Accident Overview
On 26 October 1988, the Robin DR 400-180R, registered HB-KAO, collided with a rock wall 30 meters below the crest of Risetenpass in the canton of Glarus, Switzerland. The aircraft exploded and was completely destroyed by fire. The pilot and three passengers were killed instantly. Minor ground damage occurred.
Flight History
The aircraft departed Bad Ragaz airfield at 12:00 local time with the pilot and three passengers. Earlier that day, the pilot had learned that two of his colleagues would be at Risetenpass and expressed a desire to greet them by flying over the pass. At approximately 12:30, two witnesses observed HB-KAO approaching Risetenpass from the Weisstannental valley, flying from east to west at low altitude. The aircraft crossed the pass nearly vertically above the signpost. After crossing, the pilot initiated a 180-degree turn to re-enter the pass. During the turn, the aircraft lost altitude for unknown reasons. Witnesses noted the aircraft descended steeply before recovering, then shortly afterward it struck the rock wall while climbing, almost parallel to the slope, and exploded immediately.
Weather Conditions
According to the Swiss Meteorological Institute, the general weather situation was high pressure with high fog in the lowlands. At the accident site and time, cloud cover was 1/8 with base at 4000 meters, visibility was more than 10 km, wind was variable at 5–10 knots, temperature 10°C, dew point 8°C, and QNH 1021 hPa. No hazards were reported.
Aircraft and Pilot Information
The aircraft was a Robin DR 400-180R, a single-engine, four-seat low-wing monoplane with fixed landing gear, powered by a 180 hp Lycoming engine. It was manufactured in 1984, serial number 1681, and owned by Segelfluggruppe Bad-Ragaz. It was certified for VFR day and night operations. At the time of the accident, the aircraft had accumulated 1144 total operating hours. The last 100-hour inspection was performed on 21 September 1988 at 1107 hours, and the last 50-hour check on 25 July 1988 at 1045 hours. Fuel quantity could not be determined but was estimated between half and three-quarters full.
The pilot, a Swiss citizen born in 1949, held a private pilot license issued on 3 June 1987, valid until 3 January 1990. He had 185 total flying hours, 78 of which were on the accident type, and 335 hours of glider experience. His last medical examination on 23 September 1988 found him fit without restrictions. The three passengers were all Swiss citizens, born in 1929, 1953, and 1953; none held aviation credentials.
Investigation Findings
The investigation determined that the pilot lost altitude during the 180-degree turn for reasons that could not be conclusively identified. The Risetenpass is narrow, requiring a near-frontal approach rather than the typical 45-degree angle that allows for escape maneuvers. The pilot may have been focusing on locating his colleagues. During the turn, the pilot lacked a normal horizon reference while flying below the crest and near the slope. The aircraft was climbing at impact, restricting forward and downward visibility over the steep terrain. Toxicological tests found no alcohol in the pilot's blood.
Probable Cause
The official finding stated that the accident was due to inadequate mountain flying tactics.