What happened
On the evening of November 2, 1987, a pilot departed from Grenchen Airport in Switzerland aboard an AS 202/15-1 "Bravo" glider-motor aircraft, registration HB-HFU, carrying two passengers. The flight was intended as a short local pleasure trip. After takeoff on runway 07, the pilot initially flew east along the Echo departure route before turning south toward the Limpachtal valley.
Witnesses observed the aircraft performing various maneuvers at very low altitudes over residential areas in Zuchwil and Biberist. The flight path was erratic; observers noted abrupt throttle adjustments and unstable handling. At one point, the pilot incorrectly reported passing the "Whiskey" reporting point while flying east, ignoring tower corrections to follow the West exit route. After correcting this communication error, the aircraft continued its low-level maneuvers.
The final phase of the flight was witnessed by multiple individuals near Küttigkofen. The aircraft approached from the direction of Jura, flew a loop, and then pulled up steeply. Witnesses described the plane entering a spiral dive before crashing into open ground south of Küttigkofen. The aircraft was destroyed upon impact, and all three occupants were killed.
The investigation
The Swiss Transportation Safety Investigation Board (STSB) examined the wreckage, medical reports, and witness testimonies. The autopsy revealed that the pilot had a blood alcohol concentration of 1.18 per mille at the time of the accident. Additionally, traces of Atrium, a sedative medication, were found in his system. The passengers were not under the influence of alcohol or drugs.
Physical evidence at the crash site showed the pilot was not wearing a seatbelt, while both passengers were secured. The aircraft's flight data indicated no technical failures; the engine and airframe were airworthy. The investigation focused on the pilot's physical state and decision-making during the low-altitude maneuvers.
Findings
The primary cause of the accident was a stall at low altitude resulting from insufficient airspeed during a maneuver. Contributing factors included:
- Pilot impairment: The pilot was significantly intoxicated with alcohol and had consumed sedatives, which degraded his psychophysical performance and judgment.
- Failure to secure: The pilot failed to fasten his seatbelt before takeoff.
- Spatial disorientation/errors: Repeated confusion regarding position reporting to air traffic control indicated impaired situational awareness.
The aircraft entered a spin after stalling, which the pilot partially recovered from but was unable to recover fully due to the low altitude. The crash was unsurvivable for all occupants.
Safety action
No specific safety recommendations were issued in this report beyond the standard findings of pilot impairment and procedural failures.