What happened
On July 15, 2008, a Rolladen-Schneider LS4 glider, registration HB-1687, was performing a private VFR flight at Montricher aerodrome. After completing a local flight in the Col du Mollendruz area, the pilot initiated the approach for landing on runway 03. During the base leg, the pilot partially deployed the airbrakes. However, as the aircraft entered the final approach, the pilot discovered that the airbrakes could not be extended further.
Due to the low altitude and the need to avoid nearby railway power lines, the pilot continued the approach without being able to increase the descent rate effectively. The aircraft touched down three meters beyond the runway threshold and subsequently collided with a hedge. The pilot sustained significant injuries to the back, and the aircraft sustained damage.
The investigation
Investigators examined the wreckage and the cockpit environment. While no mechanical defects were found in the aircraft's systems, the investigation focused on the cockpit's contents. A blue A5-sized folder was identified as having been carried in the cockpit. Although the folder was not found at the scene, the pilot later provided it to investigators.
Tests conducted on a repaired fuselage of the same model demonstrated that such a folder could become wedged between the airbrake linkage and the cockpit rear wall, specifically near the speaker. This obstruction was capable of preventing the full extension of the airbrakes. Experiments confirmed that once such a blockage occurs, repeated operation of the airbrake lever does not clear the obstruction.
Findings
- The primary cause of the accident was that the airbrakes were only partially extended during the final approach, leading to an overshoot and collision with a hedge.
- A folder wedged in the cockpit linkage likely prevented the unrestricted operation of the airbrakes.
- The pilot did not perform a side slip (glissade) to manage the landing, an option that could have resulted in a controlled touchdown on the runway.
- The pilot had limited experience with this specific aircraft model and had not previously performed a side slip in an LS4.