What happened
On January 24, 1965, a Piper L4 (registration HB-OXL) was conducting an aerial photography mission over the Vaudois Alps. The flight, operated by the Aérodrome régional de Montreux, involved the pilot and a photographer flying at low altitudes to capture images of the Chamossaire region and the Roc d'Orsay cable car station.
During the third pass of the mission, the pilot performed a descending right-hand sideslip at reduced engine power. The pilot was waiting to hear the specific click of the camera shutter to signal that the photo had been taken before applying power to climb. On this occasion, the pilot did not perceive the sound and continued the descent far too low. By the time the passenger alerted the pilot that the photo was captured, the aircraft was only 100 meters from a restaurant at the same altitude.
In an attempt to clear the ridge and overhead cable car lines, the pilot executed a sharp right turn. This maneuver induced a stall on the right wing. The aircraft descended into a steep, snow-covered slope, where the landing gear struck the deep snow, causing the plane to pitch vertically into the ground. The impact destroyed the aircraft, though no fire occurred.
The investigation
The investigation examined the aircraft's mechanical condition, the meteorological environment, and the flight maneuvers. The Piper L4 was found to be in excellent mechanical condition, with no evidence of engine or structural failure prior to the impact. The engine responded normally to pilot inputs, and the aircraft's weight and balance were within prescribed limits.
Meteorological conditions were ideal, with high visibility and calm winds. Investigators also reviewed witness accounts, noting that bystanders observed the aircraft flying at an extremely low speed, which created an optical illusion of the plane appearing stationary in the air.
Findings
- The primary cause of the accident was a loss of airspeed resulting from an excessively prolonged sideslip at a low altitude.
- The pilot committed an error in judgment by prioritizing the confirmation of the camera shutter sound over maintaining safe flying speed and altitude.
- The pilot's experience led to an overestimation of the aircraft's performance capabilities during the low-speed maneuver.
- The sharp turn executed to avoid obstacles triggered a wing stall.