Event Description
During a positioning flight, the airplane was taking off when, at approximately 40 knots during the takeoff roll, the flight crew heard a loud bang. The engine fan then passed by the right side cockpit window. The captain aborted the takeoff, secured the affected engine, and exited the runway. Only the two flight crew members were onboard; no injuries were reported.
Examination Findings
Initial on-scene examination of the No. 2 engine revealed a penetration of the engine case in the plane of the high-pressure compressor (HPC) impeller. A large hole was found in the top of the engine cowling at approximately 1:00 aft looking forward, just forward of the thrust reverser clamshell. The missing segment of the HPC impeller was not located. The HPC impeller had separated from the HPC and high-pressure turbine (HPT).
Metallurgical Analysis
A metallurgical examination of the impeller showed that the fracture was consistent with a low-cycle fatigue crack that initiated along a circumferential machining feature on the aft face of the impeller. River lines emanating from the aft face indicated that the crack started in the area of a groove and ultimately led to the separation of the HPC impeller from the engine.
Maintenance History
According to maintenance records, the impeller had accumulated 7,311.5 hours and 6,116 cycles at the time of the last engine overhaul on December 13, 1996. Since that overhaul, it had accrued an additional 1,582.1 hours and 1,760 cycles, for a total of 7,876 cycles since new. The cyclic life limit for the impeller is 8,400 cycles.