What happened
On 5 June 2001, a Fokker F27 Mk 500 Friendship, registration G-CEXF, was performing a takeoff from Jersey Airport in the Channel Islands. Immediately following takeoff, the number one engine suffered a catastrophic failure. This event caused an instantaneous loss of power and triggered a significant fire outside the engine nacelle. The failure of the turbine components resulted in a severed low-pressure fuel pipe, which leaked fuel and served as the primary fuel source for the intense fire. The crew managed the emergency by executing a tight left-hand circuit to return to the airfield, successfully landing the aircraft as soon as possible.
The investigation
The AAIB investigation focused on the mechanical failure of the engine's high-pressure turbine (HPT) disc. Investigators examined the wreckage of the engine and the turbine assembly, specifically looking at the HPT disc and its relationship to the intermediate pressure turbine (IPT) seal arms. The analysis involved reviewing the engine's maintenance history, including previous failures in the fleet, and evaluating the effectiveness of recent service bulletins. The investigation also looked into the structural integrity of the turbine components and the presence of any gaps in the turbine stack that could have contributed to the failure.
Findings
- The engine failure was caused by the fracture and non-containment of the HPT disc.
- The HPT disc failure was driven by extensive high cycle fatigue (HCF) cracking caused by resonant vibration.
- This vibration likely occurred because a gap existed between the HPT and IPT seal arms, which lowered the disc's natural frequency into the engine's normal operating speed range.
- The HPT disc was an older design with a minimal fatigue strength margin, making it highly susceptible to rapid cracking when subjected to such resonance.
- The fire was fueled by significant leakage from a severed low-pressure fuel pipe following the turbine break-up.
- While a service bulletin had been issued in April 2001 to address similar issues, there was insufficient time for the aircraft to undergo the necessary modifications before this accident occurred.