What happened
On July 10, 1975, a Robin DR 400/180, registration HB-EXG, departed from Triengen for a local VFR flight. The aircraft was carrying the pilot and one passenger. During the flight, while passing over Härkingen, the pilot observed that the oil pressure gauge indicated zero. Fearing an imminent engine failure, the pilot decided to perform an emergency landing in a field near Usserdorf.
As the pilot initiated the landing pattern, he shut off the master switch, ignition, and fuel selector. Due to a low approach, the left wing of the Robin DR 400/180 struck an oat field. The aircraft subsequently spun 40 degrees around its longitudinal axis and slid along the ground for approximately 40 meters. There were no injuries to the occupants, though the aircraft sustained heavy damage.
The investigation
Investigators examined the engine and found it to be in good working order, with sufficient oil levels (approximately 6.5 U.S. qts) and functioning oil pressure. The investigation revealed that an extra fuel gauge, intended for an auxiliary tank not present in this aircraft, had been installed on the instrument panel. Because this gauge was not connected to any system, its needle remained at zero. This specific gauge was clearly labeled "FUEL," but the pilot misidentified it as the oil pressure gauge.
Furthermore, the investigation found that the pilot's type rating training for this specific model had not been properly documented or completed according to regulations. It was also noted that the non-functional instrument had previously caused confusion for other pilots.