On 15 December 2016, an Airbus A330-202 aircraft, registered VH-EBA and operating Qantas Flight (QF) 652, was on descent to Brisbane Airport, Queensland, arriving from the south-west from Perth, Western Australia. QF652 was sequenced to follow another Qantas Airbus A330-303 aircraft, registered VH-QPG and operating QF62, which was also on descent to Brisbane Airport, but arriving from the north-west from Narita, Japan.
For noise abatement, reciprocal runway operations were in progress at Brisbane, with arriving aircraft landing on runway 19, and departing aircraft taking off from runway 01.
At 0516:25 Eastern Standard Time (EST), the approach controller cleared QF62 to descend to 5,000 ft.
At 0517:55, a Qantas Boeing 737-838 aircraft, registered VH-VXF and operating QF601, (departing Brisbane for Melbourne, Victoria) took off from runway 01 and was tracking to the south-west. At 0519:15, the approach controller cleared QF601 to climb to 8,000 ft.
Five seconds later, the approach controller cleared QF652 to descend to 9,000 ft for separation with QF601 travelling in the opposite direction. The controller advised the crew of QF652 that they would be cleared for further descent once they had passed opposite direction traffic. The controller then also advised the flight crew of QF601 that there would be a short delay at 8,000 ft due to opposite direction traffic above.
At 0520:20, the controller inadvertently cleared QF652 (instead of QF62) to descend to 2,500 ft and conduct an ILS approach to runway 19. The crew of QF652, still on descent to 9,000 ft, read back the clearance and set their assigned altitude to 2,500 ft (which was normal procedure having been cleared for the descent). The crew sighted the opposite direction aircraft out to their right and continued their descent.
About 30 seconds later, the air traffic system identified a discrepancy between the controller-cleared flight level of 9,000 ft and the flight crew-entered altitude of 2,500 ft. The controller received a predicted level mismatch (PLM) alert, which displays as ‘cleared flight level (CFL?)’.[1] The controller asked the crew of QF652 to confirm they were maintaining 9,000 ft, and the crew responded that they were on descent to 2,500 ft as cleared. The aircraft was passing 9,200 ft at this stage. The controller immediately responded ‘no, that was for Qantas 62, Qantas 652 maintain 9,000’. By that time, radar data indicated that QF62 was at 4,900 ft. No read back was heard from the crew of QF62 to the clearance inadvertently issued to QF652.
The flight crew of QF652 reported that they were passing about 8,600 ft, when the controller instructed them to maintain 9,000. The crew stopped the descent and climbed the aircraft back up to 9,000 ft. The crew received a traffic alert[2] for about 5 seconds on the reciprocal aircraft. At 0521:19, the controller cleared the flight crew of QF652 to descend to 8,000 ft and the aircraft subsequently conducted a normal approach to Brisbane.
Figure 1: Traffic disposition and PLM alert
Source: Airservices Australia – annotated by ATSB
Safety analysis
Separation
As the two aircraft passed each other, radar data showed QF652 at an altitude of 9,000 ft and QF601 at 8,000 ft, with 2.3 NM lateral separation (Figure 1). Figure 2 shows QF652 at 8,700 ft and lateral separation with QF601 of 2.6 NM (Figure 2). The incorrect descent clearance resulted in a loss of separation with QF601, where the separation required was 3 NM or 1,000 ft and the minimum separation recorded was 2.5 NM and 700 ft.
Figure 2: Loss of separation
Source: Airservices Australia – annotated by ATSB
Controller comments
The approach controller had been in the position since 0200 and reported feeling alert, well rested and that things were going very well in the minutes prior to the incident in adhering to noise abatement requirements and keeping the traffic moving. The controller commented that between 0500 and 0600 they get busy; departures tend to conflict with arrivals and traffic can be quite complex at times. The controller assessed that their workload at the time was moderate.
The controller commented that when they identify similar call signs, there are techniques they employ such as appending ‘heavy’, or the aircraft’s position in the sequence, to the call sign, but did not do that in this instance. Both inbound aircraft were ‘heavy’ so it would not have helped to resolve the possible confusion.
After giving the clearance (inadvertently) to QF652 that was meant for QF62, both aircraft appeared to descend.[3] When the flight crew read back ‘Qantas six fifty two’, the controller did not identify the mismatch of the data in the aircraft label with the response, possibly because it was the expected response to the clearance instruction.
Flight number call signs
According to the Australian Aeronautical Information Publication (AIP) General 3.4 paragraph 4.17, rules for aircraft call signs include that flight numbers should ‘take into account flight numbers already in use by the operator and other agencies in the intended control environment, operational area or nearby’.
Call sign confusion
The Manual of Air Traffic Services (MATS) 6.2.1.1 Callsign confusion stated:
When similar callsigns may cause confusion you may take action to minimise errors including:
a) emphasising certain numbers/letters;
b) repeating the entire callsign e.g. QANTAS451 QANTAS451;
c) repeating the prefix e.g. QANTAS451 QANTAS;
d) advising pilots that there are aircraft with similar callsigns on frequency; or
e) instructing pilots to use a different callsign either temporarily or for the duration of the flight.
Airservices Australia initiative
After a number of REPCON (confidential reports) related to flight number call sign confusion in the Brisbane area, Airservices Australia (Airservices) established a process to monitor and increase awareness of reported call sign confusion issues. The process involves reviewing the call sign confusion occurrences reported through their internal reporting system and notifying relevant airlines of the reported occurrence. In addition, Airservices provides a ‘call-sign conflict report’ to domestic aircraft operators each month.
Airservices advised that the distribution of the monthly call sign confusion reports to domestic operators was paused in 2016. This was to allow for an upgrade to an improved information system as the basis of the report. However, given a new system has yet to be commissioned Airservices has reinstated use of the previous system, and will continue to distribute monthly call sign confusion reports while working on improvements to the advice provided to industry.
Airservices also commented that a number of current mitigation measures currently exist for pilots and controllers to respond to call sign confusion, including documented AIP and MATS procedures to minimise the likelihood of call sign confusion. Additionally, Australia utilises 'group format' as the preferred means of transmitting call sign/flight number within Australian airspace in an effort to reduce the possible confusion with assigned flight levels or headings.
Findings
These findings should not be read as apportioning blame or liability to any particular organisation or individual.
The controller inadvertently assigned descent to QF652 instead of QF62 due to call sign confusion, resulting in a loss of separation with QF601.
The two inbound aircraft were operating on the same frequency with similar call signs and call sign confusion mitigation strategies were not used by air traffic control.
ATSB comment
According to the article Callsign Confusion, the US Aviation Safety Reporting System (ASRS) receives a large number of reports of call sign confusion, some of which result in losses of separation. The article states that communications technique is pilots’ and air traffic controllers’ primary defence against confusion and that they need to continue to bring call sign problems to the attention of management.
The Skybrary article Call-sign confusion lists contributory factors including:
failure of operator to give sufficient consideration in allocation of call signs
pilot and controller workload
interruption or distraction
airspace and procedure design
traffic density.
Safety message
Air traffic control and flight crew need to be vigilant when they identify the potential for call sign confusion.
Flight numbers are assigned by airlines, some of which operate call sign de-confliction programmes. The ATSB encourages aircraft operators to use these strategies to help prevent similar incidents occurring. Air traffic control is encouraged to consider liaising with airlines to enhance call sign de-confliction programmes.
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.
At about 0730 Eastern Daylight-saving Time (EDT) on the 14 December 2016, a Pelican Airlines British Aerospace Jetstream 32 aircraft, registered VH-OTQ (OTQ), departed Newcastle (Williamtown) Airport for Dubbo, New South Wales (NSW). Two flight crew and six passengers were on board the regular public transport flight.
Just after the aircraft reached the cruising altitude of FL 160,[1] the captain who was the pilot monitoring,[2] noticed the right engine exhaust gas temperature (EGT) gauge was indicating just outside the top of the green arc (650 °C) and was indicating about 655 °C in the yellow arc. The captain reduced the power to the right engine, but there was no corresponding reduction in the EGT.
The flight crew conducted the quick reference handbook (QRH) emergency checklist for the lack of response to power lever movement, which included the engine ignition selected to continuous operation and the engine and airframe ice protection turned on. In accordance with the checklist, the power lever was checked after about 5 minutes and was found to still be unresponsive. The captain indicated that this was very unusual and turned off the engine computers to try to isolate the fault, but this made little difference and so they turned the computers back on. The captain then moved the power lever further back and noticed a momentary increase in EGT, by about 8 °C to 10 °C, as well as an increase in torque.
At this stage of the flight, the aircraft was at a position where they would ordinarily change frequency to a different air traffic controller. However, the flight crew decided to remain on this frequency and return to Newcastle Airport. When the controller instructed the crew to change frequency, the crew advised the controller of their situation and requested a new clearance to return to Newcastle. The crew also advised the controller that as a precaution they might conduct an in-flight engine shut down. The controller gave them a clearance to descend and track direct to Newcastle and subsequently confirmed with the crew that the airport emergency services were required to be available. The controller initiated an alert phase[3] and the airport emergency services were requested to be on standby.
The flight crew followed the guidance in the QRH checklist to continue to operate the engine and noted that an engine shut down may be necessary for the approach and landing. As the aircraft was lightly loaded, the captain believed that there would be no issues operating on one engine. The crew conducted the QRH engine in-flight shutdown checklist and shutdown the right engine prior to commencing their descent to Newcastle. The captain briefed the passengers through the aircraft’s public address (PA) system about the precautionary engine shut down and instructed them to familiarise themselves with the passenger safety card.
At about 50 km from Newcastle and on descent passing through about 8,000 ft, the captain became the pilot flying and the first officer the pilot monitoring. They reviewed the QRH abnormal checklist for landing with one engine inoperative. The crew conducted a visual approach and landed on runway 30 without further incident. The two crew and six passengers were not injured, and the aircraft was not damaged.
Captain’s comment
The captain reported that they were flying at a level where icing conditions may be encountered and from previous experience, flying in a different country, it was not uncommon to have an unresponsive power lever control in icing conditions.
The captain reported that they had adequate time to assess the unresponsive power lever, evaluate the performance of the aircraft with only one engine operating and plan for the landing. The workload was not high as they were flying in visual meteorological conditions with adequate time and no other traffic.
On reflection, the captain indicated that although the situation did not appear like an emergency, making a PAN PAN[4] call to the controller would have eliminated any uncertainty.
The captain indicated that they had only conducted engine shut downs in a training environment and this was the first time landing with one engine inoperative.
Operator comment
The operator reported that the aircraft had been in storage in Australia from 2007 to March 2016. Since March, the aircraft had undergone major maintenance at an aircraft maintenance facility. The right engine involved in the incident had undergone maintenance at an engine overhaul facility and had been preserved during its time of inactivity, prior to its installation on OTQ. The aircraft was released to service 11 days (about 26 flight hours) prior to the incident occurring.
Aircraft maintenance personnel inspected the right engine after the flight and found that the engine’s fuel control unit[5] was at fault. An examination of the fuel control unit at a component overhaul facility found that the input drive shaft was not free to move. The fuel control unit was inspected and a bearing was found to have failed (Figure 1). The phenolic bearing cage[6] that separates the bearings was found broken (Figure 2) with many small fragments found to be interfering with the operation of the fuel control unit in that area.
Figure 1: Failed bearing assembly
Source: Aircraft operator
Figure 2: Pieces of the failed phenolic bearing cage
Source: Aircraft operator
Findings
These findings should not be read as apportioning blame or liability to any particular organisation or individual.
The engine issue related to a failed fuel control unit bearing, where fragments of the bearing cage interfered with the unit’s operation.
Safety message
It is important when time permits to broadcast a ‘pan’ or ‘mayday’, whichever is applicable, to air traffic control to alert the controller and remove any uncertainty about the severity of the situation. If controllers receive a ‘pan’ or ‘mayday’ broadcast, they will organise (depending on the situation) a priority landing to allow an aircraft that might have a problem to land as soon as possible. A situation that seems relatively innocuous can deteriorate quickly. Hesitating or not broadcasting the situation can result in help being delayed.
Airservices Australia defines the two levels of emergency notifications as:
MAYDAY: My aircraft and its occupants are threatened by grave and imminent danger and/or I require immediate assistance.
PAN PAN: I have an urgent message to transmit concerning the safety of my aircraft or other vehicle or of some person on board or within sight but I do not require immediate assistance.
Additional information is provided in the following publications:
Airservices Australia In-flight emergencies, is available from the Airservices website.
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 13 December 2016, a Beech Aircraft Corporation B200, registered VH-MVL, conducted a visual approach to Moomba Airport, South Australia (SA), following a medical services flight from Innamincka, SA. As the aircraft turned onto the base leg of the approach, the pilot observed the left engine fire warning activate. The pilot shut down the left engine and continued the approach to the runway. The aircraft landed in the sand to the left of the runway threshold and after a short ground roll, spun to the left and came to rest. There were no injuries, and the aircraft was substantially damaged.
What the ATSB found
The ATSB found that the pilot did not feather the left propeller (rotate the blades to an edge-on angle to the airflow) after the left engine was shut down, causing it to windmill, resulting in considerable drag. In addition, the aircraft was in a right turn, towards the engine developing power, with the landing gear extended and the flaps set to approach. This combination resulted in more thrust being required for continued safe flight than was available.
No engine fire damage was found and it was therefore concluded that the observed fire warning was almost certainly a false warning. The aircraft manufacturer had previously published a service bulletin for the optional replacement of the engine fire detection system with a system less susceptible to false warnings. However, the operator, who had limited experienced with false engine warnings in their fleet which were also considered as low risk, elected not to replace the fire detection system on the accident aircraft.
The accident pilot did not receive the operator’s published syllabus of training for the B200 King Air. Instead, a tailored training program was delivered in consideration of the pilot’s experience on the C90 King Air with another operator and advice the operator received from the Civil Aviation Safety Authority. This training did not cover all the elements required under the Civil Aviation Safety Regulations.
What's been done as a result
As a result of this occurrence, the Civil Aviation Safety Authority (CASA) intends to take steps to refresh industry and CASA officers’ knowledge of particular terms and concepts within the flight crew licencing regulations to remove any doubt that might exist as to their interpretation and applicability.
The operator has undertaken to take safety actions in the areas of pilot recruitment, training and checking, aircraft and systems, safety and quality assurance, and communications.
Safety message
Following the accident, the pilot reported that their biggest lesson was not to hesitate during emergency procedures. They believed that their doubt in the veracity of the warning resulted in their hesitation while completing the four engine fire drill (memory) actions, resulting in them missing the step to feather the propeller.
This accident also highlights the need for organisations to consider all the relevant information available to them when making decisions, such as the process for reviewing non‑mandatory service bulletins. Organisational decision-making should consider the potential consequences of human error when evaluating changes.
The occurrence
On 13 December 2016, a Beech Aircraft Corporation B200, registered VH-MVL, conducted a medical services flight from Innamincka, South Australia (SA) to Moomba, SA. On board the aircraft were the pilot and two passengers.
On arrival at Moomba at about 1250 Central Daylight-saving Time (CDT), the pilot configured the aircraft to join the circuit with flaps set to the approach setting and the propeller speed set at 1900 RPM.[1] They[2] positioned the aircraft at 150–160 kt airspeed to join the downwind leg of the circuit for runway 30, which is a right circuit.[3] The pilot lowered the landing gear on the downwind circuit leg. They reduced power (set 600-700 foot-pounds torque on both engines) to start the final descent on late downwind abeam the runway 30 threshold, in accordance with their standard operating procedures.
At about the turn point for the base leg of the circuit, the pilot observed the left engine fire warning activate. The pilot held the aircraft in the right base turn, but paused before conducting the engine fire checklist immediate actions in consideration of the fact that they were only a few minutes from landing and there were no secondary indications of an engine fire. After a momentary pause, the pilot decided to conduct the immediate actions. They retarded the left engine condition lever[4] to the fuel shut-off position, paused again to consider if there was any other evidence of fire, then closed the firewall shutoff valve, activated the fire extinguisher and doubled the right engine power[5] (about 1,400 foot-pounds torque).
The pilot continued to fly the aircraft in a continuous turn for the base leg towards the final approach path, but noticed it was getting increasingly difficult to maintain the right turn. They checked the engine instruments and confirmed the left engine was shut down. They adjusted the aileron and rudder trim to assist controlling the aircraft in the right turn. The aircraft became more difficult to control as the right turn and descent continued and the pilot focused on maintaining bank angle, airspeed (fluctuating 100–115 kt) and rate of descent.
Due to the pilot’s position in the left seat, they were initially unable to sight the runway when they started the right turn. The aircraft had flown through the extended runway centreline when the pilot sighted the runway to the right of the aircraft. The aircraft was low on the approach and the pilot realised that a sand dune between the aircraft and the runway was a potential obstacle. They increased the right engine power to climb power (2,230 foot-pounds torque) raised the landing gear and retracted the flap to reduce the rate of descent. The aircraft cleared the sand dune and the pilot lowered the landing gear and continued the approach to the runway from a position to the left of the runway centreline.
The aircraft landed in the sand to the left of the runway threshold and after a short ground roll spun to the left and came to rest (Figure 1). There were no injuries, and the aircraft was substantially damaged.
Table 1 is a list of key events from the accident flight cockpit voice recorder. Events marked with inverted commas (‘’) are automated voice from aircraft systems, such as the ground proximity warning system. Time is from the start of the recording in minutes and seconds.
Table 1: Key events
Time from start
Event
26:10
Pilot reported joining downwind runway 30 Moomba
26:41-26:47
Sound of mechanical movement (consistent with pilot report of lowering landing gear)
27:32
Warning horn activation (consistent with master warning horn frequency, repetition rate and duty cycle) (consistent with pilot report of observing a left engine fire warning)
27:47-end
Propeller speeds separate – one maintains about 1,900 RPM and the other reduces to and then fluctuates around 1,650 RPM (consistent with pilot report of shutting down left engine)
28:17
Warning horn activation (consistent with master warning horn frequency, repetition rate and duty cycle) (consistent with the pilot report of observing activation of the left engine oil pressure and fuel pressure light after the left engine was shutdown)
28:20-28:26
Sound of mechanical movement (consistent with pilot report of raising the landing gear)
Intermittent warning horn activation (likely stall warning, but different frequency to the frequency supplied by the manufacturer (windmilling propeller is slowing down and flaps are retracted))
30:21-30:27
Sound of mechanical movement (consistent with pilot report of lowering the landing gear)
30:25
Sound of momentary impact
30:29-end
Subsequent sounds of impact
Post-accident aircraft information
Following the accident, an inspection of the left engine revealed the fire extinguisher bottle was discharged, but there were no physical indications of a fire. Damage to the left propeller was consistent with rotation of the propeller at impact and the propeller appeared to be in an unfeathered position (Figure 1). Both propeller control levers were at the 1900 RPM setting (Figure 2). The pilot reported that after the aircraft came to rest, they shut off fuel and activated the firewall shutoff valve for the right engine, but were unsure of any other changes they made to switches and controls in the cockpit.
Figure 2: VH-MVL pedestal
Source: Operator, annotated by ATSB
Engine shutdown information
Engine fire emergency procedure
A left engine fire warning is annunciated by the aircraft master warning system, which activates the master warning horn, master warning light and L ENG FIRE light on the master warning panel. The operator’s emergency checklist procedure applicable for an inflight engine fire was the ‘emergency engine shutdown’. The procedure included boxed bold type immediate actions, which were performed from memory. The company procedure was to complete the immediate actions from memory and then reference the checklist to confirm immediate actions were completed before completing the remainder of the actions. The immediate actions for the emergency engine shutdown were:
Condition Lever……FUEL CUT OFF
Prop Lever...…FEATHER
Firewall Shutoff Valve……CLOSED
Fire Extinguisher……ACTUATE (If required)
The pilot reported that their attention was drawn to the warning light in the top left corner of the master warning light panel (location of the left engine fire warning light).[6] They pulled the condition lever, then paused, then closed the firewall shutoff valve and pressed the extinguisher and confirmed it had discharged, all from memory, but there was no time to reference the checklist during the approach.
Propeller autofeathering system
The aircraft was fitted with an automatic feathering system of the propeller, which required the activation of two electrical interlocks for operation. The first interlock is achieved by setting the autofeather switch in the cockpit to ARM. The second interlock is achieved by advancing the power levers to a position which equates to about a 90 per cent N1[7] power setting. When both power levers are advanced to this position, a mechanical activator, connected to each power lever, will close its respective switch and complete the circuit to the high- and low-pressure switches mounted on each engine. This will activate the green AUOTFEATHER advisory lights for the left and right engine in the cockpit.
The autofeather switch is required to be set to ARM in the approach checks. However, the engine fire warning activated after the pilot had set their descent power of about 600–700 foot‑pounds torque[8] (about 75–80 per cent N1) and the left engine was shut down from this power setting. This was below the setting which would activate autofeather when the system is armed.
One engine inoperative performance
The B200 aeroplane flight manual (AFM) recommended procedure to obtain best performance[9] with one engine inoperative is to bank the aircraft 3° to 5° into the operating engine while maintaining a constant heading. The AFM one engine inoperative best rate of climb speed was 121 kt.
Acceleration and climb performance is a function of the excess thrust and power. Therefore, any increase in drag will reduce the aircraft performance. A windmilling propeller can produce a significant amount of drag, which is estimated to be comparable to a parachute canopy of the same area as the propeller disc area (Figure 3).[10]
Figure 3: Windmilling propeller drag
Source: Aerodynamics for naval aviators, annotated by ATSB
The pilot reported that, from their simulator experience, the aircraft performed well with one engine shut down. If an engine was shut down for an approach, then doubling the power on the other engine was sufficient to maintain the correct profile. In the accident flight they initially set about 1,400 foot-pounds torque on the right engine, but then increased the power to the climb power setting of about 2,230 foot-pounds torque. Based on the ground proximity warning height annunciations, the rate of descent from 1,000 ft to 700 ft was about 1,000 ft/min, which then reduced to about 440 ft/min from 500 ft to 200 ft.
