What happened
On 11 June 2004, an MD Helicopter (Hughes) 369D, registered as C-GWPQ, was engaged in a sling load operation, lifting a 900-pound weight, when a loud bang and a partial loss of engine power occurred. In response to the power loss, the pilot executed a forced landing. During the landing, the aircraft struck the ground and rolled onto its right side while the main rotor blades were still in motion. The engine remained running after the impact until the pilot manually shut it down. There was no fire following the crash, and while the pilot suffered health issues related to the accident at a later date, there were no fatalities or injuries reported at the scene.
The investigation
Investigators examined the Rolls Royce Allison 250-C20B engine, specifically focusing on the compressor assembly. The investigation revealed significant internal damage, including the shedding of all rotor blades from the second and third stages, as well as major penetration of the compressor case halves. Analysis of the stator vanes showed that their failure was secondary, caused by the initial destruction of the rotor blades.
Engineers also looked into the possibility of foreign object damage (FOD). While an impact mark and aluminum metal transfer were found on a first-stage rotor blade, the evidence was inconclusive. An oxidized mark on a support vane suggested some damage might have been old, and while a piece of an aluminum rivet was found in the engine cowl, it could not be definitively linked to the compressor failure.
Findings
- The primary cause of the compressor failure was the separation of a second-stage rotor blade caused by high cycle fatigue.
- The fatigue failure originated at or near the leading edge of the blade.
- The failure of the stator vanes was a secondary effect of the rotor blade separation.
- The role of foreign object damage as a precursor to the fatigue fracture could not be confirmed.