Accident Overview
On the afternoon of 20 May 1977, a private pilot departed Bienne-Kappelen airfield with three passengers for a local VFR flight of about one hour. Approximately 25 minutes later, witnesses near Châtelat in the Jura region heard the aircraft and saw it emerge from a cloud performing erratic maneuvers. The aircraft suddenly disintegrated and crashed into a forest. A wing fragment was later found over one kilometer from the main wreckage. A thunderstorm had passed through the area shortly before the accident. All four occupants sustained fatal injuries and the aircraft was destroyed.
Investigation
The Swiss Federal Commission of Aircraft Accident Investigation conducted the inquiry. The investigation examined the wreckage, weather conditions, pilot history, and toxicological findings.
Pilot Information
The pilot, born 1941, held a private pilot license issued in 1964, valid until May 1978, with a type rating for the Piper PA-28R-200 obtained in 1969. His last medical examination was in May 1976. He had accumulated 410 total flight hours, with over 50 hours on the accident type. In the preceding three months, he had flown about 3 hours, including a 24-minute flight on the accident aircraft. A previous forced landing incident occurred in 1967 on a Piper J3C.
Aircraft Information
The aircraft was a Piper PA-28R-200 Cherokee Arrow II, serial number 28R-7435090, built in 1973. It was powered by a Lycoming IO-360-C1C engine (200 hp) and a Hartzell two-blade constant-speed propeller. Owned by the Groupe de vol à moteur de Bienne, it had 836 total hours. The last 100-hour inspection was performed on 4 April 1977. Weight and balance were within limits with 110 liters of fuel and no baggage.
Meteorological Conditions
The general weather was characterized by a ridge of high pressure from the Azores to Scandinavia and a weak depression over France and southern Germany, with cold continental air to the north and warm maritime air to the south. In the accident region, conditions included 8/8 cloud cover (cumulus, cumulonimbus, altocumulus, and fractostratus), visibility 10-20 km reduced by showers and thunderstorms, wind light northwesterly with gusts, and strong turbulence under storms. A thunderstorm with hail had occurred over Châtelat around 1600 hours but was subsiding at the time of the crash. The sky to the north-northeast remained very dark, but surrounding ridges were clear.
Wreckage Examination
The main wreckage, excluding the tail and a portion of the left wing, impacted a wooded slope. The right wing had separated at the root. The rear fuselage, horizontal stabilizer, vertical fin, rudder, and some fuselage pieces were scattered about 80 meters away. The missing left wing section was found in a field 1200 meters from the main wreckage. Structural failure originated at station 118 of the left wing, where the upper spar cap buckled under a high positive load factor. After separation, the wing fragment struck the rear fuselage and tail. Laboratory analyses confirmed that materials met specifications and all fractures were static overload; no pre-existing damage was found.
Medical Findings
Autopsy indicated the pilot died instantly from accident injuries with no endogenous lesions to explain abnormal behavior. No medications were detected, but a muscle sample showed a blood alcohol concentration of 0.9‰. Blood carbon monoxide was 5%. Passenger alcohol levels were 0.3‰, 0.1‰, and 1.0‰. All occupants wore seat belts; survival was impossible.
Cause
The commission stated the accident cause as:
- Pursuit of VFR flight in adverse weather conditions
- Exceedance of permissible structural loads in flight
- Impairment of pilot's abilities due to alcohol