In this configuration,[11] there would be a yawing moment to the left produced by asymmetric thrust, (which would be exacerbated by a windmilling left propeller), and a rolling moment to the left from the right propeller slipstream over the right wing. This results in asymmetric lift. The left engine is the critical engine for asymmetric flight.[12] Consequently, full right rudder trim and full right aileron trim were applied by the pilot during the (right) base leg turn.
A right turn flown against these forces will produce more drag than a left turn, which will produce more drag than maintaining a constant heading (Figure 4). The extension of landing gear and flap will also increase drag. The combination of factors which increase drag can lead to a critical condition where the thrust required to maintain the planned flight path exceeds the thrust available.
Figure 4: Thrust required for asymmetric turning flight
Source: Aerodynamics for naval aviators, annotated by ATSB
The Raisbeck Engineering[13] flight manual supplement for the B200 indicated that the minimum control speed - air (VMCA) is 88 kt (indicated airspeed) with the flaps in the approach setting and 91 kt with the flaps retracted.[14] However, there is a flight manual supplement caution that ‘with one-engine either at idle or inoperative, flaps up and propeller windmilling, VMCA may be as high as 108 kt.’ This was inside the approach airspeed range reported by the pilot (100-115 kt).
Training and checking
Pilot’s training
The pilot joined the operator in early 2015. The operator noted that the pilot had a licence for multi-engine aeroplane with endorsements for gas turbine engine and pressurisation, and had flown the Beechcraft C90.[15]
In February 2015, the operator provided the pilot with 26.1 hours of line training on the B200 aircraft, which started on 10 February. They were also provided with two simulator training sessions of 3.7 hours, which included instrument approaches and asymmetric flight exercises. On completion of the second simulator session, the trainer reported that the pilot had ‘very good asymmetric control of aircraft’ and could progress to the instrument proficiency check (IPC). They progressed to a third simulator session of 1.9 hours, which was their IPC on 22 February. During the IPC, the pilot was exposed to an engine fire in the cruise and engine failure after take-off. The testing officer reported that the IPC was ‘completed to a very good standard.’ The pilot’s line check was conducted on a medical flight on 27 February. They were assessed as ‘all ok’ and cleared to line for clinic operations only.
The pilot completed three further flight checks within the operator’s cyclic training and proficiency program (CTPP) between their conversion and the accident flight. In 2015, the pilot conducted two checks in the simulator. In 2016, the pilot conducted their March check in the aircraft and their August check in the simulator.
The simulator field of view for the pilot is less than what is available in the aircraft. Due to the restricted field of view to the sides, the operator assessed it as inappropriate to initiate emergencies in the simulator from a circuit base leg position. Therefore, critical situation emergencies, such as an engine fire indication on approach, were generally initiated on the final approach of an instrument approach. This provided a critical decision-making scenario for the pilot, in which they could initiate the immediate actions while in the final stages of an approach, or alternatively land the aircraft before initiating the immediate actions.
The pilot was exposed to engine fire indications in the cruise and on instrument approach during the CTPP. No knowledge deficiencies were noted with their immediate actions and the four CTPP checks were assessed as completed to the required standard.
Development of the pilot’s training program
The pilot started training with the operator about five months after the introduction of the then new flight crew licencing regulation, Civil Aviation Safety Regulation (CASR) Part 61. Under the previous regulation for flight crew licencing (Civil Aviation Regulation (CAR) 5), the C90 and B200 aircraft were separate class endorsements (BE-90 and BE‑200, respectively). However, with the introduction of CASR Part 61, both aircraft types were included in the ‘multi-engine aeroplane (MEA) class rating’ and did not require type specific ratings.[16]
In January 2015, the Civil Aviation Safety Authority (CASA) published edition 1 of legislative instrument ‘Prescribed aircraft, ratings and variants for CASR Part 61 Instrument 2014’. Paragraph 25 and Schedule 13 of the instrument identified the Beechcraft King Air 90 series and King Air 200/250 series as aircraft types, for which each required initial type-specific training. The training required was in accordance with all the units of competency published in the Part 61 Manual of Standards[17] for the class rating that are relevant for the aircraft type. Although both aircraft may be referred to as King Air series aircraft, they have different Type Acceptance Certificates and therefore are different aircraft types.
The explanatory statement associated with the legislative instrument indicated that the aircraft listed in Schedule 13 were ‘identified as being sufficiently complex or have performance or handling characteristics[18] that warrant initial type-specific training and a flight review in the specific type’. However, the operator was not aware of this instrument or associated explanatory statement at the time of the pilot’s employment. The pilot started training about one month after the publication of the legislative instrument and the operator developed their training program before the pilot started their training.
The operator tailored the pilot’s training program in consideration of the fact that the pilot was trained on the C90 King Air with a previous operator. Consequently, the pilot did not receive the operator’s B200 syllabus of training, as published in their training and checking manual, which included five simulator training sessions (excluding IPC). The operator’s training and checking manual permitted this for a pilot with previous King Air series experience.[19] This was the operator’s understanding of CASR Part 61 after consultation with their respective CASA Flying Operations Inspector.
During the course of the investigation, the ATSB received several responses from different positions within CASA that ‘differences training’[20] was an acceptable approach to transition a pilot from the C90 to the B200. This included the CASA Flying Operations Inspector assigned to the operator and the CASA Flight Standards Branch. On review of the pilot’s training records, the ATSB could not find evidence that the pilot received training in stalling or upper air asymmetric handling in accordance with the operator’s B200 syllabus.
Civil Aviation Safety Regulation 61.747
The relevant regulation to transition a pilot onto a new aircraft within the multi-engine aeroplane class rating system was CASR 61.747 ‘Limitations on exercise of privileges of class ratings in certain aircraft-flight review’. Regulation 61.747 was a competency-based training regime, which required pilots to be trained in all the units of competency in the Part 61 Manual of Standards relevant for the aircraft type, followed by a flight review. Competency based training allows an operator to consider the pilot’s previous qualifications and experience in developing their training and assessment program to demonstrate all the relevant units of competency.
Civil Aviation Advisory Publication 5.23-2(0)
In July 2007, CASA published Civil Aviation Advisory Publication (CAAP) 5.23-2(0) ‘Multi-engine aeroplane operations and training’. CAAP 5.23-2(0) was the second CAAP written on this subject and has been superseded by CAAP 5.23-1(2), published September 2015. The CAAP was written following ‘a number of multi-engine aeroplane accidents caused by aircraft systems mis‑management and loss of control by pilots.’ The CAAP indicated that during training, ‘pilots should be shown all the flight characteristics[21] of the aircraft, and be given adequate time and practice to consolidate their skills.’
The VMCA (minimum control speed – air) demonstration sequence was identified in the CAAP as one of the ‘more important in asymmetric training.’ The instructor should ‘point out the yaw, wing drop and change to attitude.’[22] When a trainee pilot conducts the VMCA exercise, the instructor should ask them to ‘identify when the aircraft starts to yaw and roll’ to determine if they are ‘recognising these conditions early enough.’ The CAAP also discussed the technique to recover from a critical asymmetric situation, with low airspeed near the ground and a windmilling propeller. The risks associated with VMCA training are explained in the CAAP. The operator had managed the risks associated with VMCA training by moving their syllabus of training for the B200 from the aircraft to the simulator.
The CAAP highlighted that it was important for the pilot to recognise and avoid a stall in any aircraft and that instructors must conduct this exercise in multi-engine aeroplanes. Instructors should ‘stress the characteristics and devices that warn the pilot of the stall’ and allow the trainee pilot to ‘experiment with these characteristics and practice them in different configurations and flight situations.’
The references to CAAP 5.23-2(0), published July 2007, were consistent with the guidance in CAAP 5.23-1(2), which was the current CAAP on the subject at the time of the accident.
Flight review
The pilot successfully completed an instrument proficiency check during their initial B200 training, which the operator believed fulfilled the requirements for a flight review. However, CASR 61.747 required the pilot to demonstrate competency in all the units of competency prescribed for the multi-engine aeroplane class rating. A flight review means an assessment of the competency of a flight crew member to perform an activity authorised by the rating. Following advice from CASA Flight Crew Licencing, an instrument proficiency check could fulfil the flight review requirements of CASR 61.747 provided the check included all the units of competency for the multi-engine aeroplane class rating. If units of competency are missed, then the flight review does not comply with the intent of the CASR 61.747 flight review.
Fire detection system
Beech service bulletin 2596
In 1995, Beech Aircraft Corporation[23] issued a service bulletin, SB 2596, which announced the availability of a ‘continuous loop fire and overheat detection system’ as a replacement for the aircraft engine optical fire detection system. This was the most recent design incorporated into production aircraft to improve reliability and maintainability of the engine fire detection system.
The operator reviewed SB 2596 and the decision was made not to incorporate the modification on 15 July 2003 due to cost considerations. An earlier service bulletin, SB 2005, which relocated one of the fire detectors to an area less susceptible to external light and added an additional light shield to the system, was already incorporated in the aircraft from manufacture.
On 10 April 2013, CASA issued an airworthiness bulletin (AWB 26-005) for the Beech B200 Series engine fire detection systems. The purpose of AWB 26-005 was to ‘provide information to operators and maintainers regarding improved engine fire detection systems to avoid false in-flight engine fire indications’.
AWB 26-005 indicated that operators using the optical flame detectors continue to experience false indications of engine fire warnings and that the continuous loop and overheat detection system kits introduced in 1995, through SB 2596, have proven reliable and eliminated false indications. CASA strongly recommended operators install the continuous loop engine fire detection systems to avoid false in-flight fire warnings.
The operator reviewed AWB 26-005 on 12 April 2013, but elected not to incorporate the modification, based on their prior review and decision on SB 2596.
Previous false engine fire warnings
The operator identified four previous reports of false in-flight engine fire warnings recorded in their database for their B200 aircraft fleet, three incidents in 2003 and one in 2005.
A left engine fire warning, which extinguished after about 30 seconds (13 March 2003).
A left engine fire warning, which extinguished after about 30 seconds. A fire detection probe was replaced (22 March 2003).
A left engine fire warning. The pilot conducted the immediate actions. The response recorded in the report was to check the fire detection probes for serviceability (24 April 2003).
A left engine fire warning which activated momentarily on approach. After landing, the warning activated and remained illuminated. The pilot conducted the immediate actions. There was no evidence of fire found and a fire detector was replaced. The warning light activated three times on the return flight. A fault in the wiring harness connector was recorded as the reason (10 July 2005).
The pilot commented that they were aware that the fire detection system was susceptible to false indications due to sunlight entering the engine compartment, but had not previously experienced such an incident. The operator acquired VH-MVL in 1997 and had no prior reported incidents of false fire warnings for that particular aircraft prior to the accident.
The pilot reported there was a left engine fire warning, which resulted in them performing an emergency engine shutdown and activating the fire extinguisher. On inspection by the operator, the left engine fire bottle was found to be discharged, but there was no evidence of fire damage. The activation of the master warning followed by the separation of the propeller speeds, as detected by the cockpit voice recorder, were consistent with the pilot’s report of a fire warning and left engine shutdown. Therefore, the ATSB concludes that the pilot likely experienced a fire warning, which was almost certainly a false indication.
The ATSB did not establish what initiated the fire indication. However, it was noted that the optical fire detection system fitted to the aircraft was susceptible to false indications. In 1995, Beechcraft issued a service bulletin (SB 2596) for a continuous loop fire and overheat detection system to ‘improve reliability and maintainability.’ In July 2003, after three reports of false engine fire indications earlier that same year, the operator reviewed the bulletin but elected not to incorporate the modification. The operator also decided not to incorporate the modification after a Civil Aviation Safety Authority (CASA) airworthiness bulletin in 2013 recommended incorporating the manufacturer’s modification. Neither review made reference to the flight risk of false engine fire indications. However, the operator’s previous false engine fire warning reports recorded them as low risk and their last report was in 2005.
The earliest safety management manual the operator was able to provide the investigation was dated 2006, some three years after the operator’s review of SB 2596. Therefore the operator’s risk assessment process, as it applied to the earlier false engine fire warnings and review of SB 2596 was not investigated any further.
In consideration of CASA’s findings of the effectiveness of SB 2596 to eliminate false fire indications, it is apparent that the incorporation of the manufacturer’s modification would have reduced the risk of a false fire warning occurring.
One engine inoperative performance
The pilot reported that, following their observation of an engine fire indication, they completed three of the four immediate memory actions, but omitted to manually feather the left propeller. They then experienced considerable difficulty handling the aircraft in the right turn and were unable to reach the runway, despite applying climb power to the right engine.
Although the aircraft was fitted with an autofeathering system for the propellers, the system was only operative at high power settings. As the pilot had reduced power for descent by the time of the engine fire indication, the autofeathering system was inoperative, as per design, when the engine was shutdown.
As a result, the approach was flown with the left propeller unfeathered and windmilling. When combined with the drag from the landing gear, flap and right turn, the additional drag from the windmilling propeller resulted in more thrust required for the approach than was available.
Pilot’s actions
The pilot reported that they hesitated in their decision-making and subsequent engine fire drill actions because of their uncertainty in the veracity of the indication and their proximity to landing. At the time of the master warning, they had just started the base turn on approach to land, which required their attention to be divided between the cockpit settings and indications, and the external cues for the visual approach. It is possible that divided attention, combined with their hesitation while performing the steps of the drill, contributed to them omitting the step to feather the propeller in their immediate actions.
After the pilot shutdown the left engine, they experienced increasing difficulty controlling the aircraft in the right turn. They checked to confirm the left engine was shutdown, applied full right aileron and rudder trim, applied climb power to the right engine, retracted the landing gear and flap, and finally extended the landing gear for the landing. However, they did not attempt to feather the propeller at any stage during the approach. This indicates that the pilot did not recognise that their asymmetric handling difficulties were the result of a windmilling propeller, despite the need for climb power on the right engine. The aircraft configuration and performance on approach resulted in the aircraft operating within the airspeed caution range for a loss of directional control.
The pilot’s training and assessment reports indicated that their asymmetric flight experience on the B200 extensively involved engine failures on take-off and engine fires in cruise. In the case of engine failures on take-off, the autofeather system will feather the propeller of the failed engine. In the case of engine fires in cruise, the propeller is manually feathered by the pilot in the emergency engine shutdown procedure. The operator’s performance standards for asymmetric flight included that the pilot was able to identify the correct control lever and feather the propeller, which was consistent with the performance standards required in the Part 61 Manual of Standards. The pilot was assessed as competent to this standard by the operator with no knowledge deficiencies identified. The pilot’s previous successful handlings of an engine fire in the simulator, and their inability to stop the aircraft descending, likely contributed to them continuing the approach.
Based on the above asymmetric training experience, it is likely the pilot had no prior experience of the B200 handling characteristics with a windmilling propeller, which likely contributed to them not recognising (and recovering) from that condition within the timeframe of the accident sequence. However, the pilot’s C90 training experience with another operator was not investigated for potential knowledge transfer to the B200. The ATSB only offers this as a possible explanation for why the pilot did not associate the performance and handling difficulties with a windmilling propeller. Operating the aircraft with a windmilling propeller was not a competency requirement.
Differences training
Within CASR Part 61, differences training applied to the ‘type rating’ system, but not the ‘class rating’ system. The training requirements for a type rated aircraft are considered more complex than for a class rated aircraft. Therefore, differences training is employed in the type rating system to transition a pilot from the variant[24] the pilot conducted their type rating on, onto another variant covered by the same type rating.[25] The legislative instrument ‘Prescribed aircraft, ratings and variants for CASR Part 61 Instrument 2014’ (Edition 1), indicated when differences training was required for type rated aircraft, in addition to when initial type-specific training was required for class rated aircraft. The instrument identified the Beechcraft King Air 90 series and King Air 200/250 series as aircraft types, which required initial type-specific training.
Within the differences training system, it is permissible to not deliver all the units of competency from the Part 61 Manual of Standards.[26] This avoids unnecessary duplication of training while ensuring the pilot receives the training necessary to operate variants, which are different to the variant the pilot conducted their type rating on. In contrast, a class rated aircraft requires all the units of competency relevant to the aircraft type to be delivered. However, for a class rated aircraft there may be no additional training requirement for a pilot to operate different models (variants) of the same type, as prescribed in the respective legislative instrument. Therefore, the requirement for differences training increases the overall training burden within the type rating system, in line with the greater complexity of the aircraft, when compared to the class rating system.
The ATSB acknowledges that an operator may consider previous qualifications and training in determining the number of sequences required to deliver the units of competency within the class rating system. However, reference to differences training may inadvertently imply that not all units of competency are required to be delivered or assessed. In the case of the accident pilot, the ATSB could not find a training or assessment record for the competency ‘A5.1 – Enter and recover from stall’[27] in addition to the upper air asymmetric sequences.[28] This would have been captured if the operator delivered their B200 syllabus of training to the pilot.
Upper air asymmetric training sequences are used to teach a pilot the performance and handling characteristics, specific to the aircraft type, in various configurations and flight path parameters. It provides the opportunity for the instructor to direct the trainee pilot’s attention to changes in aircraft performance associated with changes in attitude and configuration, without the distraction of checklist actions or instrument approach procedure requirements. This can lead to more effective learning of the underpinning knowledge and skills required to operate a new aircraft type. At the time of the accident, the pilot had operated the B200 for 22 months without training or assessment in stalling.
The ATSB determined that the application of differences training, as defined in CASR Part 61, to the transition of a pilot onto the B200 was inconsistent with the requirement for initial type-specific training in accordance with CASR 61.747. The omission of training or assessment in flight regimes near to or in a loss of control situation (for example, VMCA demonstration and stalling), may result in a degradation of knowledge and skills that are only required in rare, but time-critical, emergency situations.
From the evidence available, the following findings are made with respect to the collision with terrain involving Beech Aircraft Corporation B200, registered VH-MVL that occurred at Moomba Airport, South Australia on 13 December 2016. These findings should not be read as apportioning blame or liability to any particular organisation or individual.
Contributing factors
The operator did not modify the aircraft to include a more reliable engine fire detection system in accordance with the manufacturer’s service bulletin, and as subsequently recommended by the Civil Aviation Safety Authority’s airworthiness bulletin. The incorporation of the manufacturer’s modification would have reduced the risk of a false engine fire warning.
During the approach phase of flight, the pilot shutdown the left engine in response to observing a fire warning, but omitted to feather the propeller. The additional drag caused by the windmilling propeller, combined with the aircraft configuration set for landing while in a right turn, required more thrust than available for the approach.
Other factors that increased risk
The advice from the Civil Aviation Safety Authority to the operator, that differences training was acceptable, resulted in the pilot not receiving the operator’s published B200 syllabus of training. The omission of basic handling training on a new aircraft type could result in a pilot not developing the required skilled behaviour to handle the aircraft either near to or in a loss of control situation.
Other findings
The pilot met the standard required by the operator in their cyclic training and proficiency program and no knowledge deficiencies associated with handling engine fire warnings were identified.
Safety issues and actions
Additional 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.
Civil Aviation Safety Authority
As a result of this occurrence, the Civil Aviation Safety Authority (CASA) advised the ATSB that they concur that the regulatory requirements for pilots transitioning between aircraft models of a type listed in Schedule 13, including from the Beechcraft King Air 90 series to the King Air 200/250 series aircraft, might be open to misinterpretation, and they are taking the following safety action:
Education
CASA intends to take steps to refresh industry and CASA officers of particular terms and concepts within the CASR 1998 flight crew licensing suite to remove any doubt that might exist as to their interpretation and applicability. For example, terms such as differences training, flight review, competency, competency-based-training, recognition of prior learning, qualifications and experience will be clarified.
Operator
As a result of this occurrence, the aircraft operator conducted an internal investigation and advised the ATSB that they are taking the following safety actions:
Recruitment
Conduct a review of their current recruitment process, including entry standards and consideration of additional processes to the current standard of interview and simulator test.
Engage with a university to study pilot recruitment in order to better understand the ideal pilot traits required for the company’s operations.
Training and checking
Conduct a review of existing pilot induction/training/clearance to line procedures, and increase use of Level D simulator wherever possible for initial and recurrent emergency procedures.
All new pilots will complete the company’s full induction training, including aircraft endorsement training.
Review and rewrite of the company operations manual, and training and checking manual.
Safety and quality assurance
Accelerate the introduction of the flight data analysis program and undertake a trial of line orientated safety audit.
Aircraft and systems
Install flight data recorders on all aircraft and include flight data recorders as a mandatory item for aircraft standards.
Install Pratt & Whitney flight acquisition, storage and transmission (FAST) on all aircraft and include FAST as a mandatory item for aircraft standards.
Communications
In-person briefing program with the pilot workforce to discuss findings and agreed safety actions from the company’s internal investigation with a focus on lessons learned from the accident.
Sources and submissions
Sources of information
The sources of information during the investigation included the:
Civil Aviation Safety Authority
Textron Aviation (B200 Type Certificate Holder)
operator
pilot.
