Accident Overview
On 8 September 1972 at 1045 hours MEZ, a Piper J3C, registration HB-ODZ, was involved in a hard landing accident on a private field near Diemtigen, Bern, Switzerland. The pilot, born in 1925, held a restricted commercial pilot license. He had logged a total of 453 flight hours, with 50 hours on the accident type and 28 hours in the preceding 90 days. The pilot was accompanied by an avalanche specialist as a passenger. The flight was conducted under visual flight rules (VFR).
Flight History
The pilot departed Kägiswil airfield at 1015 hours with the intention of performing an off-field landing at a site known as "Styg" near the Küng property in Diemtigen. The pilot flew from the rear seat, while the passenger occupied the front. As a member of the Swiss Ski Association, the pilot was tasked with evaluating projected and existing ski slopes for a new ski lift project. He had been commissioned to prepare an avalanche report for the concession authority and occasionally consulted a specialist for specific avalanche issues.
To expedite the one-day operation, the pilot reconnoitered the landing site on foot on 2 September and by aircraft on 3 September, during which he performed four practice landings on the intended meadow. The meadow is located at the entrance to Diemtigen, about 130 meters to the right of the main road on a hill. It measures 250 meters in length and 60 meters in width. Its southern boundary drops to a plateau about 20 meters lower, while the northern boundary is bordered by trees approximately 25 meters high.
On the day of the accident, the pilot telephoned the landowner to inquire about weather conditions in the Diemtig Valley and requested that a pole with a cloth attached be held aloft as a windsock at the landing site upon his arrival. The pilot reported that the flight to Diemtigen was conducted under fairly good weather conditions. Instead of flying a downwind leg, the pilot flew directly over the landing site to observe wind conditions, which he assessed as weak, variable, and aligned with the approach path.
Accident Sequence
From a distance of about 500 meters to the intended touchdown point, the pilot initiated a right turn into the approach, which proceeded normally. With engine power reduced to idle and speed approximately 10 km/h above the "red line" (stall speed), the aircraft first touched down hard with the main wheels on the steep slope, about 15 meters short of the intended touchdown point. After a bounce, the aircraft came to rest on its fuselage a few meters uphill, with the right main landing gear broken. The accident occurred at 1045 hours.
Findings
- The pilot held a valid pilot license for the flight.
- The pilot possessed a temporary permit for off-field landings at Diemtigen, issued by the Swiss Federal Office for Civil Aviation.
- No medically relevant information regarding the accident was known to the investigation.
- The aircraft had no prior accident or incident recorded with the aviation authority.
- The aircraft was certified and airworthy; weight and balance were within prescribed limits.
- The airspeed indicator system was tested and found to be leak-free, but the instrument indicated approximately 2–4 km/h too low in the speed range of 80–130 km/h.
- Weather at the accident site, as reported by the meteorological station: 7/8 stratus at 2600 ft AGL, occasional light rain showers, wind from northwest at about 2 knots, visibility 6 km (possibly less in heavy showers).
- Microscopic examination of the main landing gear attachment fracture showed only signs of overload fracture, no pre-existing cracks. The central tube in the landing gear spring exhibited typical signs of tensile overload.
Assessment
The pilot apparently misjudged the height and distance during the approach to the landing site and did not adequately account for approach speed. At a relatively low speed, the aircraft touched down hard approximately 4–5 meters lower than the intended touchdown point. The aircraft HB-ODZ was used as a group aircraft for training. It is possible that hard landings during student training had previously caused deformation of the central tube in the landing gear spring.
Probable Cause
The accident resulted from the pilot flying too low in the approach to the landing site and touching down prematurely due to inappropriate landing tactics in rising terrain.