What happened
On the morning of July 9, 1971, a Piper J3C, registration HB-OIS, departed from Reichenbach airfield with a pilot and one passenger. The pilot intended to perform an unauthorized drop of provisions to workers at the Lämmerenhütte construction site.
At approximately 06:15, the aircraft flew at a low altitude over the construction site heading west. After performing a left turn toward Gemmipass, the pilot attempted a second, climbing approach to facilitate the drop. During this maneuver, the aircraft suddenly pitched to the right and struck the ground approximately 50 meters from the site. The impact, which occurred at an altitude of roughly 2,480 meters, resulted in two fatalities and the total destruction of the aircraft.
The investigation
An investigation conducted by the Swiss Transportation Safety Investigation Board (SUST) and the Valais Cantonal Police examined the wreckage and flight path. Investigators found that the aircraft's right wing, engine, and cabin were destroyed, with the debris pattern indicating a steep right-hand spin at impact.
Key findings from the wreckage included the discovery of a cassette tape recorder and a box of provisions. Notably, the upper door on the right side of the cabin was found locked in the open position. While the aircraft's weight and center of gravity were within limits, the open door was noted to have negatively impacted the aircraft's climbing performance. The investigation also determined that the pilot's mountain flying experience was insufficient for the technical demands of the terrain.
Findings
- The pilot attempted a cargo drop without the required legal authorization.
- The second approach was executed with insufficient altitude and airspeed reserves.
- The aircraft's airspeed fell below the minimum required speed during the climb.
- The low altitude prevented the pilot from recovering the aircraft's flight attitude before impact.
- The open cabin door reduced the aircraft's ability to climb effectively.