What happened
On July 23, 2013, a Grob Flugzeugbau G-103 Twin Astir, registration F-CFYR, was performing a specialized training maneuver known as a "ground return" at the Saint-Martin-de-Londres airfield. The flight, involving an instructor and a student, was part of a glider pilot license training program. During the maneuver, the aircraft was being towed by a powered aircraft on the runway.
As the flight approached the landing phase, the instructor began retracting the airbrakes to prepare for a go-around by the tug aircraft. During this process, the glider's speed increased relative to the tow plane, causing the cable to slacken. When the tug aircraft applied power for the go-around, the cable suddenly tensioned and snapped due to overload.
At an altitude of approximately 30 meters, the instructor attempted a right-hand turn to avoid obstacles and find a safe landing area. During this maneuver, the glider struck the ground, causing the pilot to lose control. The aircraft subsequently collided with another glider that was being moved by a ground vehicle on a taxiway. The collision resulted in one student injury and one minor injury to a person on the ground, while both gliders sustained heavy damage.
The investigation
The BEA examined the condition of the towing cable and found no evidence of prior damage or significant weakening; the break was caused by a sudden overload. The investigation also reviewed the flight data from the FLARM systems installed in both aircraft, which confirmed the descent rate and approach speeds.
Crucially, the investigators looked into the specific training technique being used. While the French Gliding Federation (CFVV) had updated its recommendations in 201ered to advise against staying attached to the cable during such maneuvers, the local club had continued using the older "ground return" method. This method involved the glider remaining attached to the cable during the tug's go-around, a practice that the investigators noted carried inherent risks of cable slackening and subsequent snapping.
Findings
- The primary cause of the accident was the use of a specific ground return technique without adequate coordination between the tug pilot and the flight instructor.
- The sudden tensioning of the cable following a period of slackness caused the overload failure.
- A lack of communication regarding the specific execution of the maneuver contributed to the unexpected behavior of the tug aircraft during the landing flare.