What happened
On 7 April 2023, a private flight involving a Piper PA-2SB-180, registration G-AXSG, was landing at St Mary’s Airport, Isles of Scilly. As the pilot applied the brakes following touchdown, the aircraft veered left onto the grass airfield. During this maneuver, the left main landing gear collapsed, causing the remaining portion of the gear to dig into the turf. This action forced the aircraft to rotate 180 degrees before coming to a complete stop. There were no injuries to the pilot or the two passengers on board.
The investigation
Investigators examined the wreckage and found that the left landing gear wheel, torque link, and oleo strut assembly had detached from the main cylinder, though it remained connected via the brake hose. The inspection revealed that the upper torque link attachment lugs had broken away from the cylinder, and the base of the cylinder itself had fractured into several pieces near the attachment points. There was also secondary damage to the left wing and flap surfaces.
Microscopic analysis of the fracture surfaces using scanning electron microscopy identified areas of stable, progressive fatigue crack growth on both lugs. These cracks originated at the inner lower radii of the lugs, reaching depths of up to 3 mm before the final instantaneous failure occurred. The investigation also noted that the last recorded inspection of the gear, following the manufacturer's Service Bulletin, had been performed 141 flying hours prior to the accident, which exceeded the recommended interval.
Findings
- The left main landing gear torque link attachment lugs failed due to fatigue cracking.
- The failure of these lugs caused the wheel assembly and oleo strut to detach from the cylinder during landing.
- The fatigue cracks may have been present during the previous inspection but went undetected due to the difficulty of inspecting the area while the gear was installed and the limitations of the dye penetrant technique on porous alloy castings.
- The aircraft had exceeded the recommended inspection interval for the Service Bulletin by 41 flying hours.
Safety action
- The AAIB has issued Safety Recommendation 2024-001 to the CAA, requesting an unsafe condition assessment for cast main landing gear cylinders on PA-28 and PA-32 aircraft to ensure the continued level of safety.