots and, in this case, had possibly become a stored condition-action pattern.
Surprise is a cognitive-emotional response to something unexpected. It results from a mismatch between the individual’s mental expectations and what actually happens around them. Experiencing surprise is a combination of physiological, cognitive and behavioural responses (Rivera and others 2014). If a pilot is not expecting things to go wrong, then the level of surprise can result in taking no action, or the wrong action (Martin 2012).
In this case, the FO reported feeling a ‘pinch’ when CWS-P activated. This, combined with feeling a high g loading, led the FO to abruptly release the amount of back pressure 1 second after its application.
A combination of a sudden increase, followed by a sudden decrease in g loading would have first pushed the occupants of the aircraft towards the floor, followed shortly after by a feeling of weightlessness. This would have increased the difficulty of moving around the cabin and the risk of injury.
Flight management computer data entry procedures
In this occurrence the QNH variation, temperature deviations and descent winds were insufficient to contribute to an inaccurate VNAV PATH construction. In addition, at the time of the occurrence there was no procedural requirement after pre-flight to enter QNH and temperature deviation data, nor to update descent wind data in the descent forecast page of the flight management computer. There was also no guidance on the benefits of entering that data into the computer to produce a more accurate calculated vertical flight path. In some circumstances, the use of pre-flight data would reduce the accuracy of the calculated vertical flight path and result in increased crew workload in managing the energy state of the aircraft.
Training in the management of overspeeds
At the time of the occurrence, Virgin’s Flight Crew Training Manual and other guidance material included information on how to effectively handle an impending overspeed. However, the simulator training session in which crews practiced overspeed management (including on descent) had not been completed by the crew. This simulator session was subsequently completed by all Virgin B737 flight crew, and additional guidance has also been provided.
Early preparation of the cabin for landing
The procedures for preparing the cabin for landing required their commencement no later than FL 200. In this case, the flight crew identified that turbulence on descent may increase the risk of injury to crew and passengers and therefore decided to initiate the cabin preparation at about FL 270. Flight data for the descent showed that this provided an additional 2 minutes before the occurrence for the crew to secure galley equipment and prepare the cabin, including seating all passengers. This reduced the risk of more serious and numerous injuries to the cabin crew and passengers.
Findings
From the evidence available, the following findings are made with respect to the flight path management occurrence involving a Virgin Australia Airlines Pty. Ltd. B737-8FE, registered VH‑YID, on descent into Adelaide Airport, South Australia on 9 May 2015. These findings should not be read as apportioning blame or liability to any particular organisation or individual.
Contributing factors
Although routinely used for high-speed descents, the selected speed for the descent of 320 kt was close the aircraft’s maximum speed of 340 kt and, in combination with the increased headwind as the aircraft descended through about 8,000 ft, increased the risk of an overspeed.
After identifying the unexpected rapid increase in airspeed, the first officer applied sufficient back pressure on the control column to override the autopilot with the intention of avoiding the impending overspeed. This increased the g loading on the aircraft to an extent where safely walking in the cabin would be difficult.
In response to feeling the increased g loading, the first officer abruptly released the back pressure on the control column, resulting in a sudden pitch change and reduced g loading that led to the cabin crew member losing their footing and sustaining a knee injury.
Other factors that increased risk
The Virgin Australia Airlines Pty. Ltd. procedures did not require flight crew to update the QNH, temperature deviation or the descent winds in the flight management computer after departure. In some circumstances, this would reduce the accuracy of the calculated flight path and increase crew workload in managing the aircraft’s energy state.
At the time of the occurrence, the Virgin Australia Airlines Pty. Ltd. training included a focus on the management of overspeeds. However, the associated simulator training session had not been completed by the crew, increasing the risk that they would not react in accordance with the published operational guidance material.
Other findings
The earlier-than-usual preparation of the cabin for landing meant that, at the time of the occurrence, the cabin crew were in the final stages of that activity. This reduced the risk of more serious and numerous injuries to the cabin crew and passengers.
About this report
Decisions regarding whether to conduct an investigation, and the scope of an investigation, are based on many factors, including the level of safety benefit likely to be obtained from an investigation. For this occurrence, a limited-scope, fact-gathering investigation was conducted in order to produce a short summary report, and allow for greater industry awareness of potential safety issues and possible safety actions.
Publishing information
Released in accordance with section 25 of the Transport Safety Investigation Act 2003
Ownership of intellectual property rights in this publication
Unless otherwise noted, copyright (and any other intellectual property rights, if any) in this report publication is owned by the Commonwealth of Australia.
Creative Commons licence
With the exception of the Coat of Arms, ATSB logo, and photos and graphics in which a third party holds copyright, this publication is licensed under a Creative Commons Attribution 3.0 Australia licence.
Creative Commons Attribution 3.0 Australia Licence is a standard form licence agreement that allows you to copy, distribute, transmit and adapt this publication provided that you attribute the work.
The ATSB’s preference is that you attribute this publication (and any material sourced from it) using the following wording: Source: Australian Transport Safety Bureau
Copyright in material obtained from other agencies, private individuals or organisations, belongs to those agencies, individuals or organisations. Where you wish to use their material, you will need to contact them directly.
On 6 August 2015, TasRail northbound intermodal freight train 532, travelling from Boyer (near Hobart, Tasmania) to Burnie derailed on a section of track near Nala. The train consisted of two locomotives hauling 34 wagons. The train had an overall length of 557.8 m and a trailing mass 1,345.3 t. The driver was uninjured, but there was significant damage to rolling stock and about 200 m of track was destroyed.
What the ATSB found
The ATSB investigation determined that the leading wheelset on the front bogie of container wagon TQMF03G, derailed at the 95.185 km point south (kps). After the wagon derailed, the train travelled a further 2.3 km before it came to a stand.
Post-derailment measurements identified a series of track geometry defects in advance of the point of derailment (PoD). The largest defect exceeded safety limits specified in TasRail’s Track and Structure Maintenance Standard (INF-TS-211). A review of maintenance records found that a defect was identified (near the PoD) three days before the derailment. The defect was categorised as priority 1 requiring immediate attention, but did not result in the maintenance response specified by the standard.
The ATSB also identified that the track through the area had an elevated risk for geometry defects. Difficulty in maintaining track geometry through the area was probably related to poor track formation, ballast quality and the use of steel sleepers, which demand considerable maintenance effort to hold track alignment. However, there was no record of the track having been identified as a hazardous location, so it had not attracted greater analysis focus or maintenance attention.
Computer modelling showed that the TQMF wagons (compare to TQAY wagons) were more susceptible to derailment at a critical speed of 36 km/h, when traversing the track irregularity as existed at the derailment site.
What's been done as a result
TasRail have implemented a range of initiatives to reduce the risk of a similar occurrence including, changes to operational and maintenance procedures, enhanced strategies for responding to twist defects, and the consideration of fitting constant contact side bearers to the TQMF wagon fleet.
Safety message
Early detection, assessment and effective management of track defects are critical in minimising the risk of derailment and maintaining safe rail operations.
Derailed portion of train 532
Source: ATSB
The occurrence
At about 1554[1] on 6 August 2015, TasRail intermodal freight train 532, (carrying rolls of newsprint and empty containers), departed Boyer in southern Tasmania (Figure 1) for Burnie in the north. The driver (driver only operation) involved in the occurrence booked on for duty, earlier that day (1430) at the East Tamar depot, Launceston. He then drove by car, to Campania where a crew change occurred at 1710. Train 532 departed shortly thereafter, the driver having obtained authority to work through to Parattah.
Figure 1: Location map – TasRail network
Source: NatMap, Geoscience Australia
The passage of the train through to Colebrook, about 30 km south of Nala, was uneventful. Shortly after departing Colebrook, the driver experienced degraded train performance and needed to stop on several occasions to rectify a fault[2]. At about 1841, the driver cleared the fault and then proceeded towards Parattah.
At 1856, the driver received authority to work through to Conara Junction. The train subsequently passed through Parattah, (about 9 km south of Nala) at 1911. At about 1921, the train passed over the Inglewood Road railway crossing (Figure 2) before entering a sweeping left curve (170 m radius). Just after passing, the 95 km point south, (kps)[3] the train traversed a short straight section of track, and then crossed over the Inglewood rail over-road bridge. The train continued to snake its way north towards Nala.
As the train approached the Nala Road railway crossing, the driver advanced the throttle to maintain speed. However, the train slowed, so the driver opened the train window, looked back towards the rear of the train, and saw sparks part way along the train. At about the same time as the train brakes began to apply automatically, the driver throttled off to reduce power. The lead locomotive TR15 stopped about 120 m past the Nala Road railway crossing.
Figure 2: Derailment site near Nala
Source: Google Earth
Post occurrence
The driver contacted train control to advise that the train had come to a stand just past the Nala Road railway crossing and had probably derailed. After speaking to train control and activating his personal alarm monitor, he detrained and walked the length of the train to inspect for damage. On completing the inspection, he returned to the cab and communicated with train control, advising that a number of wagons had derailed and that there was extensive track damage (Figure 3).
Figure 3: Rear part of train 532 adjacent 97.5 km post
Source: ATSB
At about 1930, train control called the incident co-ordinator. Operations staff, investigation and recovery crews were then dispatched to site.
The line was re-opened to rail traffic at about 0200 on 9 August 2015, three days after the occurrence.
The derailment occurred near Nala, which is about 98 km north by rail from Hobart, Tasmania (Figure 1). The track, (south line) connects the north and south of Tasmania.
TasRail own and manage the network, and are based in Launceston.
Track information
The track from Boyer (near Hobart) through to Burnie substantially comprises a single line with crossing loops strategically located throughout its length. Authority to travel between sections was by way of a track warrant.
The derailment occurred near Nala, midway between Campania and Conara Junction, (Figure 1) about 98 km north by rail from Hobart, on the south line. The track through the derailment site consisted of narrow gauge (1,067 mm), 41 kg/m rail, mounted on steel sleepers, with resilient fasteners (E Clips) on a nominal 100 mm bed of ballast. Axle loads were limited to a maximum of 18 t. The track leading into the derailment site was on a downgrade of 1:83 (Figure 4) through a nominal 200 m radius left-hand curve (direction of train travel). The track speed limit through the derailment site was 40 km/h and there was no temporary speed restriction (TSR) in place.
Figure 4: Curve and gradient chart, showing Point of Derailment (PoD)
Source: TasRail, annotation ATSB
Environmental conditions
The closest weather station was located at Tunnack, about 24 km north of Nala. On the day of the derailment, the maximum temperature recorded at Tunnack was 8.1°C, and there was no rainfall recorded in the 24-hour period preceding the derailment. At the time of derailment, the weather was fine and cool, probably about 0°C. It is unlikely that weather was a factor that contributed to the derailment.
Train and train driver information
Train 532 was a regular TasRail intermodal freight service, carrying newsprint and empty shipping containers. The service operated between Boyer, near Hobart (Tasmania) and the port of Burnie in the north. Train 532 comprised two locomotives (TR15 leading and TR13 trailing) hauling 34 wagons. The train had an overall length of 557.8 m and a trailing mass 1,345.3 t. It was loaded and marshalled in accordance with TasRail requirements: heavy wagons were towards the front and empty wagons towards the rear.
The lead locomotive of train 532 stopped about 2,640 m past the point of derailment. The eighteen wagons that derailed were positioned 14 – 31 (inclusive) behind the locomotives.
Rolling stock
The majority of wagons (TQAYs) were about one year old and in as new condition. The remaining wagons (TQMF/QM and IB) were refurbished, and considered to be in good condition, and fit for purpose. A post-derailment inspection confirmed that the wagons, (wheels, suspension elements, springs, friction wedges and wear surfaces) were generally in good condition and in compliance with TasRail’s engineering tolerances.
The first seven derailed wagons showed very little in the way of wheel tread damage. Considering the distance from the point of derailment, the lack of damage suggested that they were not part of the initial derailment.
The first wheelset to show significant tread damage (Figure 5 and Figure 6), consistent with a wheelset riding on ballast over an extended distance, was wagon TQMF03G. It was concluded that wagon TQMF03G, located at position 21, was likely to have derailed first. The wagons ahead of TQMF03G (positions 14 to 20) had probably derailed later in the sequence, as train 532 negotiated a number of tight curves.
Figure 5: TQMY03G – Leading bogie, leading wheelset, right wheel (direction of train travel) showing evidence of extensive of tread damage
Source: ATSB
Figure 6: Derailed wagon TQMY03G (looking north) showing final positioning of bogies
Source: ATSB
At the time of derailment, wagon TQMF03G had an overall length of 16.7 m and gross mass of 47.69 t. The wagon was carrying two 6 m (20’) containers. Inspection of the containers substantiated each was packed with eight 1.265 m diameter (1.6 m high) rolls of newsprint, stacked four long and two wide. The centre of gravity for the wagon was calculated to be 1.38 m above the top of the rail. Examination of newsprint rolls within the containers established that it was unlikely that a load shift had occurred, and loading was within specification.
A review of TasRail records, established that, as part of a major refurbishment program, wagon TQMF03G had all primary springs replaced in May 2012, and the wagon was fully overhauled (including bogies) in July 2014. The wagon was serviced in accordance with TasRail's requirements and there were no outstanding maintenance issues.
Following the derailment, an inspection of TQMF03G included bogie frames, side-bearer assemblies, friction wedges, wheelsets and wheel profiles. All were found to be operationally fit for purpose, and in compliance with maintenance standards.
