Elfe S4-A s'écrase près de Birrfeld après la perte de surfaces de contrôle

Le 31 août 1986, un Neukom Elfe S4-A s'est écrasé à 2 km au sud-ouest de l'aéroport de Birrfeld en Suisse. Le pilote avait effectué plusieurs vols courts plus tôt dans la journée avant d'entreprendre un voyage plus long. Environ deux heures après le décollage, des témoins ont observé l'avion perdre des pièces en vol, suivi de manœuvres incontrôlées. Le planeur a plongé abruptement de 250 mètres, entraînant la mort du pilote et la destruction de l'appareil. L'enquête officielle a suggéré une probable défaillance mécanique impliquant le contrôle de la profondeur.

1. Cruise near Birrfeld: After a cross-country attempt from Birrfeld, the Elfe S4-A was cruising at low to moderate altitude near the home airfield, apparently returning to join the circuit.
2. High airspeed attained: Witnesses and barograph data indicate the glider accelerated to a very high speed, likely near or above the 210 km/h limit, at low altitude with little height margin.
3. Elevator inputs at speed: At this elevated speed, the pilot made significant pitch control inputs (pulling on the stick), subjecting the all-flying tailplane torque tube and rear fuselage to high bending and torsional loads.
4. Elevator structure failure: The elevator torque tube on the left side bent and fractured under load, leading to the left elevator half departing the aircraft and the right half being torn from its securing mechanism.
5. Tail and fuselage breakup: Loss of the elevator surfaces and associated loads caused severe torsion and structural failure of the rear fuselage, with multiple tail and fuselage pieces separating in flight and scattering along the flight path.
6. Uncontrolled high-speed maneuvers: With the elevator lost, the glider entered uncontrolled steep dives, a pushed-over looping and rolling motions, accompanied by strong vibrations and canopy breakage that likely impaired or removed the pilot’s ability to respond.
7. Crash - fatal: Approximately 2 km southwest of Birrfeld, the uncontrollable glider descended from about 250 m in a steep attitude, impacted a dirt road, overturned, and was destroyed, fatally injuring the pilot.