What happened
On August 18, 2004, a Discus b glider, registration HB-1860, was participating in a VFR training flight towed from Bex airfield. The flight began with a routine tow toward the Chamossaire peak in the Alps. At approximately 15:21, the pilot released from the tow aircraft at an altitude of 1,900 meters.
Shortly after the release, the aircraft entered a series of maneuvers that appeared to be flat spins, as observed by a student pilot on the ground. The glider eventually struck a heavily wooded slope in the Bois des Léchières, north of Villars-sur-Ollon. The impact destroyed the aircraft and resulted in the death of the pilot.
The investigation
Investigators examined the wreckage and the flight conditions, which included south-southwest winds with gusts up to 20 knots. The investigation focused on the aircraft's weight and balance, as well as the pilot's physical state. Technical inspections of the HB-1860 revealed that the aircraft was well-maintained, though the altimeter had a pressure setting error of 135 meters. The Emergency Locator Transmitter (ELT) failed to activate because the battery was depleted and past its expiration date.
Findings
While the exact reason for the loss of control could not be formally identified, investigators established that the aircraft collided with the terrain following a loss of control. Two contributing factors were identified: a potential unwellness or medical episode affecting the pilot, and an aft center of gravity position.
Specifically, the aircraft's center of gravity was approximately 3 mm beyond the prescribed 400 mm limit. Additionally, the payload was 1.9 kg below the minimum required weight for the pilot's seat. The investigation noted that the aircraft drifted from the windward side of the ridge to the leeward side, where strong downdrafts were present, likely leading to the fatal spin.
Safety action
Following the discovery of the weight and balance discrepancy, a safety recommendation was issued. The Swiss Federal Office of Civil Aviation (FOCA) is required to ensure that aircraft certification standards regarding mass and center of gravity are strictly respected during both initial registration and throughout the entire operational life of the aircraft.