What happened
On September 10, 2002, at approximately 17:30, a Rolladen Schneider LS-6 glider, registration D-6175, crashed into a mountainside near Lecherines Peak in the Aisa municipality of Huesca. The aircraft was engaged in non-commercial, private ridge soaring maneuvers. While flying near the upper part of an east-southeast facing slope at an altitude of approximately 2,250 meters, the glider struck the terrain. The impact resulted in the total destruction of the aircraft and caused one pilot to sustain serious injuries to his legs, spine, ribs, and lungs.
The investigation
The investigation focused on the flight path, the wreckage distribution, and the local topography. Flight data recovered from the aircraft's logger indicated the pilot was performing "figure-eights" along the ridge at altitudes between 2,100 and 2,300 meters. The final recorded data showed an indicated airspeed of 115 km/h and a vertical speed of 0.5 m/s just prior to impact.
Analysis of the wreckage showed that the aircraft struck the ground in a nearly level flight attitude. The right wingtip was the first part of the aircraft to make contact with the terrain, which induced a roll toward the right, subsequently causing the nose and the remainder of the fuselage to strike the slope. Investigators also examined the meteorological conditions, which were clear with visibility exceeding 10 kilometers and no significant wind gusts.
Findings
- The investigation found no evidence of mechanical failure contributing to the accident.
- The topography at the impact site featured significant changes in slope, ranging from a gentle 30-45 degree incline to much steeper, nearly vertical terrain. Such variations can create turbulence in orographic updrafts and significantly affect a pilot's visual perception of ground distance.
- The pilot's erroneous perception of altitude relative to the terrain was the primary factor. The gentle slope of the mountainside likely induced a visual illusion, leading the pilot to believe the aircraft was at a safer height than it actually was during the ridge soaring maneuvers.