On 19 May 2013, the pilot of a Pietenpol Air Camper commenced pre-flight checks in a paddock behind his home in St Leonards, about 9 km north of Launceston Airport, Tasmania. The pilot was taking a passenger on a scenic flight around Launceston.
The pilot had operated the aircraft from the paddock in the past, but not for a few years. Prior to landing in the paddock, a week earlier, the pilot had surveyed the area by car.
The aircraft was operating normally and became airborne at about 35 knots indicated airspeed. The pilot held the aircraft low, aiming to clear a fence at the end of the paddock. Nearing the fence, the pilot heard a loud noise, and the nose of the aircraft jolted to the right.
The airspeed quickly decreased, as the pilot attempted to hold the wings level. After initially climbing to about 10 ft, the aircraft impacted the ground, breaking the landing gear. The aircraft skidded on its nose and then pitched over onto its back, breaking the propeller.
Both the pilot and the front seat passenger exited the aircraft without injury. On surveying the accident site, the pilot realised the aircraft’s landing gear had caught the top wire of an electric fence he had not been aware of, located a short distance before the paddock’s main fence.
When not operating from a designated landing area, pilots should ensure the area is suitable. A thorough survey of the area to be used for take-off and landing should be completed prior to use.
On 10 May 2013, at about 2000 Eastern Standard Time, a Sunstate Airlines Bombardier DHC‑8‑402 aircraft, registered VH‑QOD (QOD), departed Townsville on a scheduled passenger flight to Cairns, Queensland.
About 20 minutes into the flight, the aircraft was in the cruise at FL 180 and flying in clear air when the aircraft encountered light turbulence. The captain immediately switched on the seat belt sign. A second later, the aircraft encountered abrupt severe turbulence.
The autopilot disconnected and the captain, as pilot flying, assumed manual control of the aircraft. The flight crew reduced the speed of the aircraft to below the turbulence penetration speed. The turbulence event lasted about 10 seconds, during which time the aircraft climbed about 400 ft above the cruising altitude. The flight crew then re-engaged the autopilot and returned the aircraft to the assigned level.
The weather radar did not show any significant weather for the entire flight. Both members of the cabin crew were standing when the aircraft encountered the turbulence and impacted the roof before falling to the floor. Both sustained head injuries and one was knocked unconscious.
The aircraft landed in Cairns about 20 minutes later, without further incident and the cabin crew were transferred to hospital.
In this event, all passengers were seated with their seat belts fastened, even though the seat belt sign had been switched off earlier. The fact that none of the passengers were injured highlights the benefits of keeping your seatbelt fastened during the flight.
Cabin crew are at greater risk of injury during turbulence encounters as they are moving around the cabin and not seated with a seat belt fastened.
On 2 May 2013, a Mooney M20 aircraft, registered VH‑FRO (FRO) was inbound to Dubbo, New South Wales. The pilot was conducting a private flight and was the only person on board. The pilot reported that he broadcast on the Dubbo common traffic advisory frequency (CTAF) indicating that he was on descent and would join base for runway 05.
At about 1217 Eastern Standard Time, the pilot of a Piper PA‑31 aircraft, registered VH‑HJE (HJE) was preparing to depart Dubbo. He broadcast on the Dubbo CTAF his intention to conduct a flight under instrument flight rules from Dubbo to Lighting Ridge. The pilot and a flight nurse were on board. The pilot taxied via taxiway A, to the holding point for runway 05. At the holding point, the pilot conducted his engine run ups and pre-flight checks.
The pilot of FRO reported that he heard the pilot of HJE’s broadcasts and when he broadcast that he was on final for runway 05, he saw HJE stationary at the holding point.
At about 1220, the pilot of HJE had completed the engine run ups and broadcast his intention to enter and back track to runway 05. Before moving, the pilot reported that he looked down the flight path of runways 05 and 23 and did not see any aircraft. He stated that he had not heard any broadcasts from FRO.
On short final, about 200 feet above the runway, the pilot of FRO heard the broadcast from HJE and saw HJE move. At the same time, the pilot of HJE spotted an aircraft, which was previously obscured by the aircraft’s window frame, on short final for runway 05 and brought the aircraft to a stop. The pilot of FRO applied full power and commenced a go around.
This incident highlights the importance of not solely relying on monitoring the radio to achieve traffic awareness, especially around non-towered aerodromes.
On 3 May 2013, the pilot of a Cessna 182 aircraft, registered VH‑EFY (EFY), was conducting parachute operations overhead Nagambie (ALA). The pilot of a Piper PA‑28 aircraft, registered VH‑FZW (FZW), was conducting a private ferry flight from Mangalore to Bendigo and planned to track from Mangalore to the Nagambie Township and then to Bendigo, to avoid the Restricted Area, R351, and Danger Area, D360.
After completing the parachute drop, the pilot of EFY conducted a circling descent, to the west of Nagambie ALA. He joined the base leg of the circuit for runway 02, at about 4,500 ft, and made a broadcast on the CTAF.
