What happened
On April 15, 2014, at the Baille/Armenonville airfield, a Rolladen-Schneider LS4 glider, registration F-CGYH, was performing a local flight. Earlier that afternoon, a Robin DR400-180R tow plane, registration F-GEIT, had departed to tow a glider from a different club. After releasing a glider at an altitude of approximately 500 to 600 meters, the pilot of the F-GEIT began a left turn toward the west to rejoin the airfield traffic pattern.
At the same time, the pilot of the F-CGYH was executing a descent via a spiral maneuver to reach the prescribed altitude for the airfield pattern. During this maneuver, the tow plane and the glider converged. The pilot of the F-GEIT reported a brief visual sighting of the glider passing beneath him and felt a physical impact. The contact caused the tow cable to snap at two-thirds of its length and struck the left wing of the glider, partially tearing away the airbrake.
Despite the damage, the pilot of the F-CGYH was able to maintain control and performed a normal landing on runway 36. The pilot of the F-GEIT landed safely on runway 08.
The investigation
The BEA investigation focused on the failure of the "see and avoid" principle and the lack of secondary detection. Investigators examined the flight paths, the operational procedures of the two local aero clubs, and the use of radio communications.
Key elements examined included:
- The lack of radio transmissions from both pilots regarding their positions or intentions.
- The operational status of the FLARM traffic detection system on both aircraft.
- The coordination and shared procedures between the two clubs using the airfield.
- The physical damage to the F-CAYH wing and the state of the tow cable.
Findings
The investigation established that the collision resulted from a failure to visually detect the other aircraft. Several contributing factors were identified:
- The two aircraft were flying at altitudes that provided only a 100-meter vertical separation.
- Neither pilot used the radio to announce their position or intentions, which would have increased mutual vigilance.
- The FLARM system on the F-GEIT was non-functional at the time of the incident.
- The glider had low detectability, particularly during a head-on convergence.
- Low traffic density on the day may have reduced the pilots' overall situational awareness.
Safety action
Following the incident, the airfield users implemented several measures, including the standardization of airfield usage instructions into a single document, the mandatory reporting of non-functional FLARM systems, and reinforced radio communication practices for announcing positions and post-release status.