Incident
On 23 June 2005, at approximately 1500 hours UTC, a Piper PA-18-150, registration G-SUPA, experienced a landing gear support frame failure while taxiing to the hangar at Headcorn, Kent, following an uneventful landing. The right wing slowly dropped until it rested on the ground. The engine was shut down, and the propeller remained clear of the ground. The aircraft was on a private flight with one pilot and one passenger; neither was injured. The damage was confined to the main landing gear support frame.
Aircraft and Crew Information
The aircraft, a single-engine Piper PA-18-150 manufactured in 1957, was powered by a Lycoming O-320-A2B piston engine. The commander, aged 52, held a Private Pilot's Licence and had accumulated 1,283 flying hours, of which 479 were on type. In the preceding 90 days, he had flown 11 hours, with 6 hours in the last 28 days.
Examination and Discussion
An examination revealed that the left side of the V-section support frame, which supports the main undercarriage suspension units, had failed across the hole where it is bolted to the airframe mounting lug. The landing gear support frame is constructed from two steel tubes welded together to form a V-section. At the end of each tube, a bush mounted on the tube end is held in place by a shaped plate welded around the tube. A comparison of the left and right attachment fittings, sectioned for inspection, showed that the bush on the left fitting was missing. The repair agency for the aircraft confirmed that the bush was not attached to the securing bolt, which remained fitted to the aircraft. Witness marks inside the tube indicated that a bush had originally been fitted, suggesting it may have come out when the frame was removed from the aircraft. Reassembly of the V-section frame without the bush installed would have left the securing bolt in contact with the welded plate, which then failed in overload during normal operations. The frame had last been inspected during the annual maintenance six months and eight flying hours before the incident. While the maintenance organisation stated that the assembly felt secure with no sign of excess movement at that time, there was no requirement during that inspection to remove the fitting from the aircraft to inspect the bolt holes.