Train driver
The driver in control, at time of derailment, had worked for TasRail for about 45 years and had driven trains for the last 25 years. He held the required qualifications to drive trains on the TasRail network and was route certified for the track where the derailment occurred.
An examination of the driver’s records confirmed that he had been assessed as meeting the medical standards prescribed by the National Standard for Health Assessment of Rail Safety Workers. The ATSB examined the driver’s roster and determined that fatigue impairment was unlikely to have affected his performance. The driver said he felt well when signing on for duty and at the time of the derailment.
After the derailment, the driver underwent drug and alcohol testing, the results of which were negative.
Train Handling
Locomotives TR15 and TR13 were equipped with Wabtec event recorders (loco-log) and CCTV cameras. These systems were used for capturing information such as date/time, speed, brake pipe pressure, throttle position, distance travelled and video imagery. Analysis of the data (Figure 7) established:
The train was travelling at about 33 km/h (7 km/h below maximum track speed) when the lead locomotive TR15 passed over the point of derailment (PoD).
The speed of the train increased slightly, on a downgrade of 1:83, reaching 36 km/h (4 km/h below maximum track speed) as TQMF03G passed over the PoD. At the time of derailment, the train was in dynamic brake (DB).
At 1925:25 the driver moved the throttle to idle (Idle) and then over the duration of about one minute, progressively increased the throttle to position T5 (in anticipation of a grade increase).
At 1926:29 brake pipe pressure (BPP) began to reduce. At about the same time the driver increased the throttle position to T7, (to maintain speed) and then almost immediately reduced the throttle position to T2, then idle, realising the train may have derailed.
The train slowed down, coming to a stop at 0926:39, about 2.6 km past the PoD.
Figure 7: Graph derived from Wabtec loco-log data, lead locomotive TR15
Source: TasRail, graphed by ATSB
A review of the loco-log data corroborates the driver’s recollection of events, and strongly indicates that train handling and driver performance were unlikely to have been factors that contributed to the derailment.
Examination of the track
The point of derailment (PoD) was identified at the 95.185 kps. The track leading into/out of the derailment site was found to be in fair condition. Both rails were good, with little evidence of side and top wear. There were no broken rails at or before the PoD. However, there did appear to be some geometry and condition irregularities leading up to the PoD. The ballast layer through the derailment site was shallow with evidence of pumping (vertical track movement) and there were signs of ballast fouling (fine materials, dirt/sand within the ballast layer).
Further examination of the track established signs of pre-existing damage to some steel sleepers. The damage was quite minor, probably related to dragging equipment, a previous derailment or similar event, and not considered a factor in this derailment. There was no evidence of track spread leading into or out of the derailment site. Gauge at the PoD was 1,069 mm; this was within TasRail tolerance (Refer Figure 11 – Response code/Tolerance, item re Track Gauge).
At the PoD there was evidence of flange climb,[4] (direction of train travel) on the right side running rail, (high rail) followed by witness marks, over a distance of about 5 m, which is consistent with a wheel flange crossing over the railhead (Figure 8).
Figure 8: Witness marks at PoD (95.185 km) shown by line of arrows on railhead
Source: ATSB
Beyond the PoD, the leading wheelset of derailed wagon TQMF03G had dropped off the rails. It damaged the track structure both within the gauge side[5] and on the field side[6] of the track (direction of travel). Initially the damage was not significant.
When locomotives TR15 and TR13 travelled through the PoD, they were initially in dynamic brake (Figure 7). At that time, the trailing wagons were in buff (light compression), almost free rolling. When the locomotives were about 1.8 km from the PoD, the driver began to accelerate the train, for an upcoming grade increase. At that time, the wagons would have gone into draft (tension) and the derailed wagon (TQMF03G) pulled to the right, through the right hand curve, (96.5 kps) where it dropped off the ballast shoulder and rolled over.
This most likely caused the wagons ahead to roll over, and wagons behind to derail, resulting in the multi-wagon pile-up shown at Figure 3. Wagon TQMF03G had travelled about 2.3 km beyond the initial PoD before coming to rest.
While track damage was evident along the 2.3 km length of the line, there was no track damage at or before the PoD. The majority of track damage was about 2 km beyond the PoD. It is therefore most likely that any post incident survey measurements through the derailment site would reflect the condition of the track at the time of derailment. Any measured track defects probably existed prior to the passage of train 532.
Post-derailment track measurements
The post-derailment survey, undertaken by TasRail, measured a range of track parameters including track gauge, alignment, superelevation, twist and top. Figure 9 illustrates the geometry in terms of track twist[7] – green line at 10 m intervals and the red line at 3 m intervals. The survey confirmed on-site visual observations that a series of geometry irregularities existed leading up to the point of derailment.
Figure 9: Twist measurements taken at derailment site (95.185 kps)
Source: TasRail – annotations ATSB
Track inspection and maintenance standards
The inspection and maintenance practices used by TasRail for its track and civil infrastructure are prescribed in the ‘Track and Structure Maintenance Standard’ (INF-TS-211 Ver 2.0 dated 26 August 2014).
The standard provides for two inspection routines: unscheduled and scheduled inspections. These routines adopt two main methods for assessing track geometry and identifying defects, visual inspections of track, and the use of mechanised track geometry vehicles.
Unscheduled
Unscheduled inspections are generally in response to defined events, such as extreme weather conditions known to increase the risk of geometry defects. Unscheduled inspections can also be triggered by third-party intervention, such as a train driver’s report of a rough riding track.
Scheduled
Scheduled inspections, in this case, for continuous steel sleeper track, (section length greater than 200 m) comprise:
‘on-track vehicle’ (weekly – No leeway, must complete inspection within 7 days, on or before last inspection date)
In accordance with the standard, track defects are grouped into one of three tolerance bands/codes, S, M or L, as defined in the table at Figure 10, ‘Track assessment response codes’.[8]
Figure 10: Track assessment response codes
Source: TasRail: Track and Structure Maintenance Standard Table 5 (INF-TS-211 Ver 2.0 dated 26 August 2014)
The tolerance limits for each specific defect band/code, are as defined in the table at Figure 11, ‘TasRail Category B Lines where Track Segment Speeds are up to 70km/h’.
Figure 11: TasRail Category B Lines where Track Segment Speeds are up to 70km/h
Source: TasRail: Track and Structure Maintenance Standard (INF-TS-211 Ver 2.0 dated 26 August 2014)
The work priority (urgency) assigned against each specific code, S, M or L, is as prescribed in the table at Figure 12 ‘Inspection Guidelines, Prioritisation and Sub-Categorisation of Defects’.
Figure 12: Inspection Guidelines, Prioritisation and Sub-Categorisation of Defects
Source: TasRail: Track and Structure Maintenance Standard Table 6(INF-TS-211 Ver 2.0 dated 26 August 2014)
On 6 August 2015, TasRail intermodal freight train 532, travelling from Boyer to Burnie, derailed near Nala, Tasmania. The ATSB determined that the derailment was initiated by a track defect (twist irregularity), located just before the 95.185 km point south (kps). It was likely that the track defect induced significant body roll in wagon TQMF03G, and that the right wheel of the leading axle on the leading bogie was in an unloaded state when it contacted the running face of the right hand rail, resulting in flange climb, and subsequent derailment. Consequently, examination of track/rolling stock interaction and track inspection/maintenance operations became necessary to determine whether these areas were factors in the derailment.
Track inspection and maintenance
An extract of TasRail records (Figure 13) showed that scheduled inspections were regularly performed, and generally met or exceeded target dates. The last on-track vehicle inspection, highlighted in orange (Figure 13), was completed on schedule, three days before the derailment. A track defect was located just before the POD (95.130 kps) during that inspection, and resulted in the issue of a repair job advice on 4 August 2015, as highlighted in orange (Figure 14).
Figure 13: Scheduled track inspection history, period preceding derailment
Source: TasRail
Post-derailment analysis suggests that the geometry defects observed following the derailment of train 532 were probably consistent with the defects identified on 3 August 2015. Twist measurements taken post-derailment (Figure 9) showed the existence of a (10 m) twist defect 30 mm (medium) in size, followed by a (large) 36 mm defect, located 60 m and 40 m, respectively, before the PoD. Closer towards the POD were a series of smaller yet significant defects, with a 26 mm (medium) defect at the PoD. The magnitude and cyclic nature of these defects, in advance of the PoD, would have initiated significant body roll in wagons as they travelled through the derailment site.
TasRail maintenance standards prescribe that, for any twist defect greater than 30 mm, (10 m chord) it is mandatory to allocated a code L, and should be given a priority ‘1’ urgency response. Examination of the repair advice sheet (Figure 14) shows that the track inspector identified that spot tamping was required near the 95.130 kps, due to irregular top. The defect was not physically measured and was probably under estimated as a medium defect, M (>25 – 30mm). While the defect was identified as medium, (M) and would typically be allocated a priority 2 or 3 response, on this occasion it was allocated a priority 1 response, which was outside the instructions defined in TasRail’s maintenance standard INF-TS-211. A priority 1 response requires ‘Immediate attention is required’ under TasRail maintenance standard INF-TS-211 (Figure 12). The standard also clearly mandates that ‘No on-track vehicles can pass without the approval of District Track Manager or Track Manager Systems’. However, this response was not undertaken.
Figure 14: Extract from repair advice sheet dated 4 August 2015
Source: TasRail
An examination of other inspection and maintenance records found:
A front of loco inspection was also completed on 3 August 2015, 3 days before the occurrence. There were no ride quality issues or defects reported, at or near the derailment site.
A twist trolley inspection was completed on 18 June 2015, about 2 months before the occurrence. There were no repair advice notifications or identified issues at or near the derailment site. However, it was noted that the report did not include a category for 10 m twist defects.
The track through the site was examined using a mechanised track geometry inspection car on 5 May 2015, about 3 months before the derailment.
Figure 15 (top portion) is a graphical extract of that track geometry car report of 5 May 2015. It shows a series of twist irregularities before the 95.185 kps location. The largest was a 32 mm twist defect at the 95.179 kps, close to the POD. The twist defect was categorised as a priority 1 defect and recorded in an exceedance report (Figure 15 – bottom portion). TasRail’s maintenance records show no evidence of any corrective action in response to this priority 1 defect.
Subsequent advice by TasRail stated that:
This defect was also not considered a priority in the context of the overall volume of identified defects. Consequently these defects were not scoped and/or repaired prior to 06 August 2015.
This statement, and maintenance action following the identification of a priority 1 defect three days before the derailment, suggests that TasRail did not enforce documented maintenance standards, which required immediate attention and exclusion of vehicles until approval was given by the track manager.
Figure 15: Extract of track geometry car, report of 5 May 2015 near PoD (95.185 kps)
Source: TasRail – annotations ATSB
Track history
An extract of TasRail’s maintenance records (Figure 16) established that there were at least five instances of track geometry/stability issues, (not including the track geometry car inspection of 5 May 2015 and on-track vehicle inspection of 3 August 2015) at or near the PoD requiring maintenance intervention since 2008.
Figure 16: Extract of maintenance records Campania to Conara Junction (near derailment site)
Source: TasRail
TasRail acknowledged that the formation was generally in poor condition through the area. A 100 mm ballast layer over fouled ballast was considered typical. TasRail also identified at least two locations just before the POD that showed evidence of track pumping. This suggested the possibility of voids under the track that may have contributed to track geometry irregularities as vehicles passed through the area.
The track structure through the derailment site adopted the use of steel sleepers. While steel sleepers provide good gauge holding, they demand considerable maintenance effort to manage track stability/alignment. A study in NSW[9] found that steel sleepers need to have correct installation as they do not perform well in situations where the track structure (ballast and formation) is poor. The report highlighted that correct tamping is essential to ensure the insertion of the ballast into the underside of the steel sleeper. Any lack of ballast under the sleeper void is difficult to observe visually and may reduce the structural stability of the track, especially in tight curves.
In this case, steel sleepers had been installed, the track contained a series of tight curves and the structure was known to be in relatively poor condition with fouled ballast. The repetitive nature of track geometry defects identified through track inspections also suggests the area was prone to track stability issues. TasRail’s track and maintenance (INF-TS-211 at section 3.8.1, general item 8) states that track sections prone to stability failure should be identified and managed as hazardous locations. There was no record of the track near the 95.5 kps having been identified as a hazardous location, so it had not attracted greater analysis focus or maintenance attention.
Other occurrences involving track twist irregularities
The ATSB has previously investigated two derailments in Tasmania involving track twist irregularities involving train 331 near Lowdina, on 9 April 2013 (RO-2013-012), and train 135 near Kimberley on 25 January 2015 (RO-2015-001).
Track geometry was identified as the underlying factor in these derailments including the derailment of train 532 on 6 August 2015. All three derailments occurred on steel sleeper track through areas having tight curves, and involved older rolling stock exhibiting less tolerant dynamic performance.
Rolling stock
To assist in understanding the mechanism of derailment, and help in developing strategies to mitigate the risk of future derailment, TasRail engaged consultants to model the dynamic performance of the older TQMF class of wagon (type that derailed) and TQAY wagons, using the Vampire computer simulation package. The track criterion incorporated into the simulation model was based on survey work undertaken post-derailment. The dynamic performance of the wagons was modelled for varying characteristics and a range of speeds, including the derailment speed of 36 km/h.
