What happened
On June 30, 1966, a Piper J3C, registration HB-OAL, was conducting a private VFR flight from Ascona to Berne. After an initial leg from Berne to Ascona earlier that day, the pilot decided to return to Berne in the afternoon. To avoid adding weight to the aircraft, the pilot opted not to refuel in Ascona, estimating approximately 50 liters of fuel remained in the tanks.
During the flight, the pilot encountered heavy turbulence in the Centovalli and diverted through the Maggia Valley to find calmer air. While navigating the high terrain near the Nufenen Pass, the pilot encountered cloud cover on the northern slope. Fearing insufficient fuel to clear the peaks and return, the pilot decided to divert to Sion to refuel. However, 82 minutes after departing Ascona, the engine failed due to fuel exhaustion.
While attempting an emergency landing in a field near the Rhône river, the pilot encountered a strong headwind and obstacles. During the maneuver to avoid a tree, the right wing struck the ground, causing the aircraft to spin 180 degrees before coming to a halt. The two occupants sustained serious injuries, including fractures, but were able to evacuate the wreckage themselves.
The investigation
The investigation examined the aircraft's fuel system and the pilot's decision-making process. The Piper J3C featured a non-standard, custom-built fuel system consisting of two 32-liter wing tanks and a 20-liter collector tank. While the wing tanks had rudimentary transparent gauges, the collector tank lacked any means of monitoring fuel levels.
Investigators also analyzed the fuel consumption, noting that the engine typically consumes about 25 liters per hour. The investigation confirmed that the engine failure was caused by the depletion of all available fuel.
Findings
- The pilot significantly overestimated the remaining flight endurance and miscalculated the available fuel.
- The lack of a gauge for the 20-liter collector tank meant the pilot was unaware of exactly how much fuel remained once the wing tanks were empty.
- The pilot failed to utilize available intermediate airfields for landing despite knowing the fuel levels were critically low.
- The chosen emergency landing site was narrow and obstructed by ditches, making a safe touchdown difficult even without the wing strike.