What happened
On 6 July 2023, a Grumman FM2 Wildcat, registration G-KINL, was participating in a flying display and concours event at the Heveningham Hall Estate in Suffolk. The aircraft, a restored World War II-era fighter, was landing on a grass runway (06/24) used for vintage aircraft during the annual Heveningham Country Fair.
As the pilot performed a three-point landing at approximately 85 knots, the aircraft initially maintained a straight track. However, during the landing roll, the tail began to rise unexpectedly. Despite the pilot applying full back stick to counteract the movement, the aircraft's tail continued to lift. The aircraft subsequently pitched forward, with the propeller striking the ground, before the aircraft completed a full nose-over and came to rest inverted.
The pilot sustained serious injuries during the impact. Following the accident, fuel began leaking from the wing tanks into the cockpit. The pilot, remaining conscious, managed to use his helmet to enlarge a gap in the broken canopy to facilitate his eventual extraction by ground crew.
The investigation
The AAIB investigation examined the runway conditions, the aircraft's mechanical state, and the event's organizational procedures. Investigators found that the aircraft's braking and control systems were functioning normally. The investigation also noted that while lighter aircraft had landed on the same runway earlier that day without incident, the G-KINL had a higher ground pressure due to its narrow, high-pressure tyres and relatively high centre of gravity.
Subsequent testing of the runway surface revealed a hard crust approximately 2 cm thick overlying a much softer sub-soil. This condition was likely caused by significant rainfall in the preceding weeks followed by warm, dry weather, which hardened the top layer while leaving the underlying ground soft.
Findings
- The primary cause of the accident was the compression of the runway surface crust by the aircraft's narrow, high-pressure tyres, which created significant rolling resistance.
- This resistance caused rapid deceleration, and because the engine's mass created a large rotating moment above the main wheels, the aircraft was pulled forward onto its nose.
- The specific surface condition—a hard crust over soft sub-soil—was undetected by previous inspections, as earlier inspections were conducted with lighter vehicles that did not penetrate the surface.
- There was no specific risk assessment in place for operations on Runway 06/24, and the organizers had not reviewed the specific risk assessment for the visitors' fly-in for the 2023 event.
Safety action
Following the accident, the event organizers committed to several improvements for future fairs, including:
- Implementing a formal review of risk assessments for all fly-in components in advance of the event.
- Conducting dedicated risk assessments for the use of Runway 06/24.
- Appointing a qualified person to coordinate all aviation operations.
- Ensuring firefighting and lifting equipment is available at the runway for aircraft movements in the days leading up to the fair.