1973 Piper PA-18-150 Super-Cub accident near Magden, Switzerland (HB-OYD)

Flight details and accident sequence On Wednesday, 4 July 1973, the pilot departed Bonn-Hangelar Airport in Germany at 0900 MEZ in a Piper PA-18-150 Super-Cub, registration HB-OYD, for a VFR flight to Bern. The aircraft initially climbed to 3,500 ft MSL. Near St. Peter, the pilot switched fuel from the right tank to the left tank and began climbing to 5,500 ft MSL. After crossing the Feldberg, poor visibility caused by heavy haze led to a descent. In the area of Wehr, the aircraft flew level at 200 to 250 m AGL, with the carburetor preheat left half-extended from the descent. Over the village of Mägden in the canton of Aargau, the engine stopped abruptly. The pilot checked the mixture, carburetor preheat, fuel valve position, fuel gauge, and ignition switch, then looked for an emergency landing field. He found only two small fields, approximately 100 by 20 m and 80 by 30 m. After beginning an approach to the first field, he noticed a ditch crossing it at about 50 m AGL and switched to the second field. A grain field lay in front of that field; the aircraft struck it 15 m before the meadow, overturned, and came to rest on its back at 11:25. ## Damage and pilot condition The pilot was uninjured. The aircraft was heavily damaged, and there was minor crop damage. ## Findings The pilot, born in 1946 and a mechanic, held valid commercial pilot licenses for fixed-wing aircraft and helicopters. His total flight experience was 745:31 hours, including about 27 hours on the accident type. In the preceding 90 days, he had flown 7:39 hours, of which 5:15 were on the accident type. Swiss Federal Air Office records showed no incidents in the previous five years, and nothing indicated that the pilot’s health was impaired at the time of the accident. HB-OYD was approved for commercial operations, and its weight and center of gravity were within limits during the flight. Before departure from Bonn-Hangelar, the aircraft was fully fueled with 136 liters. Examination of the engine and fuel system, except for the fuel strainer, found no indication of the cause of the sudden loss of power. The fuel strainer was so badly damaged in the accident that its level of contamination could not be determined. Dirt particles and pieces of newspaper were found in the left tank; their total surface area was about one-third of the flow cross-section of the in-tank fuel filter. The report concluded that the paper fragments and dirt particles found in the left tank could not have caused such an interruption. Based on the technical investigation, the sudden loss of power was attributed to an interruption in the fuel supply. ## Assessment Calculations based on the flight data indicated that 61 liters of fuel were available at the time of the accident, which was sufficient for the flight to Bern. The report listed three possible hypotheses: the no-longer-inspectable fuel strainer was so contaminated that fuel flow was no longer possible; the right fuel tank was exhausted and the pilot did not switch to the left tank, or did so too late; or, when switching, the valve remained in the “off” position.