What happened
On July 10, 1971, at approximately 15:48, a Jodel-D 11-2, registration HB-SUO, crashed into the Thur riverbed near the Amlikon airfield. The aircraft was performing a private VFR flight intended to transport a flight instructor trainee from Amlikon to Sitterdorf.
Prior to the accident, the aircraft had landed at Amlikon and taxied to a parking area. During this time, glider winch operations were being prepared. The flight instructor trainee requested permission from the flight service manager to depart in the HB-SUO, with the instruction that the departure must wait until a glider winch launch had been completed.
Shortly after a glider had launched via winch and reached an altitude of approximately 400 meters, the cable was being retracted. As the cable descended toward the ground, the HB-SUO took off directly from its parking position and taxied onto the runway, initiating takeoff without waiting for the cable to be fully cleared. At an altitude of between 40 and 80 meters, the aircraft struck the descending tow cable. The impact caused the aircraft to roll left and enter an uncontrolled descent, crashing into the riverbed where a post-crash fire destroyed much of the wreckage. The two fatalities were the pilot and the passenger.
The investigation
The investigation examined the sequence of events, the mechanical state of the aircraft and winch, and the actions of the personnel involved. Investigators reviewed the flight logs of the crew, noting the pilot had significant experience, though the passenger had never flown the Jodel model.
Technical examinations of the Jodel-D 11-2 showed the aircraft was in good condition and the engine was functioning at the time of impact. The investigation also looked into the winch mechanism, finding that the cable cutter required approximately 50 kg of manual force to operate. The winch operator reported being heavily blinded by the sun during the retrieval process and attempted to cut the cable once he realized the collision was imminent, but was unable to do so in time.
Findings
- The primary cause of the accident was the collision between the aircraft and the descending winch cable immediately after takeoff.
- It could not be determined if the flight instructor trainee communicated the flight service manager's restriction to the pilot.
- The aircraft departed the parking area and entered the runway without waiting for the completion of the glider winch operation.
- The winch operator's ability to intervene was hindered by sun glare and the rapid speed of the approaching aircraft.