What happened
On June 25, 1972, a Piper PA-28 Cherokee, registration HB-OKF, was conducting a visual flight rules (VFR) passenger flight from Cannes to Geneva. While flying over the village of Allos in the French Alps, the pilot encountered rapidly deteriorating weather conditions. Low-hanging clouds obscured the surrounding mountain peaks, effectively trapping the aircraft within a mountain cirque.
Unable to climb above the cloud layer or fly through the terrain, the pilot attempted to turn back toward the coast. However, rising clouds from the valley also began to obstruct the southern ridges. Faced with the prospect of being trapped, the pilot searched for a suitable landing site, scouting various fields at low altitude for approximately 10 to 15 minutes.
The pilot eventually selected a sloping meadow on a plateau for an emergency landing. During the approach, the aircraft struck a 220-volt electrical line consisting of three wires. The impact severed the wires and deflected the aircraft's trajectory. Shortly after, the aircraft clipped the tops of two trees and continued descending for approximately 100 meters before striking the steep wall of the Ubac ravine at a speed exceeding 100 km/h. The impact caused a post-crash fire that destroyed the aircraft. All four occupants (the pilot and three passengers) were killed.
The investigation
The investigation focused on the sequence of events leading to the impact and the mechanical state of the aircraft. Investigators examined the propeller to determine if the electrical wires had caused a blade to break during the initial contact, which might have induced vibrations and forced a power reduction. Technical analysis by the Propulsion Test Center at Saclay concluded that the propeller blade failure was not caused by the wires, as the wire diameter was significantly smaller than the blade section and no friction marks were present; instead, the blade likely broke upon impact with the ravine wall.
Findings
- The rapid deterioration of meteorological conditions in the mountains was the primary cause, as the encroating clouds blocked all escape routes from the Allos area.
- The pilot's decision to land in a field was the only viable option given the lack of IFR capability and the obscured terrain.
- The impact with an obscured electrical line during the final approach caused the loss of control and the subsequent collision with the ravine wall.