The computer modelling clearly showed that the older generation TQMF, when compared to the newer TQAY wagons, were much more susceptible to derailment over the track defect at the 95.185 kps. Modelling suggested that the newer generation TQAY wagons were able to negotiate the same track defect without derailing.
At the critical speed of 36 km/h, the modelling established that the TQMF wagons derailed when traversing the track irregularity. This speed gave rise to the highest wheel unloading at a time when the wheel came into contact with the rail face at the 95.185 kps, resulting in flange climb and subsequent derailment.
It is likely that cyclic body roll due to a series of track irregularities caused the right-hand wheel on the lead axle on the leading bogie (TQMF03G) to lift. At the same time, the process of negotiating a left-hand curve placed that wheel in contact with the right-hand rail running, resulting in flange climb of the lightly loaded wheel and subsequent derailment. Although it was determined that TQMF03G was in good condition, the suspension characteristics of this wagon type, compared to the newer TQAY wagons, were probably key factors that contributed to the derailment.
The results of the computer modelling were used by TasRail to identify a number of strategies that could be used to enhance the dynamic performance of the TQMF wagon and reduce the risk of future derailments, including the use of constant-contact side-bearers.[10] TasRail proposes to adopt the recommendations of the report.
On 6 August 2015, TasRail intermodal freight train 532, travelling from Boyer (near Hobart) to Burnie derailed on a section of track near Nala, Tasmania.
From the evidence available, the following findings are made with respect to the derailment and should not be read as apportioning blame or liability to any particular organisation or individual.
Contributing factors
The derailment of train 532 was probably initiated by a track defect (twist irregularity), just before the 95.185 km point south (kps).
The wagon (TQMF03G) suspension characteristics, loading, critical train speed, (36 km/h), and nature of the track defect, were factors that contributed to the derailment.
A track defect was identified three days before the derailment, categorised as priority 1 requiring immediate attention, but did not result in a maintenance response as specified in TasRail’s maintenance standard INF-TS-211.
Other factors that increased risk
TasRail maintenance standard INF-TS-211 does not provide guidelines for the determination of track defect size.
There were no documents that could establish whether the track inspector met mandated reporting requirements, (specified within TasRail’s maintenance standard INF-TS-211) where on-track vehicles are not permitted to pass a priority 1 defect, without approval of the track manager.
TasRail records showed a history of track geometry defects near the derailment site, but monitoring strategies did not alert maintenance staff to the possible need for higher vigilance through this area.
The track stability problems near the derailment site were probably a reflection of poor track formation, ballast quality and the use of steel sleepers, in particular the packing of ballast under the sleeper and at the sleeper ends.
Other findings
Train handling and driver performance were not factors that contributed to the derailment.
Environmental conditions were not factors that contributed to the derailment.
Safety actions
Whether or not the ATSB identifies safety issues in the course of an investigation, relevant organisations may proactively initiate safety actions in order to reduce their safety risk. The ATSB has been advised of the following proactive safety actions in response to this occurrence.
Additional safety action taken by TasRail
TasRail has advised of the following proactive safety actions:
Computer modelling by Worley Parsons to identify any additional criteria that could be used to interpret geometry measures to identify situations where a combination of defects could contribute to a heightened derailment risk.
Update the TasRail Operational Risk Register V5 when outcome of modelling known - Hazard 2 - Train Derailment.
Track Maintenance Standard INF-TS-211 has been updated (Version 3) on 04 April 2016 with respect to various operational and maintenance procedures, including:
- Removes the requirement to obtain track manager permission to travel over large faults and introduces geometry defect thresholds at which TSRs shall be applied enabling consistent management by the track inspector.
- Removes hazardous locations and introduces unstable twist defects which are locations that must be measured by inspectors during every patrol to mandate more rigorous monitoring of areas that rapidly deteriorate.
- Has been updated to include a revised repair advice sheet which now requires that measurements be taken for all reported geometry defects.
- Includes specific actions to be taken for each defect size
Geismar digital track geometry trolleys issued to all track inspectors to enable accurate sizing of defects.
Track geometry vehicle now operated six weekly on busiest lines (South and Western).
TasRail has committed to invest in its own, vehicle mounted, track geometry measuring equipment enabling more frequent and accurate track monitoring
Update Infrastructure Derailment Form INF-FRM-019 to include the measurement of voiding following incident investigation.
Fitting of ‘Constant Contact Side Bearers’ on the fleet of TQMF and IB wagons.
Update standard RS-TS-006 to include side-bearer gaps clearances.
Inspect TQMF wagons side-bearer gaps and friction wedges to ensure all are within specification.
Update 'A' service sheet RS-FRM-242 to include inspection of side-bearer gap clearances measurements.
Update wagon work instruction RS-Wl-531 to include correct service limits and measurement criteria.
Sources and submissions
Sources of information
The sources of information during the investigation included:
TasRail
References
ARA Glossary for the National Codes of Practice and Dictionary of Railway Terminology
Bureau of Meteorology - Weather Observations for Tunnack, Tasmania (6 August 2015)
Steel Sleeper Introduction on NSW Class 1 Main Line Track.1996 - 2004 (OTSI File Ref: 02619)
RISSB Glossary of Railway Terminology – Guideline
RO-2013-012 – Derailment of train 331 near Lowdina, Tasmania on 9 April 2013
RO-2015-001– Derailment of TasRail train 135, Kimberley, Tasmania on 25 January 2015
TasRail – Track and Structure Maintenance Standard (INF-TS-211) Ver 2.0 dated 26 August 2014
Submissions
Under Part 4, Division 2 (Investigation Reports), Section 26 of the Transport Safety Investigation Act 2003, the ATSB may provide a draft report, on a confidential basis, to any person whom the ATSB considers appropriate. Section 26 (1) (a) of the Act allows a person receiving a draft report to make submissions to the ATSB about the draft report.
A draft of this report was provided to:
Driver of train 532
Office of National Rail Safety Regulator
TasRail
Submissions were received from the Office of the National Rail Safety Regulator, and TasRail. The submissions were reviewed and where considered appropriate, the text of the report was amended accordingly.
Purpose of safety investigations
The objective of a safety investigation is to enhance transport safety. This is done through:
identifying safety issues and facilitating safety action to address those issues
providing information about occurrences and their associated safety factors to facilitate learning within the transport industry.
It is not a function of the ATSB to apportion blame or provide a means for determining liability. At the same time, an investigation report must include factual material of sufficient weight to support the analysis and findings. At all times the ATSB endeavours to balance the use of material that could imply adverse comment with the need to properly explain what happened, and why, in a fair and unbiased manner. The ATSB does not investigate for the purpose of taking administrative, regulatory or criminal action.
Terminology
An explanation of terminology used in ATSB investigation reports is available here. This includes terms such as occurrence, contributing factor, other factor that increased risk, and safety issue.
Publishing information
Released in accordance with section 25 of the Transport Safety Investigation Act 2003
Ownership of intellectual property rights in this publication
Unless otherwise noted, copyright (and any other intellectual property rights, if any) in this report publication is owned by the Commonwealth of Australia.
Creative Commons licence
With the exception of the Coat of Arms, ATSB logo, and photos and graphics in which a third party holds copyright, this publication is licensed under a Creative Commons Attribution 3.0 Australia licence.
Creative Commons Attribution 3.0 Australia Licence is a standard form licence agreement that allows you to copy, distribute, transmit and adapt this publication provided that you attribute the work.
The ATSB’s preference is that you attribute this publication (and any material sourced from it) using the following wording: Source: Australian Transport Safety Bureau
Copyright in material obtained from other agencies, private individuals or organisations, belongs to those agencies, individuals or organisations. Where you wish to use their material, you will need to contact them directly.
On 6 August 2015, the pilot of a Grumman G164 aircraft, registered VH-LKN, was conducting aerial spreading of superphosphate on a property about 33 km south-west of Tharwa, Australian Capital Territory. The target zone for the spreading was about 7 km to the south-east, and at an elevation about 1,000 ft higher than the airstrip and loading site.
The pilot commenced operations at about 1000 Eastern Standard Time (EST) and completed spreading of six loads of superphosphate. The pilot then had a lunch break and refuelled the aircraft to a total of about 180 L of fuel. The aircraft was also loaded with about 500 kg of superphosphate, which was about half its carrying capacity. The pilot observed a light, westerly wind of about 2 to 5 kt in the vicinity of the airstrip.
At about 1400, the pilot commenced the take-off run for the seventh load of the day. As the aircraft became airborne, the aircraft started to sink (Figure 1). To stop the aircraft sinking, the pilot applied the dump lever to start dumping the load of superphosphate. The aircraft then started to climb, so the pilot stopped dumping the load. The pilot also commenced a shallow left turn, away from rising terrain. As the aircraft turned, when at about 100 ft above ground level, it started to sink again. As it sank, the pilot felt a shake through the airframe, indicating that the aircraft was close to stalling. The pilot re-applied the dump lever to open the hopper door and try to reduce the aircraft load. Simultaneously, the pilot lowered the aircraft’s nose and rolled the wings level, to try to recover from the incipient stall.
Figure 1: Departure airstrip, aircraft track and accident location
Source: Google earth and pilot recollection – annotated by the ATSB
The pilot sighted powerlines, a road and a row of trees ahead, beyond which the terrain rose steeply. The aircraft continued to descend and the pilot maintained the aircraft in a normal nose attitude for landing. As the aircraft neared the ground, the pilot reduced the throttle to idle and held the aircraft control stick in the full back position. The tailwheel struck the ground first, and then the right main landing gear dug into soft ground. The aircraft flipped over and came to rest inverted.
The pilot sustained minor injuries and the aircraft was substantially damaged (Figure 2).
Figure 2: Damage to VH-LKN
Source: Pilot
Pilot comments
The pilot provided the following comments:
The airstrip was at an elevation of about 2,100 ft above mean sea level. The target pasture was about 1,000 ft higher than the airstrip.
The airstrip was about 500 m in length and the fuel and chemical load was relatively light. The aircraft was well within its operational limitations.
The weather forecast had indicated calm conditions, and the temperature was about 14°C.
The sink that the aircraft encountered may have been a downdraft coming off the hill.
If the airstrip had been higher up and closer to the target zone, the pilot would have had more time to dump the load, less distance to climb on each load, and a more accurate assessment of the wind conditions.
Dumping liquid takes a few seconds, but granular substances like superphosphate take minutes for the hopper to empty when dumping the load.
After the accident, the pilot verified that the hopper door was open, and superphosphate was present in the paddock, indicating that it had been dumping at the highest rate. Despite that, about 300 kg of superphosphate remained in the hopper.
Safety message
The pilot stated that the key to avoiding similar incidents was to understand the atmospheric conditions in steep mountainous country. Variations in wind strength and direction due to terrain can have serious consequences on flight safety, particularly when operating at low airspeeds and close to the ground.
ATSB investigated a similar accident involving a Grumman G-164A, in AO-2014-001.
Decisions regarding whether to conduct an investigation, and the scope of an investigation, are based on many factors, including the level of safety benefit likely to be obtained from an investigation. For this occurrence, a limited-scope, fact-gathering investigation was conducted in order to produce a short summary report, and allow for greater industry awareness of potential safety issues and possible safety actions.
Publishing information
Released in accordance with section 25 of the Transport Safety Investigation Act 2003
Ownership of intellectual property rights in this publication
Unless otherwise noted, copyright (and any other intellectual property rights, if any) in this report publication is owned by the Commonwealth of Australia.
Creative Commons licence
With the exception of the Coat of Arms, ATSB logo, and photos and graphics in which a third party holds copyright, this publication is licensed under a Creative Commons Attribution 3.0 Australia licence.
Creative Commons Attribution 3.0 Australia Licence is a standard form licence agreement that allows you to copy, distribute, transmit and adapt this publication provided that you attribute the work.
The ATSB’s preference is that you attribute this publication (and any material sourced from it) using the following wording: Source: Australian Transport Safety Bureau
Copyright in material obtained from other agencies, private individuals or organisations, belongs to those agencies, individuals or organisations. Where you wish to use their material, you will need to contact them directly.
On 20 July 2015, the pilot of a Bell 206L3 (Longranger) helicopter, registered VH-BLV (BLV), conducted a charter flight from Essendon Airport to Falls Creek, Victoria, with five passengers on board. The aircraft took off from Essendon close to its maximum take-off weight. Due to the weight, and therefore fuel limitations, the pilot landed and refuelled at a property near Lake Eildon. At about 1000 Eastern Standard Time (EST), the helicopter departed from the property for the 60 NM flight to Falls Creek, again close to its maximum take-off weight.
At about 1030, while 700 ft above ground level and tracking from the north-west, the pilot conducted a shallow approach towards the helipad at Falls Creek (Figure 1). As the helicopter descended to about 50 ft above ground level, the pilot found that significantly more power was required to conduct the approach than anticipated. The pilot assessed that there was insufficient power available to continue to land, and elected to abort the approach. The pilot pushed forwards on the cyclic[1] to increase the helicopter’s airspeed and conducted a left turn towards the valley.
Figure 1: Falls Creek helipad, approximate helicopter track and wind direction
Source: Google earth and pilot recollection – annotated by the ATSB
As the helicopter turned left, it started to yaw[2] rapidly towards the right. The pilot applied full left pedal to counteract the yaw, but the helicopter continued to yaw. The helicopter turned through one and a half revolutions, as the pilot lowered the collective.[3] Lowering the collective reduced the power demand of the power rotor system, thereby increasing the ability of the anti-torque pedals to stop the right yaw. The combination of lowering collective and applying forward cyclic to gain forward airspeed, allowed the pilot to regain control of the helicopter. The pilot then conducted a left turn towards the helipad and made an approach to the helipad from an easterly direction. The helicopter landed following the second approach without further incident.
