What happened
On March 19, 1969, at approximately 15:40, a Zlin 326 (registration HB-URY) was performing aerobatic maneuvers near the Wangen-Lachen airfield in Switzerland. The flight involved two pilots operating the aircraft in a dual-control configuration. The aircraft was performing advanced maneuvers, including snap rolls, at a very low altitude, estimated by witnesses to be between 200 and 30 and 300 meters above the ground.
During the execution of a snap roll, the aircraft entered a flight attitude that the pilots could not recover from. The aircraft subsequently impacted the marshy ground approximately 300 meters east of the airfield runway with a longitudinal pitch of about 20 degrees. The impact resulted in two fatalities and the total destruction of the aircraft.
The investigation
The investigation examined the aircraft's technical condition, the pilots' experience, and the environmental conditions at the time of the accident. Investigators found no evidence of mechanical failure or technical defects in the Zlin 326. While it was noted that the leading-edge slats had been removed by a previous owner without being reported to the authorities, it remained uncertain if this contributed to the accident.
The investigation also reviewed the pilots' backgrounds. The pilot in the front seat was highly experienced in general and military aviation but had very limited experience with the Zlin type, having flown it for only one hour prior to the accident. The pilot in the rear seat, a flight instructor, had recently passed his aerobatic exam and possessed approximately 10 hours of aerobatic experience.
Findings
- The aircraft was performing a snap roll at an insufficient altitude to allow for recovery.
- The pilots attempted to stop the snap roll, but the maneuver resulted in the aircraft entering a spin or a spiral dive that could not be arrested before impact.
- Poor visibility due to low-hanging fog and a lack of a clear horizon likely hindered the pilots' ability to recognize the aircraft's attitude in time.
- The pilots' limited experience with advanced aerobatic maneuvers in this specific aircraft type may have contributed to an incorrect control input during the attempt to stop the rotation.