References
Civil Aviation Safety Regulation Part 61, dated 4 November 2014
Civil Aviation Safety Authority legislative instrument ‘Prescribed aircraft, ratings and variants for CASR Part 61 Instrument 2014’ (Edition 1), dated 5 January 2015
Civil Aviation Safety Authority explanatory statement ‘Prescription of aircraft and ratings – CASR Part 61 (Edition 1), dated 5 January 2015
Civil Aviation Advisory Publication 5.23-2(0): Multi-engine aeroplane operations and training, dated July 2007
Civil Aviation Advisory Publication 5.59A-1(0): Competency based training and assessment in the aviation environment, dated July 2009
Raytheon Aircraft Company, Beechcraft King Air B200 & B200C pilot’s operating handbook and FAA approved airplane flight manual, dated 2004
Raisbeck Engineering Company, pilot’s operating handbook and FAA-approved airplane flight manual supplement for the Beechcraft Super King Air models B200/B200C/B200T/B200CT, dated 2016
Operator’s training and checking manual, version 2.1, dated 19 January 2015
Operator’s quick reference handbook for Raisbeck B200/C, dated 15 June 2004
Beechcraft service bulletin 2596, Fire protection – continuous loop fire and overheat detection system installation, dated October 2015
Civil Aviation Safety Authority airworthiness bulletin 26-005, Beech B200 series engine fire detection systems, issue 1, dated 10 April 2013
Super King Air 200 series maintenance manual, propeller autofeathering system – description and operation, revision D4, 1 November 2016, printed from Beechcraft Corporation Interactive Maintenance Library
H. H. Hurt, Jr., Aerodynamics for naval aviators, NAVAIR 00-80T-80, University of Southern California, USA, 1965.
United States Federal Aviation Administration advisory circular (AC 120-53B CHG 1), guidance for conducting and use of flight standardisation board evaluations, dated 5 November 2013
Submissions
Under Part 4, Division 2 (Investigation Reports), Section 26 of the Transport Safety Investigation Act 2003 (the Act), 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 the Civil Aviation Safety Authority, Textron Aviation, the operator and the pilot.
The submissions from those parties were reviewed and where considered appropriate, the text of the draft 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 27 September 2016, at about 0030 Eastern Standard Time (EST), an Avions de Transport Regional ATR42-300 aircraft, registered VH-TOX (Figure 1), was being loaded at Sydney Airport, New South Wales, for a freight charter flight to Brisbane, Queensland.
The freight had arrived from a freight facility where it had been weighed and a load plan completed, with a total freight weight of 2,281 kg.
Prior to loading the freight, a representative from the aircraft operator was unsure of the accuracy of the provided weights and requested ground staff reweigh the freight using calibrated scales at the airport. The measured total weight was 3,215 kg, which was 934 kg more than stated on the load plan.
The flight crew, consisting of a captain and first officer, completed the trim sheet using the actual weights, and the aircraft was within its weight limitations and the allowable centre of gravity envelope. The aircraft operated to Brisbane without incident.
Figure 1: VH-TOX
Source: Daniel Vorbach edited by ATSB
Freight weighing
The freight was weighed at the freight facility using a forklift fitted with scales. Each item of freight was then allocated to a loading position on the aircraft using a spreadsheet from which the aircraft load plan was derived.
The aircraft operator commented that they had previously advised the freight company that forklifts should not be used for the weighing of freight when intended for carriage by air, as they were not sufficiently accurate. The loading supervisor, who was employed by the freight company and responsible for loading the aircraft in accordance with the load plan, was not aware that the weights recorded on the load plan were inaccurate.
The ground handling agreement between the aircraft operator and freight company did not include Sydney as a port of service at the time of the incident. Until recently, the operator’s Sydney operations were based at Bankstown Airport, where calibrated floor scales were used to weigh the freight.
Findings
These findings should not be read as apportioning blame or liability to any particular organisation or individual.
The freight company weighed the freight using inaccurate (forklift) scales, resulting in a discrepancy of 934 kg from the actual freight weight. The aircraft load plan was derived from the inaccurate freight weights.
The aircraft operator discovered the inaccuracy before loading and the aircraft was subsequently loaded within its weight and balance limitations.
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 they are taking the following safety actions:
Change of port
The operator ceased operations into and out of Sydney Airport and reverted to Bankstown Airport, where calibrated floor scales are used to determine the freight weight for the load plan.
Safety message
Accurate aircraft weight and balance information is vital for the safety of flight, particularly during take-off. Inaccurate weight of freight items can lead to incorrect flight management selections such as power and trim settings. Discrepancies in these can result in reduced take-off performance and incidents such as tail strikes and runway overruns.
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 9 December 2016, a QantasLink Bombardier DHC-8-402, registered VH-LQG (LQG), departed runway 16 left at Sydney Airport. The aircraft was operating a scheduled passenger flight from Sydney to Tamworth, New South Wales. The captain was the pilot monitoring (PM) and the first officer the pilot flying (PF).[1] At the time of departure, windshear conditions existed in the vicinity of Sydney Airport and because of this, the flight crew used normal take-off power.[2]
When LQG departed, an Air New Zealand Boeing 777-219ER, registered ZK-OKF (OKF), operating a scheduled passenger flight from Auckland, New Zealand, was on descent to Sydney from the east, assigned 6,000 ft by the Sydney Approach controller. The projected routes of the aircraft crossed approximately 11 km east of Sydney (Figure 1) and the Approach controller had assigned OKF an altitude of 6,000 ft to provide separation with LQG, who would be assigned 5,000 ft.
At 1407 Eastern Daylight-saving Time (EDT), LQG became airborne and after passing 500 ft, the PF turned the aircraft to an assigned heading of 090. When this turn was made, the flight crew had the go-around (GA) vertical mode selected on the aircraft flight guidance control panel with the altitude select (ALT SEL)[3] mode. After passing the acceleration altitude[4] of 1,100 ft, the PF requested the PM to select the indicated airspeed mode and a speed of 185 kts. The PM did this and then, at 1407:45, they contacted Sydney Departures while the PF engaged the autopilot.
When the PM contacted Sydney Departures, they reported passing 1,900 ft, heading 090 and climbing to an assigned altitude of 3,000 ft. Sydney Departures identified LQG on radar and instructed them to climb to an altitude of 5,000 ft. The PM read back this instruction and the flight crew correctly updated the autopilot with the new altitude and engaged the ALT SEL mode.
At 1408:12, as the aircraft climbed through 2,600 ft, Sydney Departures instructed LQG to track direct to waypoint KAMBA.[5] The position was entered into the flight management system and the autopilot was set to the lateral navigation mode. The aircraft then commenced turning left towards KAMBA.
At 1408:38, as the aircraft climbed through 3,800 ft (Figure 1), Sydney Departures advised LQG there would be a short delay at 5,000 ft due to traffic above them. This was acknowledged by the PM.
Figure 1: Disposition of aircraft when LQG was passing 3,800 ft direct KAMBA and showing the projected point of crossing.
Source: Airservices Australia, modified by the ATSB
Also, around this time, with the aircraft now tracking to KAMBA, the PF increased the airspeed setting from 185 knots to 210 knots. Almost simultaneously, the autopilot altitude mode changed to capture the assigned altitude.
The adjustment of the airspeed setting, while the autopilot was in altitude capture mode, resulted in the autopilot reverting from altitude capture mode to pitch mode, which meant the autopilot would now not stop the aircraft climb at 5,000ft.
Consequently, the PF decided to disconnect the autopilot and commenced hand flying the aircraft. They pitched[6] the aircraft nose down, to reduce the rate of climb, and simultaneously the PM selected the autopilot indicated airspeed and ALT SEL modes. Once these modes were selected, the PF attempted to reconnect the autopilot so the aircraft would maintain 5,000 ft. Before ensuring the autopilot had reconnected, they became aware of the conflicting traffic (OKF) and obtained its position by referencing the traffic alert and collision avoidance system (TCAS)[7] display. During this time, as the autopilot had not been correctly reconnected, the aircraft continued to climb.
After sighting OKF, the PF looked back at the aircraft instrumentation and observed the aircraft had climbed through 5,000 ft. This coincided with an altitude alert from the autopilot, which indicated that the selected altitude was exceeded. The PF responded by again pitching the aircraft nose down to stop the climb and return the aircraft to 5,000 ft. The maximum altitude LQG reached was 5,600 ft[8] before the aircraft began to descend.
Prior to the altitude excursion, the air traffic control system presented a short-term conflict alert (STCA), to both the Sydney Approach and Departures controllers. In response to the STCA, both controllers monitored the altitude of LQG to ensure the aircraft would maintain 5,000 ft. When the Sydney Departures controller observed LQG continue to climb, they issued the flight crew a safety alert,[9] requested confirmation that the aircraft was maintaining their assigned altitude and issued them a heading instruction to turn away from OKF. The Sydney Approach controller issued the flight crew of OKF a safety alert and instructed them to stop their rate of descent. In response, the flight crew of OKF advised they would level out and reported they were over the top of LQG and would be able to sight them again shortly. During the conflict, the lowest altitude OKF reached was 6,800 ft.
Separation Standards
The Sydney Approach and Departures controllers had anticipated that LQG and OKF would pass with less than the required 3 NM (5.6 km) surveillance separation between the aircraft. LQG subsequently passed approximately 0.5 NM (1 km) behind OKF. As surveillance separation did not exist, 1,000 ft vertical separation was required. In applying vertical separation, using pressure derived altitude information, tolerances need to be applied. When these tolerances are considered, the 1,200 ft displacement between the aircraft was not adequate to apply vertical separation. Consequently, the level excursion by LQG resulted in a loss of prescribed separation.
Operation of Autopilot
In multi-crew operations, standard operating procedures are established to support the principles of crew resource management (CRM). This includes defining the roles of the PF and PM in relation to autopilot selections. The captain of LQG reported that if the autopilot is engaged, the PF will make the autopilot selections. If the PF is hand flying the aircraft, the PM will make the selections, under the direction of the PF. In both sets of circumstances, visual and verbal cross-checks are made to help identify any potential errors.
Pilot monitoring comments:
After they had selected the correct modes, they believed the PF had reconnected the autopilot. At this time, their attention was divided between managing other radio transmissions and monitoring the PF’s actions.
The requirement to maintain 5,000 ft on departure was received regularly and something they monitored closely. In normal circumstances, the autopilot would remain engaged.
The PM advised that they should have been monitoring the PF’s actions more closely.
Pilot flying comments:
They were aware that when the autopilot mode changed to altitude capture, as they used the speed control, the autopilot mode could change to pitch. So, when this occurred, they disconnected the autopilot rather than concentrating on changing the modes with a high rate of climb close to the required altitude.
They thought they had reconnected the autopilot after the PM had reset the modes, but were distracted by looking outside the aircraft for the conflicting traffic and did not confirm the autopilot had reconnected.
Safety analysis
When the PF initiated the speed increase to 210 knots, the autopilot had not commenced capturing the assigned altitude. The speed increase at this stage of flight was reported as consistent with company practice of increasing speed when tracking towards the intended destination.
As the PF increased speed, the autopilot started to capture the assigned altitude. These near simultaneous events resulted in the autopilot reverting to pitch mode. The potential for the autopilot to behave in this manner was known to the flight crew. It is probable that the altitude capture occurred earlier than expected, due to the aircraft’s rate of climb being unusually high. The selection of normal take-off power on departure contributed to this high rate of climb.
The PF became concerned that the autopilot was not correctly configured to maintain the assigned altitude and disconnected the autopilot to hand fly the aircraft. After the PM had selected the correct autopilot modes, the PF, believing the autopilot would successfully maintain the aircraft at 5,000 ft, decided to reconnect the autopilot. They attempted to do this but the action was not successful. The PF did not realise this and the PM did not correctly confirm the status of the autopilot.
It was probable that the PF was distracted with looking for the conflicting traffic, rather than ensuring they had successfully reconnected the autopilot.
The loss of separation subsequently occurred after LQG did not maintain 5,000ft on a track that conflicted with OKF.
Findings
These findings should not be read as apportioning blame or liability to any particular organisation or individual.
The PF increased the aircraft speed at approximately the same time as the autopilot commenced capturing the selected altitude. This resulted in the autopilot mode changing and influenced the PF’s decision to disconnect the autopilot.
The PF did not engage the autopilot correctly and became distracted before ensuring it was connected, resulting in the aircraft climbing through the assigned level. The PM was also not aware that the autopilot had not been correctly reconnected.
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.
Operator
As a result of this occurrence, the aircraft operator has advised the ATSB that they have taken the following safety action:
Further training was provided to both the PM and PF in the areas of situational awareness, human factors and operational decision-making during high workload scenarios, including a review of aircraft automation technology and procedures. The crew members were also required to demonstrate competency prior to return to flying duties.
Safety message
Maintaining separation in high traffic terminal areas, such as Sydney, requires that flight crews strictly adhere to air traffic control instructions. As highlighted in this occurrence, any deviation has the potential to reduce safety margins.
During this occurrence, the interactions between the crewmembers were not effective in responding and managing the encountered threats and highlights the importance of effective CRM.
CRM is described as the practical application of all aspects of human factors including situational awareness, decision-making, threat and error management, team cooperation and communication.
One important aspect of effective CRM, is related to successful monitoring of aircraft systems and ensuring crewmembers actively cross check each other’s actions. These skills can be improved through standard operating procedures and increased emphasis and practice.
Key flight crew monitoring principles include:
be technically proficient
keep all team members informed
ensure the task is understood, supervised and accomplished
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 December 2016, a Boeing 737-8FE aircraft, registered VH-YFT (YFT) was parked on bay 3 (Figure 1) at Hobart Airport, Tasmania, as the crew prepared to conduct Virgin Australia flight VA1531 to Sydney, New South Wales. The flight crew consisted of a captain and first officer, and a check captain seated in the jump seat between them.
Figure 1: Hobart Airport – aerodrome diagram
Source: Airservices Australia annotated by ATSB
At about 0945 Eastern Daylight-saving Time (EDT), another Virgin Australia Boeing 737-8FE aircraft, registered VH-VUP (VUP), landed at Hobart Airport and parked on bay 2, adjacent to and north of YFT. The bays required that the aircraft departs using a power-out taxi[1], as there were no tug facilities available at Hobart Airport.
By 0950, the flight crew of YFT had received the final load sheet[2] electronically via the aircraft communications addressing and reporting system (ACARS). Due to an issue with printing a copy of the load sheet on the ACARS printer, the crew requested, and received, a paper copy of the load sheet from the dispatcher.[3] This issue caused a slight delay in pre-flight preparations. After starting the engines, the captain gave the dispatcher the instruction to disconnect their headset from the aircraft, which the dispatcher did, then exchanged thumbs up to indicate all was clear. The dispatcher then walked to the left wingtip of the parked aircraft (VUP) and stood with their arms out and thumbs up to indicate YFT was clear of obstacles, particularly the wingtip of VUP.
At 1012:12, the first officer of YFT contacted the Hobart surface movement controller (SMC) on Ground frequency and requested a clearance to taxi. The SMC then instructed the crew of an Airbus A320 aircraft that had commenced taxiing from bay 4, to vacate the apron area via taxiway H (Figure 2).
Figure 2: YFT starts taxiing from bay 3 at Hobart Airport
Source: Airport operator annotated by ATSB
The SMC then advised the crew of YFT that the A320 on their ‘left hand side’ was taxiing out via H and that they were to follow that aircraft via H (and D) to holding point D for runway 30. The first officer read back ‘follow Jetstar A320 behind, behind him via hotel holding point delta runway 30’. At about 1013, the captain commenced turning the aircraft to the right, out of the bay, with the nose wheels just inside the marked lead-out line (Figure 3).
Figure 3: Hobart apron area showing the lead-out line on bay 3
Source: Google earth annotated by ATSB
At that time, another A320 aircraft had landed and was taxiing in towards the parking bays from the north. During the initial turn out of the parking position, the captain became aware of the inbound A320 on taxiway A and became uncertain as to which A320 the controller had instructed them to follow, and whether the inbound A320 would taxi past them via taxiway F. The first officer had also seen the A320 taxiing down A towards F and pointed it out to the captain.
The captain elected to stop the aircraft and clarify their taxi clearance. YFT stopped part way through the turn, about 90° from its parked position (Figure 4). At that time, the nose wheels were inside the lead-out line, and the aircraft was pointing towards the left wingtip of VUP.
Figure 4: YFT stopped taxiing during the turn out of bay 3
Source: Airport operator annotated by ATSB
The ramp supervisor[4] was at the far side of the parked aircraft (VUP) preparing it for departure, when YFT stopped. The ramp supervisor saw that YFT had stopped during the turn out, which was unusual, therefore moved to a position near the dispatcher, who was at the left wingtip of VUP, to where they could communicate with the flight crew if required and have line of sight to check for wingtip clearance between the two aircraft (Figure 5).
Figure 5: VUP parked on bay 2 with ground crew marshalling and A320 inbound
Source: Airport operator annotated by ATSB
When YFT had stopped, the flight crew noticed that they had inadvertently omitted to write the automatic terminal information service (ATIS)[5] reference letter on their take-off data card. The first officer switched their radio to the appropriate frequency to listen to the ATIS, while the captain temporarily took over responsibility for communications with air traffic control (ATC) on Ground frequency.
At 1014:00, after seeing YFT stop during the turn, the SMC instructed the crew of YFT to ‘continue to taxi via taxiway H, you are number one to inbound traffic and the other traffic is well clear’. About 20 seconds later, after confirming the clearance with the captain (and switching the radio back from the ATIS to the Ground frequency), the first officer acknowledged the clearance with the call sign ‘Velocity 1531’.
By the time the first officer acknowledged the clearance, the captain had recommenced taxiing, while watching the A320 on taxiway A to make sure that it was going to hold its position. After stopping, the captain removed their hand from the tiller, which caused the nose wheels of YFT to centre. Therefore, the aircraft moved forwards in a near straight line for about 2 seconds and crossed the lead-out line, before the right turn resumed.
As the aircraft recommenced taxiing, the dispatcher initially observed the wingtips of the two aircraft clear each other. However, as YFT then tracked towards the tail of the parked aircraft as it started to turn, the ramp supervisor assessed that a collision between the left wingtip of YFT and left horizontal stabiliser of VUP was imminent. The ramp supervisor commented that they then lowered their arms towards a crossed position to show that clearance between the two aircraft was reducing,[6] and attempted (unsuccessfully) to make eye contact with the flight crew (Figure 6).
Figure 6: Collision imminent
Source: Airport operator annotated by ATSB
About 30 seconds after recommencing the taxi, as YFT continued to turn, the left wingtip collided with the horizontal stabiliser (tailplane) of VUP (Figure 7).
Figure 7: Contact between YFT left winglet and VUP left horizontal stabiliser
Source: Airport operator annotated by ATSB
The winglet of YFT was damaged (Figure 8) as was the horizontal stabiliser of VUP (Figure 9). No one was injured.
Figure 8: Damage to YFT left winglet
Source: Aircraft operator
Figure 9: Damage to VUP left horizontal stabiliser
Source: Aircraft operator
Safety analysis
Parking bays
The Hobart Airport operator reported that the bays were surveyed regularly to ensure they met the required standards. The airport operator constructed a schematic diagram of the aircraft’s taxi path from the CCTV footage and the aircraft dimensions on the surveyed apron markings (Figure 10).
The flight crew commented that the design standard for the parking bays meant that they were far too close to be comfortably safe to conduct a power-out taxi when there is an aircraft in the adjacent bay. Furthermore, a bit more spacing between the bays may prevent a similar incident occurring. The captain also commented that consideration of operational acceptability criteria, in addition to technical design specifications, prior to the commissioning of any parking bay and its associated taxi guidance line would facilitate required changes to the bay and mitigate additional threats peculiar to the local environment.
The captain commented that the (power-out) bays in Hobart are not aligned at right angles to taxiway H. This tends to give a false sense of being clear of adjacent aircraft once the cockpit is well past the aircraft and heading towards taxiway H, as the wingtips are so far behind the flight deck and outside the normal viewing arc of the pilots.
Figure 10: Airport survey markings showing B737 aircraft taxi track with nose wheel on lead-out line (left) and approximate incident taxi path (right)
Source: Airport operator
Position of VUP
VUP was parked with the nose wheels approximately 450 mm aft of the stop mark on bay 2, and the main landing gear was offset longitudinally (relative to the aircraft’s heading on the bay) about 380 mm left of the bay centreline. These were well within allowed tolerances and the aircraft was assessed by ground crew to be parked in the correct position. The crew of VUP had been guided to the parking position by ground marshals.
However, the position of VUP’s tail slightly left of centreline and aft (measured after the accident), reduced the available clearance between the two aircraft.
Turning geometry
When the aircraft stopped, the nose wheels straightened, and the aircraft subsequently taxied outside the marked turning circle.
When the captain releases the tiller on a Boeing 737 aircraft[7] during taxi, it will tend to centre the nose-wheel steering and straighten the nose wheels. When the aircraft then starts to move, the captain cannot immediately turn the nose-wheel steering before the aircraft moves without considerable use of thrust and excessive load on the nose landing gear. As the aircraft starts to move forwards, the captain turns the tiller in the desired direction and the nose wheels will start to turn the aircraft.
When YFT stopped, the nose wheels were inside the lead-out line. If the nose wheels track on (or inside) the lead-out line, the wingtip will clear a correctly parked aircraft on the adjacent bay, but it is necessary to keep a continuous turn going. The check captain commented that if you stop the aircraft, particularly if it is heavy, a significant amount of thrust is required to then keep the aircraft on the line. The captain commented that they used caution with the thrust setting because of passengers boarding the aircraft on the adjacent bay. The check captain also stated that there was not a lot of manoeuvring room with ‘power-out’ bays. There is a risk that the aircraft has to go straight ahead for 2-3 m to get the turn going again and there is no allowance made for that in the geometry of the bay.
