Eta breaks up during certification spin test; both crew bail

The rear fuselage of an Eta sailplane failed during certification spin testing at Büchig; both occupants bailed out under parachutes, glider destroyed in the uncontrolled descent. At ~2,650 m the pilot retracted the engine, slowed to ~75 km/h with flaps +2 and entered an asymmetric right spin. After ~1.5 turns at ~140 km/h IAS he applied opposite rudder; the rear fuselage tube failed at ~2,300 m AGL. The glider was ~4% over max mass with asymmetric fuel (16 L fuselage, ~30 L right wing, empty left wing). Manufacturing irregularities at the fin and a design that did not cover combined sideslip + opposite rudder loads beyond JAR-22 contributed.

1. Self-launch for certification spin test: The Eta prototype self-launched from Büchig airfield for a flight in its type-certification programme to conduct further spin tests, this time with asymmetric fuel loading. The pilot had previously flown 12 flights on the type and brought spin-test experience from a comparable type.
2. Climb to ~2,650 m; engine retracted: The pilot climbed under power to about 2,650 m AGL, then shut down the engine and retracted it into the fuselage tube, configuring the aircraft for spin testing.
3. ~4% over max mass; asymmetric fuel: At the time of the flight the glider was loaded about 4% above maximum take-off mass. Fuel was distributed asymmetrically: ~16 L in the fuselage tank, ~30 L in the right wing tank, and the left wing tank empty.
4. Manufacturing flaws, design gap JAR-22: The rear fuselage structure near the fin attachment had manufacturing irregularities including missing 0° carbon layers. The design did not account for the high side-load case from combined sideslip and opposite rudder beyond what JAR-22 explicitly required.
5. Asymmetric right spin entry: The pilot slowed to about 75 km/h with flaps at position +2 and initiated a right spin with full right rudder and full left aileron while holding full up elevator.
6. Opposite rudder; fuselage tube fails: After roughly 1.5 turns the IAS had built to about 140 km/h in a steep attitude. The pilot applied opposite rudder to stop the rotation; at ~2,300 m AGL — immediately after the opposite-rudder input in the high-speed sideslipped condition — the rear fuselage tube failed with a loud bang. The glider entered an uncontrollable inverted attitude with the rear fuselage and tail surfaces partly separated.
7. Both occupants bail out under parachutes: Pilot and flight-test observer abandoned the aircraft and descended under emergency parachutes; both landed uninjured.
8. Uncontrolled descent into pine forest: The crewless Eta, with rear fuselage and empennage partly detached, descended uncontrolled into a pine forest where it was destroyed on impact. Minor forest damage; no injuries on the ground.