Accident Overview
On Monday, 2 July 1973, a Piper Cherokee PA-28-180, registration HB-OLK, departed from Birrfeld airfield at 1736 hours for a private sightseeing flight. The aircraft carried the pilot and three passengers. The intended route was over Lake Constance to Rapperswil and back to Birrfeld. At 1810 hours, the aircraft crashed into the forested area of Öhninger Büel (coordinates 707.360/281.460, elevation 585 m) near the Swiss-German border. The impact killed all four occupants and destroyed the aircraft.
Flight Sequence
Witnesses observed the aircraft in the Dörflingen–Stein am Rhein area. Several witnesses reported hearing fluctuating engine sounds, including increases and decreases in noise, and moments of silence. One witness, a model aircraft enthusiast, described seeing the airplane perform a steep climb at about 33° from an estimated altitude of 150–200 m above the ridge. The engine sound became low and low-rpm. When the aircraft reached low altitude (estimated less than 60 m), it abruptly changed to a steeper climb (over 45°). The aircraft slowed until it appeared to stall, then rolled right and entered a slow spin, disappearing after 180–270° of rotation. Another witness, a glider pilot, heard the engine abruptly stop, then saw the aircraft pull out into a shallow descent heading 300°, then turn left and enter a vertical dive from about 300 m above the Hohenklingen area. After about 100 m of dive, it pulled up, then entered a progressively steeper left turn and finally a vertical dive from about 100 m above the ridge. A third witness reported normal engine sound throughout and described a steep left turn.
Aircraft and Pilot Information
The aircraft was a Piper PA-28-180 (serial 28-2297) powered by a Lycoming O-360-A3A engine (180 hp). Its last airworthiness inspection was on 24 February 1972; the last 100-hour check occurred on 14 June 1973. Total airframe and engine time at the accident was 2270:21 hours with 2451 landings. Takeoff weight was estimated between 2217 and 2277 lb, within the maximum limit of 2400 lb, and center of gravity was also within limits.
The pilot held a private pilot license issued 29 July 1970, valid until 15 November 1973, with a restricted radiotelephony endorsement dated 23 March 1972. He had a total flight experience of 71 hours 53 minutes, of which 2 hours 19 minutes on the accident type. In the last 90 days, he flew 1 hour 23 minutes total, 44 minutes on the accident aircraft. His last medical examination (16 November 1971) found him fit without restrictions. The three passengers were born in 1949, 1950, and 1951 and had no aviation experience.
Weather Conditions
The weather was characterized as a high-pressure situation with fair, warm summer weather. At the accident location, winds were variable, predominantly northeast at 5–10 kt near the surface. Visibility was 10–20 km. Cloud cover was 1/8 to 3/8 cumulus with base at 1600–2000 m, with some cirrus above. Light turbulence was reported over hilly terrain. Temperature at the surface was 27°C, dew point 15°C; at 1500 m, temperature 17°C, dew point 10°C. QNH was 1022 mb.
Wreckage and Medical Findings
The aircraft struck the ground at a 31° nose-down orientation, parallel to a 35° sloping forest edge, then tumbled and was destroyed. Post-crash examination revealed: master switch off; ignition off with broken key; fuel selector on right tank; fuel pump off; throttle lever bent 40 mm from the knob; carburetor heat off; flap lever at 0 (flaps retracted); airspeed indicator needle at 105 mph. Control cables were intact and correctly attached. Seat belts at front seats were still closed but the left buckle had torn out; right rear belts were open but fastened in the buckle. Medical examination showed severe injuries causing immediate death. Blood alcohol for the pilot was 0.04/0.05 weight per mille; passengers had varying levels. No other significant findings were reported.