The pilot and passengers did not sustain any injuries and the helicopter was undamaged.
Weather
The pilot expected that the wind at Falls Creek would be variable at 2 kt, as it had been on departure from Essendon. The pilot did not see the windsock at the helipad prior to conducting the approach.
The Bureau of Meteorology provided the ATSB with a report of weather observations for Falls Creek. The automatic weather station is located south of the helipad at about 5,790 ft above mean sea level, above the village. Between 1020 and 1040, the recorded wind speed was from 17 to 20 kt, gusting to 24 kt, and wind direction was from 327° to 344° (degrees true), or 314° to 331° (degrees magnetic). The temperature was 1 °C.
Pilot comments
The pilot reported that the following combination of factors contributed to the incident:
Unfamiliarity with the landing site and area.
Inexperience operating at altitude, and unfamiliarity with the associated power requirements. The helipad at Falls Creek is at an elevation of about 5,000 ft above mean sea level.
Lack of experience in the aircraft type – although the pilot had about 60 hours experience in the Bell Jetranger, this was only the pilot’s second flight in the Longranger.
High all up weight.
Incorrect assessment of the wind direction – the pilot assumed that the wind would be light and variable at Falls Creek as it was had been on departure from Essendon. During the approach, the pilot assessed that the wind was from the right or a tailwind gusting to about 15 kt.
Operator comment
The operator of VH-BLV assessed that the unanticipated yaw was a result of too little pedal input, applied too late. This was most likely due to a combination of the pilot’s inexperience on the 206L3, and being surprised by the downwind approach.
Hover ceiling
Hovering requires more power than any other flight regime. Additionally, hovering at higher altitudes requires more power than to hover at lower altitudes. The ‘hover ceiling’ is the height at which the power available equals the power required to hover. An increase in power increases the main rotor torque. This additional torque needs increased tail rotor thrust, to prevent the helicopter from yawing.
The Bell 206 L3 flight manual provides a Hover ceiling – out of ground effect[4] chart. At 5,000 ft, a temperature of 0 °C, and a gross weight of about 1,814 kg (4,000 lb), the helicopter was just within the chart’s hover ceiling envelope. This indicates that adequate power should have been available to hover with those parameters. However, the wind direction and velocity also affect hovering performance.
A stronger head wind reduces the power required to hover, while a tailwind increases the power required to hover. On the initial approach to the helipad, a tailwind meant that an increase in power and tail rotor thrust was required. The increased tail rotor thrust absorbs power from the engine, which means less power is available for the main rotor to produce lift. This led to the pilot’s assessment of insufficient power available, and decision to discontinue the approach.
Unanticipated right yaw
The US Federal Aviation Administration (FAA) Helicopter flying handbook describes loss of tail rotor effectiveness (LTE) or an unanticipated yaw, as ‘an uncommanded, rapid yaw towards the advancing blade which does not subside of its own accord’. It is caused by an interaction between the main rotor and tail rotor.
At high altitudes, the lower air density reduces tail rotor thrust and efficiency. Therefore, when operating at high altitudes and high gross weights, particularly while hovering or at low airspeeds, the tail rotor thrust may not be sufficient to maintain directional control. This can result in unanticipated yaw or LTE. In these circumstances, the hover ceiling is effectively limited by the tail rotor thrust, rather than the power available.
In this incident, other factors may also have contributed to the unanticipated yaw: low and slow flight outside of ground effect, a low speed downwind turn and a large change of power at low airspeed as the pilot aborted the approach.
The US Federal Aviation Administration Advisory Circular, Unanticipated right yaw in helicopters, stated that unanticipated right yaw, or loss of tail rotor effectiveness (LTE) has been determined to be a contributing factor in a number of accidents. These mishaps have occurred at low altitude and in low-speed flight, often on final approach to landing. Unanticipated right yaw may occur during any manoeuvre in which the pilot is operating in a high-power, low-airspeed environment with a left crosswind (in aircraft with counter-clockwise blade rotation) or tailwind.
Three additional factors can significantly influence the severity of LTE:
gross weight and density altitude
low indicated airspeed
a rapid application of power, causing power droop.
In order to reduce the onset of LTE, when manoeuvring between hover and 30 kt, the pilot should:
Avoid tailwinds.
Avoid out of ground effect hover and high-power demand situations, such as low-speed downwind turns.
Be aware of wind direction and velocity. A loss of translational lift results in an unexpected high-power demand and an increased anti-torque requirement.
Be aware that if a considerable amount of left pedal is being maintained, a sufficient amount of left pedal may not be available to counteract an unanticipated right yaw.
Stay vigilant to power and wind conditions.
If a sudden unanticipated right yaw occurs, the pilot should:
apply full left pedal
simultaneously move cyclic forward to increase speed
if altitude permits, reduce power.
Safety message
Pilots should understand and avoid conditions that are conducive to uncontrolled yaw or loss of tail rotor effectiveness. Pilots can reduce their exposure to LTE by maintaining awareness of the wind and its effect on the helicopter. If a pilot encounters unanticipated yaw, quick application of the correct response is essential to recover control of the helicopter. The ATSB reported on an incident involving LTE in AO-2013-121.
This incident also highlights the effect of gross weight and airfield elevation on aircraft performance. Understanding controllability issues at the limits of the normal operating envelope can assist pilots in recognising the symptoms of reduced aircraft performance. Further information is available in ATSB report AO-2013-203.
Decisions regarding whether to conduct an investigation, and the scope of an investigation, are based on many factors, including the level of safety benefit likely to be obtained from an investigation. For this occurrence, a limited-scope, fact-gathering investigation was conducted in order to produce a short summary report, and allow for greater industry awareness of potential safety issues and possible safety actions.
Publishing information
Released in accordance with section 25 of the Transport Safety Investigation Act 2003
Ownership of intellectual property rights in this publication
Unless otherwise noted, copyright (and any other intellectual property rights, if any) in this report publication is owned by the Commonwealth of Australia.
Creative Commons licence
With the exception of the Coat of Arms, ATSB logo, and photos and graphics in which a third party holds copyright, this publication is licensed under a Creative Commons Attribution 3.0 Australia licence.
Creative Commons Attribution 3.0 Australia Licence is a standard form licence agreement that allows you to copy, distribute, transmit and adapt this publication provided that you attribute the work.
The ATSB’s preference is that you attribute this publication (and any material sourced from it) using the following wording: Source: Australian Transport Safety Bureau
Copyright in material obtained from other agencies, private individuals or organisations, belongs to those agencies, individuals or organisations. Where you wish to use their material, you will need to contact them directly.
On 1 August 2015, at about 1110 Western Standard Time (WST), a Cessna 210 aircraft, registered VH-ERU, departed Gidgee Gold mine for a private flight to Cue, Western Australia (Figure 1). The pilot was the sole occupant of the aircraft. The pilot reported that all engine indications were normal from the start and into the cruise at 3,500 ft above mean sea level. The elevation of the terrain in the area was about 1,700 ft above mean sea level.
Figure 1: Aircraft track and accident location
Source: Google earth – annotated by the ATSB
About 25 minutes into the flight, the pilot observed the engine oil temperature rising rapidly. The pilot opened the cowl flaps in an attempt to reduce the engine oil temperature, and noted that the cylinder head temperature and engine oil pressure were still in the normal range. As the pilot tried to determine the cause of the problem, the manifold pressure started to increase. The pilot reduced the throttle to try to decrease the manifold pressure, but it continued to rise.
The pilot then felt a slight vibration in the engine and through the aircraft controls, and broadcast a PAN[1] call on the Melbourne Centre radio frequency. The pilot did not receive any response to the broadcast, probably due to the aircraft’s remoteness and low altitude. The aircraft was descending steadily, and the pilot looked for a suitable place to conduct a precautionary landing. However, the surrounding area was heavily treed. After turning towards the north and more open country, the vibration increased, and the pilot broadcast two Mayday[2] calls. Again, the pilot did not receive any response.
When about 500 ft above ground level, the vibration further increased and the engine failed with a bang. Smoke emanated from the engine compartment and over the windscreen, reducing the pilot’s visibility through it. The pilot then sighted a fence line to the right and prepared for a forced landing, aiming to touchdown in a cleared area alongside the fence.
The pilot lowered the landing gear and extended the flap. When at about treetop height, the pilot selected the master switch and fuel off. The pilot also tightened the seatbelt and opened the aircraft door. As the pilot flared the aircraft to land, the right wing and strut collided with a tree. The aircraft yawed to the right, and the right main landing gear struck the ground and broke off. Although the pilot applied full left rudder to try to regain control of the aircraft, it collided with another tree and rolled onto its left side, before skidding and coming to rest against a third tree. The pilot suffered minor injuries and the aircraft sustained substantial damage (Figure 2).
The right fuel line ruptured during the impact sequence, causing fuel to run down into the cabin and onto the pilot. The pilot quickly exited the aircraft, concerned about the risk of fire, particularly as there was about 240 L of fuel in the tanks.
After waiting about half an hour for the fuel to stop running into the cockpit, the pilot returned to the aircraft and selected the master switch on. The pilot then made another radio broadcast requesting assistance, and again did not receive any response. The aircraft’s emergency locator transmitter (ELT)[3] did not activate on impact, and its light had not illuminated. The pilot then tried, without success, to use the aircraft battery to power the ELT.
At about 1400, the pilot again made radio broadcasts without any response. As there was no mobile phone signal at the accident site, the pilot started walking towards higher terrain. At about 2200, after walking 25 km, the pilot gained mobile phone coverage and was able to call for assistance. After making the call, the pilot lit a fire to provide warmth and to deter a pack of wild dogs that had been circling. At about 0200 on 2 August, low cloud rolled in and it started to drizzle. About an hour later, the pilot provided rescue personnel with the coordinates of the location, obtained from the mobile phone. At about 0730, a rescue aircraft located the pilot and police arrived about 40 minutes later.
Figure 2: Accident site showing damage to VH-ERU
Source: Western Australia Police
Pilot comments
The pilot provided the following comments:
The number three cylinder failed and blew a hole in the top of the engine casing.
The pilot usually carried a satellite phone, but did not have it on this flight as it was being serviced.
It was about a 40-minute flight to Cue, and the pilot would normally have advised someone of the planned route and expected arrival time, but omitted to do so on this day.
The pilot had water, a first aid kit and a lighter in the aircraft, and planned to get a personal location beacon to carry in future.
Aircraft engine
The aircraft was fitted with a Continental IO-520 engine. The pilot had owned the aircraft for about 4 years, during which time the aircraft had accrued about 60 hours of flying time. Shortly after the pilot bought the aircraft, the number three cylinder had failed and been replaced. The pilot had recently replaced the propeller in accordance with an airworthiness directive.
The aircraft was damaged beyond repair. At the time of completing this report, no engineering inspection of the engine had been, or was expected to be, conducted following the accident.
Safety message
The ATSB reminds all pilots to let someone know where they are going, and what time they expect to arrive, before embarking on a flight. Although the incident flight was not in a designated remote area, it demonstrates that it is vitally important to carry emergency supplies, such as water, food, matches (or lighter), and first aid essentials. Where mobile and radio coverage is not available, a satellite phone can provide life-saving access to help.
Electronic locator transmitters installed in aircraft should be tested in accordance with the manufacturer’s instructions. The ATSB research report AR-2012-128 found that ELTs function as intended in about 40-60% of accidents. NASA is currently conducting research to find ways to make ELTs more likely to function after a survivable crash.
Decisions regarding whether to conduct an investigation, and the scope of an investigation, are based on many factors, including the level of safety benefit likely to be obtained from an investigation. For this occurrence, a limited-scope, fact-gathering investigation was conducted in order to produce a short summary report, and allow for greater industry awareness of potential safety issues and possible safety actions.
Publishing information
Released in accordance with section 25 of the Transport Safety Investigation Act 2003
Ownership of intellectual property rights in this publication
Unless otherwise noted, copyright (and any other intellectual property rights, if any) in this report publication is owned by the Commonwealth of Australia.
Creative Commons licence
With the exception of the Coat of Arms, ATSB logo, and photos and graphics in which a third party holds copyright, this publication is licensed under a Creative Commons Attribution 3.0 Australia licence.
Creative Commons Attribution 3.0 Australia Licence is a standard form licence agreement that allows you to copy, distribute, transmit and adapt this publication provided that you attribute the work.
The ATSB’s preference is that you attribute this publication (and any material sourced from it) using the following wording: Source: Australian Transport Safety Bureau
Copyright in material obtained from other agencies, private individuals or organisations, belongs to those agencies, individuals or organisations. Where you wish to use their material, you will need to contact them directly.
On 23 July 2015, an Airbus A330 aircraft, registered VH-QPJ and operated by Qantas Airways, was being loaded at Bangkok Airport, Thailand, prior to flying to Sydney, Australia. The ground-handling agent (and loading supervisor) was in Bangkok, and the load controller was in Warsaw, Poland.
The load instruction report (LIR) displayed a pictorial representation of the planned uplift. To maximise uplift within the aircraft’s operational limitations, the report contained a set of loading instructions. These instructions identify positions within the aircraft hold for loading containers, baggage and freight.
