Incident Overview
During the takeoff rotation phase, the number 2 engine sustained an explosive rupture of its compressor rear frame (CRF). The flight crew observed a rapid deterioration in engine performance parameters and noted the illumination of the number 2 engine thrust reversers' 'unlock and in transit' lights. In response, the crew discharged a fire bottle and subsequently shut down the affected engine. After dumping fuel, they landed the aircraft without further incident.
Engine Damage
Examination of the engine revealed that damage was primarily confined to an axially ruptured outer casing of the compressor rear frame. The CRF had fractured as a result of high-stress (low-cycle) fatigue. Metallurgical analysis indicated that the fatigue crack originated at a zone of microporosity located in the ignitor pad area of the CRF outer casing.
Crew Actions
The crew's immediate recognition of the engine anomaly and appropriate actions—including fire bottle discharge, engine shutdown, and fuel dumping—enabled a safe landing. No further complications were reported during the remainder of the flight.
Investigation Findings
The investigation determined that the CRF failure was caused by high-stress (low-cycle) fatigue. The fatigue initiation point was traced to a small area of microporosity in the ignitor pad region of the outer casing. This manufacturing irregularity reduced the material's fatigue strength, leading to crack propagation under operational stresses.