On 11 Jan 2010, a Boeing 777-300ER being operated by Air France on a scheduled passenger flight from Lagos Nigeria to Paris CDG rejected the night take off on runway 36L at Lagos being carried out in normal night visibility from significantly above the applicable V1 speed when it was perceived that the control column pressure to achieve rotation was abnormal. The aircraft stopped before the end of the runway and after requesting and receiving Rescue and Fire Fighting Services cover in case of brake unit overheating, was taxied to the gate for normal passenger disembarkation. Five main landing gear tyres deflated due to thermal fuse activation approaching or at the gate. None of the 234 occupants were injured and the only aircraft damage was to the wheels and brakes.
An Investigation was carried out by the French Bureau d'Enquêtes et d'Analyses (BEA) with successful download of relevant Cockpit Voice Recorder (CVR) and Flight Data Recorder (FDR) data. It was established that the aircraft commander had been PF for the take off and that he had called a rejected take off at a speed which was 17 knots above the applicable V1 speed and 4 knots above the applicable VR speed when he perceived difficulty in moving the control column to rotate. The maximum speed reached had been 164 KCAS after which the aircraft had decelerated to a stop 900 metres from the end of the 3900 metre runway. The TODR for the incident take off was subsequently calculated to have been 2555 metres.
It was found that the PF had always previously taken off with the autothrottle (A/T) armed as per an acion detailed as part of the pre departure flight deck preparation checks and when it did not indicate as active following TOGA selection, he had intended to select it manually. He had believed that he had done so even though, at that point, the FD pitch command bars had reverted to centred instead of the 8° pitch up previously displayed, which occurs if the AP is engaged on the ground. It was noted that the Aircraft Flight Manual (AFM) does not permit AP engagement below 200 feet agl when airborne and also that a pressure of approximately 18-22 kg applied to the control column results in disconnection of the AP.
Aircraft track and recorded speeds taken from the Official Report
It was noted that the switches to select both the AP and A/T are on the MCP, although not adjacent. In addition to the A/T selection switch, L and R A/T ARM switches, of a different appearance to the AP and A/T switches, are also available on the MCP and are adjacent to the AP selection switch. Air France instructions to pilots were stated by the Investigation to include arming the A/T during pre flight preparations undertaken by the aircraft Captain although this action was not included in any checklist. During take off, the A/T is engaged when the TOGA switches are pressed provided that such action occurs prior to 80 KIAS and thrust is then automatically set to that indicated on the FMS. It was additionally noted that the “After Landing Guide” in use at Air France at the time included disarming of the A/T but that equivalent Boeing procedures did not include such an action.
The Investigation noted Boeing awareness of previous cases of inadvertent AP engagement during take off, most of which had resulted in a rejected take off. An All Operator Message had been issued to all Boeing 777 operators on the subject in 2009 noting that unintentional manual engagement of the autopilot before takeoff was possible and would significantly increase the effort required on the control column during rotation.
The Investigation Concluded that the incident was due to:
- the Captain’s failure to arm the auto-throttle during cockpit preparation
- the Captain’s decision to manipulate the auto-throttle switches on the MCP during a critical phase of the flight
- the inadvertent engagement of the autopilot during this operation on the MCP
- inadequate monitoring of the status of aircraft systems by the crew
It was also considered that the Captain’s decision to advance the flight deck preparation during the turn round at Lagos following a prior short domestic sector so as to leave him time to take a 40 minute in-seat rest may have contributed to his failure to arm the A/T.
Soon after the Investigation had begun, Boeing issued an Service Bulletin (SB) advising of the release of a new software version of the AP calculator which would prevent involuntary engagement of the AP on the ground during the takeoff roll. It was noted that the FAA had subsequently issued an AD mandating SB implementation within 90 days of 1 April 2010.
It was noted that the Air France procedure for turning thebautothrottle off after each flight were contrary to Boeing guidance and that the internal investigation of the incident by Air France “had recommended that a study be made of their documentation with a view to updating it in order to comply with that of the aircraft manufacturer on the disarming of the auto-throttle”.
The Final Report of the Investigation was released on 24 October 2010. No Safety Recommendations were made.