What happened
On April 12, 1987, the pilot of aircraft HB-HEV, an AS 202 Bravo, departed from Birrfeld Airport for a local pleasure flight with one passenger. After circling over Lake Zurich at approximately 650 meters, the pilot initiated a loop near Feldmeilen at a very low altitude of roughly 250 to 300 meters above ground. Upon reaching the apex of the maneuver, the aircraft entered an uncontrolled flight state and fell into a right-hand steep spiral. The plane collided with the terrain near Herrliberg at approximately 14:45 local time. Both occupants were killed instantly, and the aircraft was destroyed. Minor ground damage occurred.
The investigation
The Swiss Transportation Safety Investigation Board (STSB) examined the flight data, wreckage, and pilot qualifications. The pilot had obtained his private pilot license only two days prior to the accident, with a total flight experience of 49 hours. He held no aerobatic rating and had received only one brief aerobatic instruction session during his training, not formal aerobatic training. The aircraft was airworthy for aerobatics under its type certificate, but the operating school, Fliegerschule Birrfeld, had explicitly prohibited aerobatic maneuvers in this specific airframe due to maintenance simplification, displaying a "No Aerobatics" notice in the cockpit. Medical examinations revealed no impairment or pre-existing conditions for either occupant. Technical inspections found no mechanical failures; the engine and controls functioned normally up to impact.
Findings
The accident was caused by the pilot's loss of control during an aerobatic maneuver performed at insufficient altitude. Key contributing factors included:
- Insufficient safety height: The loop was initiated too low (250-300m) over rising terrain, leaving no margin for recovery from a stall or spin.
- Lack of aerobatic training: The pilot lacked formal aerobatic instruction and experience, misjudging the aircraft's performance envelope.
- Overestimation of skill: The pilot attempted his first unsupervised aerobatic attempt in an unfamiliar aircraft type immediately after obtaining his license.
- Violation of operational restrictions: Despite the airframe being certified for aerobatics, the operator had restricted it to normal flight only, a restriction the pilot ignored.
Safety action
The investigation highlighted the critical need for pilots to adhere strictly to operational limitations imposed by operators and to ensure adequate training before attempting complex maneuvers. The case underscored that possessing a private license does not qualify a pilot for aerobatics without specific endorsement and experience.