What happened
On July 8, 1968, a Diamant 18 glider, registration HB-915, departed from Altenrhein airfield at 08:00 for a planned 600 km cross-country flight toward Styria. The pilot began the flight during a period when thermal activity was not yet fully developed. As the morning progressed, the pilot struggled to find sufficient rising air, eventually communicating via radio at 10:30 that he would be forced to land in Bludenz if no updrafts were found.
At approximately 10:35, while maneuvering near the Rungelin forest, the aircraft struck the cable of a local agricultural hay transport system. While the wings and fuselage did not directly hit the wire, the elevated horizontal stabilizer became entangled with the cable. The sudden impact caused an immediate loss of airspeed, causing the aircraft to pitch and plummet vertically into the dense forest below. The pilot sustained fatal injuries and passed away shortly after the crash.
The investigation
The investigation examined the aircraft's condition, the weather at the time of the accident, and the presence of obstacles in the flight path. Investigators confirmed that the Diamant 18 was in a sound technical state and that the pilot was a highly experienced aviator with extensive flight hours.
Analysis of the weather indicated that while visibility was excellent, the thermal conditions were insufficient for the intended flight profile at that early hour. The investigation also focused on the agricultural cable system, noting that while the system was marked on aeronautical charts, the specific cable in use at the time of the accident was the load-bearing cable, and the tensioning wire was not present. The investigation concluded that the pilot had even highlighted the location of cable systems on his charts, suggesting he was aware of their existence.
Findings
- The primary cause of the accident was the unintentional flight beneath the hay cable, which the pilot failed to detect in time.
- The pilot was flying closer to the terrain and at a lower altitude than usual in an attempt to locate weak thermal updrafts.
- The timing of the departure was too early, as the necessary thermal activity had not yet developed, necessitating a search for lift that led the aircraft into a hazardous area.
- The sudden entanglement with the cable caused an instantaneous loss of airspeed, leading to an unrecoverable vertical descent.