Aircraft and Personnel
The aircraft was a Jodel D-112, a single-engine low-wing monoplane with fixed tailwheel landing gear, registration HB-SUB. It was powered by a Continental A-65 engine of 65 hp. At the time of the accident, the aircraft had accumulated 481 total operating hours. The pilot, born in 1930, held a private pilot license issued on 25 June 1958, valid until 3 May 1965, without special authorization for off-airport landings in mountainous terrain. He had a total flight experience of 140 hours and 447 flights, of which 19 hours and 50 flights were on the accident aircraft, including one previous landing at Obergrenchenberg. The passenger, born in 1940, was the pilot's brother-in-law and had no flight experience or license.
Accident Location
The accident occurred at a site about 4.5 km north of Grenchen, in the Jura mountains near the Berghaus Obergrenchenberg (1348 m above sea level). The landing area was approximately 450 m long with a 3-4% gradient in the direction of runway 25. It had been prepared by the Grenchen section of the Aero-Club of Switzerland for off-airport training but was not an officially designated mountain landing site. The terrain featured obstacles including a wall, telephone and power lines, and groups of fir trees. The ground was firm and dry with grass 10-15 cm high.
Weather
At the time of the accident, the weather was characterized by an 8/8 cloud cover with 4-6/8 at 2000 m and 6-8/8 above 3000 m, visibility 20 km, and wind 5-10 kt variable from west to north to east. Temperature was +13°C, relative humidity 80%, pressure 1 mb above standard.
Accident Sequence
On Saturday, 23 May 1964, the pilot intended to take his brother-in-law on a flight. He arrived at Grenchen, had the aircraft refueled, and did not file a flight plan or contact flight operations. He took off from Grenchen at 1530 MEZ and landed at the Obergrenchenberg landing site at 1545, proceeding to the Berghaus where he met friends. He did not consume alcohol. While preparing for departure, he remarked to a witness that the wind had shifted to a bise (northeast wind) but he could not take off into the wind due to the terrain slope. At 1640, the pilot started the takeoff roll with a tailwind, positioning the aircraft about 100 meters before the marked start of the takeoff area. The takeoff run was long; at the marked end of the strip, the aircraft bounced, touched down again, and lifted off about 25 meters beyond the strip in a steep nose-up attitude. It barely cleared a small wall and three overhead lines before striking the top of a fir tree, which caught on the nose. The aircraft then descended and struck a second fir tree about 70 meters further, at a height of 4 meters. It then nosed over to the ground, caught fire, and was consumed.
Damage
Both occupants were killed instantly. The aircraft was completely destroyed. Ground damage was minor.
Probable Cause
The accident was attributable to the pilot, who was inexperienced in mountain flying and not authorized for such operations, applying an unsuitable tactic during takeoff from a mountain landing site.