When about 6 NM to the west of the Nagambie Township, maintaining 2,500 ft, the pilot of FZW reported observing an aircraft (EFY) above, on descent, tracking from left to right. The pilot took avoiding action.
The pilot of EFY reported that, as he entered the Danger Area, descending through 2,000 ft, he sighted an aircraft (FZW) in his 12 o’clock position taking avoiding action. The pilot banked the aircraft heavily to avoid FZW and estimated the aircraft came within 50 ft of each other.
On 8 May 2013, the pilot of a Bell 206 helicopter, registered VH‑CHA (CHA), was conducting a private flight from Mangalore to Echuca, Victoria, tracking via the Nagambie Township to avoid the Restricted Areas R351, maintaining 1,000 ft.
After passing in the vicinity of the Nagambie Lakes area, the pilot received a call on the CTAF from the drop zone safety officer on the ground at Nagambie ALA advising that he had just flown over a parachuting landing area. At that time, five parachutists had just landed and six were still airborne.
It is crucial that pilots are aware of the potential hazards that exist on their planned flight routes. When operating near, or within a Danger Area, they should be mindful of the activity within that area and take any appropriate precautions.
On 7 April 2013 southbound freight train 5BM7 was travelling at near track speed (115 km/h) on the main line of the Culcairn North passing loop in New South Wales. On rounding a sweeping right-hand curve the driver saw the headlight of an opposing train and also saw that the signal (CN03) ahead was at stop. He immediately made an emergency brake application to stop the train just before signal CN03 thereby averting a collision with the opposing train which was entering the southern end of the passing loop.
There were no injuries or damage as a result of this occurrence.
What the ATSB found
The ATSB investigation of available technical evidence, showed that the signalling system was operating correctly at the time of the incident and therefore the signal (DIS-CN03) preceding the signal at stop (CN03) should have been displaying a caution aspect (yellow). However, the crew of train 5BM7 had perceived signal DIS-CN03 at clear (green) and were therefore not expecting signal CN03 to be at stop (red).
As the train was not fitted with forward facing video equipment the ATSB was unable to substantiate the observations of the train crew with respect to the aspect of signal DIS-CN03.
What's been done as a result
The train operator, Aurizon, has advised that it has forward facing cameras on about 8.5 per cent of its locomotive fleet and that it is likely that this type of technology will be fitted to all locomotives purchased in the future.
The Rail Industry Safety and Standards Board (RISSB) has advised that it will encourage its membership and the wider rail industry to adopt the use of independent data validation systems, such as forward facing video on trains, to assist with coming to a better understanding of rail occurrence events, such as signal irregularities.
Safety message
The Australian Transport Safety Bureau encourages rail operators to consider the use of independent data validation systems, such as forward facing video on trains, to provide a source of information to assist in coming to an understanding of rail occurrence events, such as signal irregularities.
On 31 March 2013, a Cessna Aircraft Company 441 aircraft, registered VH-XBC, arrived at Coonawarra Airport, SA, following a charter flight from Adelaide, SA. The pilot reported that the initial flare and touchdown was normal, however during the landing roll, he heard a distinct ‘pop’ or ‘bang’ sound, after which the aircraft began veering to the left. Initially the pilot was able to maintain directional control and keep the aircraft on the runway, however as it slowed, it began pivoting around the left landing gear and came to rest to the left of the paved runway surface. There were no injuries to passengers or crew.
What the ATSB found
The runway excursion resulted directly from the failure of the left main landing gear trunnion, which allowed the left main wheel to displace upward and contact the wing underside – producing an asymmetric and uncontrolled braking effect. Both the ATSB and component manufacturers’ laboratory examinations attributed the trunnion failure to the development and growth of progressive fatigue cracking through the horizontal beam and central gusset section, with cracking propagating to the point where nominal landing loads produced the final overstress fracture and collapse of the assembly. Due to the extent of post-failure damage sustained by the fracture surfaces, neither laboratory examination was able to specifically identify the factors behind the initial development of the fatigue cracking.
The ATSB’s research of Australian and international air safety records did not identify any other instances of this specific mode of failure within the trunnion type, nor was the manufacturer aware of any known cracking or related problems with the trunnion in the affected areas. As such, it is likely that the event was an isolated occurrence, and consequently, the likelihood of similar occurrences in the future is low.
What's been done as a result
In response to this occurrence, the aircraft operator undertook a targeted, one-off non-destructive inspection of the trunnions from the four other aircraft in its fleet. All were found to be defect free. Additionally, the operator’s maintenance schedule has been extended to include the eddy-current inspection of the trunnion gusset/web regions concurrently with the routine 2000-cycle periodic inspections specified by the aircraft manufacturer.
Safety message
While the failure sustained in this instance was an unusual and isolated case, it does highlight the necessity of general vigilance and attention to detail during general visual inspections, or during other examinations of structures and components. Such activity can present opportunities for the detection of emerging or unknown airworthiness issues that may not have otherwise been identified during prescribed maintenance programs.
On 13 April 2013, an Indonesian registered B737-800 aircraft collided with water on approach to Denpasar Airport, Indonesia.
