What happened
On June 9, 1964, at approximately 12:30, a Ka-6 glider, registration HB-618, departed from Hausen am Albis for a cross-country flight. The pilot's original intention was to fly toward Grenoble, France, to achieve a specific flight badge. However, due to weather conditions not meeting the required standards, the pilot opted for a local flight around the Hausen am Albis area instead.
During a return leg from Sihlbrugg toward the home airfield, the pilot flew at a low altitude near the crest of the Albiskette ridge. While transitioning from the windward side to the leeward side of the ridge, the aircraft encountered turbulence caused by the moderate Bise wind interacting with the terrain and tall fir trees. During a maneuver, the aircraft experienced a loss of airspeed, causing it to pitch forward. The glider struck the ground at an altitude of approximately 40 meters, resulting in the destruction of roughly 75% of the airframe.
The investigation
The investigation established that the pilot was flying at a very low height above the terrain, near 900 meters, while the ground elevation was approximately 850 meters. The investigation examined the impact of the wind conditions, specifically the presence of a tailwind and the lee-side turbulence. It was determined that the pilot likely misjudged the aircraft's ground speed due to the tailwind component. The investigation also reviewed the aircraft's technical condition, finding the Ka-6 to be in an airworthy state with no mechanical failures contributing to the accident.
Findings
- The pilot crossed the ridge crest within a turbulent zone at an insufficient height above the ground.
- The presence of a tailwind led the pilot to miscalculate the actual airspeed relative to the ground.
- A sharp control input during the turn, combined with the insufficient speed, triggered the loss of airspeed and the subsequent nose-down pitch.