What happened
On 15 December 2004, a Ken Brock KB2 gyroplane, registration G-BUYT, was performing a private flight from a grass strip at Sutton Bank, North Yorkshire. The pilot, who was flying to maintain currency, had previously completed a short flight earlier that morning. After taking off, the aircraft climbed to an altitude of approximately 20 feet before its pitch attitude abruptly changed to a nose-low position.
As the aircraft descended, witnesses heard the engine noise reduce and a crunching sound. The gyroplane drifted off the edge of the escarpment and struck the tops of several trees. The impact caused extensive damage to the airframe, including the failure of the main structural beams. The aircraft finally came to rest on a footpath, where the pilot sustained one fatal injury.
The investigation
The AAIB examined the wreckage and the seat/fuel tank assembly. While the fuel tank was found empty, evidence suggested the fuel had drained due to a rupture during the impact rather than exhaustion. The engine was found to be in good working order, and the propeller was being driven at low power at the time of impact.
Investigators focused on the seat attachment mechanism, which served as both a seat and a fuel tank. They discovered that the left side lug of the attachment bracket had failed due to fatigue cracking prior to the first tree impact. Additionally, the investigation found significant evidence of long-term fretting and looseness in the seat's support crossbar and its attachment to the rotor mast. There was also evidence that the horizontal stabiliser had not been fitted to the aircraft at the time of the accident.
Findings
- The failure of the seat top attachment bracket due to fatigue cracking was a primary concern, as it may have precipitated a loss of control.
- The seat support structure was subject to excessive vertical and lateral loading, likely caused by the looseness of the crossbar attachment bolts and in-service vibrations.
- The pilot's lack of recent experience on this specific aircraft type may have hindered the ability to respond to the emergency.
- The aircraft was flying without a horizontal stabiliser, though its impact on low-speed stability was considered negligible.
Safety action
- The Popular Flying Association (PFA) is advised to instruct inspectors and owners of Ken Brock KB2 and similar gyroplanes to rigorously check the security of all seat attachments and fittings, ensuring no cracking or deformation is present.