Overview
On 16 August 1970 at approximately 1245 hours Central European Time, a Piper J3C aircraft registered as HB-OSU was involved in an accident near Souboz in the canton of Bern, Switzerland. The aircraft was destroyed, but both occupants escaped without injury.
Aircraft and Crew
The aircraft was a Piper J3C, a single-engine, two-seat, high-wing monoplane with a tailwheel landing gear and a fixed-pitch propeller. It was built in 1943 with serial number 11256 and was powered by a Rolls-Royce O-200-A engine rated at 100 horsepower. The aircraft was owned and operated by the Motorfluggruppe Biel. At the time of the accident, the total operating time was 3666:12 hours. The last 100-hour inspection was performed on 12 August 1970, and the last state inspection by the Federal Air Office was on 6 July 1970.
The pilot was born in 1950 and held a private pilot license issued on 23 October 1969, valid until 11 March 1972. His logbook showed a total flight experience of 33:47 hours and 218 landings (excluding the accident flight), of which 16:29 hours and 82 landings were solo. The passenger, also born in 1950, had no aviation experience or licenses.
Flight History
The flight was a private training flight initially planned from Grenchen via Bern, Thun, Jaun, Fribourg, Neuenburg to Pruntrut and back to Grenchen. The pilot departed Grenchen at 1005 hours. Before departure, he telephoned his flight instructor in Biel to reserve the aircraft and discuss weather conditions. The flight to Pruntrut proceeded without incident. After landing at Pruntrut, the pilot departed again at 1225 hours for a direct flight back to Grenchen.
Accident Sequence
While flying near Souboz at an altitude slightly above 1000 m above mean sea level, the pilot entered a wooded westward-facing slope of a mountain gorge with the intention of crossing the crest of the gorge (1100 m) and the higher Jura ridges beyond. Approximately 20 meters below the crest, the left wing of the aircraft made contact with fir trees. The aircraft pitched forward and fell vertically into the trees, where it remained stuck in an upright position.
A witness from Souboz observed the aircraft flying south of the village toward the gorge and, based on the flight behavior, suspected an unfavorable outcome. Shortly after, the witness heard the crash noise and rushed to the site, finding the two occupants uninjured.
Damage
The aircraft was destroyed. No significant damage to third parties occurred.
Contributing Factors (from source)
The pilot held a valid license and was authorized for the flight. The aircraft was airworthy and certified. At departure from Grenchen, the aircraft was 27.5 kg over maximum takeoff weight, but at the time of the accident the weight and center of gravity were within limits. The pilot, inexperienced in mountain flying, lost natural horizon reference after entering the gorge at minimum ground clearance (approximately 150 m). Sitting in the rear seat, the pilot had reduced visibility of the instruments. According to the pilot, he was searching for updrafts near the slope and realized too late that insufficient speed had led to a dangerous flight situation. He had also fallen well below the required safety altitude.
Probable Cause
The accident is due to the fact that the pilot fell below the prescribed minimum altitude and subsequently collided with trees.