Arsenal Air 100 collision with trees during low altitude flight at Altwisstock, Switzerland
On July 27, 1974, an Arsenal Air 100 experienced a collision with trees near Altwisstock, Switzerland. The incident occurred during a training flight when the glider, flying at low altitude, collided with a wooded area. The pilot sustained serious injuries, and the aircraft was destroyed. The investigation found that insufficient flight training, moderate turbulence, and a rearward center of gravity contributed to the glider stalling. The glider was slightly overloaded, but this was not considered significant to the accident.
- Aerotow to soaring area: The pilot aerotowed from Schänis and released over the Oberseetal near Näfels to begin a local soaring training flight.
- Limited recent training: In the 11 months before the accident the pilot had only four short dual flights totaling 50 minutes to renew his licence, leaving him with little recent solo soaring practice.
- Aft CG and turbulence: The glider was flown with the center of gravity in the rear part of the allowable range in conditions with moderate turbulence from local thermal activity, reducing speed margin and pitch stability.
- Low-level ridge flight: After about 1 hour 30 minutes of flight the pilot was flying along the western slope of the Altwisstock at very low height above a wooded area with little speed reserve.
- Speed falls below minimum: While flying close to the slope with small speed margin, the glider’s airspeed dropped below the minimum safe speed, likely influenced by turbulence and aft CG.
- Sink and tree contact: The glider suddenly sank through in the low-level flight path and its wings or fuselage struck the treetops of the wood on the western flank of the Altwisstock.
- Crash - serious injury: Following the tree strike the glider crashed into the wooded area, seriously injuring the pilot and destroying the aircraft with minor damage to the forest.