What happened
On 5 January 2003, a Yak-52, registration G-YAKW, was performing aerobatic manoeuvres near Towcester, Northamptonshire. The aircraft, operated by a private syndicate, had departed Turweston Airfield for a period of flight training and aerobatics. During the flight, the aircraft entered a vertical climb to execute a stall turn. Following the completion of the manoeuvre, the aircraft entered a vertical descent from which the crew could not recover. The aircraft impacted the ground at high speed, directly beneath power lines. Both the pilot and the passenger sustained fatal injuries.
The investigation
Investigators from the AAIB examined the wreckage and discovered that the elevator control was restricted. While the controls could move in a nose-down direction, they could not move beyond neutral in the nose-up direction. A search of the aft fuselage revealed that a short-handled, flat-bladed screwdriver had become wedged in the elevator quadrant assembly. This obstruction prevented the control surface from moving upward to pull the aircraft out of its dive.
Further examination of the maintenance history showed that the aircraft had undergone work in November 2002. A trainee mechanic at the maintenance facility admitted to losing a screwdriver matching the description of the recovered item. Although the mechanic stated he had not used the tool on this specific aircraft, DNA testing confirmed the pilot had handled the screwdriver at some point prior to the accident. The investigation also noted that the Yak-52's design features an open internal structure, making flight controls vulnerable to foreign objects. The aircraft's design also makes it difficult to inspect the rear fuselage without removing specific access panels.
Findings
- The primary cause of the accident was a loose screwdriver jamming the elevator control.
- The screwdriver was positioned such that the elevator quadrant 'scooped' it up during the stall turn, preventing any nose-up input.
- The aircraft's design lacks bulkheads, allowing items to migrate from the cockpit to the rear fuselage.
- The maintenance organisation lacked a formal tool control system, and tools were sometimes borrowed without the owners' knowledge.
- The design of the aircraft makes it nearly impossible to detect items in the rear fuselage through standard pre-flight checks, such as 'slapping' the fuselage.