What happened
During the beginning of its takeoff roll, the airplane experienced a failure of the #1 (left) engine. The failure was uncontained, as debris from the front compressor fan hub exited the engine and penetrated the left aft fuselage. Following the event, the takeoff was rejected, and the aircraft was brought to a stop on the runway. The accident resulted in two fatalities and two serious injuries among the passengers.
The investigation
Investigators determined that the fan hub had fractured through a blade slot and a tierod hole. The investigation revealed that during the manufacturing process, an event involving drill breakage or breakdown occurred alongside localized chip packing and a loss of coolant. This process created ladder cracking and an altered microstructure within the fan hub material. The damage caused by the drilling extended much deeper into the sidewall material of the hole than had been previously anticipated by Pratt & Whitney.
Findings
Fatigue cracks originated from the ladder cracking located in the tierod hole. These cracks began propagating shortly after the hub entered service in 1990. The investigation concluded that the crack was large enough to have been identified during the most recent fluorescent penetrant inspection performed by Delta. The failure to detect the crack was attributed to a failure in the inspection processing, a failure of the inspector to identify the defect, or a combination of both factors.