As the accident took place in Indonesia, the Indonesian National Transportation Safety Committee (NTSC) is responsible for investigating this occurrence, consistent with Indonesia’s obligations as State of Occurrence under Annex 13 to the Convention on International Civil Aviation Aircraft Accident and Incident Investigation (Annex 13).
The NTSC requested ATSB assistance to seek weather and visibility reports from Australian flight crews operating into Denpasar close to the time of the accident. To facilitate this support, the ATSB appointed an accredited representative in accordance with paragraph 5.23 of Annex 13 and, in order to protect the information supplied by the NTSC, commenced an external investigation under the Transport Safety Investigation Act 2003. The ATSB completed its work as accredited representative on 26 April 2013.
The National Transport Safety Committee of Indonesia is responsible for releasing the investigation report.
National Transportation Safety Committee Ministry Of Transportation Republic Of Indonesia Transportation Building 3rd Floor Jalan Medan Merdeka Timur No. 5 Jakarta Pusat 10110 Indonesia
On 22 April 2013, the flight crew of a United Airlines Incorporated Boeing 747-422, registered N119UA, flew from Sydney, New South Wales to Melbourne, Victoria. At Melbourne, the crew taxied to gate D5 and stopped, applying the parking brake. Shortly after stopping, the aircraft started to move forward again slowly. The flight crew realised the aircraft was moving and re-applied the brakes. The aircraft’s left wing collided with the aerobridge before the movement had stopped. No one was injured during the occurrence and the aircraft sustained minor damage.
What the ATSB found
After stopping at the gate, the aircraft parking brake was likely inadvertently released before the nose wheels were chocked and the engines shut down. The flight crew’s attention was inside the cockpit, focused on shutting down the engines. As such they were not actively monitoring aircraft movement, nor was that required at this stage. In addition, the parking guidance system at the gate was set to emergency stop mode by ground personnel when the aircraft first arrived, removing the possibility of an alert for the flight crew that the aircraft had moved. The flight crew became aware of the movement when the captain detected motion through peripheral vision. The very slow acceleration, combined with a lack of visual cues available to the flight crew made it difficult for the crew to detect the movement in time to prevent the collision.
Safety message
This occurrence highlights the importance of flight crew remaining aware of the possibility of aircraft movement whenever the engines are running as aircraft movement, particularly if it is slow, is difficult to detect. Additionally, ground support crew are reminded of the need to leave the parking guidance system in normal mode, unless an emergency stop is required.
Boeing 747 N119UA
Source: Benedikt Mathweis
Sources and submissions
Sources of information
The sources of information during the investigation included:
the flight crew of N119UA
United Airlines Incorporated (United)
ground staff
Melbourne airport
data from the flight recorders on N119UA.
References
Dismukes, K 2006, ‘Concurrent task management and prospective memory: pilot error as a model for vulnerability of experts’ Proceedings of the Human Factors and Ergonomics Society 50th Annual Meeting – 2006, pp.909-913.
Monaco, W & Kalb, J 2007, Motion detection in the far peripheral visual field, U.S. Army Research Laboratory, Maryland, United States.
Reason, J 1990 Human Error, Cambridge University Press, Cambridge, United Kingdom.
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 United, the flight crew of N119UA and the Civil Aviation Safety Authority.
A submission was received from United. The submission was reviewed and where considered appropriate, the text of the report was amended accordingly.
Appendices
Appendix A - Selected parameters from the recorded flight data when the aircraft arrived at gate D5
Source: ATSB
Explanation
Recorded data
In accordance with the normal aircraft shut down procedures, the digital flight data recorder ceased recording shortly after the engines were shut down. The digital aircraft condition monitoring system recorder is normally switched off later in the shut down sequence. Therefore, the digital monitoring system recorder continued to record information including the longitudinal g[12] parameter. The plot of recorded data above shows data from both flight recorder systems and indicates the sequence of events beginning with the aircraft turning into the parking bay.
Movement
The ATSB derived the aircraft’s speed from variations in longitudinal g, correlated with video recordings from the airport terminal. This showed that:
From 0024:24, the aircraft turned into the parking bay, turning slightly right. As the aircraft approached the parking bay, there were variations in rudder pedal position and longitudinal g.
At 0024:52, there was an increasing negative longitudinal g, or deceleration, which reduced as the aircraft stopped at 0024:54. About 4 seconds later, a positive change of about 0.02 longitudinal g indicated that the aircraft began to move forward again.
The aircraft gradually decelerated as the engines were shut down by the fight crew actioning the fuel cut-off for each engine, although a video recording indicated the aircraft continued to move forward.
At 0025:13, a sharp deceleration indicated the aircraft was being stopped.
Rudder pedal position
Rudder pedal position has no influence on the aircraft when taxying at slow speed. At this speed, the aircraft is steered by a separate control, the tiller, which controls nose wheel steering. However, while taxying an aircraft, the handling pilot’s feet rest on the rudder pedals. This is done so the pilot can operate the wheel brakes by applying force to the tops of the respective rudder pedals. The continuous slight movement in the rudder pedals between when the aircraft came to a stop until the aircraft started to move again is consistent with someone having their feet resting on the rudder pedals until that time.
