What happened
On July 19, 1965, a towing operation commenced at Sion Airport involving a Piper J3C Cub, registration HB-OBV, and a DFS Meise glider, registration HB-389. The flight proceeded normally during the initial minutes of the tow. While flying at a relatively low altitude along a slope near Ayent, the pilot of the Piper J3C Cub initiated a turning maneuver away from the slope. However, the aircraft began to descend steadily.
As the aircraft turned, it began to head toward the hillside. The glider pilot, recognizing the dangerous trajectory, released the towline and performed an emergency landing nearby without further incident. The Piper J3C Cub continued its descent, striking a high-voltage power line and a house in the Blignou district before catching fire. The pilot of the towing aircraft was killed in the impact, while the glider pilot remained uninjured.
The investigation
Investigators examined the wreckage of the Piper J3 and Cub and found no evidence of mechanical failure. The flight controls were fully functional, the propeller was rotating at the time of impact, the fuel valve was open, and the throttle was set to full power. The towline release mechanism had worked correctly, as the cable was found disconnected near the wreckage.
An autopsy of the pilot was performed to determine the cause of the uncontrolled descent. The examination revealed extensive atherosclerosis in the coronary, carotid, and aorta arteries. Specifically, a fresh hemorrhage was found within an atherosclerotic patch in the posterior coronary artery. The investigation also noted the pilot's medical history, which included long-term diabetes mellitus and previous reports of shortness of breath during physical exertion.
Findings
Technical and aeronautical factors were ruled out as causes for the accident. The investigation concluded that the primary cause was an acute heart attack experienced by the pilot during the flight. This medical event likely caused a sudden loss of control or a collapse, leading the aircraft into the terrain.