The captain commented that there is an inherent error in determining where the nose wheel is tracking in relation to a taxi guidance line, in the Boeing 737, during turns. The nose wheel is behind and laterally offset from the captain’s seating position. As such, its position in relation to the line can only be estimated. On power-out bays, flight crew cannot see the position of the aircraft on the lead-out line at any time.
After stopping, the captain could no longer see the lead-out line, which was then beneath and behind the cockpit. The aircraft taxied forward across the lead-out for about 1–2 seconds then turned to the right towards the H taxiway line. There was no marked line connecting the lead-out line with taxiway H.
Ground crew interpretation of taxi track
When the aircraft stopped, the dispatcher noticed that the nose wheels were inside the line, which was normally an indication that the aircraft would stay well clear of an aircraft parked on bay 2. The aircraft then proceeded for about 2 seconds at an angle that was not normal, and both the ramp supervisor and the dispatcher thought the aircraft may have been heading towards taxiway A via the exit (F) behind bay 2 rather than continuing to turn to the right and along the normal path onto taxiway H.
The dispatcher reported that they were not initially concerned about the aircraft’s track, because a bit of momentum was needed to turn the aircraft and get moving. When the wingtip of YFT taxied clear of the wingtip of VUP where the dispatcher was standing, they assumed the aircraft would continue turning and exit the bay, but instead it kept going towards the parked aircraft, which they commented was very unusual.
Communication between ground crew and flight crew
In accordance with normal procedures, the dispatcher unplugged their radio connection to the flight crew before the aircraft commenced taxiing.
The dispatcher commented that they were unsure as to why the aircraft had stopped during the turn, but assumed it was because the flight crew were communicating with ATC. The ground crew radios are not on the ATC frequency and therefore they cannot hear transmissions between ATC and flight crew.
When the aircraft stopped, the ramp supervisor moved to where they could see if the flight crew flashed the nose-wheel lights to indicate a reconnect (of ground-air crew radio communications) was required, but they did not. There were also no hand signals from the flight crew to indicate they needed to reconnect. The ramp supervisor is the only person in the ground crew with a ground-to-air licenced, hand-held radio, so they wanted to get into position to communicate with the flight crew if they requested a reconnect.
As the aircraft continued its turn off the bay, YFT’s wingtip clearance was decreasing due to its proximity to the tailplane of VUP, although it had safely cleared the wingtip of VUP. The dispatcher was then no longer in sight of the flight crew. The ramp supervisor was unable to make eye contact with the captain (seated in the left seat) and commented that the captain appeared to be looking directly forwards.
The ramp supervisor commented that they lowered their arms towards a crossed position to indicate reducing clearance, but that action was not apparent on the CCTV footage of the accident. The check captain commented that lowering of the arms to the crossed position as stated by the ramp supervisor was not shown in the operator’s manual as a procedure to show reduced wing tip clearance.
According to the manual, the correct signal for requiring the aircraft to stop was ‘arms repeatedly crossed above head (the rapidity of the arm movement should be related to the urgency of the stop (i.e. the faster the movement, the quicker the stop)’.
The captain commented that they had seen the thumbs up from the wing walker at the wingtip of the parked aircraft (the dispatcher) and the wing walker near the tailplane of the parked aircraft (the ramp supervisor). They were the only signals the captain sighted and assumed therefore that they were clear of the parked aircraft. If there was any doubt about their clearance from the parked aircraft, they would contact ground staff via radio on their company operations frequency and request assistance, but they did not have any doubt. They had received the all clear signal from the ground crew and thought that they were clear of the parked aircraft and safe to continue.
The captain commented that it would be better to have verbal communication with the marshallers all the way out of the parking bay to have immediate communication if the clearance is insufficient. A verbal warning would be an immediate trigger to stop.
Training
The check captain commented that they consider the turning bays at Hobart to be tight. When training new captains, they always encourage them to ensure that they apply sufficient tiller during the turn out, and that sufficient thrust is applied to keep the aircraft turning. In addition, they suggest using the technique of using slightly more thrust on the outside engine to assist in keeping the aircraft turning.
The check captain also stated that there was no standard procedure in the company for training captains to taxi the aircraft. Training captains instil the importance of using a minimum radius turn out of the bay, appropriate power application and tiller technique, and instruct how to go about requesting assistance with marshaller guidance. Captains are instructed on the visual (hand) signals and where there is any doubt about clearance, to rely on the marshaller and keep a good lookout. If unsure of the clearance from any obstacle, they should stop, but in a turn, it is also important to keep the turn going – if you do stop you potentially have a problem.
When taxiing out of a power-out bay, they try to turn inside the lead-out line to ensure adequate clearance.
Role of ground crew
The operator commented that at the time of the incident, although provision of ‘wing-walkers’ was included in the ground handling contract between the aircraft operator and ground handling provider at Hobart Airport, the ground personnel were not specifically trained in wing walking. The dispatcher and ramp supervisor had proactively positioned themselves at the wingtip and horizontal stabiliser of VUP to assist the flight crew in maintaining clearance between the two aircraft. Wing walking or marshalling was normal procedure for the ground crew at Hobart Airport and both ground crewmembers had substantial experience in doing so.
Once the wingtip of YFT had passed the wingtip of VUP, the dispatcher’s responsibility was over because the next marshaller (ramp supervisor) was in line and the dispatcher was then out of line of sight of the flight deck. There was not usually a marshaller positioned beyond the wingtip.
The dispatcher commented that normally once the aircraft was clear from that position on the wingtip, the dispatcher would give a salute or wave to the captain and they would acknowledge with a wave, but that did not happen on this occasion. The dispatcher commented that the captain appeared to be looking straight ahead towards the exit, or they may have been focused on the marshaller ahead (the ramp supervisor).
Attention and time pressure
The captain initially got the thumbs up from the dispatcher and the ramp supervisor. Immediately before the collision, the captain’s attention was on the inbound A320, and they did not see any indication from the ground crew of reducing clearance with VUP (nor was there any evidence of such on the CCTV footage).
The captain commented that during the turn out, their attention was divided between the wing walker, watching where the aircraft was going, listening to ATC, communicating with the first officer, maintaining situational awareness and being aware of other traffic in the area.
The captain also commented that they[8] had to rise at 0345 to commute to Sydney Airport for the flight and had not slept particularly well as the flight was a line check. There was some pressure to perform well having a check captain in the jump seat. However, the captain felt fit to operate the flight and did not feel tired.
While waiting for the final load sheet to come out on the aircraft communications addressing and reporting system (ACARS), they had a problem with the ACARS printer and had to unjam it as the scheduled departure time was approaching. They requested a hard copy of the load sheet from the dispatcher but were also able to get the printer fixed and printed the load sheet from the ACARS. This caused them a slight delay and they were ready to go about 2 minutes late (scheduled departure was 1010 and they released brakes at 1013). This created some time pressure.
Clearance and traffic disposition
The presence of two A320s led the captain to doubt their taxi clearance after they started taxiing. The operator commented that the first officer’s read back of the taxi clearance, where they stated the A320 ‘behind’ rather than to their left, may also have affected the captain’s perception of which of the two A320s they were to follow. Once the aircraft started to turn, the captain could not see the A320 taxiing out (via H) but was concerned about the one inbound. The captain wanted to confirm that the inbound aircraft was going to stop.
Normally the captain would clarify the clearance with the first officer, but the first officer was listening to the ATIS at the time.
Findings
These findings should not be read as apportioning blame or liability to any particular organisation or individual.
When the captain became aware of the incoming A320, they became uncertain of their clearance and stopped the aircraft to clarify.
The aircraft taxied outside the marked lead-out line after stopping and without the application of sufficiently increased thrust or tiller input this resulted in insufficient clearance from the parked aircraft. The captain was unable to see the aircraft’s position relative to the lead-out line after stopping and the line did not continue to intersect the taxiway ahead of the aircraft.
The bays were marked according to the standards, but the standards probably did not allow sufficient margin for non-normal situations, such as stopping during the turn.
There was no documented procedure for either flight or ground crew to follow in the case of an aircraft stopping during the turn or crossing the lead-out line.
The operator did not have a standard training syllabus or assessment criteria for teaching captains to taxi the aircraft.
There was no direct means of verbal communication between ground marshallers and the flight deck once the aircraft started taxiing, although the crew could contact the movement coordinator if required.
Wing walkers should remain in sight of the flight crew, but the captain did not see the ramp supervisor signal to indicate reducing clearance between the two aircraft. The captain’s attention was to the incoming A320.
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 safety action in response to this occurrence.
Aircraft operator
As a result of this occurrence, the aircraft operator has advised the ATSB that they are taking the following safety actions:
Flight crew operational notice
The aircraft operator issued a flight crew operational notice (FCON)[9] which stated that:
When taxiing out of power-out bay, crew shall ensure the aircraft maintains the apron lead-out line until:
the end of the lead-out line; or
the lead-out line joins a taxiway centreline.
This may involve an exit turn of more than 180 degrees to assure clearance from adjoining bays.
Should the aircraft be stopped before completion of the entire turn to exit the apron, caution should be made when re-initiating movement to ensure the above requirements are maintained.
If at any time aircraft clearance cannot be assured, the aircraft should cease taxiing and request assistance.
Training and checking notice
The aircraft operator also issued a training and checking notice (TCN) that stated ‘All Check Captains and Training Captains are requested to ensure that wingtip geometry, turn markings, turn procedures and hazards are well understood by flight crew during line training and recurrent line checks’.
Flight crew information bulletin
The aircraft operator published a flight crew information bulletin (FCIB) for educational and standardisation purposes titled Wingtip Clearance Hazard and applicable to Boeing 737 aircraft. The FCIB included information about taxiing in accordance with lead-out lines, appropriate use of ground crew, images of Hobart and other airports used by the operator, and wing and tail turning geometry for the aircraft.
The FCIB stated:
In summary, it is recommended that taxi guidance lines be adhered to, whenever practical. Continued vigilance should be employed by crews in the monitoring of obstacles during ground manoeuvring.
If there is any doubt whatsoever regarding wingtip clearance, STOP and seek guidance.
Safety message
This incident highlights the importance of aircraft operators conducting a thorough risk assessment where ground movement is confined, particularly movements involving congested power-out bays. Effective risk assessments ensure that hazards are clearly identified and well understood, and that the associated risks are appropriately managed.
To manage clearance in congested areas, communication tools between ground and flight crew should be used where possible when ground crew are providing marshalling or wing walking assistance. Hand signals rely on constant visual contact, which cannot be guaranteed. Appropriate training of ground crew regarding the use of standard hand signals is required to ensure mutual understanding and communication between flight and ground crew.
Where possible, airport authorities should consider additional margins to accommodate unusual or irregular circumstances during taxiing.
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 25 November 2016, an Airborne Edge XT-912 microlight, registered 34-8401, collided with terrain at Hadlow, Queensland. Both of the aircraft’s occupants were fatally injured.
The Coroner investigated this occurrence and requested technical assistance from the ATSB, with respect to analysis of CCTV footage and examination of structural components from the accident aircraft. To facilitate this support, on 12 December 2016 the ATSB initiated an external investigation under the provisions of the Transport Safety Investigation Act 2003.
The ATSB completed its technical assistance at the end of April 2017. Any enquiries in relation to the investigation should be directed to the Central Queensland Coroner’s office.
___________ The information contained in this web update is released in accordance with section 25 of the Transport Safety Investigation Act 2003.
On 6 December 2016, with thunderstorm activity in the area, a Boeing 737-800 aircraft operated by Virgin Australia on a scheduled passenger flight from Melbourne, Victoria was on approach to runway 29 at Darwin Airport, Northern Territory. The flight crew established and maintained clear visual reference to the runway and surrounds until they encountered heavy rain shortly before reaching the runway threshold. Under the influence of a light but increasing crosswind, the aircraft drifted right without the flight crew being able to discern the extent of the drift.
The aircraft landed 21 m to the right of the runway centreline and, shortly after touchdown, the right landing gear departed the sealed surface of the runway, destroying six runway lights before the aircraft returned to the runway. The aircraft incurred minor damage from ground debris and there were no injuries.
What the ATSB found
A relatively small increase in crosswind resulted in a significant deviation from the runway centreline at a critical time during final approach. The absence of adequate visual cues influenced the flight crew’s ability to detect and correct the deviation.
International guidelines recommend, but do not mandate, the use of centreline lighting on wider runways. In recent years, two runway veer-offs have occurred at runway 29 at Darwin, which is the only runway in Australia that is wider than 50 m and not equipped with centreline lighting. No similar occurrence has happened at any other of the busier airports in Australia, where the runways are either narrower, or are a similar width but with centreline lighting.
A study of relevant occurrences world-wide found that the likelihood of a runway veer-off on landing increases significantly when using a runway that is wider than 50 m and does not have centreline lighting. This is likely due to limitations in the visual cues available in such circumstances.
There was no advisory information about this hazard in the operator’s manuals or in the aerodrome information provided to operators by Darwin Airport.
The ATSB also found limitations in the weather information provided to the flight crew while on approach to land.
What's been done as a result
The aircraft operator and airport operator initiated a number of safety actions as a result of the occurrence, including providing flight crews with information about the specific risks of approaches to Darwin Airport at night in conditions with reduced visibility.
The ATSB has issued a safety recommendation to the International Civil Aviation Organization and Darwin Airport to consider measures to reduce the safety risk identified in this report relating to wide runways without centreline lighting.
Safety message
Approaches in darkness and poor weather can be challenging. Centreline lighting greatly assists flight crews align the aircraft with the runway but many runways, including most in Australia, are not equipped with it. A wide runway without centreline lighting, such as that in Darwin, poses a particular challenge. Pilots and operators who are aware of any circumstances that are different to what is usually encountered and account for it in their planning are more likely to avoid being ‘caught out’ at a critical time.
The occurrence
Overview
On 6 December 2016, a Boeing 737-800 aircraft, registered VH-VUI and operated by Virgin Australia, was used for a scheduled passenger flight from Melbourne, Victoria to Darwin, Northern Territory. During the final approach to runway 29 at Darwin at night, the aircraft entered very heavy rain. The aircraft landed 21 m to the right of the runway centreline and, shortly after, the right main landing gear departed the sealed surface of the runway. Runway 29 was 60 m wide, which was 15 m wider than almost all the other runways used by air transport aircraft in Australia.
Flight planning
Prior to departing Melbourne, the flight crew reviewed relevant meteorological information for the flight including the latest aerodrome forecast (TAF) for Darwin, which was issued at 1400 Central Standard Time[1] and valid from 1530. The forecast conditions for their arrival time were good, with wind 300° at 5 kt, visibility at least 10,000 m and few cloud[2] at 2,000 ft.
There were no weather-related or other requirements for the flight crew to nominate alternate fuel or holding fuel for the flight. However, the captain ordered 1,500 kg more fuel than the minimum required for the flight (including the required reserves) due to the possibility that adverse weather conditions could develop.
Take-off and cruise
The aircraft was scheduled to depart Melbourne at 1825 (1955 AEDT) and actually departed at 1842. The captain was pilot flying (PF) and the first officer was the pilot monitoring (PM).[3]
During the flight, the flight crew obtained weather updates, which initially indicated that the weather conditions at Darwin remained good and were consistent with the forecast. A new TAF issued at 2053 and valid from 2130 was the same as the 1400 forecast.
At 2207, with the flight about 1 hour from landing, the Bureau of Meteorology (BoM) issued an amended TAF for Darwin. The amended TAF included a TEMPO,[4] which indicated that between 2230 and 0030 there could be periods of up to 1 hour with wind of variable direction at 20 kt gusting to 35 kt, visibility 4,000 m in showers of rain, and cloud broken at 1,500 ft.
Darwin air traffic control was required to pass on the availability of amended TAFs for the airport in accordance with the Manual of Air Traffic Services. The Darwin approach controller advised the Brisbane Centre en route controller of the amended TAF, and the Brisbane controller broadcast the TAF’s availability and key details at 2211. The flight crew interpreted the forecast weather as ‘thunderstorm material’ and noted that the TEMPO period covered their expected arrival time.
At 2212, the Brisbane controller who broadcast the availability of the 2207 amended TAF handed over duties to another controller. The incoming controller was advised that the amended TAF had been broadcast to all aircraft.
At 2218, the Brisbane controller issued the flight crew with a standard instrument arrival clearance to runway 29.
At 2223, the flight crew listened to the automatic terminal information service (ATIS) for Darwin Airport, which indicated the conditions were wind 300° at 8 kt, visibility at least 10,000 m, rain showers and scattered cloud[5] at 2,000 ft.
At 2224, the flight crew commenced the approach briefing. The briefing covered all the standard items, including the approach minima (290 ft elevation or 209 ft above the runway elevation and 800 m visibility) and the missed approach procedure for the runway 29[6] instrument landing system (ILS) approach procedure.
The flight crew selected an approach speed of 143 kt (reference landing speed plus 5 kt) and autobrake setting 2. They noted that the weather conditions were well above the minima at this stage, but if required they had sufficient fuel to conduct four missed approaches or hold for at least an hour.
At 2230, a SPECI[7] was issued for Darwin, which indicated that there had been a change in the actual weather conditions and that thunderstorms with rain were likely to be present. Subsequent SPECIs issued from 2247 indicated conditions were deteriorating. The flight crew did not obtain or receive these weather reports, but were aware of the developing situation. From 2232, they could see lightning in the distance and soon after, they could see rain cells on the aircraft’s weather radar.
At 2237, when VH-VUI was about 25 minutes from Darwin, BoM issued a second amended TAF for Darwin. The change to the previous (2207) amended TAF was that during the TEMPO period there was now thunderstorms with rain and visibility could be 2,000 m. For reasons that could not be established, the Darwin approach controller did not advise the Brisbane controller of the availability of the second amended TAF. Therefore, the Brisbane controller did not broadcast the 2237 amended TAF’s availability or details.
The operator’s flight following staff attempted to check that VH-VUI’s flight crew knew of the 2237 amended TAF via HF radio. Due to poor radio reception, the flight crew could not hear the message clearly but discerned that the call was about an amended TAF, and advised that they were aware of it. However, the call was about the 2237 TAF and not the 2207 amended TAF that the Brisbane controller had earlier broadcast. The flight following staff contacted Brisbane air traffic control at about 2247, and asked whether the flight crew had ‘the amended TAF for Darwin’. The controller advised that they did.
Descent and approach
At 2241, the flight crew commenced descent from flight level (FL) 380.[8] Shortly afterwards, they could discern a rain cell on the weather radar and discussed the extra fuel they had on board, and that they did not want to fly under or through any thunderstorms.
At 2249, the Brisbane controller handed over control of VH-VUI to the Darwin approach controller. The first officer contacted the approach controller and stated they were descending through FL 120 and had received (ATIS) information ‘Delta’. The approach controller advised the flight crew to expect the runway 29 ILS approach. He also advised that (ATIS) information ‘Foxtrot’ was current, and he provided the differences between ‘Delta’ and ‘Foxtrot’, which included that the wind was now 220° at 20 kt. The approach controller also advised that this wind information was only an estimate, because the airport anemometer was now unserviceable.
The flight crew discussed the situation, noting that the wind would be a predominant crosswind for the landing. They also discussed the weather around the airport and what impact it may have for their arrival on several occasions throughout the rest of the descent. The captain asked the first officer to add 10 kt to the landing reference speed to help alleviate the effect of wind gusts or changes, resulting in a selected approach speed of 148 kt.
At 2252, the approach controller provided the crew with another wind update, advising the wind speed to be 20 to 35 kt and that the crosswind for landing could be up to 20 kt. About a minute later the approach controller made an all stations broadcast, advising the runway was wet and the visibility at the airport was reducing to 5,000 m in rain.
At 2255, the flight crew requested approval to track direct to the initial approach fix (LAPAR) to avoid some of the weather, and the controller approved the request.
At 2256, when passing 5,000 ft, the flight crew began a further discussion about the airport weather. Their comments recorded on the cockpit voice recorder indicated they could see lightning ahead, and were using weather radar to determine the position of rain cells. They agreed a rain cell to the north-east of the airport would not impact the approach. In a later interview, the captain reported that it appeared as though they would easily land before the rain arrived. They began discussing the potential impact of another rain cell south-west of the airport but were interrupted by other priority tasks and did not conclude this discussion.
The flight crew selected flaps 5 at 2258 and the first officer advised Darwin tower that they were approaching LAPAR. The tower controller advised rain was now directly over the airport and the visibility was reducing to about 3,000 m. At around the same time, the flight crew selected flaps 15.
The tower controller also advised the flight crew of the settings of the high intensity approach lighting (stage three) and the high intensity runway lighting (stage five) and requested the flight crew advise if changes to the settings were necessary. The first officer asked if there was any update on the wind information, and the tower controller stated that the wind estimate remained the same as previously advised by the approach controller, and they were trying to get additional information. The first officer acknowledged the reply, and noted they now had the runway lights in sight.
At about 2259, the aircraft descended through the lowest level of the cloud base from about 2,500 ft. The crew later reported that they could see the runway and airport surrounds. They saw a rain shower at the airport, towards the far end of runway 29.
The crew again discussed the weather conditions and they discussed their options in the event a missed approach was required, and agreed they would divert to the right rather than straight ahead as published on the missed approach track (286°). The captain requested the first officer be ready to use the aircraft windscreen wipers.
At 2300, the aircraft descended through 2,000 ft at about 150 kt and the flight crew selected flap 30. The Darwin tower controller updated the wind information based on data obtained from a second, test anemometer located to the south of the runway 29 threshold that the wind was 290° at 16 kt, gusting to 22 kt. The first officer acknowledged the information and advised that if a missed approach was conducted the crew planned to turn to a heading of around 320° to ‘avoid the storm on the other side of the field.’
