1970 Piper PA-28 Cherokee Accident at Les Chevalleyres, Blonay (HB-OYY)

Incident Overview and Flight Details On Tuesday, September 1, 1970, at 0945 local time, a pilot departed from the Gruyères aerodrome in a Piper PA-28 Cherokee, registration HB-OYY, with one passenger. The intended destination was Sion. Approximately 20 minutes after takeoff, while flying low beneath a cloud layer, the aircraft struck a medium-voltage power line pole during a turn and crashed into a field at Les Chevalleyres near Blonay, Vaud. Both occupants were killed, and the aircraft was destroyed. Two power lines sustained minor damage. ## Aircraft and Occupants The aircraft was a 1967 Piper PA-28-140 Cherokee, serial number 28-24020, powered by a 150-hp Lycoming O-320-E2A engine. It was owned and operated by Société d’aviation de la Gruyère S.A. of Bulle. At the time of the accident, the aircraft had 494.16 flight hours and 1,931 landings, and its weight and center of gravity were within allowable limits. The pilot, born in 1929, held a private pilot license and had 157.29 total flight hours, including 24.36 hours on the type. The passenger, born in 1937, had no aviation experience. ## Weather and Operational Context The flight was a private visual flight rules (VFR) operation. Meteorological conditions included total cloud cover of 7/8, with stratus clouds based at 1,200–1,500 m and altocumulus at 3,000–3,500 m. Visibility was approximately 5 km with strong mist rising from the lake. Witnesses reported the aircraft flying very low, with irregular throttle changes, and noted foggy conditions. The aircraft was observed making turns and accelerating before the impact. ## Investigation Findings and Cause The investigation, conducted with the collaboration of the Vaudoise Gendarmerie, concluded that the accident resulted from the pilot continuing the flight in conditions that no longer permitted visual flight and from the pilot’s loss of control of the aircraft. The left wing struck and severed a power line pole and its brace at 7 meters above the ground. The wing was torn off, and the aircraft performed a half-roll to the left before crashing onto its back 93 meters further. No pre-accident engine failure was indicated, and autopsy results showed no health deficiency or alcohol involvement in the pilot.