What happened
On 29 October 2009, a Piper PA-25-235 Pawnee, registration G-BETM, was completing a private glider aerotow flight at Sutton Bank Airfield in North Yorkshire. Immediately after the aircraft touched down on the grass runway, the pilot heard a loud noise originating from the left landing gear damper unit. Believing the sound was related to the landing gear, the pilot switched the magnetos to the OFF position. In an attempt to prevent the aircraft from tipping, the pilot tried to keep the left wing elevated. However, the left wing subsequently dropped, resulting in the wingtip contacting the grass surface. The aircraft then performed a slow 180-degree turn before coming to a halt. There were no injuries to the pilot, and the aircraft was vacated without difficulty.
The investigation
The investigation focused on the source of the noise heard by the pilot and the subsequent wing strike. Examination of the left landing gear damper unit revealed that the attachment lug had experienced a structural failure. Specifically, inspection of the fracture surfaces showed that the eye-end of the component had been subject to cracking for a period of time prior to the final failure during this specific landing.
Findings
- The primary cause of the wing strike was the failure of the attachment lug on the left landing gear damper unit.
- The fracture surfaces indicated that the eye-end of the component had been progressively cracking for some time.
- The aircraft was used primarily for aerotowing duties, typically performing approximately six flights per hour from a grass runway.