At 2301, the flight crew commenced the landing checklist, and the captain asked the first officer for his opinion on the situation. The first officer noted the approach was stable, the missed approach altitude was set and it was apparent they would be able to land. They could see the runway lights clearly, and although there was rain ahead, it looked like it was some distance down the runway.
Final approach and landing
The events during the final approach and landing are summarised in Table 1, including the time, airspeed and radio height (or height above ground) from 500 ft. Figure 1 also shows the aircraft’s lateral displacement from the runway centreline.
Table 1: Summary of events during final approach and landing
The captain asked the first officer to turn the wipers on using the fast setting, which was actioned.
2302:01
153 kt CAS
267 ft
The captain disengaged the autopilot. At this point, the aircraft was on the glidepath, on track and close to the extended runway centreline. The first officer advised that the wind was 280° and up to 25 kt.
2302:07
148 kt CAS
207 ft
The aircraft passed through the decision height for the ILS approach, and the aircraft’s automated ‘minimums’ annunciation occurred. The captain stated they would try to land. The first officer acknowledged and stated the wind was steady.
2302:12
148 kt CAS
179 ft
The aircraft entered rain, which intensified over the next few seconds.
2302:18
152 kt CAS
131 ft
The crossbars of the approach lights would no longer have been visible to the crew under the aircraft’s nose. The crosswind dropped from about 4 kt to 1 kt for 2 seconds, and then began a slow increase
2302:21
151 kt CAS, 133 kt GS
98 ft
The automated ‘100 feet’ annunciation occurred. The runway threshold lights would have no longer been visible to the crew under the aircraft’s nose. Later analysis indicated that, at about this time, there was an increase in the average crosswind from 3 kt to 6 kt, and the aircraft started drifting to the right of the extended runway centreline.
2302:23
152 kt CAS, 134 kt GS
50 ft
The aircraft crossed the runway threshold, about 3 m to the right of the runway centreline and drifting about 3° to the right. The automated ‘50 feet’ annunciation occurred.
2302:25
134 kt GS
35 ft
The captain initiated the landing flare.[10] The aircraft was about 11 m to the right of the runway centreline.
2302:30
135 kt GS
0 ft
The aircraft touched down wings level within the touchdown zone, 440 m from the threshold, about 21 m to the right of the centreline and drifting about 3° to the right.
2302:31
133 kt GS
0 ft
The aircraft’s nose gear touched down.
2302:33
126 kt GS
0 ft
The right main landing gear departed the sealed surface of the runway about 235 m after touchdown, 675 m from the runway threshold at about 126 kt groundspeed. The gear’s maximum distance from the runway edge was around 1.5 m.
23:02:41
92 kt GS
0 ft
The right main landing gear returned to the sealed runway surface at a groundspeed of about 92 kt, after having been off the sealed surface for about 394 m.
23:02:45
78 kt GS
0 ft
The captain deployed the thrust reversers.
23:02:52
60 kt GS
0 ft
The aircraft reached 60 kt groundspeed.
The approach was stable at 500 ft, and the captain disconnected the autopilot at about 270 ft. The wind was gusty, requiring constant correction, and the crosswind varied between 0 kt and 5 kt from the aircraft’s left. At the decision height (about 210 ft) the flight crew were still visual and decided to proceed with the landing. Soon after, at about 180 ft, the aircraft entered heavy rain. The crew later reported that they had expected to land well before encountering the rain.
The air traffic controllers in the Darwin tower reported that they could see the aircraft’s lights (including the logo light on the near side) throughout the final approach and landing from the tower, about 1.8 km north-west of the runway threshold.
From about 100 ft, the flight crew would not have been able to see the approach lights or runway threshold lights below the aircraft’s nose (see Aerodrome information). In addition, the crew later described the rain from this point as a ‘heavy deluge’. Their vision of the runway and the surrounding airport environment was obscured. Only the runway edge lights and precision approach path indicators remained visible, and they became blurred and no longer sharp and distinct, particularly between each pass of the windscreen wipers. The crew reported that they felt at the time that the visibility remained sufficient to complete the landing.
At about 100 ft (2302:21), the aircraft started to drift to the right of the runway centreline, and this deviation increased until the aircraft landed 8 seconds later (2302:29). Other than the lateral deviation, all other aspects of the final approach and landing were normal.
The aircraft touched down within the touchdown zone, about 21 m to the right of the centreline. The maximum recorded vertical acceleration was 1.74 g, within the normal range for landing, and there was no evidence that the aircraft bounced.
When the captain lowered the aircraft’s nose he realised the aircraft had landed ‘well right’ of the centreline but with the obscured visibility he could not readily ascertain how far. He later recalled trying to steer the aircraft towards the centre of the runway but being very wary of oversteering and losing control on the wet runway.
At 2302:33, 4 seconds after landing, the right main landing gear departed the right side of the runway. The captain recalled hearing a repeated, light thudding noise. He asked the first officer if they had hit the runway lights and the first officer responded that that they were just missing the lights. The aircraft’s nose was oriented to the left of the direction of travel, placing the flight crew and nose gear over the sealed surface and inside the painted runway edge markings. The first officer later reported feeling a shudder, as though the wheels were skidding. Both flight crew recalled that the physical sensation and noise were not as strong as they would have expected from the wheels departing the runway.
Figure 1: Final approach and landing roll of VH-VUI
Image shows the aircraft’s path crossing the runway threshold near the centreline and deviating to the right edge of the runway before returning.
Source: ATSB / Google Earth
Taxi and disembarkation
The flight crew taxied to the bay and stopped short at 2309, remaining there until the weather eased enough for safe groundwork and disembarkation. During this time, the crew discussed the approach and landing. The captain asked whether the first officer was sure the aircraft had stayed on the runway, and the first officer reiterated that he was sure they had.
At 2322, the ground marshaller installed the wheel chocks and the passengers soon started disembarking. At 2329, one of the flight crew also disembarked and inspected the aircraft. He observed the aircraft damage and immediately realised they had departed the sealed surface of the runway on landing. After returning to the aircraft, the flight crew reported the incident to the operator and air traffic control at 2331.
The airport operator inspected the runway and identified that at least four runway lights were inoperable, but at the time saw no debris other than grass on the runway. The flight crew of the next arriving flight was advised of the situation and elected to continue, landing at 2336. Subsequent inspections found debris from the runway lights on the runway surface.
Damage and injuries
Six runway edge lights were hit and destroyed as the landing gear impacted concrete pads located just off the runway edge (Figure 2). Debris from the lights and ground impacted the aircraft and littered the edge of the runway surface.
The right main gear tyres sustained deep cuts during the impacts with the runway edge lights and concrete pads (Figure 3).
Debris impacted the aircraft resulting in minor damage to areas of the right aft fuselage and right horizontal stabiliser (Figure 4). A large quantity of grass accumulated in the vicinity of the right wheel well, landing gear and wing flaps.
There were no injuries.
Figure 2: Wheel tracks where VH-VUI departed the runway 29 sealed surface and destroyed runway edge lights[11]
Image shows the tracks from the right main landing gear through grass and over concrete pads near the runway edge. Photo facing the opposite direction to the landing. Source: ATSB
Figure 3: VH-VUI tyre damage
Image shows cut damage to the right main landing gear outboard tyre. The chevrons in the centre of the tread are normal. Source: ATSB
Figure 4: VH-VUI fuselage damage, marked with green tape
Image shows the locations of skin damage to the right side of the aircraft fuselage marked with short sections of tape on the underside of the fuselage. Longer sections of tape mark the locations of longitudinal and vertical fuselage reference lines. Source: Virgin Australia
At the time of the occurrence, the captain had a total of 22,559 hours flight time with 9,206 hours on Boeing 737 variants. The first officer had a total of 7,000 hours flight time with 3,500 hours on 737 variants. Both flight crew were appropriately qualified to conduct the flight.
The flight crew’s last night landing was conducted together the previous night, and each had conducted several night landings into various Australian airports in the previous month. The captain’s last flight into Darwin Airport was five and a half months previous, and the first officer’s most recent landing there was 16 months previous. Both were night landings. The captain reported having flown to Darwin many times before.
The first officer reported not having encountered rain conditions like those on approach during the occurrence flight before. The captain recalled having seen such conditions only once before, about 30 years prior, during a flight into Darwin that resulted in a hard landing.
Both flight crew were based in Melbourne. They had no duty on 3 and 4 December 2016. On 5 December, they both flew as passengers to Canberra in the afternoon, and then conducted a series of flights, ending their duty time at about 2300 AEDT.[12]
On 6 December, they signed on for duty at Canberra Airport at 1600 AEDT. They then operated a flight from Canberra to Melbourne, before beginning preparations for the Melbourne to Darwin flight. They had both been on duty for 8.5 hours at the time of the occurrence.
The captain reported getting about 6 hours sleep the night before the occurrence and normal sleep in the nights before. The first officer reported getting a normal amount of sleep the night before the occurrence, and the nights before that. Both crew reported being a little tired at the time of the occurrence. However, there was insufficient evidence to suggest that the flight crew were operating at a fatigue level known to affect performance, and both had sufficient sleep opportunity in the nights prior to the occurrence.
Aircraft information
VH-VUI, a Boeing 737-800 aircraft, was manufactured in 2006. No problems with the serviceability of any relevant aircraft systems were reported or identified. The aircraft was fitted with the appropriate equipment for category I, II, and III ILS approaches and was capable of autoland at suitably equipped airports.[13] The aircraft was not fitted (nor required to be fitted) with an aircraft communications addressing and reporting system (ACARS) to receive data messages.
Boeing 737-800 aircraft (as well as the 600, 700 and 900 series 737s) were certified for operation with windscreen wipers and without any other rain removal system. The aircraft was not fitted with a rain repellent fluid dispensing system, which had been fitted to earlier versions of the 737. This system was no longer in use because of environmental concerns about the fluid available at the time.
Additional visual enhancements available for 737-800 windscreens include a hydrophobic coating. The aircraft manufacturer stated these coatings were an enhancement to the wiper system but were not required for safe operation of the aircraft. It stated that the service life of hydrophobic coatings varied significantly from operator to operator due to the operating environment, particularly in terms of how often windscreen wipers were used and the areas where particulates such as dust were encountered on flights.
The operator reported that 43 of its 79 Boeing 737 aircraft had a hydrophobic coating applied at the time of aircraft production. However, regular maintenance of the coatings was not required by the operator’s system of maintenance, and the coatings had not been routinely replaced in service. The windscreen of VH-HUI was delivered to the operator in 2013 with a new hydrophobic coating.
The aircraft was fitted with anti-skid wheel brakes. Post-occurrence inspections found no evidence of rubber reversion hydroplaning (which leaves distinctive marks on the runway and tyres); however, other types of hydroplaning leave no direct evidence. The touchdown point could not be identified, suggesting that some initial hydroplaning may have occurred. There were black particles in the runway surface that indicated a transfer of rubber from the aircraft’s tyres continuously along the aircraft’s path from near where the aircraft touched down, consistent with some degree of traction.
Meteorological information
Weather observations
The approach and landing were conducted in darkness. Weather radar data provided by the Bureau of Meteorology (BoM) showed two areas of rain near and over Darwin Airport on the night of the occurrence (Figure 5).
Table 2 summarises meteorological information from routine weather reports (METARs) and special weather reports (SPECIs) during the period from 2100 local time. As indicated in the table, visibility started decreasing at about 2247, and it decreased to 2,000 m at 2257. There was heavy rainfall recorded by a rain gauge near the runway 29 threshold at Darwin Airport after 2247, peaking at about 24 mm/hour for a period of several minutes around the time the aircraft landed.
A 2300 observation from the test anemometer at Darwin Airport (see Weather information services) recorded a westerly surface wind of 16 kt. The Darwin tower controller reported the windsock nearest the runway 29 threshold indicated a relatively steady wind but as with windsocks in general, it was not responsive to short gusts.
Closed-circuit security video showed rain at the terminal (2 km north-west of the runway 29 threshold) starting and increasing from about 2250, and becoming heavy by 2302. Over this period, the video showed four brief, bright flashes consistent with lightning strikes.
Recorded lightning strike data showed significant activity in the area. In the 5 minutes before VH‑VUI landed (at 2302), there were several lightning strikes within 5 NM of the airport and two within 5 NM of the aircraft. Some of these may not have been visible to the flight crew due to them potentially being obscured by cloud.
Figure 5: Ground-based radar images showing rainfall near Darwin Airport (blue arrow) during the approach, with the aircraft’s position at 2300 indicated by an aircraft symbol
Image shows heavy rain approaching Darwin Airport from the south-east over a period of 30 minutes, and arriving at the airport while VH‑VUI approached. The tan circle has a 20 km (10.8 NM) radius. Note that the picture displayed on the aircraft’s weather radar would not be the same. Source: Bureau of Meteorology, modified by ATSB
Table 2: Darwin METAR and SPECI summary
Time
Wind direction (° M)
Wind speed (kt)
Visibility
Precipitation
2100
290
7
> 10 km
None
2130
320
10
> 10 km
Light rain
2200
310
9
> 10 km
Showers in the vicinity
2230
250 (variable)
7
> 10 km
Light thunderstorm and rain
2247
230
9
7 km
Moderate thunderstorm and rain
2257
290
16
2 km
Heavy thunderstorm and rain
2300
290
15
2 km
Heavy thunderstorm and rain
2312
320
11
5 km
Light thunderstorm and rain
2330
310
7
> 10 km
Showers in the vicinity
0000
340
4
> 10 km
Showers in the vicinity
0030
340
2
> 10 km
None
Weather information services
BoM was responsible for the provision of aerodrome forecasts and weather reports at Darwin Airport. An aerodrome forecast (TAF) was issued every 6 hours with a validity period of either 24 or 30 hours from defined commencement times. When significant variations from the mean conditions, of a temporary nature, were expected to occur within the forecast period they were indicated by the use of the term TEMPO in the forecast.
Aerodrome weather reports were generated by an automatic weather station with manual input from approved weather observers. Routine reports (METAR) were issued every 30 minutes. Special reports (SPECI) were triggered by a significant change in a set of parameters, including wind, visibility and cloud.
In Australia, air traffic control (ATC) was required to pass on TAF and amended TAF information to flight crews that were within an hour of their destination. ATC was not required to pass on SPECI reports if those reports were available through a local broadcast service such as the Aerodrome Weather Information Service (AWIS) available at Darwin.
Availability of wind information
The Darwin control tower was equipped with displays that showed the wind direction and speed sourced from the airport anemometer via the BoM Observations office. This anemometer was located near the centre of the airport, about 2.4 km west of the runway 29 threshold (Figure 6).
Figure 6: Location of anemometers at Darwin Airport
Image shows the primary anemometer’s location near the centre of the airport and the second (test) anemometer near the runway 29 threshold. Source: ATSB / Google Earth
Due to a failure attributed to a lightning strike,[14] the airport anemometer was unserviceable at the time of the occurrence and no wind information was being displayed in the control tower. Darwin tower controllers obtained wind information from windsocks located at the airport, and through BoM observers via telephone for information from a second, test anemometer about 550 m south of the runway 29 threshold. Wind data from this anemometer was relayed to the tower controllers by a trained BoM observer.
BoM reported that the last performance checks on the test anemometer were conducted in June 2014. BoM was unable to verify the integrity of the anemometer’s wind data but stated that it was a standard installation using the same type of anemometer as the airport anemometer, and BoM considered the wind information to be a reasonable indication of local conditions. Performance checks before and after the occurrence showed the test anemometer to be operating within specifications. There may be some difference in wind speed and direction readings between the two sites due to local variations, and obstructions near the secondary site.
According to fault records, the primary anemometer was unavailable or exhibited faults on 32 occasions from February 2013 to December 2016, including 21 occasions in the wet season (November to April). The median time to repair was about 2.5 hours and the average was 14.5 hours. On four occasions, the repair took longer than 24 hours.
BoM advised that its anemometers were installed and maintained to meet International Civil Aviation Organization (ICAO) Annex 3 standards and recommended practices. For anemometers at Australian airports, there was no minimum availability[15] requirement and no requirement to have a secondary anemometer.
Landing visibility criteria
Civil Aviation Regulation (CAR) 257(4) stated that an aircraft may not land if any element of the meteorological minima was below that published for the operation. The published ceiling minimum (and decision height)[16] for an ILS category I approach to Darwin was 200 ft, and the visibility minimum was 800 m.
CAR 176A(2) stated that:
In determining visibility, the pilot in command of an aircraft must take into account the meteorological conditions, sunglare and any other condition that may limit his or her effective vision through the windscreen of the cockpit of the aircraft.
CAR 257 noted that determinations about the meteorological minima for landing must be published in the Aeronautical Information Publication (AIP). The AIP (ENR 1.5, paragraph 4.11) stated that conditions were below the minima when ‘the total amount of cloud below the ceiling minimum specified is continuously greater than SCT’ [scattered], or ‘the visibility is continuously below the visibility specified’.
Flight data recording
The aircraft manufacturer performed kinematic analysis of the recorded flight data, which provides a more accurate representation of wind than the raw recorded data.
With the autopilot engaged, the aircraft accurately maintained the glideslope and localiser during the approach. To maintain the steady approach in turbulence, constant corrections were required including control wheel (yoke) deflections up to 20°. The captain maintained runway alignment after disengaging the autopilot at 2302:01 until almost at the threshold.
The kinematic analysis indicated that in the few seconds before crossing the threshold (2303:23), the crosswind varied but it was not significantly more than it had been previously (Figure 7). However, in a gradually increasing crosswind from about 140 ft, about 5 seconds before crossing the threshold, the aircraft banked slightly right and began drifting right, without correction. A combination of momentum and continuing crosswind meant that the drift to the right continued until touchdown.
Figure 7: Recorded data showing the aircraft’s drift from centreline. The runway width is exaggerated and the markings are different to those at the time of the occurrence.
Source: Boeing, annotated by ATSB
Aerodrome information
General information
Darwin Airport consists of both civil and military facilities and is classified as a joint-user aerodrome. The civilian airport operator is Darwin International Airport. Responsibilities between the Department of Defence and Darwin International Airport are defined in a joint-user deed. The runway infrastructure is the responsibility of the Department of Defence.
Runway information
Runway 29 was 3,354 m long and 60 m wide, and the centre 45 m was grooved to aid water displacement and had a retractable arrestor cable in the touchdown zone for military use. The runway was equipped with an instrument landing system (ILS) that allowed for precision approaches in operations to category I minima (without autoland).
The runway had white markings along the centreline, an aim point starting 342 m from the threshold, and five touchdown zone markings from the threshold to 900 m. The runway had high intensity approach lights, runway threshold lights, and runway edge lights spaced at 60 m intervals.[17] There were also precision approach path indicator lights each side of the aim point (Figure 8).
Figure 8: General arrangement of runway lighting at Darwin Airport runway 29
Light locations are approximate, and actual light colours are not represented. Source: ATSB / Google Earth
Runway 11/29 at Darwin was significantly wider than most others in Australia (see Related occurrences in Australia), resulting in the visual cues and runway perspective being different to those normally available to complete a landing. The runway was not equipped with centreline or touchdown zone[18] lights.
There were two distinct crests that could obstruct distant portions of the runway and some edge lights when viewed very close to touchdown. ATSB analysis of topographic survey data indicated that runway 29 met relevant standards for slope and variation.
The Civil Aviation Safety Authority (CASA) outlined Australian requirements for aerodromes in Civil Aviation Safety Regulation (CASR) 139 and the associated Manual of Standards (MOS) for CASR Part 139. Testing conducted in 2016 and 2017 found that the ungrooved runway edge on the northern side of runway 11/29 at Darwin did not meet the surface texture or friction requirements of the MOS.
Runway design standards and guidance
The International Civil Aviation Organization (ICAO) specifies standards and recommended practices (SARPS) for international aviation operations in a series of Annexes. ICAO Annex 14 (Aerodromes, Volume 1 Aerodrome Design and Operations, 7th edition July 2016) stated that runway centreline lights and touchdown zone lights shall be provided for runways with a category II or III[19] precision approach. It also stated:
5.3.12.2 Recommendation— Runway centre line lights should be provided on a precision approach runway category I, particularly when the runway is used by aircraft with high landing speeds or where the width between the runway edge lights is greater than 50 m.
Annex 14 had included the same or similar recommendation since 1966. There was no recommendation for touchdown zone lights for category I runways.
ICAO also published other guidance about aerodrome lighting. For example, ICAO document 9157 (Aerodrome Design Manual, Part 4 Visual Aids) stated:
The function of the centre line lighting is to provide the pilot with lateral guidance during the flare and landing ground roll or during a take-off. In normal circumstances, a pilot can maintain the track of the aircraft within approximately 1 to 2 m of the runway centre line with the aid of this lighting cue. The guidance information from the centreline is more sensitive than that provided from the pilot’s assessment of the degree of asymmetry between the runway edge lighting. In low visibility conditions, the use of the centre line is also the best means of providing an adequate segment of lighting for the pilot to use. The greater distances involved in viewing the runway edge lighting together with the need for the pilot to look immediately ahead of the aircraft during the ground roll also contribute to the requirements for a well-lit runway centre line.
Another section of the manual stated:
…Some of the most difficult tasks when flying an aircraft visually are judging the approach to a runway and the subsequent landing manoeuvre. During the approach, not only must the speed be carefully controlled, but continuous simultaneous corrections in all three dimensions are necessary in order to follow the correct flight path.
