What happened
On May 1, 1971, a Cessna 172H, registration HB-CSE, operated by SATA, was performing a non-scheduled commercial flight from Geneva to Sion. Due to adverse weather conditions in the Saint-Maurice pass, the pilot diverted to the Bex aerodrome, where the passengers disembarked.
Later that evening, the pilot planned a return flight via the Rhône Valley toward the French side of Lake Geneva. While flying at low altitude, the pilot encountered rapidly deteriorating visibility due to emerging fog and twilight. To avoid obstacles such as high-voltage lines and trees, the pilot performed a tight turn to align with runway 33. The approach was flown at a relatively high altitude, and the aircraft touched down approximately in the middle of the runway at roughly 70 mph.
Upon landing, the pilot deployed brakes, but the wet grass surface reduced their effectiveness. The aircraft traveled 290 meters down the runway before exiting the paved surface and striking a 50 cm deep construction trench on a nearby road. The impact caused the nose wheel to be torn off, bringing the aircraft to a halt. One passenger sustained slight injuries, while the other three occupants were uninjured.
The investigation
Investigators examined the mechanical condition of the aircraft and the environmental factors present during the landing. The inspection of HB-CSE revealed that the brake discs on both sides suffered from deep corrosion, which had reduced the effective braking surface by 20% to 40%. Furthermore, the outer lining of the left brake segment was worn beyond the limits specified in the maintenance manual, causing rivet heads to contact the disc.
While the static braking torque appeared normal during low-speed operations, the investigation established that the combination of the wet runway and the degraded mechanical state of the brakes significantly extended the required stopping distance.