What happened
On July 27, 1974, an Arsenal Air-100 glider, registration HB-553, began a training flight after being towed from Schänis airfield. The pilot released from the tow rope approximately ten minutes into the flight over the Oberseetal region near Näfels. After roughly ninety minutes of flight time, the aircraft was observed flying at a very low altitude near the western slope of the Altwende/Altwisstock area. While traveling toward Wängital, the glider struck trees in a wooded area, resulting in the destruction of the aircraft and one serious injury to the pilot.
The investigation
Investigators examined the pilot's recent flight history and the technical state of the Arsenal Air-100. The pilot held a valid glider license but had undergone very limited training in the eleven months preceding the accident; his only recent flight activity consisted of four instructional flights in June 1974 to renew his license. Medical examinations confirmed the pilot was not under the influence of alcohol and showed no signs of impairment at the time of the accident.
Technical inspections of HB-553 found no pre-existing mechanical defects. However, the investigation noted that the aircraft's center of gravity was positioned at the rear limit of the permissible range. While the aircraft was approximately 5 kg overweight, this was not considered a significant factor in the crash.
Findings
- The pilot was flying at a very low altitude with low airspeed and minimal speed reserves.
- The aircraft fell below its minimum flying speed, leading to a stall.
- Local thermal turbulence contributed to the loss of airspeed.
- The rearward center of gravity position made the aircraft more susceptible to the stall.
- The pilot's recent lack of flight training may have contributed to poor flight tactics and insufficient clearance from the terrain.