The load controller in Warsaw issued a load instruction report (LIR) to the loading supervisor in Bangkok (Figure 1). The loading supervisor was required to load the aircraft in accordance with the LIR. The LIR also contained ‘Special instructions’ and ‘Special load details’. The Special instructions for QF24 stated that the freight pallet shown on the LIR in position 23P was on standby. The loading supervisor then called the load controller by telephone to provide a ‘partial read back’. The supervisor read back to the controller how the aircraft had been loaded, based on the LIR.
The loading supervisor commenced by reading out the description and weight of the pallet loaded into position 23P. The load controller responded that the pallet in 23P was on standby as per the Special instructions, and directed the loading supervisor to offload that freight. The supervisor responded ‘yes’, and stated that the loading was in accordance with the LIR. The loading supervisor then continued to read the loading to the controller, again commencing with the pallet in 23P, followed by the rest of the loaded freight. The pallet in 23P remained loaded on the aircraft.
Figure 1: Load instruction report showing freight positions and special instructions
Source: Aircraft operator
After completion of the loading, the loading supervisor again phoned the load controller to provide the final read back of the loading. The loading supervisor stated ‘forward compartment no change’, to which the load controller responded clarifying position 23P was ‘no fit’[1]. The loading supervisor replied, ‘yeah, no change’ and the load controller responded ‘ok’.
The load controller then prepared the final load sheet for the flight, based on the information provided over the phone by the loading supervisor. The load controller transmitted the final load sheet to the flight crew via the Aircraft Communications Addressing and Reporting System (ACARS). The load sheet included the calculated aircraft total and component weights including fuel, passenger, baggage and freight weights. It also provided the aircraft balance details including the aircraft take-off trim setting position.
The flight crew then used this data to calculate reference speeds for take-off, fuel consumption rates, and initial climb altitude. At about midday local time, the aircraft departed Bangkok for Sydney and the flight crew did not detect any abnormal flight characteristics, nor did they receive any warnings related to the aircraft’s weight or balance.
After the flight had closed, the load control system automatically generated a Container Pallet Message (CPM) report. The report was based on the input from the load controller, and therefore did not include the pallet in 23P. The loading supervisor identified that the pallet in 23P was not on this report and contacted the load controller. The load controller confirmed that the pallet should have been offloaded, and was therefore not included in the uplift weight calculations. The load controller then contacted the Qantas Integrated Operations Control (IOC) in Sydney and advised them that a pallet had been loaded onto the aircraft, which was not included in the load sheet, and that some operational limitations had been exceeded.
About 75 minutes after the aircraft departed from Bangkok, the IOC advised the aircraft flight crew of the error. The flight crew entered the amended aircraft weight into the flight management computer.
Load discrepancy
The weight of the standby pallet for 23P indicated on the LIR was 2,785 kg. The final load sheet indicated 1,225 kg of freight in compartment 2. Compartment 2, depicted in Figure 1, included a number of freight positions including 23P. The calculation for total freight weight in Compartment 2 was based on freight loaded in positions 26L (615 kg), 26R (610 kg) and zero in 23P.
Based on the final load sheet, the taxi weight was calculated to be 235,485 kg (maximum 233,900 kg) and the take-off weight was 232,300 kg (maximum 233,000 kg).
As a result of the discrepancies, Qantas advised that the maximum taxi weight had been exceeded by 1,585 kg, and the maximum take-off weight by 2,085 kg. The initial cruise altitude of 35,000 ft did not exceed the maximum altitude when the actual weight was subsequently entered into the aircraft flight management computer.
Qantas investigation
Qantas conducted an investigation into the incident, which included a review of the transfer of load control operations to Warsaw (from its previous location in Hong Kong), the systems supporting the load controller and loading supervisor, and their individual actions.
The investigation identified a number of safety factors that contributed to the incident. These included the following.
Depiction of standby freight
The load controller represented the standby freight as listed on the LIR, with the freight depicted in the loaded position, and a standby notation included in the Special Instructions box. The Qantas investigation found that was not a documented procedure for handling standby freight, but it was an accepted practice. The training of loading supervisors did not include how standby freight was to be documented on the LIR.
Communication
The communications between the loading supervisor and load controller were open to misinterpretation, had ambiguous phraseology, untimely transmissions, and did not involve a read-back hear-back process.
During the partial read back, the offload instruction caused confusion as to whether the pallet in 23P was to be loaded or not, and that confusion was not resolved.
During the final read back, a misunderstanding resulted from the load controller’s use of the phrase ‘no fit’, meaning not loaded, and the loading supervisor’s use of the phrase ‘no change’ meaning no change to the loading depicted on the LIR.
Training
Irregularities were identified with the training regarding LIR presentation and interpretation. Specifically, the training on procedures for handling standby items provided to load controllers did not cross-reference the training provided to loading supervisors and vice versa.
Safety actions
Whether or not the ATSB identifies safety issues in the course of an investigation, relevant organisations may proactively initiate safety action in order to reduce their safety risk. The ATSB has been advised of the following proactive safety action in response to this occurrence.
Aircraft operator
As a result of this occurrence, Qantas advised the ATSB that they are taking the following safety actions:
Immediate action taken
For all flights out of Bangkok, the loading supervisor must receive a scanned copy of the final LIR before transmitting the final load sheet to the flight crew (by ACARS).
Standard phraseology is to be used for all read back communications.
Standby freight procedure
Load Control will document the following:
procedures for listing standby freight in the LIR Special Instructions
use of LIR Special Instructions
sample communications for instructions to offload and the required response from loading supervisors.
Training
The training provided to load controllers and loading supervisors was to be coordinated. The training procedures will include a standardised process for handling standby freight.
A process for updating load control training material will also be implemented.
Firstload
An automated read back system, ‘Firstload’, is scheduled to be introduced to Bangkok and other international ports in November 2015. Firstload is an iPad-generated LIR and read back system. Implementation of the system will remove the requirement for verbal read backs.
Safety message
This incident highlights the importance, particularly when dealing with safety-critical data, for:
standard phraseology in verbal communications
ensuring a verbal instruction has been understood and complied with
validating verbal communication with written documentation.
The ATSB SafetyWatch highlights the broad safety concerns that come out of our investigation findings and from the occurrence data reported to us by industry. One of the safety concerns is data input errors.
Decisions regarding whether to conduct an investigation, and the scope of an investigation, are based on many factors, including the level of safety benefit likely to be obtained from an investigation. For this occurrence, a limited-scope, fact-gathering investigation was conducted in order to produce a short summary report, and allow for greater industry awareness of potential safety issues and possible safety actions.
Publishing information
Released in accordance with section 25 of the Transport Safety Investigation Act 2003
Ownership of intellectual property rights in this publication
Unless otherwise noted, copyright (and any other intellectual property rights, if any) in this report publication is owned by the Commonwealth of Australia.
Creative Commons licence
With the exception of the Coat of Arms, ATSB logo, and photos and graphics in which a third party holds copyright, this publication is licensed under a Creative Commons Attribution 3.0 Australia licence.
Creative Commons Attribution 3.0 Australia Licence is a standard form licence agreement that allows you to copy, distribute, transmit and adapt this publication provided that you attribute the work.
The ATSB’s preference is that you attribute this publication (and any material sourced from it) using the following wording: Source: Australian Transport Safety Bureau
Copyright in material obtained from other agencies, private individuals or organisations, belongs to those agencies, individuals or organisations. Where you wish to use their material, you will need to contact them directly.
On 28 July 2015, the pilot and owner of an amateur-built Cicaré CH-7BT helicopter, registered VH‑JEW, was conducting a ferry flight from Indee Station to Roy Hill Station, Western Australia. When about 8.5 NM north‑east of Roy Hill Station, the stabiliser assembly fractured leading to an in-flight break up and collision with terrain. The pilot, and sole occupant, was fatally injured and the helicopter was destroyed.
What the ATSB found
The ATSB examined the helicopter wreckage and identified that the stabiliser had separated in‑flight from the tail boom as a result of fatigue cracking of the stabiliser mount. This was the second fatal accident in Australia involving in-flight stabiliser separation on a Cicaré CH-7B helicopter (In-flight break-up involving Cicaré CH-7B, VH-SWQ, 43 km north-west of Barcaldine Airport Queensland on 12 May 2014 (AO-2014-086)). Following the event in 2014, the helicopter manufacturer, Cicaré S.A., released a mandatory service bulletin, BSC007, which required inspection of the stabiliser assembly. However, the bulletin did not include an initial or recurrent time interval for that inspection.
The ATSB found that there were notable differences between VH-JEW and SWQ, and the accidents were not directly comparable. However, it was established that both helicopters were fitted with an external storage pod, likely without the appropriate engineering assessment to ensure there would be no adverse effects on the performance, handling and structure of the helicopter. In addition, both helicopters had previously been used for mustering operations, although the helicopters were designed be used for recreational use only. The ATSB found other Cicaré CH-7B owners were also likely using their helicopters for aerial mustering and other agricultural activities. The addition of unapproved modifications and use for mustering operations can produce unintended stresses on the airframe leading to premature failure of components.
The ATSB determined that a combination of factors could have contributed to the development of the fatigue crack including, the stabiliser design, operating the helicopter in high load mustering activities, and the use of untested accessories. However, the investigation was unable to determine the contribution of these factors.
What's been done as a result
On 6 August 2015, the ATSB emailed an information letter to registered Cicaré CH-7B owners, informing them of the second accident, the mechanism of stabiliser failure, and a recommendation to ensure the integrity of the stabiliser prior to further operation and on an ongoing basis.
The ATSB has also released a Safety Advisory Notice (AO-2015-089-SAN-014) to raise awareness among amateur-built helicopter owners and the aerial mustering community regarding the risks associated with operating outside the recommended design intent.
A revision to the original bulletin, BSC007, was released in September 2015, which provided some additional information with regard to disassembly of the component to allow examination. The contents of this bulletin was incorporated into the ongoing maintenance documentation for the helicopter in March 2016, with the inspection required to be performed every 100 hours. The stabiliser was also redesigned, originally for the bigger CH-8 series helicopter. The latest design was incorporated into all new Cicaré helicopters and is available for retrofit on the CH-7T/B/BT. A number of operators in Australia have already installed the new stabiliser assembly.
Safety message
The addition of external loads may result in forces in excess of the manufacturer’s limitations. This accident highlights the significance of ensuring that any modifications, such as external accessories, are appropriately assessed, and the effects on structural integrity and handling characteristics are considered prior to flight.
Further, it emphasises the importance of operating aircraft in accordance with the manufacturer’s intent and limitations. Operating outside these has the potential to induce stresses on the aircraft, leading to premature wear and possible failure.
Lastly, as detailed in the information letter released in March 2016, the ATSB reinforces the importance of CH-7B owners ensuring the integrity of the stabiliser on an on-going basis. If any doubt arises concerning the inspection or maintenance of any part, piece or component, owners should immediately contact Cicaré.
The occurrence
On 28 July 2015, at about 1535 Western Standard Time,[1] the pilot and owner of an amateur-built Cicaré CH-7BT helicopter, registered VH-JEW, departed Indee Station for a 2.5-hour flight to Roy Hill Station, Western Australia. The flight was a repositioning flight, for mustering work at Roy Hill Station, which was to commence the following day.
At about 1810, a company pilot who had arrived at Roy Hill Station about 2 hours prior, phoned another pilot who had remained at Indee Station to advise that VH-JEW had not yet arrived. They decided to give the pilot a little more time, however, when the helicopter still had not arrived by about 1930, it was reported missing to search and rescue, and the police. A search and rescue operation commenced the following morning.
On 29 July 2015, at about 1500, the wreckage was located about 8.5 NM north-west of Roy Hill Station, and 0.5 NM west of the intended track between Indee and Roy Hill Stations (Figure 1). The pilot was fatally injured, and the helicopter destroyed.
Figure 1: VH-JEW accident site location, near Roy Hill Station
The pilot held a Commercial Pilot (Helicopter) Licence, issued on 13 June 1980. The pilot last completed a single-engine helicopter and low-level flight reviews in June 2015, valid until 30 June 2017 and 24 June 2017 respectively.
At the time of the accident, the pilot’s Class 1 Aviation Medical Certificate required for conducting commercial operations[2] had expired on 13 April 2015 and the pilot was in the process of revalidation. The pilot held a Class 2 certificate, valid to 13 April 2016.
In May 2015, the pilot indicated on his aviation medical questionnaire that he had accumulated a total of 28,559 hours, with 78 hours of helicopter operations in the previous 6 months. The pilot was reported to have had extensive experience as a cattle mustering pilot. Anecdotal information supplied to the ATSB indicated that most of this flying had been completed in a Robinson Helicopter Company R22. The pilot had only recently starting flying the Cicaré CH-7BT, and it was reported that the pilot had been conducting commercial mustering operations[3] in the weeks leading up to the accident.
Witness reports from family and acquaintances indicated that the pilot was in good health and mental state prior to the flight. A post-mortem examination did not reveal any preconditions that would have affected the pilot’s ability to fly the helicopter.
Helicopter information
VH-JEW was a single-seat, amateur-built[4] Cicaré CH-7BT helicopter, serial number 032, which was first registered with the Civil Aviation Safety Authority (CASA) on 25 June 2015 (about one month before the accident). It had a two‑bladed, semi-rigid main rotor system, a two-bladed tail rotor system, and was powered by a Rotax 914 UL turbo-charged, four-cylinder piston engine. The helicopter kit manufacturer was located in Argentina with the kits and product support available through an Australian distributor. As at March 2019, there had been 39 CH-7B[5] kits sold worldwide, 13 of which were in Australia. At time of publication, there were six on the CASA VH‑register.
