U.K. Air Accidents Investigation Branch (AAIB) investigation has determined that a maintenance error had led to the detaching of the fan...
U.K. Air Accidents Investigation Branch (AAIB) investigation has determined that a maintenance error had led to the detaching of the fan cowl doors on both engines of the British Airways Airbus A319 jetliner, while taking off from the London Heathrow Airport on 24 May 2013.
During takeoff from Runway 27L, the fan cowl doors from both IAE V-2500 engines detached from the Airbus A319 aircraft, registration G-EUOE, damaging the airframe and a number of aircraft systems. The flight crew elected to return to Heathrow and on the approach to land on Runway 27R, leaking fuel from a damaged fuel pipe on the right engine ignited and an external fire developed.
The left engine continued to operate satisfactorily throughout the flight. The right engine was shut down promptly, reducing the intensity of the fire, and the aircraft landed safely. It was brought to a stop on the runway and the emergency services were quickly in attendance. The fire in the right engine was extinguished and the passengers and crew evacuated via the emergency escape slides on the left side of the aircraft.
The fan cowl doors on both engines being were left unlatched following scheduled overnight maintenance on the aircraft. The unlatched condition of the fan cowl doors was not identified prior to the aircraft’s departure the next morning. A number of organisational factors were contributory to the maintenance error. British Airways has since taken action to address these issues.
The fan cowl doors were unsecured because the technicians did not follow the proper procedure in securing the doors when they left the aircraft unattended, and because the aircraft was subsequently signed off as serviceable. The procedure was not followed partly because an essential tool to maintain the engines was not readily available, and so the technicians decided to postpone the task until they had an opportunity to collect the tool from a stores building.
They did not properly close the fan cowl doors or prop them open on stays when leaving G-EUOE. The investigation found that this particular procedure was routinely violated in the maintenance organisation.
The aircraft was signed off as serviceable mainly because the technicians later returned to the wrong aircraft, G-EUXI rather than G-EUOE, to complete their work on it.
This, and numerous other similar events, shows that Airbus A320-family aircraft have a history of departing with the fan cowl doors unlatched. It is also evident that, in practice, the flight crew walk-around inspection is not entirely effective in detecting unlatched fan cowl doors and therefore a design solution is necessary. Enhanced methods of detection through design solutions are being considered by the aircraft manufacturer.
As a result of this investigation, five Safety Recommendations were made concerning: fatigue risk management; fan cowl door position warnings; fan cowl door certification requirements; in-flight damage assessments by cabin crew and aircraft evacuation procedures.
 |
| Fig.1 Right engine fan cowl door seen unlatched |
 |
| Fig.2 Two left engine unlocked latches protruding |
During the takeoff roll a number of passengers observed the engine inboard fan cowl doors “flapping”. As the aircraft rotated, some passengers witnessed the fan cowl doors opening and then being forcefully detached from the engines by the airflow.
Pilots of an aircraft lining up on Runway 27L after G-EUOE’s departure observed a significant amount of debris on the runway, prompting them to transmit a PAN call to air traffic control (ATC).
After Take Off
A number of passengers on both sides of the aircraft pressed their cabin call buttons and shouted to attract the cabin crew’s attention.
The Senior Cabin Crew Member (SCCM) considered the passenger behaviour highly unusual and attempted to call the flight deck on the interphone. The commander noted the interphone call signal, which occurred as the landing gear was being selected up.
As the aircraft was below 1,000 ft agl, he disregarded the call and concentrated on monitoring the aircraft’s flightpath. Cabin crew member No 2 (CCM2) observed that an internal trim panel on the right overwing emergency exit appeared damaged and reported this to the SCCM via the interphone. As the aircraft climbed through the acceleration altitude of 1,100 ft, Autopilot 2 was engaged and the co-pilot moved the thrust levers to the CLIMB detent.
One second later the autothrust disengaged and the master caution activated. The flaps were retracted as the aircraft accelerated to the target climb speed of 250 kt. After confirming that both engines appeared to be operating satisfactorily, the crew continued climbing the aircraft on the SID track to the first cleared altitude of 6,000 ft.
On checking the Electronic Centralised Aircraft Monitor (ECAM), the commander saw that the eng 2 epr mode fault message was displayed. He noted that the No 2 (right) Engine Pressure Ratio (EPR) gauge was blank. He followed the ECAM actions, selecting the N1 MODE ‘on’ for engine No 2 and then engine No 1 (left engine). Four seconds later the master caution sounded again, with the ECAM indicating a Yellow hydraulic system loss.
The commander turned off the Power Transfer Unit (PTU), in accordance with procedures, and the flight crew began reviewing the situation. When the aircraft levelled at 6,000 ft, the co-pilot reported to the commander that he believed something had hit the right wing, as he could see damage to the wing leading edge.
At 0720:20 hrs, after being transferred to the Departure radar frequency, the commander declared a PAN (urgency) to ATC, reporting that the aircraft had an engine problem and had lost a hydraulic system. He requested radar vectors and informed ATC that the aircraft would be returning to Heathrow. ATC acknowledged and confirmed that radar vectors would be provided to keep the aircraft in the vicinity of Heathrow.
The commander then returned to the ECAM actions for loss of the Yellow hydraulic system, during which he identified an ECAM indication associated with the right overwing emergency exit. The ECAM drill for this item required the pilots to monitor the cabin pressure and the aircraft to remain below flight level (FL) 100.
The aircraft successfully landed at 0743:51 hrs, at an indicated airspeed of 149 kt and ground speed of 138 kt.
