What happened
On May 22, 1970, during an aerobatic training session at Birrfeld airfield, a SZD-22 B Mucha Standard glider, registration HB-661, entered an unrecoverable spin. The pilot was performing a prescribed training program that included various maneuvers such as loops and rolls. Following a series of maneuvers, the pilot initiated a left-hand descending spiral. During this maneuver, the aircraft's nose was slightly high, causing the airspeed to decrease. This loss of speed led the aircraft to transition into a left-hand spin at a low altitude. Despite attempts to recover, the aircraft continued to spin for several rotations before impacting the ground at approximately 15:50 local time. The impact resulted in one fatality and the total destruction of the aircraft.
The investigation
An investigation was conducted with the assistance of the Aargau Cantonal Police. Investigators examined the aircraft's maintenance records, flight logs, and physical wreckage. The investigation confirmed that the HB-661 was properly registered, maintained, and airworthy at the time of the accident. The weight and center of gravity were found to be within the permitted limits. Examination of the wreckage showed that the control linkages, including the elevator, ailerons, and rudder, were intact and functioning correctly. There was no evidence of mechanical failure or toxicological impairment of the pilot. The investigation also reviewed the pilot's training progress, noting that he had recently completed several solo aerobatic flights and was nearing the level required for an official aerobatic rating.
Findings
- The aircraft transitioned from a descending spiral into a left-hand spin due to a decrease in airspeed caused by a high nose attitude.
- The pilot was unable to recover the aircraft from the spin because of the critically low altitude available for recovery maneuvers.
- It is possible that the pilot attempted to arrest the spin prematurely before the rotation had fully ceased, which may have inadvertently re-initiated the spinning motion.
- While wind gusts were present in the area, their specific role in triggering the spin could not be definitively established.