What happened
On 5 June 1998, a Hawker Hunter F 4, registration G-HHUN, was performing a pair display practice at Dunsfold Airfield. The flight was intended to prepare for upcoming airshows at Biggin Hill and Dunsfold. During the final stages of a display sequence, the aircraft experienced a sudden engine failure. The pilot transmitted a Mayday signal, reporting an engine failure while heading for the airfield.
Witnesses observed a flame emanating from the aircraft's jet pipe and the rear fuselage. The aircraft attempted an emergency landing on Runway 25 but struck a disused runway with its left drop tank before landing heavily on its main gear. The aircraft then bounced, rolled, and struck the ground a second time, eventually sliding across the runway surface. The pilot, who was released from his safety harness during the impact sequence, suffered fatal injuries.
The investigation
The AAIB investigation focused on the cause of the engine failure and the subsequent fire. Examination of the Rolls-Royce Avon Mk 1/22 engine revealed that the turbine blades had suffered an uncontained failure due to excessive temperatures. This overheating was caused by gross overfuelling of the engine.
Investigators found that while the high pressure pump isolation switch was in the 'NORMAL' position, the engine had been subjected to enough fuel to destroy the turbine blades within seconds. The investigation also examined the cockpit's ejection seat and canopy jettison systems. It was determined that the pilot did not attempt to eject before impact, and the structural deformation of the cockpit during the crash caused the ejection seat to move in a way that prevented the pilot from successfully exiting the aircraft.
Findings
- The engine experienced an uncontained failure of the high and low pressure turbine blades due to extreme overheating.
- The overheating was caused by a period of massive overfuelling.
- It is probable that the pilot momentarily selected the high pressure pump isolation switch to the 'ISOLATE' position without first closing the throttle, which would have caused the rapid overfuelling.
- The pilot may have performed this action in response to an initial engine malfunction or by error while attempting to use the smoke system.
- The pilot's limited experience on this specific aircraft type may have contributed to a lack of awareness regarding the dangers of operating the isolation switch with an open throttle.
- The pilot elected to attempt an emergency landing rather than ejecting, possibly due to the proximity of the airfield or the desire to recover the historic aircraft.