What happened
On Wednesday, May 21, 2003, at 13:44, a Schleicher ASW 20 glider, registration 939, was involved in a takeoff accident at the Sisteron Thèze aerodrome. The pilot was participating in a glider activity session with two friends. Following the cancellation of flights the previous day due to poor weather, the glider was removed from its trailer and assembled with the assistance of the two companions.
The takeoff was performed via aero-tow, heading north. Shortly after leaving the ground, the glider pitched up sharply and entered a steep climbing turn. After the pilot released the tow cable, the aircraft stalled and struck the ground at the end of the runway. The impact resulted in the destruction of the aircraft and caused one injury to the pilot.
The investigation
The investigation focused on the mechanical state of the aircraft's control surfaces. Examination of the wreckage revealed that the elevator control linkage ball joint had not been properly seated in its housing at the end of the control chain. The securing pin was found hanging from its lanyard, and the assembly showed no signs of structural failure or deformation.
Investigators determined that the pilot had failed to complete the assembly of this specific component. This error went undetected during both the initial assembly process and the subsequent pre-flight inspection. The investigation also noted that standard checks, such as verifying the free movement of the controls via the stick, are insufficient to confirm that the linkage is correctly locked.
Findings
- The primary cause of the accident was the incomplete assembly of the elevator control linkage.
- Pre-flight inspections were insufficient to identify that the ball joint was not properly secured.
- A relaxed atmosphere and a degree of haste during the assembly process acted as contributing factors.
- The pilot failed to follow manufacturer-defined maintenance and pre-flight procedures, which specifically require verifying that all assembly connections are locked and checking the tightness of the elevator attachments.