Pilatus B4 disintegrates during inverted-flight attempt — VNE exceeded, no bail-out

The pilot of a Pilatus B4-PC 11AF was fatally injured at 400-500 m AGL near Müllheim, Switzerland, when the aircraft disintegrated. After aerotow release the pilot half-rolled to inverted flight; the nose dropped 20° below horizon. Instead of rolling back upright, the pilot dived out without airbrakes. VNE was significantly exceeded; both wings failed. The pilot carried a rescue parachute but made no attempt to leave the cockpit; fatal. Cause: overspeed; contributing — insufficient preparation, recovery decision, no airbrakes deployed.

1. Aerotow to aerobatics: The pilot aerotowed from Amlikon to about 1100 m above ground for aerobatic training, intending to practise inverted flight north of the airfield.
2. Unstable inverted entry: After release, the pilot rolled the glider inverted via a half-roll; the nose dropped 20° below horizon immediately and kept steepening, and the inverted attitude was not held.
3. Aerobatic figure beyond training: Higher figures like inverted flight should be practised with an instructor on a powered aircraft first, and the club required prior approval — neither had happened here.
4. Lower harness belt unbuckled: The lower strap of the 5-point harness was not connected, possibly from inattention before takeoff; this may have let the seating shift or a ballast cushion slide and impair the controls.
5. Recovery by dive instead of roll: Faced with an unstable inverted attitude and the nose already dropping, the pilot chose to recover by diving through a steep descent rather than completing the half-roll back to upright.
6. Airbrakes not deployed: During the resulting steep descent toward the ground, the pilot did not extend the airbrakes (which on the B4 are cleared up to VNE). SUST contributing factor.
7. VNE exceeded — wing breakup: VNE was significantly exceeded; torsional overload tore the leading-edge skin, sheared rivets, and tore off both wings. The aircraft broke into four main parts at about 400-500 m AGL.
8. No bail-out attempt — fatal: The cockpit forward section, with the pilot still strapped in, fell to the ground; the pilot carried a rescue parachute but never attempted to leave. Pilot died, glider destroyed.