What happened
On January 11, 2010, an Air France Boeing 777-300ER, registered F-GSQI, was preparing for departure from Lagos, Nigeria, on flight AF855. To maximize rest time in the cockpit, the commander had completed the cockpit preparations early. During the takeoff roll on runway 36L, the pilot noticed that the autothrottle had not been armed during the initial preparations.
As the aircraft accelerated, the commander attempted to arm the autothrottle by manipulating the Mode Control Panel (MCP). During this process, the pilot inadvertently engaged the autopilot. While the crew focused on addressing the lack of autothrottle engagement and manually adjusting thrust, the aircraft reached a speed of 164 kt. Upon reaching the rotation speed, the commander felt a heavy resistance in the pitch controls—a result of the engaged autopilot—and immediately initiated a rejected takeoff.
The aircraft came to a stop approximately 900 meters before the end of the runway. The heavy braking required for the high-speed stop caused significant heat buildup in the braking system. The temperature of the third wheel brake exceeded safety thresholds, leading to the melting of several thermal fuses and the subsequent deflation of multiple tires as the aircraft taxied to its parking position.
The investigation
The BEA investigation focused on the sequence of cockpit actions and the automation settings. Investigators examined the flight data recorder (FDR) and cockpit voice recorder (CVR), which revealed that the commander had released the thrust levers to manipulate the MCP, leading to the accidental autopilot engagement. The investigation also reviewed the manufacturer's history, noting that Boeing had previously identified similar instances of unintentional autopilot engagement on the ground. Furthermore, the investigation compared the operator's procedures regarding autothrottle disarming with the manufacturer's guidelines, finding a discrepancy in how the system was managed during post-flight phases.
Findings
- The primary cause of the incident was the unintentional engagement of the autopilot by the commander while attempting to rectify the autothrottle status.
- The crew's failure to monitor the aircraft's automation state during the critical takeoff phase contributed to the error.
- The commander's decision to manipulate flight control switches on the MCP during the takeoff roll was a significant contributing factor.
- The initial failure to arm the autothrottle during the early cockpit preparation phase, driven by a desire to secure additional rest time, set the chain of events in motion.