What happened
On June 4, 1967, at approximately 16:25 local time, a PIK-l60 Vasama glider, registration HB-741, was performing a solo training flight at the Sion aerodrome. After completing a flight of over two hours, the pilot began the approach to land. During the final turn, the aircraft encountered heavy turbulence and a crosswind. The pilot, attempting to manage the descent, initiated a right-hand turn with a bank angle of approximately 50 degrees. During this maneuver, the glider experienced a sudden loss of airspeed and dropped onto its right wing, striking the ground nose-first. The impact caused the fuselage to break near the trailing edge. The pilot sustained serious injuries and was transported to the Sion Hospital.
The investigation
The investigation examined the aircraft's maintenance history, the pilot's qualifications, and the local meteorological conditions. The PIK-l60 Vasama was found to be in good condition, with a valid certificate of airworthiness and no recent incidents recorded. The pilot, an instructor candidate, was in good health and possessed a valid glider pilot license. Meteorological data confirmed that while visibility was excellent, the area was subject to significant ground-level turbulence and sink caused by the nearby terrain, specifically the Maladaires ridge and Mont d’Orge. Witnesses and wind indicators confirmed a crosswind of approximately 10-15 km/h originating from the direction of Mont d’Orge.
Findings
- The pilot became aware of the strength of the crosswind and the associated turbulence only while in the holding pattern.
- Due to the loss of altitude caused by these atmospheric conditions, the pilot opted to shorten the landing circuit.
- The primary cause of the accident was a loss of airspeed during the final turn, triggered by a gust while the aircraft was flying into a headwind/crosswind component.
- The aircraft was at an altitude too low to allow for any corrective recovery maneuvers once the stall initiated.