Speed brake position
The speed brakes are hinged panels on the upper surface of the wing that may be extended to reduce aerodynamic lift from a wing. A speed brake may also be called a spoiler, as can be seen in this plot. The spoiler handle position was moved from 100 per cent to 0 per cent, commanding a retraction of the spoilers at the same time as the aircraft started to move.
The captain had about 28,000 hours aeronautical experience with 15 years flying Boeing 747 aircraft.
The first officer (FO) had about 10,000 hours aeronautical experience and had recently completed training for the Boeing 747 type rating, having 16 hours experience on this aircraft type. The flight from Sydney to Melbourne was part of the initial operating experience[4] requirement and was the FO’s first flight as pilot monitoring under the captain’s supervision.
Fatigue
Both crew reported that they were well rested after having about 25 hours rostered time off prior to commencing duty for the 1.5 hour flight from Sydney to Melbourne. They had been rostered together for the previous 3 days. The FO’s roster and reported sleep during that period indicated that fatigue should not have been an issue.
The captain’s sleep history was not obtained. However, as they had been working to the same rostered schedule as the FO, there was nothing to indicate that fatigue would have been an issue.
Workload
The captain reported feeling that there was a slight increase in their workload because this was the FO’s first flight as pilot monitoring. That workload increase was expected and the captain reported no problem in handling it.
Aircraft information
Wheel brake system
The Boeing 747 has independent left and right side, hydraulically-powered wheel brakes to all the main landing gear wheels.
The wheel brakes are controlled by applying force at the top of the captain’s or FO’s rudder pedals. The rudder pedals for each pilot are mechanically interconnected. Therefore, either pilot can apply input to all wheel brakes as required.
Activating the brakes allows the brake metering valves to supply hydraulic pressure to the wheel brakes. Removing the force from the tops of the rudder pedals returns the metering valves to neutral through the action of the return springs (Figure 2). This relieves the hydraulic pressure to the wheel brakes.
Flight crew normally position their feet to operate the rudder with their heels on the floor. In that position, the height of the rudder pedals above the floor makes it necessary for them to slide their feet up the rudder pedals to apply the wheel brakes.
Figure 2: Boeing B747-400 wheel brake system schematic. The upper-left image shows the mechanical interconnection between depressing the top of the rudder pedal and the movement of the brake cables, the centre image the wheel brake cables’ layout and the lower-right image a hydraulic metering valve (the return spring is shown in blue)
Source: Boeing, modified by the ATSB
Parking brake
The 747-400 wheel brake system incorporates a parking brake function that retains hydraulic pressure in the wheel brakes. The parking brake is used during:
the installation or removal of chocks after an aircraft stops or is about to move in the bay
taxi manoeuvres, when the aircraft must wait for other traffic to clear
short-term parking.
The parking brake system is controlled using a parking brake lever situated on the left (captain’s) side of the flight deck centre console. The lever is connected mechanically to a pawl at the rudder pedals (Figure 3). Once the tops of either pilot’s rudder pedals are pressed to at least 15°, the lever can be raised allowing engagement of the pawl. The pawl retains the rudder pedals in this position and the metering valves allow continued supply of hydraulic pressure to the brakes.
The pawls are themselves held in position by the force applied by the metering valve return springs. Applying additional force to the tops of the rudder pedals results in the pawls moving away from the ‘locked’ position, releasing the wheel brakes.
The parking brake also activates an isolation valve to trap the hydraulic pressure in the brake lines at the wheel brakes. As a result, once the parking brake is set, fluctuations in hydraulic system pressure do not have an effect on the wheel brakes.
Figure 3: Boeing B747-400 Parking brake system, showing the mechanical interconnection (in yellow) between the parking brake lever (in red) and the parking brake pawl (in orange) and the location of parking brake switch (switch S313)
Source: Boeing, modified by the ATSB
Parking brake engagement activates the parking brake switch that in turn annunciates the ‘Park brake set’ message on the engine indicating and crew alerting system (EICAS)[5]. The captain reported seeing this message when the parking brake was engaged.
Aircraft wheel brake system examination
Following the occurrence, a review of data recorded on the aircraft’s central maintenance computer found no defects for the aircraft’s wheel brake system.
United Airlines Incorporated (United) inspected the aircraft’s wheel brake system and conducted a number of functional tests in accordance with the manufacturer’s maintenance manual. No anomalies or defects were found in the aircraft’s wheel brake and parking brake systems.
Airport information
Visual docking guidance system
Gate D5 was equipped with a visual docking guidance system (VDGS). The VDGS provided guidance for crew in terms of aircraft centre-line position and nose wheel position.
Crew use the guidance system to bring the aircraft to a stop at the correct point for an aerobridge disembarkation of passengers. After the aircraft has stopped, the aerobridge is moved forward to the aircraft fuselage.
