What happened
On July 30, 1964, at approximately 16:48 CEST, a mid-air collision occurred over the Oberwalder Blasen, a ridge in the upper Rhone Valley near Oberwald, Switzerland. The accident involved two gliders: a Rhönlerche II, registration HB-573, and a Mucha Standard SZD-22B, registration HB-659.
The incident took place during a joint gliding training camp organized by the Akademische Fluggruppe Zürich and the Sportfluggruppe Swissair. The pilot of the HB-573 was performing a solo flight with instructions to remain in the area and return to the launch site if altitude dropped below 2100 meters. Meanwhile, the pilot of the HB-659 had launched via aero-tow shortly before the collision.
Witnesses on the ground provided varying accounts, but evidence suggests the aircraft were circling in opposing directions or that one aircraft intercepted the path of the other. Upon impact, the outer half of the left wing of the HB-573 was lost, sending the aircraft into a steep spin that resulted in a fatal crash. The HB-659 also suffered the loss of its left wing section; however, the pilot was able to deploy a parachute and land, though they sustained serious injuries due to impact with the aircraft's tail fin.
The investigation
An investigation by the Swiss Transportation Safety Investigation Board established that there were no technical failures or mechanical deficiencies in either aircraft prior to the collision. The wreckage analysis confirmed that the collision occurred via the leading edges of the left wings of both gliders.
The investigation also examined the flight conditions and pilot backgrounds. The pilot of the HB-573 was a student pilot, while the pilot of the HB-659 was more experienced. Investigators noted that while the student pilot may have been focused on cockpit instruments to maintain flight parameters, the more experienced pilot also failed to detect the approaching aircraft.
Findings
The primary cause of the collision was insufficient airspace surveillance by both pilots. The investigation concluded that a continuous and intensive scan of the surrounding airspace by either pilot would likely have prevented the frontal impact.
Contributing factors included the high temptation for pilots to focus on flight instruments—such as the variometer and airspeed indicator—to optimize soaring performance in weak lift, which diverted attention away from external traffic. Additionally, while no specific regulation mandated a specific direction of circling when multiple gliders are present, the investigation noted that the pilots failed to adopt a precautionary turning direction to avoid conflict.