What happened
On 13 January 2005, two Pilatus PC-21 prototypes were conducting a formation training flight at Buochs aerodrome, Switzerland. The flight was intended to prepare for upcoming international display performances. The formation consisted of a lead aircraft (P01) and a wingman (P02), identified by the registration HB-HZB.
During the aerobatic sequence, the aircraft performed several maneuvers, including a steep dive and a low pass. Following a 360-degree turn, the formation split. While the lead aircraft performed a loop, the wingman, HB-HZB, executed a tight 360-degree turn at a low altitude. During the final stages of this turn, the aircraft entered a shallow dive, causing the right wing to strike the ground. The high-speed impact destroyed the aircraft and ignited a fire. The pilot of the Pilatus PC-21 sustained fatal injuries, while a passerby on the ground was seriously injured.
The investigation
The investigation examined the flight paths, aircraft technical condition, and the maneuvers performed by both aircraft. Investigators analyzed flight test instrumentation, video recordings from the lead aircraft, and wreckage distribution. The investigation also reviewed the pilots' training, medical fitness, and the specific parameters of the aerobatic maneuvers being practiced.
Findings
- The primary cause of the accident was a collision with the terrain during an aerobatic formation flight.
- The pilot of HB-HZB was likely focused on the complex task of closing the distance with the lead aircraft, which led to a loss of situational awareness regarding altitude.
- The pilot of the wingman aircraft had not undergone systematic formation flying training, unlike the lead pilot.
- The maneuver being executed was highly demanding, requiring intense concentration on convergence vectors.
- Contributing factors included the pilot's visual impairment (refraction defect), the high workload and time pressure during the joining phase, and a failure to maintain agreed-upon altitudes and separations.