The normal sequence of operation for the VDGS is as follows:
prior to an aircraft’s arrival, a ground engineer selects the aircraft type on the VDGS control panel
the VDGS starts scanning for the aircraft
the VDGS matches the approaching aircraft with the selected aircraft type and:
- if correct, the VDGS guides the aircraft using directional and speed arrow messages
- if incorrect, the VDGS displays STOP and the aircraft is stopped short (up to about 20 m).
at the correct stop position, the VDGS displays STOP and:
- if the aircraft stops in time, the VDGS waits for 5 seconds and then signals OK, alerting flight crew that parking is complete
- if the aircraft does not stop in time or moves forward more than 30 cm within 5 seconds, the VDGS displays TOO FAR, alerting flight crew that the aircraft has overshot the stop position.
The VDGS control panel includes an emergency stop button that can be activated by ground crew at any time. Once the emergency stop button is activated, the VDGS displays the STOP signal and ceases monitoring the aircraft’s position and movement.
The displayed STOP signal is the same for normal and emergency stopping conditions. However, the STOP signal is displayed for more than 5 seconds for an emergency selection.
Flight crew procedures for use of the VDGS
The VDGS instructions available to the flight crew stated that the OK signal indicated that the aircraft was parked in the correct position but did not provide information about the TOO FAR signal display. The flight crew’s procedures also stated that once the aircraft was chocked, ground staff would manually change the display to CHOCK ON. However, the CHOCK ON message was not available at gate D5. This meant that any communication about the position of the chocks would be verbal.
Ground procedures and actions for use of the VDGS
The ground standard operating procedures (SOP) applicable to gate D5 stated that ground personnel could initiate the emergency stop signal if required. Under those circumstances, once the emergency had been addressed, the ground engineers would marshal the aircraft to complete the parking procedure manually.
As an aircraft approaches the relevant gate, one of the ground crew stands near the VDGS control panel, ready to press the emergency stop button if the need arose. In this occurrence, the VDGS equipment log recorded that, almost immediately after the normal STOP signal was displayed, the emergency stop button was pressed. As a result, the STOP message remained displayed, even though the aircraft started to move again shortly after and collided with the aerobridge about 15 seconds later.
The ground engineers stated that they sometimes pressed the emergency stop button to ensure the STOP message was displayed in good time.
Flight Recorders
Cockpit voice recorder
The aircraft’s cockpit voice recorder[6] continued to record for some time after the aircraft collided with the aerobridge as it remained powered. As a result, the recorder had recorded over the events from the time of the aircraft’s arrival at gate D5, until the collision.
Recorded flight data
The aircraft was equipped with a digital flight data recorder, and a digital aircraft condition monitoring system recorder[7]. Analysis of data from those media showed:
slight movement of the rudder pedals while the aircraft was stopped at the gate
all four engines were running at idle thrust while the aircraft was stopped at the gate
the aircraft was stationary for 4 seconds before commencing forward movement
the forward movement commenced at the same time as the speed brakes were stowed
once the aircraft started to move, there was hardly any further movement on the rudder pedals
all engines were shut down about 5 seconds after the aircraft started to move
about 15 seconds after the aircraft commenced moving, it collided with the aerobridge
at the same time as the aerobridge collision, the wheel brakes were applied.
Flight recorder sampling of the parking brake lever position data occurred once every 64 seconds. At the time the aircraft started to move, the parking brake lever was recorded as being ‘not on’. However, as the occurrence happened between two recorded samples, the actual position of the parking brake lever for the 4 seconds between when the aircraft stopped and commenced movement again, could not be determined.
Additionally, the recorded data indicated that sufficient hydraulic pressure was available to the aircraft wheel brake systems throughout the occurrence.
Selected parameters from the recorded flight data are at appendix A.
Wreckage and impact information
Damage to the aircraft
The left wing inboard leading edge was damaged by the collision with the aerobridge (Figure 4). A landing light cover was also damaged. Before the aircraft was ferried to United’s home base, the leading edge and landing light covers were temporarily repaired. Permanent repairs were carried out in the United States.
Figure 4: Close up of the damage to the left wing inboard leading edge and landing light cover
Source: United
Organisational and management information
Ground handling
Another airline was contracted to provide ground handling services to United at Melbourne Airport. There were three ground engineers awaiting the arrival of the aircraft at gate D5. They included a licenced aircraft maintenance engineer (LAME) and two unlicensed aircraft maintenance engineers. Other ground crew were located outside the aircraft’s designated parking area. Additionally, ground staff were positioned at the entrance and halfway along the aerobridge.
The SOP for ground personnel actions upon arrival of an aircraft contained the following steps (in part):
…
4.When meeting an arriving aircraft the person who is assigned to communicate with the flight
crew on the headset must ensure:
a. The aircraft has stopped and brakes are on before connecting the headset.[[8]]
b. All engines are shut down and no abnormal conditions exist (such as tail pipe fire, wheel
or brake fire etc) before disconnecting from the headset.
c .Chocks are placed just Fwd and Aft of the tires on the nose landing gear once the park
brake has been set.
Place chocks Fwd and Aft of the outboard (or inboard) set of tires of each main landing
gear.
