What happened
On May 13, 1973, at approximately 18:03, a mid-air collision occurred near Bern-Belp Airport involving three aircraft. A Piper PA-18-150 acting as a tow plane, pulling a Kranich III glider (HB-563), collided with an SF-25 B motor glider (HB-2017) at an altitude of approximately 120 to 150 meters.
The tow aircraft was performing a flight to Birrfeld. During the flight, the tow pilot initiated a left turn to cross the airfield. Simultaneously, the motor glider, which was flying with its engine shut down, was in the glider circuit. The collision occurred when the tow aircraft intercepted the path of the descending motor glider. The impact was severe, causing the HB-2017 to enter a spiral dive, which resulted in the two fatalities of the pilot and passenger on board. The Piper PA-18-150 sustained heavy damage but the pilot managed an emergency landing south of the airport. The glider, HB-563, was able to unhook and land safely at Bern-Belp.
The investigation
The investigation examined the flight paths, pilot performance, and environmental conditions. Investigators established that the motor glider was operating within the designated glider circuit area. The investigation also noted that the tow pilot had completed 27 tow flights earlier that day, totaling over three hours of flight time. Regarding communications, the glider pilot had not switched on his radio, preventing him from warning the tow aircraft of the impending collision. The investigation also looked into the visibility conditions, noting the position of the sun at the time of the accident.
Findings
- The primary cause of the accident was the unsuitable flight path chosen by the tow aircraft.
- There was insufficient airspace observation by the pilots, particularly the tow pilot.
- Potential contributing factors included pilot fatigue following a long day of operations and the motor glider pilot being potentially blinded by the low sun.
- The motor glider was flying with its engine shut down and was in a steep left turn attempting to avoid the collision at the moment of impact.