Damages to aircraft
The inboard and outboard fan cowl doors from both engines had detached, close to the pylon attachment hinges. Whilst three of the four fan cowl doors had separated by delamination of the fan cowl’s composite structure, the forward section of the right inboard door, together with the inboard nacelle aerodynamic strake, had remained attached to the aircraft.
Aerodynamic loads imparted to the engine pylons by the departing fan cowl doors had caused a severe buckle in the primary structure of the right pylon and damage to the forward fairing of the left pylon. The detached fan cowl doors had struck and damaged the inboard leading edge slats, the fuselage skin close to the overwing emergency exits, the overwing fairings, the right inboard flap and the left belly fairing. The impact to the right overwing emergency exit had dislodged the cabin trim cover on its interior handle, causing a door r emer exit ECAM message to be generated.
In addition, the right engine’s outboard fan cowl had struck the right wing leading edge at the outboard end of Slat 3, damaging this slat and the inboard end of Slat 4. The outboard flap track fairing on the right wing was punctured and the left horizontal stabiliser leading edge
and lower skin were damaged. The fixed leading edge structure behind the right inboard slat was damaged and a wing stringer was cracked. The right wing lower skin behind Slat 2 was gouged.
Debris had also struck the left main landing gear, damaging the leading edge of the fixed landing gear door, a wiring loom and a hydraulic brake pipe. The right main landing gear outer tyre was damaged during the landing roll and had fully deflated.
Damage to engines
The left engine fan cowl doors had failed cleanly along the hinge line. There was no other damage to this engine. The right engine and its attached cowlings were extensively heat damaged. The most significant damage was concentrated in the left and right thrust reverser C-ducts.
These consist of two large half-annulus shaped doors extending from the rear of the engine fan case to the common nozzle assembly at the rear of the core engine. The outer ‘barrel’ of the front section of each C-duct consists of a carbon fibre grid structure called cascade vanes. These are normally covered by an outer sleeve. When thrust reverse is selected, the sleeve slides backwards and blocker doors extend into the duct, directing engine bypass air forward through the cascade vanes.
 |
| The right engine on fire, snapped by a passenger during landing |
Conclusions
Within the scope of this report, the immediate cause of the incident was that the fan cowl doors were not closed and secured following the maintenance activity. This was partly because the technicians did not follow procedure in securing the doors when leaving the aircraft unattended, and partly because the aircraft was subsequently signed off as serviceable.
Although the technicians performed a procedural violation in not securing the fan cowl doors or propping them open on the stays, this was not uncommon amongst the team and was therefore not reported.
Meanwhile, the non-availability of equipment (the IDG gun) nearby to G-EUOE may have played a role in the error by inciting the technicians to postpone completion of the work until they had an opportunity to collect the IDG gun from stores.
The main reason that the aircraft was then signed off as serviceable is that the technicians returned to the wrong aircraft to complete the weekly check after their other work was completed. Whilst aircraft misidentification errors are not uncommon, in most cases they are benign, with other workers detecting the error if they were due to work on the aircraft as well. In this case, because the same technicians worked on the misidentified aircraft and the incident aircraft, there was no such opportunity for detecting the error.
The fact that the same technicians worked on both aircraft meant that G-EUXI was familiar to them, particularly since both aircraft were also weekly checks on their work list for the night.
The pre-departure walk-around inspections by both the pushback tug driver and the co-pilot did not identify that then fan cowl doors on both engines were unlatched.
An opportunity to detect the error was available in the two technicians cross‑checking each other’s decisions when travelling between aircraft. But this opportunity was missed because the technicians became separated by deciding to take two vans, in order to complete their work more efficiently. These factors, combined with an unreliable and confusing information system for organising engineering work at Terminal 5, probably contributed to the error.
A key barrier designed to prevent this kind of incident was the signing and countersigning of paperwork to confirm that maintenance on the aircraft was complete. This barrier failed because the paperwork was physically separated from its aircraft at the time (because it was a weekly check and hence held in the office).
Ultimately, the aircraft misidentification was probably more due to a memory error than a navigation error in the terminal area. Nevertheless, it is possible that the similarity of aircraft stands and lack of distinctive signage played a role in the error.
Underlying these factors was evidence of non-reporting of errors and procedural violations. Better reporting could also have alerted management to the frequency and potential consequences of these errors much earlier. In response, measures could have been put in place to mitigate such errors before an incident occurred.
Both technicians were at an elevated risk of suffering from fatigue at the time of the incident, and this would probably have affected their propensity for a ‘slip’ type of error, such as aircraft misidentification.
The lack of a formal fatigue risk management system for maintenance workers, which was not a requirement at the time of the accident, meant that a key barrier to this kind of error was not in place.
The lack of the majority of the high-visibility paint finish on the latch handles reduced the conspicuity of the unfastened latches.
Safety Recommendations
- Effective fatique management system
- Modification to Airbus A320-family aircraft to incorporate a reliable means of warning when the fan cowl doors are unlatched.
- EASA to bring amendment to Certification Specification 25.901(c), Acceptable Means of Compliance (AMC) 25.901(c) and AMC 25.1193, to include fan cowl doors in the System Safety Assessment for the engine installation and requires compliance with these amended requirements during the certification of modifications to existing products and the initial certification of new designs.
- It is recommended that British Airways reviews, and amends as appropriate, its pilot and cabin crew training, policies and procedures regarding in-flight damage assessments and reporting by cabin crew in light of the lessons learned from the G-EUOE fan cowl door loss event.
Download the full report here
Content: Crown Copyright 2015