Meteorological information
Personnel on the ground at Ginbata aerodrome (about 10 NM from the accident site) described the weather conditions on the day as fine and clear with light wind. This was consistent with the Bureau of Meteorology area forecasts for the afternoon.
Sunset was recorded to be at 1737 and last light[6] at 1801. The helicopter departed Indee Station at about 1535, which would have put the arrival time at Roy Hill at about 1800. However, a worker at the nearby Roy Hill mining camp reported seeing black smoke for about 20 minutes at about 1720. Therefore, it was considered unlikely that the weather and available light conditions were a contributing factor to the accident.
Wreckage and impact information
The helicopter was found in an open area, having broken into multiple fragments. The fuselage was subject to a post-impact fire, and the tail rotor stabiliser assembly was identified some distance away from the main wreckage (Figure 2).
Figure 2: Wreckage distribution showing main body and tail rotor stabiliser assembly, the blue arrow shows direction of travel
Source: ATSB
The stabiliser assembly and the tip from one tail rotor blade were the first items identified in the wreckage trail. The main rotor head components were located about 70 m beyond the stabiliser. The tail boom was still attached to the main wreckage, which was lying on its left side and facing opposite to the intended direction of travel, and was a further 180 m along. The tail rotor gearbox assembly was located near the fuselage. Overall, the wreckage distribution was about 250 m long in a southerly direction and consistent with an in-flight break-up.
The helicopter had been subjected to a post-impact fire, which destroyed much of the fuselage. Examination of the remaining wreckage identified:
all major components of the helicopter were accounted for
flight control damage was consistent with the in-flight break-up and did not indicate any pre‑existing issues
no indications of any issues with the engine and its related systems that may have contributed to the accident
the stabiliser assembly had separated at the point where it mounted to the tail boom
the tail rotor gearbox had fractured at its mount in overstress
the main rotor head assembly had separated from the main mast in a manner consistent with severe mast bumping.[7]
The fracture surfaces of the stabiliser assembly attachment bracket that remained with the tail boom appeared to correspond to those of the separated stabiliser assembly in shape and irregular texture. The rear section of the tail boom, including tail rotor components and the stabiliser assembly were retained by the ATSB for further examination (see Stabiliser assembly below).
Similar occurrence
The ATSB investigated a similar fatal accident where the stabiliser assembly on a Cicaré CH-7B had separated from the tail in-flight leading to a collision with terrain (In-flight break-up involving Cicaré CH-7B, VH-SWQ 43 km north-west of Barcaldine Airport Queensland on 12 May 2014 (AO-2014-086)). The investigation found that fatigue cracking of the stabiliser mount had led to the failure of the stabiliser assembly. The helicopter was reported to have had an issue with airframe vibration, and thee stabiliser had undergone two weld repairs following the identification of cracking of the stabiliser mount tube. The first weld repair was at about 130 hours’ total time-in-service, after the fins were removed following reports of movement within the stabiliser structure. The second weld repair was performed at about 295 hours’ total time-in-service. The investigation found these repairs were performed by a welder who did not hold a CASA-issued aviation welding authority, and that the first unauthorised welding carried out on the mount did not prevent further in-service metal fatigue cracking. The helicopter had also experienced a hard landing, sufficient to distort the rear cross-tube on the skid-landing gear. The investigation also found that the helicopter had undergone modifications, including the addition of heli-baskets and larger fuel tanks, which were not approved by CASA and/or the kit manufacturer, and could have affected the serviceability and flight characteristics.
Following this accident, the ATSB sent an advisory letter to all Australian registered owners of the CH-7B on 6 March 2015 which detailed the in-flight separation of the stabiliser.
The kit manufacturer advised that the accidents involving VH-SWQ and VH-JEW were the only known stabiliser fractures in the worldwide fleet of Cicaré 7 series helicopters[8].
Stabiliser assembly
The stabiliser assembly consisted of one horizontal and two vertical aerodynamic fins fitted to the helicopter tail boom. The fins generate aerodynamic forces during forward flight that keep the helicopter level and reduce the thrust required from the tail rotor.
Flight characteristics without stabilisers
The kit manufacturer advised that they had performed testing of the flight characteristics of the helicopter when the stabiliser assembly was not fitted and found the following:
…proving that for hovering flight condition and low speeds, the change in controllability was verily [sic] noticeable and for translational flight over 30 knots the helicopter showed a light instability in pitch and yaw that can be easily corrected by the pilot, a pilot with standard training is able to execute the emergency maneuver [sic].
However, the manufacturer also noted that:
In case of loss of stabilizer [sic] in flight, even if the stabilizer doesn’t hit the tail rotor, sudden change on aerodynamic loads and CG [centre of gravity] balance due to the sudden absence of the stabilizer would cause an unstable flight condition.
With regard to the failure of the tail rotor/gearbox, the manufacturer advised:
For the case of an eventual tail rotor loss, during flight-testing there was no presence of “loss tail rotor effectiveness” under normal flight operations. In case of tail rotor or tail rotor gearbox failure, due to the variety of conditions that may occur it’s not possible to determine the exact behaviour of the aircraft.
Assembly build and fitting
While the build manual provided instructions for manufacturing this component, the kit manufacturer and Australian distributor advised that the CH-7B kits for Australia were supplied with the stabiliser assembly as a pre-assembled component (inset, Figure 3).
Figure 3: Stabiliser assembly showing location of fracture on VH-JEW
Source: Cicaré, modified by the ATSB
The CH-7BT kit build manual provided instructions for fixing the stabiliser on the tail boom. A factory pre-drilled hole in the stabiliser mount was to be positioned 115 mm forward of the tail rotor gear box mount and aligned with the top centreline of the tail boom. A hole was then drilled into the boom skin, using the locator hole as a guide, and a bolt inserted through the mount and boom.
Technical examination of the stabiliser assembly
While it was outside the scope of the investigation to conduct an engineering assessment of the helicopter design, a detailed examination of the retained tail components was conducted at the ATSB’s technical facilities in Canberra, with a focus on the fracture of the stabiliser support. That examination found that the failure had occurred adjacent to the welded region of the support. The location of the cracking was also coincident with the point at which the upper and lower vertical stabiliser fairings met the mount (Figure 4).
Figure 4: Location of the stabiliser failure adjacent to the welded region
Source: ATSB
Stabiliser mount
The stabiliser fins were removed from the stabiliser assembly in order to completely expose both portions of the fractured stabiliser mount (Figure 5). The stabiliser mount was comprised of three main sections; a clamp for attaching to the tail boom, conical support, and three oval-shaped, thin‑walled seamless metal tubes that were used to locate and secure the fins into position (Figure 5). During manufacture at the factory, the three tubes had been cut to fit and then welded together at the conical support.
Figure 5: Location of the stabiliser failure following removal of the fins
Source: ATSB
Detailed microscopic examination of the stabiliser mount fracture surfaces was accomplished using a binocular microscope. The examination revealed that the fracture path primarily followed the welded portions of the tube junction. A large portion of the fracture surface was discoloured, and exhibited fretting and corrosion product along with the presence of a series of finely spaced continuous progression marks. Such features were consistent with a fatigue crack growth mechanism as a result of in-service cyclic stresses and suggested that the crack had been present for some period of time prior to final fracture.
The fatigue crack had propagated in a circumferential manner through about 75 per cent of the structure prior to the failure (Figure 6). Once a significant portion of the cross section had fractured, the remaining section could no longer sustain in-flight loads and the stabiliser failed due to overstress. The origin of the fatigue cracking could not be clearly identified due to post‑accident damage. No obvious defects or anomalies were observed in the welded regions that might have otherwise contributed to the growth of the fatigue cracking.
Figure 6: Stabiliser fracture surface showing fatigue and overstress areas
Source: ATSB
Sectioning of the fracture surface for detailed microstructural examination and hardness testing did not reveal the presence of any anomalies that might have contributed to the failure. Chemical analysis of the stabiliser mount tubes was consistent with an SAE grade 4130 steel, as specified by the manufacturer.
Comparison between the stabiliser mount of VH-JEW and VH-SWQ
The two stabilisers had failed in a similar location, however, three differences were observed between the construction of the stabiliser mount of VH-JEW and VH-SWQ[9] including:
The vertical and horizontal tubes had been manufactured from welded tube for VH-SWQ, and seamless tube for VH-JEW.[10]
The mount on VH-SWQ was hollow through the joins in the horizontal tube where the vertical tubes were attached (Figure 7 left). For VH-JEW, the horizontal tube was not hollow (intact tube) where the vertical tubes were attached (Figure 7 right).
The horizontal tube for VH-JEW was welded at the conical support, while for VH-SWQ the tube was welded in two locations – at the conical support and just outboard of the intersection with the vertical tubes. (Figure 7 left).
Figure 7: Comparison between stabiliser fracture on VH-SWQ (left) and VH-JEW (right)
Source: ATSB
VH-JEW information and history
Construction and certification
VH-JEW was constructed as an amateur-built and experimental (ABE) aircraft under the Civil Aviation Safety Regulations 1998 (CASRs) Part 21 Subpart H, and Civil Aviation Regulations 1988 (CAR 1988) 262AP. Regulation 21.191 outlined the reasons an experimental certificate may be issued. Referring to the operation of amateur-built aircraft, sub-part (g) stated: ‘the major portion of which has been fabricated and assembled by a person who undertook the construction project solely for the person’s own education or recreation’. CASA Advisory Circular AC-21.4(2) Amateur-built Experimental Aircraft – Certification, provided guidance and information to those applying for an experimental certificate.
An aircraft that does not have a standard certificate of airworthiness[11] cannot operate unless it has been issued with a special certificate of airworthiness (including an experimental certificate) or a special flight permit. According to CASA Advisory Circular AC-21.10 v4.2 (issued March 2019), Experimental certificates:
Special certificates of airworthiness (CofA), which include experimental certificates, are issued to permit certain kinds of operations of aircraft that do not meet the requirements for a standard CoA or that, because of certain modifications, do not conform to their type certificates, but are capable of safe operations under defined operating conditions and purposes.
In recognition of the lack of compliance with some of the airworthiness standards, the aircraft is normally permitted to be operated under more restrictive operating conditions than in the case of a comparable aircraft operating on a standard CofA.
An authorised person (AP)[12] could issue experimental certificates under CASR 21.195A to allow operation of amateur-built and kit-built aircraft. This special certificate of airworthiness detailed the conditions under which the aircraft was permitted to be operated. For example, the helicopter involved in the previous ATSB investigation (refer to Similar occurrence), VH-SWQ, had a special certificate of airworthiness with a condition that it was not to be flown for commercial operations.
Under the experimental certificate, ABE aircraft were inspected at least once prior to the initial test flight by CASA or by an AP, who may operate under the Sport Aircraft Association of Australia (SAAA) maintenance procedures. Advisory Circular AC-21.4(2) described that the purpose of the inspection was to:
allow the inspector to make a subjective assessment of the workshop methods, techniques and practices used in the construction of the aircraft solely for the purpose of prescribing appropriate conditions and operating limitations necessary to protect other airspace users and persons on the ground or water, i.e. to protect persons and property not involved in the activity.
As part of the certification process, an ABE aircraft was initially limited to operations within an assigned flight test area for at least 25 hours, to demonstrate it was capable of safe flight.
VH-JEW was built by the pilot and owner in south-east Queensland in early 2015 from a kit supplied by the manufacturer. It was reported to the ATSB that the helicopter build took longer than the pilot expected. Below is a timeline of the events related to the helicopter build:
26 March 2015: The pilot initially contacted the SAAA requesting an onsite inspection of VH‑JEW on 4 May 2015.[13] According to documentation provided by the SAAA, that visit was cancelled and rescheduled as the helicopter was not ready for inspection.
The onsite inspection was rescheduled to 27 May 2015, however, it was again delayed as the helicopter was not ready for inspection.[14]
3 June 2015: The pilot submitted an application for a special certificate of airworthiness in the experimental (kit-built) category.
4 June 2015: A visit was carried out by the SAAA AP, however, it was reported that the helicopter was still not completed, and some of the required documentation was not completed or available. Following that visit, the pilot continued discussions with the SAAA about completion of the relevant requirements. The outstanding items were not related to the stabiliser or tail boom assemblies.
16 June 2015: The SAAA AP received an email containing a copy of the helicopter logbook and test flight record pages, dated 28 June 2015, indicating that 26.2 flight hours had been completed.[15]
25 June 2015: The helicopter was registered with CASA.
15 July 2015: As the SAAA AP had not issued the authorisation for test flights to commence, a letter was sent to the pilot,[16] advising that:
You are currently flying your aircraft without a Certificate of Airworthiness
The process of submitting the requested information listed on previous email has not been received
Copies of certifications for duplicate inspections from airframe log book not received
Submission of the nominated pilots and nominated flight test area not received.
As a result, the SAAA advised that they were unable to proceed any further with the application at that time. Due to the limited timeframe between when the letter was dated, and the date of the accident, the investigation could not be assured that the pilot had received the letter.
