Accident Summary
On 5 July 1969 at 16:46 local time, a Piper PA-18 (registration HB-ORB) departed from Les Eplatures aerodrome towing a glider HB-768. After 2–3 minutes of flight, at approximately 80 m above ground, the engine stopped abruptly. The pilot released the tow rope and attempted a forced landing in a sloping hayfield. The aircraft touched down with the tail still high, lost control due to windrows, and overturned. The pilot exited the aircraft without injury. The glider landed safely at the aerodrome.
Aircraft and Pilot Information
The aircraft was a Piper PA-18 built in 1939, equipped with a Lycoming O-320-A2B engine. It had two wing fuel tanks, each with a capacity of 18 US gallons, selectable via a fuel selector valve. The pilot was 42 years old with 476 hours of powered flight experience and 192 hours of glider experience. The aircraft’s last 33-hour check had been performed 3.5 hours before the accident.
Investigation and Findings
After the accident, the aircraft was examined. The right fuel tank was empty, while the left tank indicated slightly above half. The engine ran normally when drawing from the left tank but stopped when switched to the right. The right fuel gauge tube was found blocked by a black, sticky substance. Analysis by EMPA identified the blockage as corrosion products, primarily zinc oxide, talc, and zinc fluoride, originating from the metal components. The blockage prevented the gauge from correctly indicating the fuel level.
Probable Cause
The accident was due to a dry fuel failure, consequent to a malfunction of one of the two fuel gauges.