What happened
On July 5, 2012, a SN Centrair 34C glider, registration F-CJBF, was performing a winch launch for a training flight at the Tours-le-Louroux aerodrome. Immediately following takeoff, the student pilot transitioned into the climbing attitude (second attitude) without completing the required acceleration leveling phase. During the launch, the winch operator detected an abnormal noise and a burning smell originating from the winch mechanism. Consequently, the operator aborted the winch tow while the glider was at an altitude of approximately 30 meters. The instructor took control of the aircraft but was unable to regain sufficient airspeed at such a low altitude, resulting in a hard landing on the runway. The incident resulted in one injury (the instructor) and heavy damage to the glider.
The investigation
The investigation examined the flight data from the glider's logger, which recorded a takeoff phase of 4 seconds, a free flight phase of 20 seconds, and a total altitude gain of 30 meters. The instructor, who had approximately 2,000 flight hours, stated that the lack of an acceleration level meant the glider was traveling at a low velocity when the winch was interrupted. To maintain speed, the instructor adopted a nose-down attitude, but the low altitude prevented the recovery of enough energy to avoid the hard impact.
Technical examination of the winch revealed that a loop had formed on the cable winding drum at the start of the launch. This loop rubbed against the winch fairing and eventually broke, causing the noise and burning smell noted by the operator. While the 1,500-meter cable had been replaced two weeks prior and had only been used for about 100 launches, investigators found several winding defects on the cable stored on the drum.
Findings
- The primary cause of the accident was the failure to perform the acceleration leveling phase during the winch takeoff, which left the aircraft with insufficient airspeed when the tow was terminated.
- The winch operator's decision to interrupt the launch was consistent with established safety procedures following the detection of mechanical issues.
- A defect in the cable winding, specifically the formation of a loop on the drum, contributed to the mechanical failure of the winch operation.