Incident Overview
On May 1, 1971, a Cessna F 172H with registration HB-CSE, operated by S.A. de Transport Aérien (SATA) of Geneva, was involved in an accident at the Bex aerodrome in Switzerland. The aircraft was conducting a non-scheduled commercial flight from Geneva to Sion with three passengers on board. Due to adverse weather conditions in the Saint-Maurice gorge, the pilot diverted to Bex, where the passengers disembarked and continued their journey by road.
Flight Operations and Approach
At 18:45 local time, the pilot contacted Geneva airport for a weather update before planning the return leg. A flight plan was filed for a route via the Rhône valley to Douvaine, with special VFR authorization in the Geneva control zone. The aircraft departed Bex runway 33 at 19:05 under light rain and calm winds. While flying along the Rhône, visibility improved briefly near Vouvry, allowing an altitude increase to 400 meters above ground level. However, near Saint-Gingolph, clouds descended to lake level, prompting the pilot to return to Bex.
During the final approach, rapidly forming fog and twilight significantly reduced visibility. The pilot executed a tight turn to align with runway 33, noting high-tension lines and poplar trees nearby. With visibility limited to approximately 6,700 meters, the aircraft crossed the runway threshold at an altitude of 6–7 meters and touched down at roughly 70 mph.
Accident Sequence
After touchdown, the pilot retracted the flaps and applied brakes. The wet grass surface reduced braking efficiency. After rolling 290 meters, the aircraft overran the end of the runway. It crossed a 5-meter-wide construction road with a 50-centimeter deep excavation. As the nose wheel entered the trench at approximately 20 mph, it was torn off, bringing the aircraft to a stop six meters further along. The pilot had instructed passengers to brace and cut engine power prior to impact.
Damage and Injuries
One passenger sustained minor injuries, while the other three occupants were unharmed. The Cessna F 172H suffered severe damage, but no ground property was damaged.
Investigation Findings
The pilot, a SATA employee with 1,113 total flight hours, held a valid professional license and was familiar with the Bex aerodrome. No health issues or prior incidents were recorded. The aircraft had 650 flight hours and 1,943 landings at the time of the accident.
Technical examination revealed significant corrosion on both brake discs, reducing braking surface area by 20–40%. Additionally, the outer lining of the left brake segment was worn beyond maintenance limits, causing rivet heads to contact the disc. Although static braking torque tests showed performance comparable to new brakes, dynamic testing on similar wet grass surfaces indicated landing distances of 190–210 meters for an aircraft of similar weight.
Probable Causes
The investigation concluded that the accident resulted from a combination of factors: unexpected deterioration of weather conditions, a high approach due to reduced visibility leading to a long landing at excessive speed, and reduced braking effectiveness caused by the wet runway surface and defective wheel brakes that had not been detected during routine maintenance.