What happened
On July 17, 197 and, a private pilot departed from Pruntrut airfield in a Bücker-Jungmeister HB-MIX for a recreational flight. After an initial climb, the aircraft was observed performing an aerobatic sequence consisting of a half-roll followed by a half-loop. Following this maneuver, the aircraft entered a steep climb. As the pilot attempted to recover, the aircraft's airspeed dropped below the minimum threshold, causing it to bank sharply to the left and enter a spiral dive. The aircraft struck the ground near Mormont/BE at a high angle of descent, resulting in the death of the pilot and the total destruction of the aircraft.
The investigation
Investigators examined the aircraft's condition and the pilot's flight history. The Bücker-Jungmeister was found to be in good mechanical condition, with no evidence of pre-existing technical defects in the control linkages or engine. The aircraft's weight and center of gravity were within legal limits for aerobatic flight. Medical examinations confirmed the pilot was not under the influence of alcohol, drugs, or carbon monoxide, though significant food intake was noted in the stomach. Flight testing of the aircraft type demonstrated that certain control inputs during high-G recovery maneuvers could lead to a spiral dive or spin if the pilot failed to maintain proper rudder and aileron coordination.
Findings
- The pilot experienced a loss of consciousness (blackout) during the high-G recovery phase of the maneuver.
- The high acceleration, potentially reaching 5g, likely caused a physiological impairment.
- Factors such as the pilot's age, recent fatigue from a long day of travel, and the physiological effects of a heavy meal likely reduced his tolerance to G-forces.
- The removal of the parachute from the cockpit at the pilot's request prior to flight meant there was no means of egress during the emergency.