Helicopter flight history
Following the build, the pilot departed Queensland in VH-JEW on the morning of 27 June 2015 and arrived in Western Australia on the evening of 29 June 2015. At the time of the accident, the most recent entry on the maintenance release (5 days prior on 23 July 2015) showed the helicopter had accumulated 168.7 hours’ total time-in-service. Of the eight entries recorded, six of them showed the helicopter had accumulated between 8.3 and 11 hours on these days. This, together with information supplied by associates of the pilot, indicated that it was likely that the helicopter had been involved in some (commercial) aerial work, including aerial stock mustering and/or spotting, since arriving in Western Australia. It was also reported that the pilot was generally happy with the operation of the helicopter, and had not mentioned any major issues or the presence of vibrations.
Following the accident, a colleague of the pilot stated that there was a report of the temperature gauge reading above the normal operating range, however, it was mentioned that it was a one‑time occurrence and the reason for this was not determined. An acquaintance of the pilot reported to the ATSB that the pilot had advised him that the helicopter had experienced a hard landing in early July 2015, but it didn’t appear to have caused any damage to the helicopter.
Airworthiness and maintenance
Under sub-regulation 42ZC(6) of CAR 1988, the owner/builder of an amateur-built aircraft may be authorised to carry out maintenance on the aircraft, if they were the primary builder. CASA Instrument 33/13 Authorisation of person to carry out maintenance on certain amateur-built, kit‑built and light sport aircraft with a special certificate of airworthiness, detailed the conditions of the owner/builder’s maintenance authorisation. One of the conditions was that the owner/builder was required to have satisfactorily completed a course in maintenance procedures.[17] Further, maintenance conducted could only be on the elements of the aircraft that they had assembled.
The most recent maintenance release, issued by the pilot on 16 July 2015, at 105.9 hours’ total time‑in‑service, indicated the helicopter was to be maintained in accordance with the manufacturer’s maintenance schedule manual. The maintenance manual recommended a complete inspection of the helicopter every 12 months or 100 hours’ time-in-service. This included:
During inspection, check the general condition of the components and observe if there is evidence of damage, color change due to high temperatures, dents, scratches, notches, corrosion and specially cracks. Also check for any sign of friction in the parts that are near one another.
Specific to the stabilisers, the manual stated the following:
Check the whole surface of the stabilizers. Verify there are no scratches or cracks.
Check each stabilizer bearing. Verify there are no cracks around the attachment holes. Also check that the attachment screws are in proper condition.
Check the tailskid. Verify if there is evidence of strikes against the ground.
As the helicopter logbooks were not located, the ATSB was unable to determine what, if any, maintenance and/or inspections had been carried out on VH-JEW since leaving Queensland.
In addition, the ATSB also noted that there were several omissions and inaccuracies with how the maintenance release had been completed, making it invalid. However, as the aircraft had not been authorised for flight operations, it was determined there would be little benefit in further investigation. While these irregularities did not likely contribute to the accident, continued operation and maintenance outside of the regulations increases the risk that the safety protections they offer will be eroded.
Manufacturer’s stabiliser mount inspection
Following the accident involving VH-SWQ (refer to Similar occurrence), the manufacturer released a service bulletin on 24 September 2014 (BSC007) requiring dye penetrant inspection of the stabiliser. This document included instructions on how to perform the testing on the stabiliser mount. However, there was no mention of how to remove the support assembly from the horizontal and vertical fins to perform the inspection, which would have been necessary to inspect the relevant area. For VH-JEW, as this component had been pre‑assembled by the manufacturer for import into Australia, this maintenance would need to have been performed by an appropriately qualified person, such as a licensed aircraft maintenance engineer. Additionally, the document did not include any inspection interval requirements (initial or recurrent). The manufacturer reported that owners were advised to evaluate the stabiliser mount every 100 hours, or if there were any signs of wear on the stabiliser. No evidence was supplied to the ATSB as to how this information had been disseminated to owners.
External storage pod
The helicopter had been modified with an external storage pod, attached to the rear strut of the right skid-landing gear (Figure 8). The storage pod was not included on the weight and balance documents provided as part of the special certificate of airworthiness approval process. It was reported that this pod was fitted for the flight from Queensland to Western Australia. However, as the helicopter logbooks were not located, the ATSB was unable to establish if the storage pod remained fitted for the life of the helicopter, or if any authorisations[18] had been received.
Figure 8: External storage pod as fitted to VH-JEW at Indee Station on 23 July 2015
Source: Andrew Miles, annotated by the ATSB
Helicopter landing gear is designed to provide energy absorbing capabilities during landing. Fixing external loads to the landing gear can result in forces applied to the landing gear in excess of the design limit and can also increase the in-flight dynamic loads due to increased vibration. Advice published by Robinson Helicopter Company for the R22 in the pilot operating handbook included a safety notice, SN-13, which stated that;
…even a small weight attached to the landing gear may change the natural frequency[19] enough to cause high loads to inflight vibration.
The ATSB could not determine whether the potential effects on the in-flight loads, flight characteristics and operating weight were considered by the pilot prior to the fitment of the external storage pod.
The Cicaré CH-7B was promoted in the Australian website Beef Central[20] in a 19 April 2011 article Heli-mustering game-changer, which included the promotion of the use of an external storage box:
While the Cicaré has a payload limit of around 100kg (not including pilot), it can be set up with a storage box to carry a chainsaw, fencing tools and enough wire for many on-the-job fencing repairs, for example.
However, correspondence from the kit manufacturer advised that the helicopter was not designed to carry external loads, and had not been tested under asymmetrical load conditions. The kit manufacturer was of the opinion that the difference between the two helicopters with cracked stabilisers and the rest of the Cicaré fleet with unaffected stabilisers was the addition of accessories (the storage pod in the case of VH-JEW and a heli-basket and larger fuel tanks for VH-SWQ), ‘making it very hard to ignore that this [sic] accessories could be related to the premature wear of the stabilizer’.
Ground handling
The flight manual contained the procedures for moving the helicopter on the ground, using the wheels provided, which attached to the landing gear. These procedures stipulated that the helicopter was to be pushed or pulled by holding the tail rotor gearbox. Additionally, the flight manual included the following caution:
Do not move [the] Cicaré CH-7BT by holding either the horizontal or vertical stabiliser, or from the tail rotor, or the tail rotor controls, or tailskid.
Manoeuvring the helicopter via the tail skid, particularly over rough terrain, could induce unintended forces on the stabiliser mount. However, as the pilot’s ground handling practices could not be established, the ATSB was unable to determine if this contributed to the development of the stabiliser mount fatigue crack.
Commercial flying
In order to conduct commercial aerial work operations, including aerial mustering and spotting, at the time of the accident, the pilot was required to hold a Commercial Pilot Licence. Additionally, Civil Aviation Regulations 1988 (CAR) 206 stated that an Air Operator’s Certificate was also required to conduct commercial operations.
The pilot held a Commercial Pilot Licence (Helicopter), and had regularly conducted commercial flying operations in helicopters. The pilot also held an AOC, on which two Robinson Helicopter Company R22’s were listed. VH-JEW was not listed on the Air Operator’s Certificate.
Operational aspects
The Cicaré S.A. website stated that the Cicaré CH-7B was a helicopter ‘for sport use’. However, the Australian experience indicated that these helicopters were increasingly being used for agricultural operations and other aerial work, such as mustering and spotting.
Both VH-SWQ and VH-JEW had been used for mustering operations during their lifetime, and the ATSB was aware of one other reported accident involving another Cicaré CH-7B helicopter while engaged in agricultural operations in October 2018.
While the use of an amateur-built helicopter for private agricultural operations, including mustering and spotting, was not specifically excluded under the CASA regulations, such operations can involve extremely frequent manoeuvring and rapid power changes that can apply very high loads on the helicopter. The fatigue life of various components can be adversely affected by the type of operation and loading history of the components. CASA Airworthiness Bulletin (AWB) 02-015 Helicopter – Effects on fatigue on life limited components described some operational situations where the fatigue life might be affected, and included:
…Operations of helicopters in low level flying, agricultural, mustering or other operations where high loads may be encountered more frequently than envisaged by the designer/manufacturer.
Cicaré CH-7B flying activity
Activity data for the CH-7B between 2011 and 2018 was supplied by the Bureau of Infrastructure, Transport and Regional Economic (BITRE) is shown in Table 1.[21] This data was reported to BITRE by registered aircraft owners in the annual BITRE General aviation activity survey.
Table 1: Reported flights and hours for Cicaré CH-7B aircraft between 2011 and 2018
2011
2012
2013
2014
2015
2016
2017
2018
Number of aircraft
3
4
8
4
7
5
6
5
Number of landings
24
35
62
10
89
51
293
562
Total hours
17
28
52
19
83
43
457
408
Private
17
28
52
-
-
-
-
-
Agriculture mustering
-
-
-
0
6
0
0
0
Agriculture-other
-
-
-
19
0
19
397
0
Other aerial work
-
-
-
0
0
0
0
181
Pleasure and personal transport
0
48
8
57
7
Other sport and pleasure flying
-
-
-
0
29
16
3
7
Other flying
-
-
-
0
0
0
0
213
Source: Bureau of Infrastructure, Transport and Regional Economics
The data showed that only 6 hours total had been attributed to agricultural mustering over this period. However, in 2017-2018, there was a significant increase in the reported landings/hours for the Cicaré CH-7B fleet, together with an increase in the number of hours attributed to ‘agricultural-other’ (which includes all non-mustering and non-spraying agricultural activities including stock spotting), other aerial work and other flying categories.
The manufacturer advised that a number of helicopters within the fleet had accumulated up to 400 hours in Argentina and at least one helicopter in Australia had reached 1,500 hours total time-in-service. However, they were unable to provide any information on what types of operations these helicopters may have been performing when these house were accumulated.
Previous research
Stress loads from aerial stock mustering and spotting
In 2004, the ATSB commissioned AeroStructures, an Australian engineering company, to undertake a study of the forces acting on a Robinson Helicopter Company (RHC) R22 (also extensively used in mustering operations in Australia) while engaged in aerial mustering operations. The study (Robinson R22 helicopter aerial mustering usage investigation) provided a comparison of the flight profiles in aerial mustering operations and compared these with the flight profiles used during certification.
The report found that aerial mustering exhibited frequent low speed manoeuvres and rapid power changes, and five measurements showed higher peak stresses than for the certification flights, one of which was the tail rotor drive shaft torque. The report stated that:
Owners and operators need to fully appreciate the stresses placed on aircraft during mustering operations, and the characteristics of aerial mustering operations, which may be quite different [to] the type of flying for which the type originally received certification
Advice was contained in a safety notice produced by the Robinson Helicopter Company, who manufactured the R22 helicopter. Safety Notice, SN-37 - Exceeding approved limitations can be fatal discussed how fatigue damage can accumulate within components without a visible indicator.
The kit manufacturer, Cicaré S.A, advised that
experimental category covers recreational and sport use. However, this won't prohibit anyone to use it for other activities.
Amateur-built aircraft research
ATSB research has identified that amateur-built aircraft are over-represented in aviation accidents and incidents in Australia (AR-2007-043 (2) Amateur-built aircraft Part 2: Analysis of accidents involving VH-registered non-factory-built aeroplanes 1988-2010). The research found that, although pilots of amateur-built aircraft involved in accidents were significantly more experienced overall than pilots of accidents in equivalent factory-built aircraft, they were less experienced on the type that they were flying at the time of the accident.
While this report did not include amateur-built helicopters due to the small numbers in operation at that time, much of the data and outcomes of the report were relevant to aeroplanes and helicopters. The prevalence of amateur-built helicopters in Australia is also increasing.
While on a ferry flight from Indee Station to Roy Hill Station, Western Australia, the stabiliser assembly on VH-JEW fractured leading to an in-flight break-up and collision with terrain. The pilot was fatally injured, and the aircraft was destroyed.
Available information indicated that it was unlikely that the pilot became incapacitated during the flight, and pilot fatigue, weather and poor manufacturing of the welded stabiliser structure were not considered factors.
This analysis will examine the potential factors that may have led to the failure of the stabiliser and resulting in-flight break-up.
In-flight break-up
The fracture of the stabiliser mount and subsequent in-flight separation of the stabiliser from the tail boom led to severe mast bumping sufficient to sever the mast and main rotors. Consistent with the wreckage distribution, the helicopter broke up in-flight, resulting in a collision with terrain.
In the event of a stabiliser failure, the manufacturer indicated that, although the helicopter was theoretically controllable under certain circumstances, the sudden change to the aerodynamic loads and centre of gravity balance, would lead to an unstable flight condition. Additionally, this was the second accident where a loss of control had resulted following the loss of the stabiliser assembly.
Stabiliser mount cracking
Analysis of the tail components identified that the stabiliser assembly mount was significantly weakened by cracking associated with metal fatigue. While the ultimate fracture of the mount was due to overstress, a fatigue crack was found to have propagated about 75 per cent of the way around the mount’s circumference, adjacent to the welded region. The investigation considered the potential factors that contributed to the cyclical loading that resulted in fatigue cracking of the stabiliser mount. These included, in no particular order:
fitment of the external storage pod
possible operations exceeding the manufacturer’s limitations
stabiliser assembly design.
The helicopter had been fitted with an external storage pod attached to the rear strut of the right skid‑landing gear, although it was unknown if it was in place on the accident flight. The storage pod was not on the weight and balance documents associated with the special certificate of airworthiness process, and a special certificate of airworthiness had not been issued. While the helicopter logbooks were not located, it was unlikely that an engineering assessment had been conducted prior to the helicopter departing Queensland.