…
The engineers stated that they provided ground handling services for a number of different operators and aircraft types. They stated that some operators were proactive with communicating to the ground crew on arrival while others were not.
The LAME reported that the aircraft came to a stop at the designated parking location. The two aircraft mechanical engineers then moved into a position to place a chock at the rear of the nose wheel.[9] After placing the rear chock, they moved to place the forward chock in position. At that moment, the aircraft started to move forward. The engineers expected the aircraft to stop again quickly, but it did not. They became aware of the aircraft’s engines nearing their positions and abandoned any further attempt to chock the wheels.[10] Instead, they rapidly moved clear of the aircraft.
The LAME also reported that they had not spoken to the flight crew before the aircraft started to move again. The LAME stated they had insufficient time or opportunity[11] to connect ground communications to the aircraft.
Flight crew after landing procedures
According to United’s procedures, the after landing flow can be conducted any time after landing, when time permits. The flight crew indicated that it was usually conducted as soon as the aircraft had exited the runway. The procedures stated that the captain’s first action was to stow the speed brake by moving the speed brake lever to the forward stowed position (see the section titled Additional information).
Recorded flight data indicated that all the after landing flow actions were completed by the crew soon after landing, except for retracting the speed brakes. The speed brakes were retracted by the captain after the aircraft stopped at the gate.
The concept of prospective memory is described as ‘remembering to perform an action that cannot be executed when the intention is formed’ (Dismukes, 2006), and is typified by:
an intention to perform an action at some later time when circumstances permit
a delay between forming and executing the intention, typically filled with activities not directly related to the deferred action
the absence of an explicit prompt indicating that it is time to retrieve the intention from memory.
The crew reported that after landing, their focus was on remaining clear of ground traffic and on specific aircraft parking requirements. This focus on different activities may have distracted the crew from retracting the speed brakes until the aircraft arrived at the gate. The captain’s retraction of the speed brake after arriving at gate D5 was consistent with a lapse in prospective memory.
Flight crew parking procedures
The flight crew parking procedures required that once the aircraft had stopped at its intended parking position, the flight crew were to start the parking flow sequence of actions. In this sequence, the captain conducted 11 actions and the FO conducted nine actions. A notice at the start of the actions stated that:
Ground personnel expect the right engines to be shut down, or ready for immediate shut down, upon arrival at the parking location.
The captain’s first action was to set the parking brake lever. The procedure for setting the parking brake stated:
The parking brake lever is pulled to set the brakes, after both pedals are fully depressed.
The captain stated that when applying the parking brake they feel for the ‘click’ in the parking brake lever, and felt that had occurred in this case. In order to feel a click in the parking brake lever, the parking brake lever would already have to be pulled when the brake pedals were pressed. This would have meant that the engaging pin was in contact with the pawl as the pin was moved by pedal depression. That action may have influenced the likelihood of an incomplete parking brake engagement.
To minimise the likelihood of the parking brake not being engaged, the procedure incorporated the following verification actions:
The captain was to check:
- the parking brake lever position - an EICAS memo message PARK BRAKE SET was displayed - the BRAKE SOURCE light was off - there was no aircraft movement.
The FO’s second action was to verify:
- the parking brake lever position - there was no aircraft movement.
Aside from the status of the BRAKE SOURCE light, which was not mentioned at interview, the crew stated that they conducted all of these actions to verify that the parking brake was set and the aircraft was not moving.
The remaining actions directed both pilots’ attention inside the cockpit. They mostly involved the overhead control panel or the centre console between the pilots’ seats. None related to aircraft movement, brake or chock status. Despite both crew having their attention inside, the captain did notice aircraft movement through peripheral vision and the FO reported that the VDGS STOP indication appeared closer, although any change was insidious. In the event, the captain’s perception of the aircraft’s movement did not occur in sufficient time to prevent the collision.
Additional information
Parking brake and speed brake controls
The speed brake lever and the parking brake lever are in the same area of the flight deck, however they are different in size and shape (Figure 5). While the speed brake lever can be moved without any additional action, the parking brake lever only operates in coordination with pressing the brake pedals.
The FO reported paying specific attention to the captain setting the parking brake in Melbourne because of the unintended wheel brake disengagement at Sydney. The FO recalled the parking brake lever remained raised (brake engaged) after the captain removed their hand from the lever.
Figure 5: Cockpit control layout, showing the location of the speed brake and parking brake controls
Source: Boeing, modified by the ATSB
Other occurrences
The aircraft manufacturer reported that it had been notified of an occurrence when a Boeing 747‑400 aircraft started to move after the parking brake had been incompletely engaged. No defect was identified in the aircraft.
A review of the ATSB occurrence database identified seven reported occurrences between 2008 and 2013 in which jet aircraft moved after coming to a stop during parking. Of these:
In one occurrence, the park brake was reportedly set and the aircraft rolled forward on a downslope during engine shutdown. No fault was found with the brake system.
Another occurrence involved a mechanical issue with the park brake, which led to it disengaging.
The remaining five occurrences involved the wheels not being chocked prior to park brake release or having the chocks in the incorrect position.
There were no occurrences relating to inadvertent park brake release.
