What happened
On September 11, 2016, an LS-4a sailplane, registered as HB-1595, departed from Bellechasse Aerodrome for a thermal flight in the Chasseral region. The flight began with a ten-minute tow operation provided by an aircraft with registration HB-PNU. At an altitude of 1,690 meters, the pilot released from the tow rope north of the Chasseral antenna.
Shortly after release, the aircraft entered a descent of approximately 1 to 2 meters per second. Seeking better conditions, the pilot attempted to maneuver toward a cloud located south of the Chasseral. However, the aircraft descended rapidly below the ridge line. Realizing that a return to Bellechasse was no longer feasible, the pilot opted to perform an emergency landing in a field situated south of the Lignières circuit.
During the final approach, the pilot failed to deploy the landing gear. The LS-4a struck the ground with the undercarriage retracted, causing the aircraft to come to an abrupt halt. While there were no fatalities, one person sustained slight injuries, and the aircraft suffered heavy damage, including cracks in the lower fuselage.
The investigation
The investigation focused on the sequence of events leading to the forced landing and the specific mechanical configuration of the aircraft at the moment of impact. Investigators established that the pilot was navigating difficult atmospheric conditions characterized by a loss of altitude following the release from the tow plane. The inquiry examined the pilot's decision-making process regarding the flight path and the subsequent failure to execute the landing gear extension checklist during the emergency approach to the field.