What happened
On 13 June 2002, a Boeing 747-240B, registration AP-BAT, was completing a scheduled flight from New York Kennedy Airport to Manchester International Airport. Following a routine touchdown on Runway 2HD, the crew applied reverse thrust on all four engines. As the aircraft decelerated, the flight deck indicators showed that while the reversers for engines 1, 2, and 4 had stowed normally, the No 3 engine reverser remained in an unlocked and in-transit state.
During the landing roll, a significant piece of the engine cowling detached from the aircraft. The separation was observed by the crew of a Boeing 757 crossing the runway behind the heavy jet. Air Traffic Control immediately took action to halt other arrivals to prevent potential collisions with the debris. The crew of the Boeing 747-240B continued to taxi to their parking stand, and the 303 passengers were disembarked without injury.
The investigation
The AAIB investigation focused on the structural integrity of the No 3 engine's thrust reverser assembly. Investigators identified the detached component as the outboard half of the No 3 engine thrust reverser translating sleeve, also known as the transcowl.
Examination of the wreckage revealed that the upper and centre clevis fittings had separated from the transcowl. The investigation found that the lower clevis fitting had undergone a progressive failure. Evidence of fatigue was discovered where the clevis pin had repeatedly struck the internal structure of the engine nacelle. Furthermore, investigators discovered that previous failed rivets in the attachment area had been replaced with incorrect, non-standard blind rivets. This undocumented and improper repair meant the structural integrity of the joint was not restored, and the use of the incorrect hardware made the degradation harder to detect during routine inspections.
Findings
- The separation was caused by the unnoticed degradation of the lower clevis fitting attachment.
- An improper repair had been performed using incorrect rivet types that did not meet design specifications.
- The failure to record this repair in the maintenance logs prevented the operator from identifying the compromised structure.
- The degradation likely caused a drift in the thrust reverser rigging, which had prompted recent maintenance adjustments.
- The structural failure of the attachment was exacerbated by the loss of the bond between the honeycomb panel and the inner skin.