…There are two reasons why approach and runway lighting systems are provided with patterns that emphasize the centre line. One obvious reason is that the ideal landing position is along the centre of the runway. The other is that the fovea of the eye, the region of sharp vision, is only about 1.5 degrees in width…
Studies have shown that the average time required for a pilot to switch from outside visual cues to instruments and back to outside cues is about 2.5 seconds. Since high performance aircraft will travel at least 150 m in this time period, it is apparent that in so far as possible the visual aids should provide the utmost in guidance and information, enabling the pilot to proceed without the necessity of cross-checking the instruments…
Consistent with Annex 14, the MOS for CASR Part 139 required centreline and touchdown zone lighting for runways with category II or II approaches and recommended centreline lighting for category I runways with a width of more than 50 m.
Simulation of visual cues provided by runway lights
The ATSB examined the relative effectiveness of the visual cues provided by runway edge lights on late final approach at Darwin during the 6 December 2016 occurrence flight compared with other situations.
Visual images were created to simulate a captain’s view of runway lights when on approach to a runway. These simulations were based on a highly simplified model of the cues that would normally be available to flight crews. For example, they did not include visual cues available from approach lighting, runway texture or surrounding areas, and did not account for the effects of rain and windshield wipers on the visual appearance of the runway edge lights. They also did not account for the effects of aircraft movement and associated visual cues such as optic flow. Nevertheless, they provided some indication of the relative ability to identify a lateral deviation from the runway centreline during the later stages of the final approach.
The simulations indicated:
A significant deviation from the runway centreline (11 m lateral displacement at 24 ft above the ground) appears much easier to detect on a 60 m wide runway if runway centreline lights are provided.
A significant deviation from the runway centreline is more difficult to detect on a 60 m wide runway without centreline lighting compared to a 45 m wide runway without centreline lighting.
It may be difficult to distinguish being on centreline and wings level from being off centreline with a slight bank in the direction of the closest row of edge lights. However, the deviation from the centreline is much easier to detect when runway centreline lights are present.
Further details of the simulation method and simulation images are provided in Appendix A.
En route supplement information
CASR 139 required an aerodrome operator to ensure there was adequate particulars about the aerodrome published in the En Route Supplement Australia (ERSA).[20] The types of information required included telephone numbers, runway specifications, lighting, visual aids, available ground services, special procedures and local precautions.
The MOS for Part 139 provided more details regarding the types of information to be included in the ERSA. This included the width and lighting information for each runway and ‘important cautionary or administrative information relating to the use of the aerodrome’. The ‘Additional information’ section of the ERSA for the aerodrome was also required to include ‘significant local data’, such as animal or bird hazards or areas to avoid overflying.
The ERSA information for many Australian aerodromes includes some types of hazards in the ‘Additional information’ section, such as birds, weather balloon launches, or the likelihood of turbulence on approach to particular runways. Specific guidance with regard to visual issues on approach was uncommon. One example was the ERSA entry for Mackay Airport, which stated that in conditions of light mist or fog, high intensity floodlighting adjacent to the final approach to a runway could ‘cause distraction’. A small number of entries cautioned that nearby roads or other objects may be mistaken for a runway.
The ERSA information for Darwin stated there was a possibility of windshear or turbulence on short final approach for all runways and bird hazards. No advisory information was provided about the potential for visual illusions or potential problems with visual guidance during landing associated with the runway width, lack of centreline lighting or touchdown zone lighting, or the crests in the runway.
Operator information
Approach to land near storms
The Virgin Australia flight crew operations manual stated:
In the interests of safety, prevention of aircraft damage, and passenger comfort, avoiding thunderstorms is of paramount importance.
- Visually avoid thunderstorm cells, or radar returns, including those with prominent 'hooks', 'scallops' or 'fingers' which indicate severe hail and signify strong vertical shear
- Avoid flying under anvils
- Avoidance shall be upwind of the weather, where possible
- Do not attempt to overfly a thunderstorm…
In terms of the descent and approach to land, the manual also stated:
Fly the aircraft clear of thunderstorms either by holding or adopting an alternative approach track. The circuit and approach to land should not be closer than 5 nm to an approaching storm at any time.
A note in the relevant section stated:
During take-off and landing, storms that have passed may be approached closer than 5 nm, as the rear of storms is considered to be comparatively inactive.
Transition to manual flight
In relation to flight path management, the operations manual stated that the auto flight system (AFS) on an aircraft ‘should be used to enhance operational capability, improve safety and reduce workload’. In addition:
Flight crew should use available AFS to the fullest extent that meets operational requirements considering the current flight conditions.
The manual also stated that the autopilot should be engaged:
… On all Instrument approaches, when cloud is within 500 ft of the minima or when the reported visibility is less than required visibility +2000 m…
In a section discussing the flare and touchdown, the operator’s flight crew training manual for the 737 stated:
When a manual landing is planned from an approach with the autopilot connected, the transition to manual flight should be planned early enough to allow the pilot time to establish airplane control before beginning the flare. The PF should consider disengaging the autopilot and disconnecting the autothrottle 1 to 2 nm before the threshold, or approximately 300 to 600 feet above field elevation.
Guidance for Darwin Airport
An examination of the Virgin Australia’s flight operational quality assurance data suggested off-centreline landings were very rare, including at Darwin.
Virgin Australia used aeronautical charts that were provided by a third party (Jeppesen), and also published its own supplementary port information when there was a need to provide additional information to flight crews. The supplementary port information for Darwin Airport included a caution for flight crew about turbulence and windshear on short final, and bird hazards. There was no specific guidance for other weather conditions, runway characteristics, or local lighting.
The ATSB reviewed the supplementary guidance for Darwin Airport provided by two other major Australian airlines. Following a veer-off runway excursion at Darwin in 2003 (see Related occurrences in Australia), one operator introduced additional guidance to flight crews for approaches to Darwin, including notes about runway surface, slope, width, lighting, and ambient light. The guidance stated:
CAUTION:
Be aware of the possibility of loss of visual cues when landing on RWY 29 at night, particularly in conditions of reduced visibility.
Contributing factors include:
- Runway surface condition;
- Runway slope;
- Runway width of 60 m;
- No centreline lighting;
- No touchdown zone lighting;
- Lack of surrounding ambient light, particularly approaching the flare, i.e. black hole effect.
It is recommended that approach and landings at night onto RWY 29 auto-coupled to the ILS for as long as possible, commensurate with the limitations. Crew must exercise vigilance and if any doubt exists as to the safe continuation of the approach, a Missed Approach must be executed.
The second operator, which had an association with the first operator, provided similar guidance to its flight crews.
Related occurrences
Previous studies of runway excursions
A study by the ATSB (2009) examined 141 runway excursions involving commercial jet aircraft during 1998–2007. About 40 per cent were veer-offs[21] on take-off or landing. Weather was a significant factor in many of the occurrences. The ATSB report stated:
Appropriate lighting of the runway centreline and edges has the potential to provide pilots with better spatial awareness at night or in poor visibility conditions, and may reduce the likelihood of veer-offs.
A Flight Safety Foundation (FSF) study (2009) examined 548 runway excursions, including 230 veer-offs on landing. This study also highlighted the significant effect of weather. The FSF report stated:
The frequent presence of runway contaminants in runway excursions strongly implies that they…are a significant risk factor, along with weather conditions such as rain, crosswinds, gusting winds, and low visibility.
The FSF found that runway excursions on landing were closely associated with rain, snow and wind. Importantly, about half of all landing veer-off occurrences in crosswinds or gusty, turbulent winds, followed a stabilised approach.
In July 2015, Airbus published an article titled ‘Lateral runway excursions upon landing: a growing safety concern?’ It stated that an increasing proportion of accidents were runway excursions (including both veer-offs and overruns) and that, unlike other accident types, the rate of runway excursion accidents had not changed significantly in 20 years. It also noted that generally the consequences of an overrun were more severe than a veer-off, but the reported number of veer-offs had increased in recent years. It examined 25 reported veer-offs involving Airbus aircraft and, acknowledging limitations of the data, stated:
Three main environmental factors came out of the analysis:
- Runway state, wet or contaminated
- Turbulences or cross-wind
- Visibility deterioration
Most (19) of the 25 occurrences involved at least two of these environmental factors. Twelve were associated with a deterioration in visibility, 12 involved turbulence or crosswind, and four involved both. All but two of the 12 occurrences that were associated with poor visibility involved a deviation prior to touchdown.
Related occurrences in Australia
Search criteria for related veer-off occurrences
The ATSB reviewed its occurrence database for any veer-off occurrence in Australia from 1997 to 2017 that involved:
an air transport aircraft
a loss of runway centreline alignment prior to and at touchdown
no notable problems with the serviceability of relevant aircraft equipment, runway lighting or the runway surface that significantly contributed to the veer-off
no significant problems with the stability of the approach in terms of height or airspeed.
In addition to the 6 December 2016 occurrence involving VH-VUI, two other relevant occurrences were identified: a 2003 occurrence at Darwin and a 2003 occurrence at Emerald, Queensland.
2003 veer-off at Darwin
On 19 February 2003, a Boeing 737 veered off runway 29 at Darwin while landing at night and in conditions of rain and reduced visibility.[22]
At the approach minima (about 210 ft), the flight crew were still visual and decided to proceed with the landing. About 2 to 3 seconds later, the captain disengaged the autopilot. At that time, the aircraft was established on the localiser and glideslope. About 7 seconds after the autopilot was disengaged (and 13 seconds prior to touchdown), the aircraft started deviating right. At about this time, the approach lighting was no longer in the flight crew's view. The captain considered that there was sufficient visual reference to complete the landing but did not detect the aircraft's increasing lateral displacement from the runway centreline.
The aircraft touched down close to the right edge of the runway about 520 m from the threshold. The right main gear ran off the runway 590 m from the threshold and the left main gear ran off 760 m from the threshold. All wheels had returned to the runway about 1,300 m from the threshold.
The ATSB investigation found that the flight crew may have encountered an abnormal situation where few reliable visual cues were available for determining the aircraft's position relative to the centreline of the runway. The investigation report highlighted the potential for visual illusions during a night approach to runway 29 at Darwin Airport, noting the wider than normal runway, the absence of centreline lighting and the weather conditions.
As a result of the occurrence, the operator provided flight crews with more specific information for Darwin Airport.
2003 veer-off at Emerald
On 1 May 2003, while landing in a storm at night, a DHC-8-200 veered partially off runway 24 at Emerald Airport, Queensland.[23]
The flight crew were conducting a non-precision approach. As the captain flared the aircraft for landing, the crew lost virtually all external visual reference when the aircraft encountered very heavy rain. The runway was 45 m wide and did not have centreline lighting.
The Emerald occurrence was different to the 2003 and 2016 occurrences at Darwin because it involved sudden, near zero visibility at the time of the flare. In contrast, although the two occurrences at Darwin involved a significant loss of visual references, the deviations commenced slightly earlier in the approach and the runway edge lights were still visible.
Other notable occurrences at Darwin Airport
Although not veer-off occurrences, there were two other notable occurrences at Darwin Airport:
A 2002 runway overrun involving a 737 occurred at night in clear weather.[24] The investigation report stated that the ‘operational environment was conducive to visual illusions, such as the black hole effect, during the approach and landing’. The overrun followed an unstable approach and, at the time, the runway had a displaced threshold.
A 2008 hard landing involving a Boeing 717 at night.[25] The investigation report stated ‘the degraded visual information during the landing may have increased the difficulty of judging the aircraft’s rate of closure with the runway and the required flare’. The report also included the following two safety factors (neither of which was classified as contributing to the occurrence):
The aircraft operator's Route Manual did not include all relevant information on the potential for visual illusions during a night approach to runway 29 at Darwin Airport that would have improved the awareness of flight crews.
The lack of runway centreline lighting reduced the available visual cues during the latter stages of the approach and landing to runway 29 at Darwin Airport.
As a result of the occurrence, the operator updated its route manual to provide more specific information for each aerodrome, including Darwin.
Further analysis
In summary, including the 6 December 2016 occurrence involving VH-VUI, there were three veer-off occurrences matching the selected criteria in Australia between 1997 and 2016. All were on runways without centreline lighting, and two were on Darwin’s runway 29.
Darwin runway 11/29 was the only runway in Australia that was 60 m wide and had no centreline lighting. The only other runway in Australia that was 60 m wide was runway 16/34 at Melbourne Airport, which had centreline lighting. All of the other runways in Australia that had centreline lighting were 45 m wide: runways 01/19 at Brisbane, runway 27 at Melbourne, and runways 16L, 16R, 34L and 34R at Sydney.[26]
As previously stated, Darwin runway 29 could host category I ILS approaches. Compared with category I ILS approaches, category II/III ILS approaches permit lower decision heights and landings in reduced visibility. Among other things, category II/III approaches require runway centreline lighting (or touchdown zone lighting in the case of special authorisation category II approaches). At the time of the occurrence, category III ILS approaches were only available at Melbourne Airport and category II ILS approaches only at Brisbane, Melbourne, and Sydney airports.[27]
To evaluate against exposure rates, the ATSB examined traffic, runway, and weather information for the 10 busiest airports in Australia, including Darwin (Table 3). Emerald Airport is also included in the table. As indicated in the table, Darwin experiences the most storm activity and the heaviest rainfall, but hosts only a small proportion of traffic (2 per cent of the top 10 airports).
Table 3: Information for the 10 busiest airports in Australia, and Emerald Airport
Approximate number of lightning strikes per km2 per year[30]
Approximate number of days with >25 mm rainfall per year
≤50 m
>50 m
≤50m
>50m
Busiest airports
Sydney
158,810
4
0
2
0
5 – 10
10 – 15
Melbourne
118,006
3
0
1
2
1 – 5
5 – 10
Brisbane
95,716
2
0
2
0
10 – 15
5 – 10
Perth
47,253
2
0
2
0
1 – 2
5 – 10
Adelaide
39,523
4
0
0
0
0.5 – 2
0 – 2
Cairns
24,654
2
0
0
0
5 – 10
20 – 30
Gold Coast
21,246
2
0
0
0
10 – 15
15 – 20
Canberra
18,591
4
0
0
0
5 – 10
5 – 10
Darwin
13,949
2
2
0
0
15 – 20
20 – 30
Townsville
12,806
4
0
0
0
5 – 10
10 – 15
Other airports
Emerald
4,992
2
0
0
0
5 – 10
5 – 10
In summary, Darwin had the only runway that was 60 m wide without centreline lighting, and it hosted less than 2 per cent of the total traffic of the 10 busiest airports. It is very unlikely that the only two veer-off occurrences that took place at these 10 airports should have occurred on this runway. Although another occurrence took place at Emerald, the extreme loss of visual references during the flare in that occurrence was very likely a more significant factor than the runway width or runway lighting.
Related veer-off occurrences in Canada
During the investigation, the ATSB identified that some veer-offs associated with runway misalignment during final approach had occurred in Canada. It also identified that Canada had a higher proportion of runways that were 60 m wide compared to other countries. Accordingly, the investigation examined the number and characteristics of veer-off occurrences in Canada.
The Transportation Safety Board (TSB) of Canada provided the results of a search of its database for potentially similar occurrences during the period 1997 to 2017. The ATSB reviewed this data and associated investigation reports to identify relevant occurrences, using the same criteria as listed above for occurrences in Australia. Occurrences were only considered if a final investigation report was available. During this process, some additional occurrences from the period 1991 to 1996 were identified.
In total, seven veer-off occurrences were identified that met the relevant criteria. All seven veer-off occurrences in Canada occurred at night on 60 m wide runways with no centreline lighting. In each case, there were some weather-related factors reducing visibility.
One occurrence was somewhat different to the others. It involved a Learjet, with the flight crew hand-flying a category I ILS approach. The crew attempted a missed approach after the aircraft touched down off the runway. The aircraft subsequently impacted terrain in an inverted attitude, and the two flight crew (the only occupants) were fatally injured.
All six of the other Canadian occurrences had similar characteristics to the two at Darwin:
All six involved the flight crew of a high-capacity air transport aircraft conducting a category I ILS approach at night.
Five involved a deviation from the centreline that occurred soon after the autopilot was disconnected just prior to landing (at heights ranging from 65 to 115 ft above the ground). In the other case, the approach was hand-flown.
All resulted in destroyed runway lights and/or signs, and most had some aircraft damage. None resulted in any injuries.
In addition to those seven occurrences, there were some other notable occurrences:
Two other potentially related veer-off occurrences were identified, but because they were not investigated by the TSB the full nature of the events and their circumstances could not be determined. One involved a DC9 at Calgary in 1998 and the other an A320 at Ottawa in 2017. Both occurred at night on 60 m wide runways with no centreline lighting.
A 1997 occurrence at Fredericton involved a Canadair CL600 at night during a category I ILS approach. When the aircraft was about 35 ft above the ground, the captain was aware that they were left of the centreline but was not sure how far down the runway they were. Recognising that they were not in a position to land safely, he ordered the first officer to go around. During the go around, the aircraft stalled and then struck the runway, and subsequently it struck a tree, resulting in nine serious injuries. The accident occurred on a 60 m wide runway with no centreline lighting.
A 2014 veer off occurrence at Montréal involved an Airbus A320 during the day during a category I ILS approach. The runway lights were out of service at the time. Other characteristics of the occurrence were similar to the related occurrences discussed above. It occurred on a 60 m wide runway.
In summary, all seven veer-off occurrences in Canada involving centreline misalignment during final approach occurred on 60 m wide runways without centreline lighting. Some other potentially related occurrences also involved this type of runway, but no potentially related occurrences were identified on other types of runways in Canada.
Canada’s civil air navigation service provider, Nav Canada, provided landing statistics for 115 of the busiest airports in Canada in 2017. Table 4 shows the percentage of landings at runways with and without centreline lighting, and at runways that are wider than 50 m compared with narrower runways. Data is only included for aircraft with a maximum take-off weight of more than 7,000 kg. Although this data was not presented separately for night versus day operations, and it is only for 2017, it was considered to provide a reasonable approximation of the proportion of operations occurring on different types of runways during the relevant period.
Table 4: Aircraft landing statistics in Canada
Width < or = 50 m
Width > 50 m
Total
Centreline lighting
4 %
39 %
43 %
No centreline lighting
26 %
31 %
57 %
Total
30 %
70 %
100 %
As indicated in the table, about 31 per cent of landings occurred at wider runways with no runway centreline lighting. It is statistically very unlikely that seven veer-off occurrences in 20 years with similar characteristics took place on these types of runways without any having occurred on the narrower runways, or on wider runways with centreline lighting.
In its most recent investigation report into a veer-off occurrence, the TSB stated:[31]
…On runways without centreline lighting, as the distance between runway edge lights increases, it becomes more difficult to judge lateral movement solely by assessing the degree of asymmetry between the runway edge lights—especially when the aircraft is close to the ground and the flight crew’s attention is focused directly ahead of them.
The TSB has investigated a number of lateral runway excursions that occurred on runways without centreline lighting. If the distance between runway edge lights is greater than 50 m and runways are not equipped with centreline lighting, there is a risk that visual cues will be insufficient for flight crews to detect lateral drift soon enough to prevent an excursion, while operating aircraft at night during periods of reduced visibility.
Related veer-off occurrences in other countries
The ATSB also searched for potentially related veer-off occurrences in other countries using internet search tools, reviewing the United States National Transportation Safety Board (NTSB) aviation database of accidents and selected incidents and reviewing relevant research reports. The search covered the period 1997 to 2017, and occurrences were only included if they met the same criteria as used for the Australian and Canadian occurrences, and a final investigation report was available. The search was not comprehensive, and it is likely that there were many more occurrences during this period.
Overall, five additional veer-off occurrences involving runway misalignment during final approach were identified. Two occurred in the United States, and one each in Finland, Sweden and the Solomon Islands. The basic details of these additional occurrences are provided in Table 5 (in blue shading).
All five occurrences occurred at night, during instrument approaches in conditions with reduced visibility to runways without centreline lighting. None of the occurrences resulted in serious injuries. Two of the occurrences occurred on 60 m wide runways, and three on 45 m wide runways. One of the three occurrences involving 45 m wide runways occurred during a non-precision approach in very heavy rain (Honiara, 2008), like the Emerald occurrence.
Summary of related occurrences
In summary, 15 related occurrences were identified in Australia, Canada and other countries. Basic details of these occurrences are summarised in Table 5, with the Australian occurrences highlighted in red and Canadian occurrences highlighted in blue.
With regard to all 15 occurrences:
All occurred at night.
All occurred at runways without centreline lighting.
Most (11) occurred at runways that were wider than 50 m.
Most (13) occurrences involved a category I ILS approach. The other two occurrences (Honiara 2008 and Emerald 2003) were during non-precision approaches and involved runways narrower than 50 m.
All occurred in conditions of reduced visibility (in terms of rain, fog and/or snow), with most also involving wet runways (reducing the visible texture of the runway) or snow-covered runways.
Three occurrences were in visibility conditions reported to be below the permissible minimum for an ICAO-standard category I ILS approach and landing (800 m ground visibility or 550 m runway visual range; the same distances are used in Australia). Canada applied different rules.
Most (13) occurrences involved high capacity air transport aircraft (with a capacity exceeding 38 seats). The exceptions were at Emerald in 2003, involving a low capacity air transport aircraft, and the business jet at Stephenville, Canada in 1996.
Other than the DHC-8 turboprop aircraft at Emerald, all involved turbofan (jet) aircraft.
