Flight History
On 18 May 1981, a private flight departed Môtiers airfield at 09:25 local time aboard a Bücker 131 Jungmann, registration HB-UVC. The pilot and a passenger were on board. The flight proceeded to Porrentruy, landing at 09:57, then departed at 11:42 for Buttwil, arriving at 12:41. From Buttwil, the pilot attempted unsuccessfully to contact Gruyères airfield by telephone. Despite this, he departed for Gruyères.
Accident Sequence
Overflying Gruyères, the pilot observed an aircraft taking off but later realized the airfield was closed. He continued the approach to runway 36, deciding against alternatives: Ecuvillens was considered too difficult, Yverdon too far for the remaining fuel, and he lacked the approach chart for Lausanne. The first approach was too high, so he executed a go-around and entered the downwind leg. During the base leg, he turned at an altitude of 2,700 feet—lower than the prescribed circuit altitude of 3,300 feet. Noticing his low altitude, he attempted to increase engine power but found the engine unresponsive; the propeller was windmilling. Unable to reach the runway in a glide, he aimed for a hill to avoid obstacles. The right wing struck the hill, and the aircraft came to rest on its left side after a few meters.
Investigation Findings
Post-accident examination revealed approximately 20 liters of fuel in the tank, plus 10 liters in reserve, measured about 2 hours after the crash. The pilot stated he had filled the 88-liter tank before departure and estimated 58 liters consumed during the two hours of flight. Manufacturer specifications indicate consumption of 25–35 liters per hour. The airfield was closed due to poor runway condition, indicated by white crosses at the thresholds and a signal on the signals area. The aircraft, equipped with a Walter Minor 4/III engine (105 hp), had been temporarily authorized to use automotive gasoline. Engine inspection in a workshop uncovered a malfunction in the mixture control that interfered with the throttle, causing an overly rich fuel-air mixture that could lead to power loss and misfiring, especially at low rpm. A reconstruction flight the next day confirmed the altitude at which the pilot had turned base.
Cause
The accident resulted from a missed forced landing following an engine failure.