What happened
On May 5, 2012, at approximately 16:50, a collision occurred at the Buno-Bonnevaux aerodrome in France involving a PA25 tug, registered F-GHSH, and a Slingsby T31b glider, identified as BGA 4926. The accident took place during an air display following a week-long glider championship.
The pilot of the PA25 had taken off from runway 28 to perform a glider tow. After the release, the pilot began a continuous descent to land back at the aerodrome. Simultaneously, the Slingsby T31b glider had been launched via a winch system. While flying at an altitude of approximately 100 meters over a wooded area near the southern threshold of runway 10, the two aircraft collided. The impact resulted in three fatalities (the pilot of the tug, and the pilot and passenger of the glider) and the destruction of both aircraft.
The investigation
The investigation examined the flight paths, the aerodrome's operational configuration, and the equipment installed on both aircraft. At the time of the accident, a temporary winch installation had altered the standard traffic patterns at the aerodrome. The investigation also reviewed the meteorological conditions, which were characterized by weak updrafts, and the regulatory framework regarding the simultaneous use of winch launches and tug operations.
Investigators noted that the PA25 was equipped with a FLARM traffic detection system, but the Slingsby T31b was not, as such equipment was not required for its operation. Furthermore, the glider pilot was using a portable radio, but the aircraft lacked an onboard radio for air-to-air communication. The investigation also looked into the flight paths, noting that the glider was attempting to find updrafts at a low altitude, while the tug was following an unusual descent path to integrate into the circuit.
Findings
- The primary cause of the collision was the failure of both pilots to visually detect the other aircraft in uncontrolled airspace.
- The glider was flying at a low altitude, attempting to catch updrafts, which placed its flight path in conflict with the established aerodrome circuit.
- The temporary winch installation had modified the established traffic balance, and there were no specific rules in place for the simultaneous use of winch launches and tug operations.
- The lack of air-to-air communication between the two aircraft prevented coordination.
- The absence of interoperable traffic detection systems (FLARM) on the glider prevented an automated alert.
- Contributing factors included the potential for reduced pilot attention due to fatigue at the end of a week-long competition and the lack of specific procedures for integrating traffic during winch-assisted operations.