What happened
On 28 March 2012, a P84 Jet Provost T3, registration G-BKOU, was conducting a post-maintenance flight test under clear weather conditions. The flight, which originated from North Weald, involved two experienced pilots performing checks following minor control adjustments. While descending through FL100, the crew prepared for a planned in-flight engine shutdown and subsequent cold relight.
During the procedure, the engine was shut down at an airspeed between 120 and 130 kt. The crew attempted a 'hot' relight at 160 kt, but the jet pipe temperature and engine RPM failed to increase. Following a second attempt using the emergency relight switch with non-essential electrics removed, light smoke appeared in the cockpit near the left seat. Shortly after, a fire warning light illuminated. The crew responded by donning oxygen masks and declaring a MAYDAY, initiating a forced landing at RAF Wyton.
The aircraft completed a standard forced landing pattern and touched down on Runway 26. The crew exited the aircraft normally, and although the airport fire service attended, no extinguishing equipment was required as the fire warning light had already extinguished.
The investigation
The AAIB examined the aircraft and found evidence of fire and heat damage to the jet pipe and the area where the engine exhaust cone joins the jet pipe. Inspection revealed sooting inside the fuselage and jet pipe, alongside scorched and blistered paint on the upper fuselage near the engine cone/jet pipe union.
Findings
- The engine failed to relight during the planned testing procedure.
- Fuel had likely pooled in the area of the engine cone and jet pipe union during the relight attempts and subsequently ignited.
- It was noted that while a drain exists in this area, fuel may not drain effectively if the aircraft is not in a level attitude.