What happened
On May 26, 1973, a Karpf-Baby glider, registration HB-504, was participating in a training tow at the Hausen a. Albis airfield. The flight began as a standard tow operation behind a powered aircraft. Approximately 2 km from the airfield, the towline disconnected from the glider. Following the release, the pilot flew straight for about 500 meters before initiating a left-hand turn to return to the airfield. During this maneuver, the aircraft lost airspeed and entered a steep nose-down dive from an altitude of approximately 50 meters, impacting an agricultural field with a high longitudinal pitch. The pilot sustained severe injuries, and the aircraft was destroyed.
The investigation
Investigators examined the aircraft's condition and the pilot's background. The Karpf-Baby had been correctly assembled and inspected prior to flight, with no evidence of mechanical failure in the controls, tow release mechanism, or towline. The investigation noted that the pilot had relatively limited flight experience, with only about 23 hours of total flight time and very few hours specifically on this aircraft model. Meteorological data indicated moderate to strong turbulence and gusty conditions in the area at the time of the accident. The investigation also looked into the cause of the towline release, though it could not be definitively determined if the release was intentional due to pilot stress or accidental due to turbulence.
Findings
- The primary cause of the accident was the undershooting of the minimum flight speed during the turn.
- The aircraft's center of gravity was located at the rear limit of the allowable range, which contributed to the stall.
- The high towing speed (110–120 km/h) during gusty conditions may have contributed to the pilot's loss of control or the decision to release the tow.
- The pilot's limited flight experience and the low altitude at which the stall occurred left insufficient margin to recover the aircraft.