In addition, the manufacturer indicated that the helicopter was not designed to carry external loads and expressed reservations about the addition of an accessory on both VH-JEW and VH-SWQ. Specifically, they were of the opinion that the fitment of the external accessories to both these aircraft could have been the reason for the premature failure of the stabiliser. The fitment of the pod had the potential to adversely affect the structural integrity and handling characteristics of the helicopter. However, as it was likely the pod had not been assessed, the ATSB was unable to determine the extent to which this contributed to the initiation and propagation of the fatigue crack.
While the Australian activity data indicated minimal mustering activity in the CH-7B, the ATSB was aware of three accidents where the helicopter had, at some point, been conducting this type of operation. For VH-JEW, the investigation was able to establish that the helicopter had operated for 168.7 hours up until 23 July 2015, and likely only a few hours on the day of the accident. The available records indicated that in the month prior to the accident, it had been used for at least 60 hours of low-level mustering operations. The Cicaré CH-7B helicopter is advertised as being for recreational use, and operation outside the manufacturer’s limitations has the potential to induce stresses on the airframe and components, leading to premature wear and possible failure. Further, operations such as mustering and similar activities can also increase the risk of premature ageing of aircraft structure due to an increased load spectra.
In addition, while two aircraft in Australia exhibited premature failure of the same component, in a similar location, at relatively low time in-service, these were the only two helicopters in the worldwide fleet to exhibit cracking. While there were some similarities between the accidents involving VH-SWQ and VH-JEW, in that both helicopters had been fitted with untested external accessories and were being used for mustering operations, there were some notable differences. VH-SWQ had experienced a number of other issues, including a hard landing and ongoing airframe vibrations possibly, as a result of a tail rotor imbalance, which may also have contributed to the development of a fatigue crack within the stabiliser mount. In addition, the design of the stabiliser had been modified for helicopter kits manufactured after VH-SWQ, including VH-JEW. Therefore, it was not possible to make a direct comparison between the two accidents.
While it was outside the scope of the investigation to conduct an engineering assessment of the helicopter design, the stabiliser mount has been shown to be susceptible to fatigue cracking of under certain conditions. However, if there was an inherent design issue with the helicopter, it was not unreasonable to expect more incidence of cracking in the worldwide fleet. This was particularly so given a number of helicopters in the fleet had accumulated up to 400 hours in Argentina and at least one helicopter in Australia had reached 1,500 hours total time-in-service. However, VH-JEW and VH-SWQ were the only helicopters that have exhibited cracking. As a result, the investigation was unable to determine the contribution of all factors such as design, operating conditions, untested accessories, and the magnitude of the effect these elements may have had on the development of the fatigue crack.
Manufacturer’s service bulletin
Following the accident involving VH-SWQ in 2014, the manufacturer released a mandatory service bulletin, BSC007, to all operators of the Cicaré 7 series helicopters. While the service bulletin provided a general instruction to perform a non-destructive dye penetrant inspection of the stabiliser mount, it did not include essential information such as how to disassemble the stabiliser to perform the inspection, a compliance time, or a recurring inspection interval.
Given the extent of the fatigue crack found on the stabiliser mount, it was likely that the crack had been present for some time since the helicopter entered service. However, the absence of a compliance timeframe or requirement for a recurring inspection reduced the likelihood of the crack being detected prior to reaching a critical size. Additionally, as the bulletin was released prior to the pilot purchasing and building the helicopter, it was possible that he did not have knowledge of the requirement to conduct the inspection.
Airworthiness documentation and regulatory aspects
Amateur-built experimental aircraft are not required to comply with the full range of safety regulations that are applicable to commercially manufactured aircraft. However, the regulations that do apply are fundamentally important and have been introduced to control and reduce (as much as possible) the risks associated with the operation of this category of aircraft.
At the time of the accident, the aircraft had not been issued with a Civil Aviation Safety Authority (CASA) special certificate of airworthiness. As a result, the aircraft was not on the operator’s Air Operator’s Certificate, and therefore, not authorised to be flown for commercial aerial work such as aerial spotting or mustering. Not having the certificate meant that compliance with the applicable airworthiness standards could not be assured.
In addition, as an amateur-built experimental helicopter, it was very likely that the special certificate of airworthiness would have been issued with prescriptive operational uses, which would not have included commercial mustering. It was reported that the pilot had been conducting commercial aerial mustering operations in the helicopter in the weeks leading up the accident and was intending to continue after arriving at Roy Hill Station.
While the pilot had significant aeronautical experience and held a valid Class 2 Aviation Medical Certificate, the pilot’s Class 1 certificate had expired several months prior. Although he was in the process of revalidation, the pilot was unable to exercise the privileges of a Commercial Pilot’s Licence until such time. Of note, the pilot had no apparent medical issues.
The ATSB had considered if the pilot was experiencing time or commercial pressures to complete the build of VH-JEW. However, due to the limited information available, this could not be established. Therefore, the ATSB was unable to determine if this had influenced his actions with regard to the aircraft certification process.
The pilot’s decision not to follow certain regulations may not have directly influenced the in‑flight break-up of the stabiliser assembly. However, it did result in the helicopter being used for commercial mustering operations that it was not authorised for and would very likely not have been approved for by the Civil Aviation Safety Authority. This exposed the helicopter to higher operational stress and had the potential to increase the risk to the pilot and those working around the helicopter during the flying operations.
Findings
From the evidence available, the following findings are made with respect to the collision with terrain of a Cicaré CH-7BT helicopter, registered VH-JEW, that occurred near Roy Hill Station, Western Australia on 28 July 2015. These findings should not be read as apportioning blame or liability to any particular organisation or individual.
Safety issues, or system problems, are highlighted in bold to emphasise their importance. A safety issue is an event or condition that increases safety risk and (a) can reasonably be regarded as having the potential to adversely affect the safety of future operations, and (b) is a characteristic of an organisation or a system, rather than a characteristic of a specific individual, or characteristic of an operating environment at a specific point in time.
Contributing factors
While conducting a ferry flight, the stabiliser mount fractured, resulting in an in-flight break-up and collision with terrain.
The helicopter’s stabiliser mount fractured due to overstress, following propagation of a fatigue crack in the area adjacent to the weld. While the ATSB was unable to fully determine the reasons for the intiation and propagation of the fatigue crack, it was likely the result of some combination of the design, operating conditions, and untested accessories.
Other factors that increased risk
The helicopter was modified with an external storage pod, likely without the appropriate engineering assessment to ensure there would be no adverse effects on the performance, handling and structure of the helicopter.
Although the amateur-built Cicaré CH-7B helicopter was intended for recreational and sport use only, this and other CH-7B helicopters had been used for agricultural mustering. Operating outside the manufacturer’s design intent had the potential to induce stresses on the aircraft, leading to premature wear of components and possible failure.
The Cicaré 7T/B/BT mandatory service bulletin (BSC007) for the general stabiliser support assembly provided limited guidance for disassembly of the manufactured component and did not stipulate a compliance period within which to perform the inspection nor provide consideration for repeat inspections. This potentially reduced the opportunity to detect the presence of crack initiation and growth in the stabiliser support assembly. [Safety issue]
Other findings
The helicopter was being operated without a Civil Aviation Safety Authority special certificate of airworthiness. Further, it was being used for commercial mustering operations, however, as an amateur-built experimental helicopter it would very likely not have been approved to conduct such operations. In addition, while the pilot had significant aeronautical experience, his Class 1 Aviation Medical Certificate had expired and although in the process of renewing it, the pilot was unable to exercise the privileges of his Commercial Pilot’s Licence.
Safety issues and actions
The safety issues identified during this investigation are listed in the Findings and Safety issues and actions sections of this report. The Australian Transport Safety Bureau (ATSB) expects that all safety issues identified by the investigation should be addressed by the relevant organisation(s). In addressing those issues, the ATSB prefers to encourage relevant organisation(s) to proactively initiate safety action, rather than to issue formal safety recommendations or safety advisory notices.
Depending on the level of risk of the safety issue, the extent of corrective action taken by the relevant organisation, or the desirability of directing a broad safety message to the [aviation, marine, rail - as applicable] industry, the ATSB may issue safety recommendations or safety advisory notices as part of the final report.
All of the directly involved parties were provided with a draft report and invited to provide submissions. As part of that process, each organisation was asked to communicate what safety actions, if any, they had carried out or were planning to carry out in relation to each safety issue relevant to their organisation.
The initial public version of these safety issues and actions are repeated separately on the ATSB website to facilitate monitoring by interested parties. Where relevant the safety issues and actions will be updated on the ATSB website as information comes to hand.
Safety issue description: The Cicaré 7T/B/BT mandatory service bulletin (BSC007) for the general stabiliser support assembly provided limited guidance for disassembly of the manufactured component and did not stipulate a compliance period within which to perform the inspection nor provide consideration for repeat inspections. This potentially reduced the opportunity to detect the presence of crack initiation and growth in the stabiliser support assembly.
Additional safety actions
Whether or not the ATSB identifies safety issues in the course of an investigation, relevant organisations may proactively initiate safety action in order to reduce their safety risk. The ATSB has been advised of the following proactive safety action in response to this occurrence.
Additional safety action taken by Cicaré S.A.
Cicaré have advised that they are intending to release a revision to the Pilot’s Operating Handbook at the end of January 2020, which will indicate that the helicopters are not intended or recommended for aerial work, particularly mustering operations, which can cause a significant increase of loads and affect the fatigue life.
Operating a helicopter within the stated design intent and limitations is essential for safe conduct of flight. The ATSB advises owners/operators of amateur-built experimental aircraft to be fully aware of the risks associated with this category of aircraft and that operation outside the limitations prescribed by the manufacturer, such as the addition of unapproved modifications and use for mustering operations, can produce unintended stresses on the airframe leading to premature failure of components.
ATSB information letter
On 6 August 2015, an information letter was emailed to registered Cicaré CH-7B owners, informing them of the second accident, the mechanism of stabiliser failure and a recommendation to ensure the integrity of the stabiliser prior to further operation and on an ongoing basis. The content of the letter is included as an Appendix and is also available on the ATSB website.
Sources and submissions
Sources of information
The sources of information during the investigation included the:
The Civil Aviation Safety Authority
Western Australia Police and Coroner
Cicaré S.A.
The Australian importer of Cicaré S.A. kits
Bureau of Meteorology
Sport Aircraft Association of Australia
Bureau of Infrastructure, Transport and Regional Economics.
References
Australian Transport Safety Bureau (2004), Robinson R22 helicopter and aerial mustering usage investigation (B2004/0292). Retrieved from www.atsb.gov.au/media/29947/b20040292.pdf.
Australian Transport Safety Bureau (2016), In-flight break-up involving Cicaré CH-7B, VH-SWQ 43 km north-west of Barcaldine Airport Queensland on 12 May 2014 (AO-2014-086). Retrieved from www.atsb.gov.au/media/5756707/AO-2014-086%20-%20Final.pdf.
Under Part 4, Division 2 (Investigation Reports), Section 26 of the Transport Safety Investigation Act 2003 (the Act), the Australian Transport Safety Bureau (ATSB) may provide a draft report, on a confidential basis, to any person whom the ATSB considers appropriate. Section 26 (1) (a) of the Act allows a person receiving a draft report to make submissions to the ATSB about the draft report.
A draft of this report was provided to Cicaré S.A., the Civil Aviation Safety Authority, the Sport Aircraft Association of Australia, the distributor of Cicaré helicopters in Australia, and the pilot’s next of kin.
Submissions were received from Cicaré S.A., the Civil Aviation Safety Authority, and the pilot’s next of kin. The submissions were reviewed and, where considered appropriate, the text of the report was amended accordingly.
Appendices
Appendix A – ATSB information letter
Purpose of safety investigations
The objective of a safety investigation is to enhance transport safety. This is done through:
identifying safety issues and facilitating safety action to address those issues
providing information about occurrences and their associated safety factors to facilitate learning within the transport industry.
It is not a function of the ATSB to apportion blame or provide a means for determining liability. At the same time, an investigation report must include factual material of sufficient weight to support the analysis and findings. At all times the ATSB endeavours to balance the use of material that could imply adverse comment with the need to properly explain what happened, and why, in a fair and unbiased manner. The ATSB does not investigate for the purpose of taking administrative, regulatory or criminal action.
Terminology
An explanation of terminology used in ATSB investigation reports is available here. This includes terms such as occurrence, contributing factor, other factor that increased risk, and safety issue.
Publishing information
Released in accordance with section 25 of the Transport Safety Investigation Act 2003
Ownership of intellectual property rights in this publication
Unless otherwise noted, copyright (and any other intellectual property rights, if any) in this report publication is owned by the Commonwealth of Australia.
Creative Commons licence
With the exception of the Coat of Arms, ATSB logo, and photos and graphics in which a third party holds copyright, this publication is licensed under a Creative Commons Attribution 3.0 Australia licence.
Creative Commons Attribution 3.0 Australia Licence is a standard form licence agreement that allows you to copy, distribute, transmit and adapt this publication provided that you attribute the work.
The ATSB’s preference is that you attribute this publication (and any material sourced from it) using the following wording: Source: Australian Transport Safety Bureau
Copyright in material obtained from other agencies, private individuals or organisations, belongs to those agencies, individuals or organisations. Where you wish to use their material, you will need to contact them directly.
