What happened
On July 8, 2023, a Rolladen Schneider LS6 glider, registration F-CFDG, performed a towed takeoff from Fayence aerodrome for the purpose of a long-distance cross-country flight. During the tow, the pilot noted a low rate of climb, suggesting unfavorable atmospheric conditions. Upon releasing the tow cable near Lachens mountain, the glider experienced a rapid and continuous increase in its rate of sink, reaching levels as high as 9.3 m/s.
Despite the degraded performance, the pilot attempted to locate thermals by flying toward the mountain ridge and then over a forest. As the altitude continued to drop, the pilot eventually decided to return to the valley. While flying at an altitude of approximately 25 meters, the pilot identified a clearing and attempted a landing. During the maneuver, the glider struck treetops before making a hard impact with the ground. The aircraft sustained substantial damage, including a ruptured fuselage and damaged elevator controls.
The investigation
The investigation focused on the cause of the glider's abnormal sink rate and the pilot's decision-making process. Investigators examined the aircraft's flight data via the FLARM system, which confirmed the high rates of sink. Physical examination of the wreckage revealed that the airbrake control handle was in a "retracted but not locked" position. Additionally, a tree branch was found lodged in the right-hand airbrake slot, suggesting the airbrakes had deployed during the collision with the trees.
Findings
- The primary cause of the accident was the unintended deployment or failure to lock the airbrakes, which significantly degraded the glider's lift-to-drag ratio.
- The high rate of sink recorded during the flight was consistent with the aerodynamic performance of an LS6 with the landing gear and airbrakes extended.
- The pilot's decision to continue the flight despite the deteriorating performance was influenced by the objective of completing a long-distance mission and overconfidence in finding favorable air currents.
- The investigation noted that the airbrake control on this specific aircraft had a tendency to deploy if not properly secured when unlocked.