What happened
According to the flight crew, a loud explosion was heard just seconds after reaching takeoff power, prompting an immediate abort of the takeoff. While taxiing back, air traffic control informed the crew that flames were visible coming from the number four engine. The aircrew brought the aircraft to a stop and initiated engine fire procedures, but airport fire fighters ultimately extinguished the blaze.
The investigation
An examination of the wreckage revealed that the number four engine had suffered an explosive failure. High-energy engine parts were released, causing significant damage to the airframe and the adjacent number three engine. Most rotating components located forward of the seventh-stage compressor disk assembly were ejected during the event.
A detailed inspection of the first-stage compressor fan blades identified the root cause. The number 15 first-stage fan blade (part number 531601K) had failed due to fatigue. This failure occurred only 3.2 hours after the engine had been overhauled.
Findings
The investigation determined that the explosive failure of the number four engine was caused by the fatigue fracture of a single fan blade. The release of high-energy debris resulted in secondary damage to surrounding structures and engines. Fuel exhaustion is not cited; the primary issue was mechanical component failure.