A review of global runway databases indicated that about 30 per cent of runways[32] are wider than 50 m, which is a much lower proportion than the number of relevant occurrences at such runways. In addition, the busiest runways tend to be equipped with centreline lighting. Although statistics regarding the number of movements to different types of runways was not obtained for all of the relevant countries, it is likely that there are significantly fewer landings on runways that are 60 m wide without centreline lighting than others. Subsequently, there appears to be a disproportionately high number of related occurrences at those runways, even in Canada where more runways are 60 m wide.
Table 5: Veer-off occurrences involving runway misalignment during final approach
[1] Reported conditions less than 800 m ground visibility or 550m runway visual range.
Previous ATSB recommendations
In 2004, during the investigation into the 2003 veer-off at Darwin, the ATSB advised Darwin International Airport that it was considering making a recommendation for the installation of runway centreline lighting. On 31 December 2004, Darwin International Airport advised:
A standard runway centerline system would be prohibitively expensive and is not currently a standard for our runway category.
As a result of the investigation into the 2003 veer-off occurrence, the ATSB made a recommendation on 4 March 2005:[33]
The Australian Transport Safety Bureau recommends that the Department of Defence (airport infrastructure owner) and Darwin International Airport Pty Ltd (civilian facilities operator) consider installation of centreline lighting and touchdown zone lighting, consistent with CASA recommended practices on runways wider than 50 m.
No formal response was received at the time, and the recommendation was classified as ‘Closed – Partially accepted’ based on further correspondence with the Department of Defence.
Following the release of the ATSB’s report into the 2008 hard landing at Darwin involving a Boeing 717, published in May 2010), the ATSB sought further response from the Department of Defence. On 7 July 2011, the Department of Defence responded:
Air Force has reviewed the [AO-2008-007] report, and has consulted with Darwin International Airport [DIA] on the issue of runway centreline lighting. Initial cost estimates for installation are approximately $3M, however additional costs may ensue with a potential upgrade to the lighting equipment rooms and repairs due to incompatibility of arrestor hook equipped military aircraft with centreline lighting.
The Air Force position is as follows:
a. Existing approach lighting at Darwin is appropriate for a Cat I [category I instrument landing system] precision approach runway.
b. Installation, upgrade and maintenance costs do not represent value for money.
c. The installation of runway centreline lighting is not imperative and will not be pursued (DIA are in agreement).
d. The option of reverting the runway lighting to 45m width would be costly and viewed as a low priority infrastructure change.
The ATSB reclassified the issue as ‘Closed – Not accepted’.
During the landing on runway 29 at Darwin at night, the aircraft touched down 21 m to the right of the runway centreline while tracking about 3° to the right. Apart from the sudden degradation of visibility, other aspects of the landing (in terms of the aircraft’s configuration, airspeed, distance down the runway and descent rate) were normal. Soon after touching down, the right main gear departed the sealed surface.
The runway excursion (veer-off) was due to the aircraft deviating from the runway centreline during the final stages of the final approach. There were no aircraft serviceability issues. The crosswind was not sudden or strong enough to be significant under most circumstances.
This analysis will firstly discuss the reasons for the aircraft’s deviation from the centreline. It will then discuss a range of other safety factors identified during the investigation.
Visual cues during final approach
After transitioning from autopilot to manual flight control, a flight crew needs to manage the aircraft’s airspeed, flight path (lateral and vertical), and three-dimensional attitude, and the crew must then initiate the flare at the correct height for landing. Misjudging any of these can result in a hard landing, veer-off or overrun. The landing task becomes additionally challenging when the aircraft is constantly moving in gusty, turbulent conditions. In reduced visibility, the pilot has less information to assess the aircraft’s behaviour and respond appropriately.
During a normal landing at night, a flight crew has a range of visual cues to help judge the lateral position of the aircraft:
Approach lighting gives effective cues for the key elements needed for runway alignment, and is required (where practicable) for category I ILS approaches such as to runway 29 at Darwin airport. However, from about 100 ft height to touchdown, approach lighting is no longer visible under the aircraft’s nose. Similarly, runway threshold lighting is also no longer visible.
Runway centreline markings and other surface textual cues on or near the runway can provide some useful information in appropriate ambient lighting. However, such cues may not be visible on a night approach to a wet runway when there is little or no ambient lighting available.
Runway edge lights are visible to the flight crew in most weather conditions when landing (and crews are required to conduct a missed approach if they are not visible). The relative angle and degree of asymmetry of the two rows of lights can provide useful cues in many situations. However, the salience of lights can be reduced to some extent due to environmental factors, such as rain and water on the aircraft’s windscreen.
Runway centreline lighting and touchdown zone lighting can provide very useful visual cues. However, they were not available at Darwin and they are only available at a small proportion of runways, generally those associated with a Category II/III ILS approach.
In summary, the main visual cues the flight crew of VH-VUI had in the last few seconds prior to touchdown (from 100 ft above ground level) were the runway edge lights. It was during this period that the aircraft started and then continued to deviate from the runway centreline.
It appears that the aircraft started drifting right under the influence of an increasing (although light) crosswind, and a small amount of right bank. However, deviations occur during manual control for a number of reasons, and the important aspect in this case is that the deviation was not detected and corrected. The deviation occurred in turbulent conditions, which required continuous corrections to the aircraft’s attitude and flight path, and there were insufficient external visual cues during this high workload period for the flight crew to effectively detect the deviation and make appropriate adjustments. The available evidence did not indicate fatigue, medical issues or distraction affected the flight crew’s performance.
A significant factor reducing the effectiveness of the visual cues in this case was the wider than normal width of the runway (60 m compared to the much more common 45 m), and the corresponding increased distance between the two rows of runway edge lights. As indicated by simple graphical representations (see Appendix A), it is more difficult to detect a deviation when approaching a wider runway compared to a narrower runway. By the time a deviation is identified on a wider runway, the momentum of the lateral movement may be such that the deviation is difficult to correct prior to touchdown.
More importantly, the rate of veer-off occurrences due to misalignment during late final approach is much higher at 60 m wide runways than 45 m wide runways. All of these occurrences have taken place at night in situations where rain or other environmental factors reduced other visual cues.
This problem has been recognised for a long time, with the International Civil Aviation Organization (ICAO) and regulatory authorities recommending the use of centreline lighting on runways wider than 50 m that are used for Category I ILS approaches.
Following a similar occurrence at Darwin in 2003, the ATSB made a specific recommendation that the Department of Defence and Darwin International Airport consider installing runway centreline lighting and touchdown zone lighting on its wide runways. The relevant parties advised that they did not consider any changes cost-effective.
The ATSB understands there is significant expense and logistical difficulties associated with installing centreline lighting. However, without it, there is a realistic prospect of further veer-off or related occurrences at Darwin or any other airport that has a wider runway without centreline lighting.
The 2016 occurrence involving VH-VUI at Darwin resulted in damage to six runway edge lights and minor damage to the aircraft. Most of the other veer-off occurrences due to misalignment during final approach have resulted in a similar level of damage. However, with this type of occurrence, there is the potential for more serious consequences such as undercarriage collapse, veering into other aircraft or vehicles on the ground, or a mishandled go-around with the aircraft near the ground and the engines at low power resulting in a collision with terrain. The ATSB previously found that 2 out of 48 landing veer-off accidents over a 10-year period were fatal, resulting in 93 fatalities (ATSB 2009).
Advisory material regarding hazards at airports
If a hazard such as ineffective visual cues for landing in some situations cannot be effectively mitigated by redesign, then a less desirable though beneficial option is to ensure appropriate advisory information is provided to flight crews.
At the time of the occurrence, the aircraft operator had limited guidance for flight crews approaching Darwin Airport to consider the increased risk arising from the combination of a wide runway and the absence of centreline lighting. This meant that crews were less likely to consider the risk when deciding whether to continue an approach, and potentially less prepared for the potential for undetected deviation away from the centreline on late final approach.
Both flight crew had operated to Darwin before. However, they had not done so recently, with the captain’s last flight there over 5 months before and the first officer 16 months before. As a result, neither crewmember had recent familiarity with the visual cues present on the approach, and would probably have studied any available information on hazards that was provided. Although reviewing such information would have reduced the potential risk during an approach, the extent to which it would have affected the flight crew’s decision-making or performance in this situation was difficult to determine.
The ATSB has previously identified that other operators did not provide advisory information about visual cues on approach to runway 29 at Darwin. The Boeing 737 operator involved in the 2003 veer-off occurrence did not have relevant advisory information at that time (although it introduced such information following the occurrence). Similarly, the Boeing 717 operator involved in a hard landing occurrence at Darwin in 2008 also did not have relevant advisory information for its flight crews.
The guidance that operators provide to flight crews is primarily based on the En Route Supplement Australia (ERSA). However, this document also did not provide advisory information about visual cues on approach to runway 29 at Darwin. Including relevant information in the ERSA would help ensure that all air transport operators (including international operators) conducting flights to Darwin adequately consider the potential problems associated with visual cues at night.
Provision of weather information
At the time of planning the flight, aerodrome forecast (TAF) indicated fine conditions at Darwin for the expected landing time. At 2207 Central Standard Time, with the aircraft about 1 hour from landing, an amended TAF was issued, which indicated deteriorating conditions.
The Brisbane en route controller broadcast the availability of the 2207 amended TAF. However, the flight crew were not made aware of a subsequent amended TAF, issued at 2237, which indicated a further deterioration in conditions (although the conditions were still above the landing minima).
Between the two amended TAFs, there was a handover from one Brisbane en route controller to another. When the incoming controller was queried at the time by the operator’s flight following staff as to whether the crew had received ‘the amended TAF’, the controller replied that they had. However, the Darwin approach controller had not made the Brisbane en route controller aware of the updated TAF as was done with the previous update.
Not advising the flight crew of the second amended TAF is unlikely to have influenced the flight crews’ decision to continue the approach. The wind information was the same as the first amended TAF. In addition, the crew interpreted the first amended TAF as being indicative of ‘thunderstorm material’. Within a few minutes of the second amended TAF being issued, the flight crew could also see thunderstorm activity ahead visually and with the aircraft’s weather radar. Furthermore, they were obtaining observation reports through Darwin tower, which are more relevant than forecasts when near the destination airport.
Provision of wind information
While the aircraft was on descent, the airport’s primary anemometer failed due to a lighting strike. Consequently, the Darwin approach and tower controllers were unable to provide the flight crew with real-time wind information from that anemometer during the approach and landing.
After recognising the problem, the controllers were able to obtain information by telephone from a meteorological observer with access to information from a second (test) anemometer, and through observations of the airport’s windsocks. However, the second anemometer’s integrity was unconfirmed and it could not be read in real time. In addition, the information available from windsocks was subject to interpretation. As a result, the wind information that the controllers could provide to flight crews was degraded.
Decision to continue approach and landing
The approach and landing occurred during a period of deteriorating weather conditions, which were observed by the flight crew directly and on the weather radar display, and was indicated to them by frequent updates about the conditions provided by controllers. The operator’s policies recommended that flight crews not approach within 5 NM of an approaching thunderstorm. However, this was not a strict requirement, and the decision was left to each flight crew’s judgement.
Previous research and safety investigation reports have identified that it is not unusual for flight crews to approach or penetrate thunderstorms when landing. For example, Rhoda and Pawlak (1999) reviewed radar data in the Dallas–Fort Worth airspace in the United States. They identified most (about two thirds) of the encounters with storms resulted in penetrations. The proportion of penetrations was lower as the intensity of the storms increased. However, the proportion of penetrations increased with the storm’s proximity to the airport. It also increased when flight crews were following another aircraft, flying after dark, or if they were behind schedule by more than 15 minutes.
In a recent investigation report associated with a flight crew landing close to the edge of a 60 m wide runway during daytime and in the presence of a storm, the Transportation Safety Board of Canada (TSB) noted that other flight crews had also decided to land in proximity of the storm.[34] The TSB also stated:
The hazards generated by thunderstorms are well known in the aviation industry. Crews who fly near a thunderstorm can expect to encounter the following conditions: erratic wind and gusts, squalls (violent wind blasts), turbulence, extremely violent rain, low visibility, hail, and lightning. Furthermore, there is no correlation between the appearance of a thunderstorm and the intensity of its events…
Since [the operator] relies on the experience of its crews to determine the trajectory of the flight in the presence of thunderstorms in the vicinity of airports, the margin of safety varies from flight to flight, depending on the crew…This occurrence is an excellent example of the sudden and simultaneous appearance of hazards associated with thunderstorms at a critical point during landing. This occurrence highlights the unpredictability of thunderstorms and the necessity to maintain a safe distance during the critical stages of flight.
Research has shown that many aviation accidents involve a ‘plan continuation bias’ or ‘plan continuation error’ associated with situations involving dynamically changing risk and pilots underestimating the risk level. That is, a flight crew decides to continue with the original plan of action despite the presence of cues or information that suggests changing the course of action would be the safer option (Orasanu and others 2001). Other researchers have noted that previous encounters with a situation (such as approaching near a storm) without negative consequences may reinforce such behaviour or enable flight crews to reduce their perception of the association risks (Dismukes and others 2007).
In this case, the flight crew could see lightning ahead and, during the later part of the descent, closely monitored the location of rain cells in the vicinity of the airport using the aircraft’s weather radar.
The flight crew regularly discussed the situation and their planned actions. This including obtaining additional information at times, as well as planning to vary their missed approach path (if required) in order to avoid the worst of the weather. The flight crew arrived at the decision height in conditions better than the minimum requirements for visibility and crosswind.
Soon after the aircraft descended through the decision height, it encountered very heavy rain. After this point the visibility deteriorated, and although it was not possible to reliably determine whether the visibility was below the minimum of 800 m, the aircraft’s logo light could be seen from the tower 1.8 km away. The crew could still see the runway edge lights, although they were very blurred between windscreen wiper passes, and considered that they had sufficient visual cues available for landing. Overall, the flight crew’s interpretation of the information available to them gave no compelling reason to initiate a missed approach, and they did not detect the deviation from centreline until after touchdown.
It was not possible to establish the extent to which the flight crew considered the risk of a loss of visibility before it occurred. Furthermore, the weather reports deteriorated gradually during the descent and approach and each incremental change in risk was probably not fully appreciated by the flight crew.
The crew’s decision to continue the approach after entering heavy rain would usually not result in an adverse outcome. However, the combination of a wider runway and relatively limited visual cues available at Darwin increases the potential for adverse consequences.
As with the flight crews in many previous occurrences, the flight crew may not have fully appreciated the increased risk arising from the limited visual cues presented during an approach to a wider runway without centreline lighting. A flight crew that is informed about the potential risk associated with a sudden reduction in visibility close to landing, particularly at airports with 60 m wide runways and no centreline lighting, should have greater readiness to perceive and respond to it.
Recovery actions after touchdown
When the aircraft touched down the flight crew were aware they had landed to the right of the centreline but did not fully comprehend the extent of the deviation and the rate of drift. The captain applied corrective control inputs but, by the time the situation was apparent, was unable to prevent the right main landing gear departing the sealed surface of the runway.
The amount of corrective control input applied by the captain was influenced by the potential to lose control on the wet runway, in combination with the advice from the first officer who thought that the aircraft was clear of the runway lights.
The captain delayed the application of reverse thrust after landing until the aircraft was established on the runway. This action probably helped prevent further excursion off the runway.
Given the extent of the deviation from the runway centreline at touchdown, and the time required to assess the situation, it was very likely the excursion would have happened regardless of the available traction. Traction was probably reduced to some extent after touchdown, and it may have slightly delayed the subsequent recovery back onto the runway. The ATSB notes that the outer 7.5 m of the runway was not grooved, and did not meet the relevant surface texture or friction requirements. Although not contributing factors to this occurrence, such problems could degrade aircraft control in future situations where an aircraft has significantly deviated from the runway centreline.
Post-landing actions
After the landing the crew were unsure whether the aircraft had left the runway. The flight crew discussed whether they had hit the runway lights. Based on the first officer’s perception of the situation, they thought that they had not.
There was no opportunity for ground crews to examine the aircraft and confirm a potential veer-off until the storm had cleared, but there remained a risk that following aircraft could be affected by debris on the runway, and having fewer runway lights available.
This occurrence indicates that it is important to be conservative after a potential veer-off occurrence. A timely report of the possibility that a veer-off had occurred, even if there was doubt, would have provided the airport operator and air traffic control with a better opportunity to ensure the runway was serviceable for other aircraft.
From the evidence available, the following findings are made with respect to the runway excursion (veer-off) involving Boeing 737-800, registered VH-VUI, which occurred at Darwin Airport on 6 December 2016. 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
After passing the decision height for the approach, the aircraft drifted under the influence of a slight crosswind and landed 21 m to the right of the runway centreline.
Due to heavy rain, darkness and limited visual cues, the flight crew did not detect the aircraft’s deviation from the runway centreline prior to landing.
The absence of centreline lighting and the 60m width of runway 11/29 at Darwin result in very limited visual cues for maintaining runway alignment during night landings in reduced visibility. [Safety issue]
Other factors that increased risk
Category I runways that are wider than 50 m and without centreline lighting are over-represented in veer-off occurrences involving transport category aircraft landing in low visibility conditions. The installation of centreline lighting on wider category I runways is recommended but not mandated by the International Civil Aviation Organization Annex 14. [Safety issue]
Virgin Australia did not have formal guidance for flight crews regarding the limited visual cues for maintaining alignment to runway 11/29 at Darwin during night landings in reduced visibility.[Safety issue]
The En Route Supplement Australia (ERSA) did not have formal guidance for flight crews regarding the limited visual cues for maintaining alignment to runway 11/29 at Darwin during night landings in reduced visibility.[Safety issue]
While the aircraft was on descent, the airport’s primary anemometer failed due to a lightning strike. Although there were windsocks and a second, test anemometer at the airport, the reliability and timeliness of the wind information that the controllers could provide to flight crews was temporarily degraded.
Although air traffic services broadcast details of an amended aerodrome forecast (TAF) for Darwin issued at 2207, the flight crew were not made aware of a subsequent amended TAF issued at 2237. However, the flight crew were provided with multiple updates of current weather conditions prior to landing at 2302.
Because they were unsure what had occurred, the flight crew did not report the possibility of a runway excursion to air traffic control until 29 minutes after it occurred. This delayed the response by the airport operator and air traffic control to ensure that the runway was safe for subsequent operations.
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 industry, the ATSB may issue safety recommendations or safety advisory notices as part of the final report.
Standards for installation of runway centreline lighting on wider runways
Safety issue owner: International Civil Aviation Organization
Operation affected: Aviation: Airports
Who it affects: Operators using runways wider than 50 m without centreline lighting
Safety issue description:
Category I runways that are wider than 50 m and without centreline lighting are over-represented in veer-off occurrences involving transport category aircraft landing in low visibility conditions. The installation of centreline lighting on wider category I runways is recommended but not mandated by the International Civil Aviation Organization Annex 14.
Status of the safety issue
Issue status: Safety action pending
ATSB safety recommendation to the International Civil Aviation Organization
The Australian Transport Safety Bureau recommends that the International Civil Aviation Organization review the effectiveness of Annex 14, recommendation 5.3.12.2 (for the installation of runway centreline lighting on Category I runways that are wider than 50 m), given that Category I runways that are wider than 50 m and without centreline lighting are over-represented in veer-off occurrences involving transport category aircraft landing in low visibility conditions.
Limited visual cues for approach at Darwin runway 11/29
Who it affects: Pilots operating into Darwin airport
Safety issue description:
The absence of centreline lighting and the 60-m width of runway 11/29 at Darwin result in very limited visual cues for maintaining runway alignment during night landings in reduced visibility.
Status of the safety issue
Issue status: Safety action pending
Response by Darwin International Airport and Defence Flight Safety Bureau
On 18 September 2017, Darwin International Airport (DIA) advised:
The Department of Defence position in 2011 was as follows and DIA is not aware of any change to that:
a. Existing approach lighting at Darwin is appropriate for a Cat 1 precision approach runway.
b. Installation, upgrade and maintenance costs do not represent value for money.
c. The installation of runway centreline lighting is not imperative and will not be pursued (DIA are in agreement).
d. The option of reverting the runway lighting to 45m width would be costly and viewed as a low priority infrastructure change.
In previous correspondence Defence did indicate a concern for potential damage to tail hook equipped aircraft.
Under the terms of the Joint User Agreement, Defence is responsible for airfield pavements and lighting and is considering resurfacing of Runway 11/29 in about 2022. Replacement of runway lighting may occur as part of that project. Provision of centreline lighting could be considered at that time.
On 25 January 2019, DIA advised:
Darwin Airport is a Joint User aerodrome with the Department of Defence. As previously advised, and under the terms of the joint User Deed, the Department of Defence is responsible for forward planning of pavement overlays and upgrading or replacement of airfield lighting.
DIA will continue to consult with Defence on whether lighting upgrades, including centreline lighting could be considered for future works. A planning meeting is proposed for March 2019.
On 8 February 2019, the Defence Flight Safety Bureau advised:
The lack of centre line lighting at Darwin has been an ongoing issue for some time. Under the Joint User Deed, Defence and DIA are required to work together on any infrastructure matters. To date, Defence and DIA have been in agreement that runway centreline lighting is not supported for reasons that include upfront capital cost, ongoing maintenance issues and consideration of the potential effects of runway centreline lighting on aircraft taking the arrestor cables.
On 26 March 2019, DIA advised:
Northern Territory Airports (NTAP) and Defence met on Wednesday 13th March in Canberra to discuss maintenance, projects and operational matters associated with the Joint User Area at Darwin International Airport / RAAF [Royal Australian Air Force] Darwin. A topic of tabled discussion was Airfield Ground Lighting (including a session on Runway Centreline Lighting) for RWY 11/29. Both NTAP and Defence agreed that the use of Hook Arrestor Cable System on RWY 11/29 prevented the safe introduction of CASA MOS139 compliant Runway Centreline Lighting since the risk of FOD [foreign object debris] caused via damage to Runway Centreline Lights by the Hook Arrestor Cable was of significant concern. It was however tabled that both Runway Centreline Lighting and reducing the runway width from 60m to 45m would be re-considered in future major project design briefs.
