What happened
On 30 July 2020, at the Château-Arnoux Saint-Auban aerodrome, a Schempp Hirth Discus 2A glider, registration F-CFDX, was involved in an accident during a towed takeoff. The aircraft was being towed by a WT9 DYNAMIC microlight.
During the takeoff roll, the tug microlight pilot initiated a climb before the glider had left the ground. Because the glider was heavily ballasted with 134 liters of water, it lacked sufficient speed to keep pace with the tug. This resulted in the glider falling into a "low tow" position, more than five meters below the tug. Although the glider pilot notified the tug pilot via radio that the aircraft was ballulated and requested a change in climb attitude, the tug pilot continued the climb.
As the aircraft climbed, the tension and position of the glider caused the microlight to become difficult to control. The glider pilot eventually released the cable when it became slack. Following the release, the glider's nose dropped, and the pilot, unable to maintain enough altitude to reach the runway, performed a forced landing in a nearby ploughed field. The glider sustained substantial damage.
The investigation
The BEA investigation analyzed data from the FLARM computers installed in both the microlight and the glider. The data confirmed that the glider's speed was insufficient for the heavy weight of the ballasted aircraft. The investigation also reviewed the pilot's training, the specific towing procedures used by the CNVV, and the communication between the two pilots during the takeoff sequence.
Findings
Several contributing factors led to the accident:
- Lack of communication: The glider pilot did not explicitly inform the tug pilot that the aircraft was ballasted, assuming the tug pilot was already aware due to the ongoing Pôle France training course.
- Inadequate information: The tug pilot did not identify that the glider's wings were horizontal (indicating ballast) in his rearview mirror and did not ask for clarification regarding the glider's weight or required tow speed.
- Improper takeoff technique: The tug pilot adopted a climb attitude before the glider had reached a safe speed, and failed to perform the necessary horizontal acceleration near the ground to allow the heavier glider to catch up.
- Operational assumptions: The tug pilot continued the climb despite the glider pilot's radio calls, believing the situation could be corrected without releasing the cable.
Safety action
Following the investigation, the CNVV updated its directives to make it mandatory for glider pilots to systematically announce when they are flying with water ballast and to specify the required tow speed to the tug pilot.