What happened
The incident occurred during the takeoff roll of a commercial flight when the number two engine suffered a critical structural failure. The primary point of failure was the aft engine mount cone bolt, which subsequently led to the breakage of the secondary support link, identified as a stainless steel cable. With both aft engine support assemblies compromised, the rear section of the engine descended significantly, coming within four feet of the ground surface.
As the aircraft rotated for liftoff, the lowered position of the engine caused the number two thrust reverser actuator assembly to drag along the runway pavement. This contact resulted in minor damage to one leading edge flap and slight harm to the forward engine fairing. Despite these mechanical issues, the aircraft remained controllable and was able to return to the airport, completing a safe landing without any further complications or incidents.
The investigation
A thorough metallurgical examination of the failed cone bolt provided key insights into the root cause of the accident. Analysis revealed that the bolt had failed due to fatigue cracking. Investigators determined that this fatigue was most likely initiated by improper installation practices during a previous engine reinstallation by maintenance personnel. Specifically, the bolt had been under-torqued, failing to meet the required specifications.
The secondary support link, or safety cable, also failed during the event. Examination indicated that this component failed due to overstress rather than fatigue. The excessive load was likely induced when the aircraft encountered a rough stretch of runway surface during the takeoff roll, placing additional strain on the already compromised engine mount system.