Aircraft and Flight Details
The aircraft, a Yak-52 registered G-YAKB, was manufactured in 1992 and powered by a single Ivchenko Vedeneyev M-14P radial piston engine. On 8 July 2016 at 0934 UTC, it was conducting an aerial work flight for a test pilots' school 1 nm north of Dinton, Wiltshire. The commander, a 60-year-old civilian flight instructor with 2,953 total flying hours (446 on type), occupied the rear seat. The front seat was occupied by a tutor from the school.
Background
The flight was part of a Qualitative Evaluation (QE) for the test pilots' course at Boscombe Down. The commander had sub-contracted to provide the aircraft, and the accident flight was the first of the day after a rescheduling. The front seat pilot, a Royal Air Force tutor, had not attended the mandatory cockpit familiarisation briefing given by the commander the previous day.
History of the Flight
After an uneventful start and taxi, the aircraft took off from Runway 23 at 0915 hrs and climbed to about 5,200 ft. It completed several aerobatic manoeuvres, some involving inverted flight, believed to have been flown by the front seat pilot. Following the manoeuvres, while at about 4,000 ft and descending slowly, the engine lost power without warning. The propeller continued to windmill. The commander moved the throttle but noted fuel pressure at zero and instructed the front seat pilot to operate the fuel primer handle. Each pump of the primer momentarily restored power, causing the engine to accelerate before stopping again. The commander flew high-g turns to attempt to release a possible stuck flapper valve, but to no avail.
At 0930:32 hrs, the front seat pilot transmitted a MAYDAY, reporting a major malfunction and requesting radar vectors back to Boscombe Down. ATC provided a heading and asked to squawk 7700, but the pilots were unable. At 0932:06 hrs, they reported visual with the ground and intent to perform a practice forced landing in a field west of Boscombe. At 0933:29 hrs, with the aircraft at about 1,100 ft agl, they declared a forced landing to a field and made their last transmission.
Having identified a large wheat field for landing, a farm strip came into view. The commander had an incomplete memory of one pilot declaring "there is an airstrip there" and decided to attempt landing on the strip rather than the field. The landing was unsuccessful; the aircraft struck the ground on the southern edge of the strip in a steep left bank. The front fuselage broke up, and the front seat pilot was thrown clear. The commander remained in the rear seat, seriously injured.
Eyewitness and Rescue
An eyewitness about 3 nm west saw the aircraft heading east at about 1,000–1,500 ft, with the engine faltering then stopping before restarting. A helicopter from Boscombe Down located the crashed aircraft, and its pilot assisted. The front seat pilot was unresponsive and pronounced deceased at the scene; the commander was airlifted to hospital.
Investigation
The cause of the engine power loss was not determined, but reported symptoms were indicative of a fuel system problem. One Safety Recommendation was made concerning maintenance of seat belts and harnesses.