ATSB comment
After a similar occurrence in 2003, the ATSB issued a recommendation that the Department of Defence (airport infrastructure owner) and Darwin International Airport (civilian facilities operator) consider the installation of centreline lighting and touchdown zone lighting on runway 29. The ATSB later reclassified the issue as ‘Closed – Not accepted’.
In response to safety issue AO-2016-166-SI-04, Darwin International Airport has undertaken safety action enhancing the en route supplement guidance to flight crews, which will help flight crews conducting operations into Darwin to more effectively plan for and respond to a partial loss of visual cues during approach. However, this action is not a completely effective way of addressing the risk: crew preparedness can reduce the likelihood of, but not prevent, an undetected loss of adequate visual cues.
The ATSB acknowledges the practical limitations of installing and maintaining runway centreline lighting, and notes that DIA have also stated that the feasibility will be reconsidered in future major project design briefs. The ATSB continues to encourage additional safety action by DIA and Defence, and has released the following safety recommendation.
ATSB safety recommendation to Darwin International Airport
The Australian Transport Safety Bureau recommends that Darwin International Airport address the risk of very limited visual cues for maintaining runway alignment during night landings in reduced visibility that arise from the combination of the absence of centreline lighting and the 60-m width of runway 11/29 at Darwin.
Who it affects: Virgin Australia Airlines flight crews operating into Darwin airport
Safety issue description:
Virgin Australia did not have formal guidance for flight crews regarding the limited visual cues for maintaining alignment to runway 11/29 at Darwin during night landings in reduced visibility.
Status of the safety issue
Issue status: Adequately addressed
Justification: The operator’s action, in conjunction with other safety actions, should provide crews with adequate guidance to enable them to assess risk and prepare for approaches in low visibility conditions at Darwin Airport.
Safety action taken: On 20 January 2017, the operator introduced additional guidance to flight crews for approach to Darwin airport, including notes about runway surface, slope, width, lighting, and ambient light.
Who it affects: Pilots operating into Darwin airport
Safety issue description:
The En Route Supplement Australia (ERSA) did not have formal guidance for flight crews regarding the limited visual cues for maintaining alignment to runway 11/29 at Darwin during night landings in reduced visibility.
Status of the safety issue
Issue status: Adequately addressed
Justification: The additional information provided in the ERSA should improve the risk awareness and decision-making of flight crews during low visibility approaches to Darwin airport.
Safety action taken: On 28 January 2019, Darwin International Airport initiated amendments to the ERSA entry for Darwin Airport. These amendments were introduced into the 23 May 2019 issue of the ERSA, and stated:
Under Additional information: ‘During low visibility conditions pilots of ACFT landing RWY 29 HN may experience loss of visual references due RWY WID 60 with no CL or TDZ LGT.’
Under Aerodrome and approach lighting: ‘RWY 11/29 CL and TDZ LGT not provided.’
Additional 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.
Virgin Australia Airlines
On 5 May 2017, Virgin Australia advised ATSB of the following additional safety actions:
initiated specific training to pilots for loss of visibility in heavy rain
investigated enhancements to simulator modelling of degraded visibility at low level
reviewed risk profiles for each airport including Darwin
commenced a program to investigate the potential to install hydrophobic windshield coatings on its 737 fleet
initiated a review of callouts for loss of visibility
reviewed the use of autopilot in poor weather.
Darwin International Airport
On 25 September 2018, Darwin International Airport (DIA) initiated the following amendment to the ERSA entry under Physical characteristics: ‘Central 45M grooved SFC of 7.5M outer ungrooved sections BLW MNM friction LVL when wet. 91M concrete ends RWY 11 and RWY 29 ungrooved.’
DIA also advised that the runway is due to be resurfaced in about 2022, and the airport and Department of Defence will be considering having the entire width of the runway grooved at that time.
Royal Australian Air Force Darwin
On 8 February 2019, the Defence Flight Safety Bureau advised that Royal Australian Air Force Darwin ‘will continue to investigate serviceability of MET [meteorological] instruments.’
Sources and submissions
Sources of information
The sources of information during the investigation included the:
aircraft’s flight data and cockpit voice recordings
air traffic control recorded audio
Bureau of Meteorology
Department of Defence
Airservices Australia
Bureau of Infrastructure, Transport and Regional Economics
Boeing
Virgin Australia Airlines
flight crew
Transportation Safety Board (Canada).
References
Airbus S.A.S. (2015). Lateral runway excursions upon landing: a growing safety concern?. In Safety First #20.
Australian Transport Safety Bureau (2009). Runway excursions. Part 1: a worldwide review of commercial jet aircraft runway excursion. ATSB transport safety report No. AR-2008-018(1).
Flight Safety Foundation (2009). Reducing the risk of runway excursions.
International Civil Aviation Organization (2004). Aerodrome Design Manual. Part 4: Visual Aids. Document 9157, 4th ed.
Orasanu J, Martin L & Davison J (2001). Cognitive and contextual factors in aviation accidents, in E Salas and G Klein (Eds.) Linking expertise and naturalistic decision making, Lawrence Erlbaum Mahwah NJ, pp. 209–226.
Rhoda, DA & Pawlak, ML (1999). An assessment of thunderstorm penetrations and deviations by commercial aircraft in the terminal area. Massachusetts Institute of Technology, Lincoln Laboratory, Project Report NASA/A-2.
Submissions
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 the:
flight crew
Virgin Australia Airlines
Airservices Australia
Bureau of Meteorology (BoM)
Darwin International Airport
Defence Flight Safety Bureau (DFSB)
Civil Aviation Safety Authority (CASA)
International Civil Aviation Organization (ICAO).
Submissions were received from the:
captain
Virgin Australia Airlines
Airservices Australia
BoM
Darwin International Airport
DFSB
CASA.
The submissions were reviewed and, where considered appropriate, the text of the report was amended accordingly.
Appendices
Appendix A – Simulation of visual cues provided by runway lights
The ATSB examined the relative effectiveness of the visual cues provided by runway edge lights at Darwin during the 6 December 2016 occurrence flight compared with other situations.
This examination involved the use of simple simulations based on a model with the following characteristics:
Static images were developed with white dots representing the position of runway lights on a black background.
The arrangement of the dots in each image was based on the relative location of each light from an observer in a fixed position corresponding to an aircraft’s flight path on final approach. Some fixed positions used the approximate lateral position of the aircraft during the occurrence flight over the threshold (3.4 m right of centreline) and when the flare was initiated (11.0 m right of centreline). The aircraft height was adjusted
The model assumed the observer was in the captain’s seat on the aircraft, 1 m to the left of the longitudinal axis of the aircraft and accounted for the approximate eye height above the aircraft’s nominal position. The model used a level runway.
The size of the dots varied in proportion to distance away from the observer’s position.
Visual cues from the runway texture, sky or surrounding areas were not modelled. Factors such as precipitation and other effects on visibility, windscreen effects and other influences on the brightness of the lights were not modelled. The simulations also did not account for the effects of aircraft movement and associated visual cues such as optic flow.
Figure A1 illustrates the pattern of runway edge lights visible to a pilot on approach to a 60 m wide runway. The top image shows the pattern at 60 ft, with the aircraft about 3.4 m right of centreline, and the bottom image shows the pattern at 24 ft, with the aircraft about 11 m right of centreline. The elapsed time between each view in a normal landing would be about 4 seconds. The deviation from the centreline in the top image is almost undetectable, and in the bottom image it is inconspicuous. In a high workload environment, with degraded visibility and from a constantly moving aircraft, the deviation from centreline may not be detected until it is too late to correct.
Figure A2 shows the same two situations as Figure A1, but with centreline lighting added. The aircraft’s slight deviation from centreline at 60 ft (top image) is more apparent than without the centreline (top image of Figure A1), and the deviation at 24 ft (bottom image) is easily discernible.
Figure A3 shows the potential influence of aircraft bank when only runway edge lights are visible. The top image shows the pattern of runway lights when the aircraft is on centreline at 24 ft, and the bottom image shows the pattern when the aircraft is at the same height but 11 m right of centreline with a 6° right bank. The two images look very similar. Therefore, when an aircraft is off centreline, a small bank in the direction of the nearest row of edge lights may make the aircraft appear closer to the centreline than it is.
Figure A4 shows the same two situations as Figure A3, with centreline lighting added. The deviation from the centreline in the bottom image is obvious.
Figure A5 compares a 60 m wide runway without centreline lighting (top) with a 45 m wide runway without centreline lighting (bottom). In both cases, the aircraft is 24 ft above the ground, 11.0 m right of centreline. The relative asymmetry of the two rows of lights is much easier to detect for the 45 m runway than the 60 m wide runway.
Figure A1: Simulated misaligned approach without centreline lighting
Source: ATSB
Figure A2: Simulated misaligned approach with centreline lighting
Source: ATSB
Figure A3: Simulated approaches without centreline lighting showing on centreline with wings level (top) compared to a misaligned approach with 6° right roll (bottom)
Source: ATSB
Figure A4: Simulated approaches with centreline lighting showing on centreline with wings level (top) compared to a misaligned approach with 6° right bank (bottom)
Source: ATSB
Figure A5: Simulated approaches to runways of different widths, without centreline lighting
Source: ATSB
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 26 November 2016, at about 0908 Eastern Standard Time (EST), a Bombardier DHC-8-402 aircraft, registered VH-QOV (QOV), operating scheduled passenger flight QF2320 from Brisbane, commenced descent to Bundaberg Airport, Queensland (Qld). At about the same time, a Eurocopter MBB-BK 117 helicopter, registered VH-EHQ (EHQ) was being prepared to depart Bundaberg. The crew of EHQ had been tasked to conduct a visual flight rules (VFR) flight to search for potential wreckage from a trawler missing off the Qld coast.
Bundaberg is a non-controlled airport with a common traffic advisory frequency (CTAF). A CTAF is a designated frequency on which pilots make positional broadcasts when operating in the vicinity of a non-controlled aerodrome. Bundaberg is also equipped with an aerodrome frequency response unit (AFRU) with a pilot activated light (PAL) option. When a pilot transmits on the correct frequency, the AFRU will provide an automatic response, either ‘Bundaberg CTAF’ (if the frequency has not been used in the previous five minutes) or a beep-back. At night, or at other times of low natural light levels, transmitting three one second pulses, one second apart, on the frequency will activate the runway lighting and the transmission will change to the aerodrome name and CTAF with either ‘runway lights on’ or ‘no runway lights’. At other times, this action will activate the precision approach path indicator (PAPI).
At 0912, three one second pulses were broadcast on the Bundaberg CTAF. This resulted in the AFRU correctly responding automatically, ‘Bundaberg Aerodrome no runway lighting’. Two seconds later a single one second pulse was also broadcast on the CTAF. The next recorded CTAF broadcasts were those made by the flight crew of QOV while on approach to Bundaberg. Broadcasts were made at 27 NM, 10 NM and 5 NM and on each occasion the flight crew received the AFRU beep-back. No responses from other aircraft were heard.
While QOV was on final approach to Bundaberg, EHQ taxied for departure from a position to the east of runway 32. The helicopter taxied a short distance, took off and once airborne commenced a left turn tracking initially towards Hervey Bay.
During EHQ’s departure, the flight crew of QOV received a traffic advisory (TA)[1] from their aircraft’s traffic alert and collision avoidance system (TCAS).[2] On receipt of the TA, the flight crew of QOV attempted to sight the traffic causing the alert. After a few seconds, they identified a helicopter, later determined to be EHQ, in their 2 o’clock[3] position around 1.5 NM, and around 1,000 ft below their aircraft. The helicopter was clear of their projected flight path and accordingly the flight crew continued the approach, landing without further incident.
After landing, the flight crew of QOV made two broadcasts on the CTAF to identify the helicopter. These were unsuccessful and they requested, on area frequency, if air traffic control knew the identity of the helicopter. The pilot of EHQ heard this exchange and subsequently identified themselves also advising they had not heard the earlier broadcasts made by the flight crew of QOV.
Pilot comment VH-EHQ
The pilot of EHQ provided the following comments:
The flight was routine, preparations for the flight were not rushed with normal pre-departure checks conducted. They recalled completing normal communication checks including ensuring all frequencies were set correctly and at appropriate volumes. They also recalled hearing an aircraft broadcast on the air traffic control area frequency, and a response from the AFRU when the PAPI was activated. They did not hear any other broadcasts made by the flight crew of QOV.
Normally, when departing from a location similar to the one they did on the day of the incident, the pilot advised they would make a taxi call and a call departing on the CTAF. They recalled making these calls but could not recall if an AFRU response was received.
During the left turn after departure, the crew of EHQ sighted QOV on final approach, clear of their projected flight path.
After departure, they heard the flight crew of QOV on area frequency attempting to determine the identity of the helicopter. They identified themselves and subsequently checked their communications set up, with nothing abnormal found.
Captain’s comment VH-QOV
The Captain of QOV provided the following comments:
They had made all of the necessary CTAF broadcasts, receiving the AFRU response, and did not receive any broadcasts made by EHQ.
They were surprised upon receipt of the TA, but had quickly visually identified the traffic and confirmed it was not on a conflicting flight path.
Safety Analysis
The ATSB reviewed all available recordings from air traffic control and the Bundaberg CTAF. All broadcasts made by the flight crew of QOV and the AFRU responses were recorded. There were no identifiable recordings of broadcasts made by the pilot of EHQ. The ATSB was not able to determine why the broadcasts reportedly made by the pilot of EHQ were not transmitted on the CTAF or why the crew were not able to hear the broadcasts made by the flight crew of QOV. It is probable that the pilot did not correctly configure and operate the helicopter’s communications system.
Findings
These findings should not be read as apportioning blame or liability to any particular organisation or individual.
It is probable the pilot of EHQ did not correctly configure and operate the helicopter’s communications system for CTAF operations while departing Bundaberg airport and they did not detect the error.
Safety action
As a result of this occurrence, the pilot of EHQ has advised they now transmit on the CTAF and activate the lighting to confirm they have the correct radio frequency and volumes selected.
Safety message
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 such concern is Safety around non-controlled aerodromes, which highlights that it is difficult for pilots to detect another aircraft through visual observation alone. The ATSB has identified that insufficient communication between pilots operating in the same area is the most common cause of safety incidents near non-controlled aerodromes.
This incident highlights the fundamental importance of effective communication, particularly during operations at a non-controlled aerodrome. The Civil Aviation Safety Authority (CASA) has produced several publications and resources that provide important safety advice related to operations in the vicinity of non-controlled aerodromes. Relevant guidance and explanatory material provided by CASA includes the following:
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 November 2016, at about 1656 Coordinated Universal Time (UTC),[1] a China Eastern Airlines Airbus A330-243, registered B-5821, operating flight MU-777, departed Kunming, China, for Sydney, New South Wales. On board were 14 crew and 213 passengers.
As the aircraft approached Sydney, the flight crew commenced descent from flight level (FL) 370.[2] The flight crew advised the cabin crew of the descent and illuminated the seatbelt signs. The cabin crew manager announced to the passengers that the aircraft was on descent to Sydney and that as the seatbelt sign had been illuminated they needed to fasten their seatbelts. The cabin crew proceeded to check that passengers had their seatbelts fastened, starting from the front rows and moving towards the back of the cabin.
During descent, the flight crew diverted 5 NM from the flight route due to thunderstorms. Once clear of weather, they received instructions to descend via waypoint[3] BOREE.
At 0248 UTC at FL 230, about ten minutes after the seatbelt sign had been illuminated, the aircraft experienced a severe turbulence event which lasted about 30 seconds. The flight crew commenced the turbulence checklist as per the quick reference handbook (QRH), starting with ‘ignition on’, but as the turbulence had stopped, the rest of checklist was not completed. They checked the flight instruments and engine indications, which were normal, so the flight was continued to Sydney.
Prior to the event, the cabin crew manager was at the back of the cabin checking seatbelts and observed four passengers without a seatbelt, one of whom was standing and reaching for their baggage. During the turbulence event, the cabin crew manager struck their back on a seat armrest. A cabin crewmember in front of the cabin crew manager fell to the ground. Two of the passengers without seatbelts struck their head on the ceiling. After the event, all cabin crewmembers returned to their seats.
After landing, at around 0314 UTC, a cabin crewmember informed the flight crew that there were eleven people who were injured, including three cabin crew. The aircraft sustained minor damage to the interior cabin above row 42, 64, 65, and 68 (Figure 1).
Figure 1: Damage to cabin (row 42, and 68 passenger service unit)
Source: Operator (annotated by the ATSB)
Captain’s comments
The captain provided the following comments:
On approach to Sydney, the crew did not receive any reports regarding turbulence. They did observe other aircraft divert to avoid the thunderstorms.
Once they completed the diversion around the thunderstorms, there was no further weather on the radar.
During the descent, there was some cloud scattered, but no dangerous weather, because they had diverted from the thunderstorms 5–8 minutes earlier.
The turbulence they experienced was different to any turbulence they experienced before, as it was very short, but very strong.
As the turbulence event was very short, they did not report it to ATC.
During the turbulence, there was little change in airspeed or rate of descent.
The flight crew did not realise that there were any issues within the cabin until after landing. Normally, they would be notified by the cabin crew if there were injuries.
The flight crew did not make any announcement to passengers, nor cabin crew about the turbulence, as they did not have any warning.
Cabin crew manager comments
The cabin crew manager provided the following comments:
The seatbelt sign had been switched on about 10 minutes before the turbulence.
The cabin crew were preparing the aircraft for landing, and ensuring that passengers had their seatbelts on, when the turbulence event occurred.
The cabin crew did not notify the captain until after landing as the cabin crew manager was injured and they were aware the flight crew were preparing for landing.
The cabin crew had to keep encouraging passengers to fasten their seatbelts during the flight.
Flight data
The aircraft manufacturer provided the ATSB with a report of the data extracted from the digital flight data recorder (DFDR). The data shows that when the aircraft encountered the turbulence, the vertical G[4] loadings varied between -0.20 G and 1.8 G and the lateral G loadings varied between -0.07 G and 0.12 G (Figure 2). The calculated longitudinal wind varied between around 15 kt tailwind and 5 kt headwind and the lateral wind varied between 20 kt right and 5 kt left. The vertical wind reached a maximum of about 3,100 feet per minute updraft (Figure 3). During the turbulence, the autopilot stayed engaged and the load factors experienced during the turbulence did not exceed the limits of the aircraft.
The rapid changes to wind speed and direction confirm the aircraft encountered turbulence conditions.
Figure 2: G Loadings during turbulence
Source: Airbus
Figure 3: Wind variation during turbulence
Source: Airbus
Bureau of Meteorology report
The Bureau of Meteorology (BoM) provided the ATSB with a report detailing the weather at the time of the incident, including conditions, the weather forecast, warnings, and satellite and radar imagery.
The report showed that there were light winds between 20 to 30 kt from FL180 to FL450. There was no significant weather at the time of the turbulence.
It is likely that the turbulence encountered was the result of developing thunderstorms in the area.
Clear air turbulence
Clear air turbulence (CAT) is defined as sudden severe turbulence occurring in cloudless regions that causes violent buffeting of aircraft.
CAT can be serious, because it is not shown on weather radar, meaning it is difficult for pilots, air traffic controllers, and weather forecasters to detect. It can also occur when no clouds are visible. It is common at high altitudes, especially in the vicinity of jetstreams.
Previous occurrences
A search of the ATSB database found the following occurrences where aircraft encountered clear air turbulence resulting in injuries on board:
On 27 October 2000, a Boeing 747 encountered clear air turbulence en route from Sydney to Osaka, Japan (ATSB investigation 200005031). Although the weather forecast indicated thunderstorms within 110 NM of the flight route there was no turbulence forecast. When the CAT stuck, the seatbelt sign was not illuminated, and people were moving about the cabin. Two passengers sustained broken ankles.
On 10 May 2013, a Bombardier DHC-8 encountered clear air turbulence about 49 NM north of Townsville, Queensland (ATSB investigation AO-2013-084). The turbulence lasted about 10 seconds. The crew did not observe any cloud and the weather radar did not show any significant weather for the entire flight. Two cabin crew members who were standing at the time sustained head injuries, one of whom was knocked unconscious. Two flight crew sustained minor injuries when objects were thrown around the flight deck.
Safety analysis
The aircraft encountered unforecast CAT about ten minutes after the seatbelt sign had been illuminated for the descent into Sydney. The cabin crew were preparing the cabin for landing. A number of passengers and members of the cabin crew, towards the back of the aircraft, who were not wearing seatbelts, were injured during the CAT event. They sustained head, neck, hand, back, and abdominal injuries.
Finding
This finding should not be read as apportioning blame or liability to any particular organisation or individual.
The aircraft encountered CAT. The cabin crew and passengers who were injured during the turbulence did not have seatbelts fastened, despite the seatbelt sign being switched on.
Safety message
A clear air turbulence encounter can be a surprising experience for both crew and passengers. A safety bulletin published by the ATSB Staying safe against in-flight turbulence, noted that almost all turbulence injuries involved people who are not properly seated and do not have their seatbelt fastened. This incident is a timely reminder of the importance of having the seatbelt fasted when the seatbelt sign is switched on and to pay attention to instructions given by the cabin crew, so that injuries during a turbulence encounter can be minimised.
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
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