From the evidence available, the following findings are made with respect to the collision between an aerobridge and a Boeing Company B747-422, registered N119UA, at Melbourne Airport, Victoria on 22 April 2013. These findings should not be read as apportioning blame or liability to any particular organisation or individual.
Contributing factors
A likely inadvertent disengagement of the parking brake, prior to the aircraft being chocked and while the engines were operating at idle thrust, allowed the aircraft to recommence moving forward.
While the crew were conducting the parking flow, procedural task requirements drew both flight crew members’ attention inside the flight deck. This, combined with the limited visual cues available, reduced their ability to detect the aircraft’s movement in time to prevent the collision.
Other factors that increased risk
The activation of the Visual Docking Guidance System emergency stop function inhibited display of a 'TOO FAR' message, reducing the cues available to crew and increasing the risk that any aircraft movement would not be detected.
Safety analysis
Introduction
A review of past occurrences showed that undetected movement following inadvertent disengagement of the parking brake is a rare event. In this occurrence, the aircraft started moving 4 seconds after it was stopped at the gate.
The flight crew reported that the parking brake was set after stopping and an inspection of the aircraft’s wheel brake system and a number of functional checks by United Airlines Incorporated found no anomalies or defects with the aircraft’s wheel or parking brake systems to explain the unintended aircraft movement. The application of the wheel brakes by the captain on detecting the movement would have disengaged the park brake. This was consistent with the as-found position of the park brake handle after the aircraft collided with the aerobridge.
This analysis will examine the defences in place to prevent such an occurrence and the human performance factors identified during the investigation as having influenced the flight crew’s actions and ability to detect the aircraft movement.
Parking brake
When parking at an aerobridge, the wheel brakes are applied and locked on with the parking brake system. The parking brake is the primary means of restraint for the aircraft and is regularly used when the engines are operative.
The captain’s parking brake engagement technique was not entirely consistent with the documented procedure. Despite this, the crew’s subsequent verification checks should have identified if the parking brake did not engage properly. The crew reported that the engine indication and crew alerting system indicated that the parking brake had engaged and both crew reported verifying visually that the aircraft was not moving. As such, it is likely the parking brake had engaged correctly.
The reason why the parking brake disengaged could not be determined. However, recorded data showed rudder pedal movement when the aircraft started to move after the parking brake was initially set. A properly-engaged parking brake cannot be released unless force is applied to the brakes at the top of the rudder pedals. However, the recorded flight data does not record brake pedal movement, preventing confirmation of this action from the recorded data.
Sufficient force to disengage the parking brake is more likely to be applied if a crew member has their feet positioned on the top of the rudder pedals. The captain would have had their feet in this position a short time before, in order to apply the parking brake on arrival at the gate.
The speed brakes were lowered at the same time as the aircraft started to move and this action would have put a demand on the hydraulic system. However, recorded data indicated that sufficient hydraulic pressure remained available to operate the wheel brakes. The parking brake system was independent of the hydraulic supply system, therefore changes to hydraulic pressure would not have affected the parking brake engagement.
Reason (1990) stated that ‘a necessary condition for the occurrence of a slip of action is the presence of attentional “capture” associated with either distraction or preoccupation. This means that wherever else the limited attentional resource is being directed at that moment, it will not be focused on the routine task at hand’. Reason outlined that there are two conditions necessary for a slip of action: the performance of some largely automatic task in familiar surroundings, and a marked degree of attentional capture by something other than the job in hand. The concept of ‘automatic’ action refers to the way that certain tasks can be executed without conscious oversight, thereby limiting the use of processing resources.
Stowing the speed brake was not part of the captain’s usual actions after stopping at the gate. However, this out of sequence action may have been sufficiently distracting to result in the captain’s slip of action to unintentionally activate the wheel brake pedals and release of the parking brake. At other times (such as when setting the parking brake), activating the wheel brake pedals would be intentional.
Aircraft movement
Installation of the wheel chocks
Ground staff normally installed the nose wheel chocks once the aircraft stopped and the parking brake was set. They were in the process of placing them in position when the aircraft moved forward, preventing installation of the forward chock.
The only means of communication between the ground and flight crews on the status of the wheel chocks was via hand or other visual signals, or after the ground crew plugged in their headset. The height of the pilots’ seating, and position of the ground crew generally below the aircraft, meant that visual signalling was generally not practicable in the busy/congested tarmac environment because:
one of the ground crew would need to move away from underneath the nose of the aircraft and into one of the pilot’s view
that pilot would need to establish and maintain visual contact with the ground crew member.
The ground crew’s headset could not be plugged into the nose wheel landing gear intercom socket to allow communication with the flight crew until the aircraft stopped and the parking brake was engaged. The movement of the aircraft before the forward chock was in place prevented ground crew from establishing the intercom link with the crew. This lack of communication, and therefore flight crew understanding of the status of the wheel chocks, emphasised the flight crew’s reliance on the parking brake and on comprehending any subsequent aircraft movement should that brake fail or disengage.
