Accident Overview
On 30 March 1989, at approximately 1806 local time, a Piper PA-18-150 aircraft, registration HB-OYD, sustained substantial damage during a takeoff from the Hüfifirn glacier in Switzerland. The right landing gear collapsed, causing the right wing to contact the snow surface. The aircraft then veered left and came to a stop on the firn. Both occupants were slightly injured or uninjured.
Aircraft and Pilot Information
The aircraft was a Piper PA-18-150, owned and operated by Flugsportgruppe Zürcher Oberland. It was equipped with an approved Fernandez ski kit, installed on 10 February 1989 by a recognized maintenance facility. The pilot, a Swiss citizen born in 1945, held a private pilot license and had accumulated 1,746 total flight hours, with 350 hours on type. The flight was conducted as a private operation.
Accident Sequence
The flight departed Speck-Fehraltorf at 1642 for a mountain flight with glacier landings in the Glarner Alps. The purpose was to conduct a practical examination for the mountain landing endorsement. After the candidate successfully completed the test (10 landings at three different sites), the examiner took control to demonstrate an additional landing site on the Hüfifirn. The uphill landing was normal. During the subsequent downhill takeoff, the right landing gear collapsed, leading to the accident.
Findings
Examination of the landing gear revealed that the failure occurred at the lower node of the triangular steel tube assembly, in the area of the tubular wheel hub attachment. The fracture zone exhibited signs of overstress and pre-existing cracks in the weld area. The aircraft had been used extensively for glacier operations; on the accident day alone, 82 glacier landings had been performed.
Weather Conditions
Weather at the time was characterized by a high-pressure system. The sky was cloudless, visibility exceeded 20 km, and winds were practically calm. Temperature was -2°C with a dew point of -8°C, and QNH was 1019 hPa. The glacier surface was covered with old snow.
Cause
The failure of the right landing gear was probably due to pre-existing damage.