Introduction
On 23 June 1962, a Piper PA-18 aircraft registered HB-OPH was involved in an accident near Leymen in the Haut-Rhin department of France. The aircraft was privately owned and operated by the Aéroclub Spalen in Basel, Switzerland. The pilot was the sole occupant, undertaking a local flight from Bienne, Switzerland.
Flight History
The flight originated from Basel-Mulhouse Airport at 0902 UTC, landing at Bienne at 0944 UTC. In the afternoon, the pilot departed Bienne at 1557 UTC for a local flight. Weather conditions were excellent. After approximately 33 minutes of flight, at an altitude of 3,000 feet over the last foothills of the Jura mountains near the French border, the engine began to misfire. The misfires increased, and the engine stopped. The pilot attempted to restart using the starter; the engine ran briefly but stopped again.
Accident Sequence
Believing the engine failure was mechanical, the pilot decided to perform an emergency landing. He identified a suitable field located 2.5 kilometers south-southwest of Leymen. The field was approximately 400 by 300 meters in a wide valley with a slight slope west-east and a small gradient north-south. The pilot turned with the engine off to lose altitude, extended the flaps, and approached west-east. The aircraft touched down in an oat field with stalks about 40 centimeters high, rolling 54 meters. The pilot then saw a sudden drop in terrain of about one meter ahead. Fearing he could not clear it, he braked hard. The aircraft nosed over, pivoted, and came to rest inverted.
Investigation Findings
Post-accident examination revealed that the left fuel tank was empty while the right tank was full. The fuel selector valve was positioned to the left tank. The pilot had been using only the left tank during the flight. The total flight time from Bienne was about 33 minutes, consistent with the pilot's report that the left tank had about one-quarter fuel (approximately 16 liters) at departure, enough for about 30 minutes. The engine stoppage was due to fuel starvation as the left tank was exhausted.
The pilot did not consider fuel exhaustion as the cause of the engine failure and did not switch to the right tank. The terrain drop that caused the overturn was not visible from the air due to its slight nature. The pilot overestimated its height and applied brakes abruptly.
Damage and Injuries
The aircraft sustained damage: one propeller blade bent, oil cooler cowling dented, right wing torn from fuselage front, right wing support struts bent, left wing lower skin torn, upper cabin structure dented and Plexiglas broken, vertical stabilizer top wrinkled, and engine mount deformed. The pilot suffered a fractured left little finger, considered a minor injury.
Probable Cause
The engine failure resulted from fuel starvation because the pilot had used only the left fuel tank until it was empty. The subsequent emergency landing was complicated by a small terrain drop that the pilot did not perceive from the air, leading to the aircraft nosing over after hard braking.