Overview
On 3 September 1984, the pilot and a passenger departed Birrfeld Airport at 15:20 local time for an aerobatic flight over the field. The aircraft, an AS 202/18A Bravo registered HB-HEX, was performing maneuvers when it entered an inverted descent and was pulled through a half-loop at insufficient altitude. It struck trees in the Buechholz forest, approximately 1.5 km northeast of the airport, at high speed. Both occupants were killed and the aircraft destroyed.
Flight Sequence
Witnesses, including a commercial pilot in the airport restaurant, observed the aircraft executing a loop and a retournement. Other witnesses saw the aircraft in inverted flight at about 500 meters above ground level, heading east (080°). The aircraft gradually turned north while descending and accelerating. At approximately 200–300 meters altitude, the pilot pulled the aircraft downward. It disappeared behind a wooded hill and impacted the forest in near-level attitude with high power. The accident occurred at 15:26. Tachometer reading indicated 2600 RPM, and propeller deformation confirmed full engine power.
Aircraft and Pilot Information
The aircraft was a 1975 AS 202/18A Bravo, with a Lycoming AEIO-360-B1F engine and Hartzell constant-speed propeller. It had a valid airworthiness certificate and had accumulated 1633 hours on the airframe. Weight and balance were within limits. The pilot, a Swiss private pilot born 1937, held an aerobatic rating and had 416:52 total flight hours, with 2:59 on type. He had completed aerobatic training on the Bravo, including a previous flight with the same passenger on 30 June 1984. The passenger, a Swiss woman born 1938, had no aviation experience.
Medical and Technical Findings
Autopsy and toxicology tests on both occupants were negative for alcohol and drugs. The cause of death was trauma from the impact. The cabin door was closed and locked; seat belts were worn but failed during the crash. Wreckage examination revealed no pre-existing defects in flight controls. No fire occurred.
Cause
The investigation determined the accident was due to pilot error during aerobatic flight. It could not be established whether the passenger interfered with the pilot's actions.