What happened
On the morning of April 9, 1966, a Champion 7 GCB, registration HB-UAP, departed from Winterthur airfield for a training flight. The crew, consisting of a pilot and a flight instructor, intended to perform several simulated engine-failure landings to supplement the pilot's transition training.
During the flight, the aircraft performed at least one successful simulated forced landing in a nearby field. However, while attempting a subsequent maneuver near the area of Wittenwil, the aircraft entered a steep descent. Witnesses observed the aircraft flying at a low altitude before it suddenly banked sharply to the left, completed a half-turn, and struck the ground at a steep angle. The impact resulted in two fatalities and the total destruction of the aircraft.
The investigation
Investigators examined the wreckage and the aircraft's maintenance history, finding the engine and airframe to be in excellent condition. The Lycoming engine was found to have been producing power prior to the impact, and no mechanical defects were identified in the engine or the propeller. The fuel system was intact, though fuel had leaked from the wreckage following the crash.
The investigation also reviewed the flight crew's qualifications and the aircraft's operational characteristics. It was noted that the instructor's view of the airspeed indicator was partially obstructed by the pilot in the front seat, placing the primary responsibility for monitoring speed on the student pilot. Additionally, the investigation looked into the specific flight characteristics of the Champion 7 GCB regarding low-speed handling.
Findings
- The primary cause of the accident was the underspeeding of the aircraft during a simulated forced landing maneuver.
- The aircraft's design makes it susceptible to an abrupt wing drop when flying at minimum speeds with flaps extended, particularly if rudder inputs are applied.
- The altitude at which the stall occurred—estimated at no more than 30 meters—left insufficient time for the crew to recover from the resulting roll.
- The aircraft was operating within its weight and balance limits at the time of the accident.