If the ground crew had been able to complete the installation of the nose wheel chocks before the aircraft recommenced moving, the chocks may have prevented that movement. Alternately, if the chocks were unable to prevent the aircraft’s movement, the ‘bump’ as the aircraft rolled up or over the forward chock would likely have alerted the flight crew of the movement.
Flight crew focus
After commencing the parking flow actions, the flight crew’s focus was predominantly inside the flight deck. These actions involved shutting down the engines, which at that stage remained at idle but, until shut down:
given the aircraft’s weight, provided sufficient thrust to move the aircraft if unrestrained
prevented ground crew from approaching the main landing gears and installing the associated wheel chocks.
Therefore, although not inherently conducive to looking outside the flight deck, shutting down the engines was a priority task for the flight crew.
The captain first detected movement via peripheral vision when moving their attention from the overhead panel down to the centre console. One of the main functions of peripheral vision is to detect motion (Monaco and Kalb, 2007). This ability depends on the velocity and duration of the movement, the size of the moving object and its location in the peripheral vision.
Consistent with the first officer’s report of the insidious nature of any movement when glancing out of the cockpit and seeing the VDGS, there was no salient visual stimulus when looking forward from the flight deck. The aircraft’s movement was too slow for the terminal wall to appear to move and, as a result of the ground crew activating the emergency stop function on the visual docking guidance system (VDGS), the VDGS displayed the same STOP message as when the crew first stopped the aircraft.
Utility of the VDGS
Activation of the emergency stop button on the VDGS by the ground crew provided a means for the ground crew to instruct the flight crew to stop immediately. This function was only available until the aircraft stopped at its intended parking position.
In this case, the emergency stop button was pressed immediately after the aircraft stopped the first time. As a result, in addition to the ongoing display of the STOP message, display of the TOO FAR message in the case of the aircraft recommencing moving was inhibited. This meant that, although the first officer reported periodically glancing outside the flight deck and seeing the VDGS, its display would not have assisted the crew identify any aircraft movement.
Purpose of safety investigations & publishing information
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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.
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On 11 April 2013, at about 0851 Eastern Standard Time, an Aero Commander 500 aircraft, registered VH-TQA (TQA), departed Townsville, Queensland on a private flight to Moorabbin, Victoria, under the instrument flight rules (IFR).
After take-off, passing through 200 ft, the pilot attempted to establish communications with Townsville Approach ATC, but no response was received. The Approach controller reported they did not hear this call.
While passing through 400 ft, the pilot checked his radios to confirm the correct frequency had been selected. At the same time, the Tower controller alerted the Approach controller that TQA did not appear to be turning left at 1 NM, as per the published standard instrument departure (SID) procedure. As TQA passed through 500 ft, the pilot again contacted the Approach controller. The Approach controller responded and was about to question the pilot regarding the aircraft’s track, when he noted that TQA’s predicted tracking line on the radar display indicated that a turn in the direction of the SID had commenced.
At the same time, the pilot suspected TQA may have had a partial engine failure, and started troubleshooting actions.
When at about 3 NM, the Approach controller noted that the aircraft’s predicted tracking line had changed and was pointing to the south, indicating the aircraft was not on the SID. The Approach controller reminded the pilot of the SID requirement to turn onto a track of 105o at 1 NM.
Believing this was a radar vector, the pilot read back ‘left 105°’ and commenced a turn onto that heading. The aircraft was 4 NM from Townsville Airport when it turned and about 2,000 ft when it turned, putting it in close proximity to Mount Stuart.
This incident highlights the importance of maintaining situational awareness. Much of the research on this topic provides loss of situational awareness mitigation concepts.
On 18 April 2013, a Robinson R22 helicopter registered VH‑HLY (HLY), departed from Cloncurry tracking to the north. At the same time, a Bombardier DHC‑8 aircraft, registered VH‑QOB (QOB), was conducting a scheduled service from Townsville, Queensland to Cloncurry.
The pilot of HLY broadcast his intentions and about 2 minutes later, while taxiing towards the runway intersection he looked ahead and to the left along the main runway in the most common direction of arriving aircraft operations into Cloncurry.
The pilot in command (PIC) of QOB made inbound broadcasts at 30, 10 and 3 NM on the common traffic advisory frequency (CTAF) and conducted a straight-in approach to land on runway 30.
As the helicopter crossed the runway, the pilot realised that he had not heard a response from the aerodrome frequency response unit (AFRU) on the CTAF. Simultaneously, he heard a call from QOB, which was in the landing flare on short final for runway 30, stating that he should get off the runway.
The pilot of HLY then looked to his right and observed QOB on the runway. He realised he had been broadcasting on the ultra-high frequency (UHF) radio, although he could hear calls on the very high frequency (VHF) CTAF.
HLY departed across the runway at about 100 feet. The pilot of HLY estimated that, when QOB had touched down, the distance between the aircraft and HLY was about 1,000 m horizontally. The PIC of QOB estimated that the horizontal separation reduced to about 200 m.
This incident highlights the importance of conducting pre-flight checks thoroughly and maintaining vigilance particularly at non-controlled aerodromes.
