What happened
On April 29, 2015, a Glaser Dirks DG800 S glider, registration HB-3025, departed from Serre La Bâtie, France, via aero-tow. Approximately two minutes after releasing from the tow plane at an altitude of 1,300 meters, the aircraft entered a right-hand spin. Witnesses, including an instructor and student flying nearby, observed the glider banking sharply to the right and performing roughly one full rotation before colliding with a mountain slope at an altitude of 1,200 meters. The impact resulted in one fatality and the total destruction of the aircraft.
The investigation
The investigation focused on the wreckage located in a rocky area on the southern flank of the terrain. Investigators found the left rudder pedal pressed firmly into the cockpit, suggesting the pilot attempted to counteract the rotation. Examination of the flight controls revealed that the right airbrake control rod had disconnected. Specifically, the control tube was found broken between the automatic attachment at the wing root and the airbrake itself. Certain components, including the ball end and the attaching bolt, were missing from the wreckage.
Technical analysis of the remaining parts showed that the right airbrake control rod had failed due to bending overloads. While the exact mechanism of the disconnection could not be fully determined due to the missing hardware, investigators considered the possibility that the bolt, washer, and nut assembly had progressively loosened, leading to a separation in flight. The aircraft had been reassembled following winter storage in March 2015, though no specific work had been performed on the airbrake controls during that process.
Findings
- The primary cause of the accident was the unintended deployment of the right airbrake following the disconnection of the control rod from the lever.
- This deployment created significant aerodynamic asymmetry and increased drag, inducing an uncommanded and likely uncontrollable spin.
- The low altitude at which the loss of control occurred prevented the pilot from deploying the emergency parachute.
- The investigation could not confirm whether a post-reassembly inspection had been performed or why the attachment hardware had loosened.