What happened
On 8 July 2009, a Hunting Percival P56 Provost T1, registration G-AWVF, was conducting a private flight from RAF Waddington to RAF Linton-on-Ouse. While cruising at 2,500 ft, the aircraft experienced a catastrophic mechanical engine failure that triggered an intense in-flight fire. Witnesses observed thick black smoke and flames trailing from behind the propeller.
During the emergency, the pilot attempted to declare a 'mayday', but the transmission was blocked by another aircraft's radio signal. The aircraft subsequently entered a steep, nose-down descent. The aircraft crashed into a field near Bishop Norton, Lincolnshire, with the impact causing the aircraft to be destroyed. The pilot was thrown clear of the wreckage and sustained fatal injuries. Evidence suggests the pilot likely inhaled toxic fumes from the fire, which may have rendered him unconscious before impact.
The investigation
The AAIB examined the wreckage and the Alvis Leonides 503/6A engine. Investigators found that the engine had suffered severe damage, including the detachment of several cylinders. Metallurgical analysis of the No 6 piston gudgeon pin revealed a fatigue crack that had propagated through the component. The investigation also looked into the aircraft's maintenance and usage history, noting a low utilisation rate over its 45-year lifespan.
Findings
- The primary cause of the accident was an in-flight engine fire resulting from a catastable mechanical engine failure.
- The failure originated from a fatigue crack in the No 6 piston gudgeon pin.
- The initiation of the fatigue crack was likely caused by a high-load event, such as a partial or full hydraulic lock, with corrosion pits on the pin's inner surface acting as a contributory stress raiser.
- The aircraft's low usage rate over several decades likely contributed to the formation of these corrosion pits.
- The pilot was likely incapacitated by smoke and toxic combustion products prior to the crash.