Flight Preparation
On 13 June 1978, the pilot flew from Düsseldorf to Ascona with his father, son, and another passenger, stopping in Zurich. The following day, the pilot and his father visited the flight office at Ascona airfield to prepare for a VFR flight to Essen-Mülheim. The father informed the duty pilot of their intention to fly "on top" over the Alps. The duty pilot noted that the cloud tops were too high for a Cessna 172 and also pointed out the KOSIF (coordination of shooting and air traffic) map, which indicated ongoing shooting exercises in the Gotthard-Nufenen area. The pilot used a Michelin road map for route planning.
Accident Sequence
After takeoff from Ascona at 1200 MEZ, the aircraft climbed the Leventina valley and turned toward the Nufenen Pass. The pilot reported a climb rate of 150–200 ft/min. Approaching the pass, about 1–2 km before the summit, the pilot noted a sudden 500 RPM power loss. He attempted a right turn but found the valley too narrow. He decided to perform an immediate forced landing on a snowfield straight ahead. The aircraft touched down with landing flaps retracted and engine off on a slightly rising snowfield, then overturned.
Investigation Findings
The pilot held a valid private pilot license and was authorized for the flight. The aircraft was certified for operation; its weight and balance were within limits at the time of the accident, though it was slightly overloaded (by 12 kg) at takeoff. The engine inspection revealed no mechanical defects, but all spark plugs and exhaust pipes were covered with a white deposit, indicating the engine had been operating with an excessively lean mixture. Weather conditions at the accident site included clouds with bases at 2400–2600 m and 3000–3500 m, visibility over 10 km, east wind at 10 kts, and a freezing level at 2600 m; icing was possible above about 2500 m. The pilot had been warned about shooting activities in the area but chose to cross the Nufenen Pass instead of the lower and shooting-free Lukmanier Pass.
Probable Cause
The accident was attributed to incorrect mountain flying tactics.