Accident Overview
On an unspecified date, Air France Flight 091, a Boeing 747-200, was involved in a runway excursion at Rio de Janeiro-Galeão International Airport, Brazil. The aircraft had departed from Paris-Charles de Gaulle Airport, France at 21:30 UTC, en route to Santiago, Chile, with planned stops in Rio de Janeiro and Buenos Aires, Argentina. The flight to Rio de Janeiro was uneventful and lasted approximately eleven hours.
Sequence of Events
At 08:34 UTC, the aircraft touched down on runway 14, 400 meters from the threshold. After the reversers were set, the aircraft deviated from the runway heading and, at 2,000 meters from the threshold, veered off the right side of the runway. The aircraft traveled over grass for 765 meters, then passed over a drainage ditch and a load apron concrete step, causing the landing gears to fold aft. The left wing gear separated completely. On the load apron concrete, the aircraft spun for 275 meters before stopping after the left outboard wing section struck an illumination stand.
For a few seconds, engines 2, 3, and 4 continued running at maximum reverse thrust, while engine number one operated at full forward thrust. After engines were shut down, passengers evacuated using three left-hand side escape slides. A fire started near engines 2 and 3 but was extinguished by airport fire fighters.
The investigation revealed that the number 1 engine throttle cable had broken, making it impossible for the flight crew to control engine power. The engine had accelerated to an unusually high forward thrust level, above takeoff power.
Probable Cause Findings
The official investigation reported the following findings:
1. Human Factor - Physiological Aspect: Crewmembers' physical conditions (fatigue) might have contributed to their delay in perceiving the engine failure and to inadequate reactions during the emergency.
2. Material Factor: a) Hydraulic pump ripple of the CF6-50E engine caused considerable vibration on the pulley support region, leading to cable oscillation and relative movement between cable and pulley. b) Pulley bracket design deficiency, possibly related to reduced contact area between cable and pulley, allowed wearing of these components in the presence of abrasive agents, combined with vibration in that area, with localized contact occurring almost permanently (93% of engine operating time in cruise range). c) Tests confirmed existing relative movement between cable and pulley even after modifications.
3. Maintenance Deficiency: a) Use of an unauthorized aluminum pulley instead of the recommended phenolic pulley enabled formation of abrasive agent (alumina). b) Inadequate fixation of the pulley bracket due to use of a screw with insufficient length for an additional washer, leaving the support side brace loose and increasing relative movement between cable and pulley.
4. Flight Manual Deficiency: a) The B747 AFM instructions allow the pilot flying to apply reverse thrust before knowing the effective transit of reversers. b) The AFM lacks instructions regarding a failure of reverser deployment associated with an engine runaway forward thrust, contributing to the crew not noticing the failure.
5. Training Requirement Deficiency: Lack of simulator training requirement for this type of emergency contributed to loss of control.
6. Crewmember Factor due to Operational Error: a) The captain did not observe AFM instructions about reverse levers and manual brake use. b) The FIE (Flight Engineer) did not observe AFM instructions about correct engine instrument monitoring during reverse operation.