What happened
On July 2, 1967, a training flight near the southern slope of Mount Pilatus resulted in a fatal accident. A student pilot, operating a Rhönlerche II glider with registration HB-598, was performing ridge soaring maneuvers. During the flight, the aircraft entered a zone containing obstacles and struck a 6 mm thick telephone cable belonging to the Aeschi-Chretzenalp aerial cableway. The impact tore approximately 3.20 meters of the right wing's leading edge. Following the collision, the glider lost significant airspeed, entered a spin, and plummeted into the Giessbach ravine. The pilot sustained fatal injuries upon impact with the ground, and the aircraft was destroyed.
The investigation
The investigation examined the flight conditions, the aircraft's airworthiness, and the visibility of the obstacle. Evidence from the wreckage confirmed that the collision occurred in a nearly horizontal flight attitude. Investigators also reviewed the pre-flight briefing, noting that while the flight instructor had specified the takeoff path and a minimum safety altitude of 1200 m, there was no explicit instruction to avoid the cableway zone. The investigation also looked into the local terrain and the presence of known hazards, noting that the cableway was marked on standard Swiss topographic maps and the club's internal obstacle map.
Findings
- The primary cause of the accident was that the student pilot flew into an obstacle-prone zone at a close distance to the mountain slope due to weak upward currents.
- The pilot likely focused on avoiding the larger, more visible support and haul cables of the cableway but failed to notice the thinner, higher-tension telephone cable.
- Weak thermals/updrafts forced the glider to fly closer to the terrain to maintain lift, increasing the risk of obstacle encounter.
- While the cableway was documented on official maps, the club's specialized inventory of local transport cables was still being updated at the time of the accident.