Colisión en el aire entre Elfe S4 e IS-29D cerca de Montricher, Suiza

El 22 de abril de 1978, un Elfe S4 y un IS-29D colisionaron en el aire cerca de Montricher, Suiza. El Elfe S4 estaba ascendiendo en una térmica cuando el IS-29D, que acababa de soltarse del remolque, intentó unirse a la térmica. La colisión provocó que el Elfe S4 perdiera su estabilizador, obligando al piloto a saltar en paracaídas para ponerse a salvo, mientras que el IS-29D aterrizó sin problemas en el aeródromo de Montricher. Ambos pilotos sufrieron heridas leves y el Elfe S4 fue destruido. El informe oficial citó una observación insuficiente del espacio aéreo por parte del piloto del IS-29D como la causa.

1. Thermaling after aerotow: After an aerotow from Montricher, the Elfe S4 HB-1155 pilot was thermaling in a right-hand climb north of Montricher at about 1550 m AMSL, with a second glider circling 200 m higher to the south.
2. Third glider joins area: IS-29D2 HB-1378 released from tow near Montricher and flew a straight, south–southwest approach intending to position underneath one of the two thermaling gliders while maintaining what the pilot believed was a safe distance.
3. Loss of visual contact: The IS-29D2 pilot likely saw the Elfe S4 at some point but then lost visual contact with it during the straight-in approach toward the thermal.
4. Inadequate lookout on join: While attempting to join the thermal, the IS-29D2 pilot insufficiently monitored the surrounding airspace and converged on the Elfe S4 at nearly the same altitude.
5. Evasive maneuver attempted: Seeing the IS-29D2 approaching very close on his left at about the same altitude, the Elfe S4 pilot tightened his right turn and slightly dived in an attempt to avoid a collision.
6. Mid-air impact and tail loss: The IS-29D2 cockpit structure struck the underside of the Elfe S4 fuselage between the wing trailing edge and tailplane, causing the Elfe’s empennage to break off and the main fuselage to enter an uncontrollable dive.
7. Crash - minor injury: The Elfe S4 pilot bailed out by parachute and suffered minor leg injuries when the glider crashed and was destroyed in a field south of Montricher, while the IS-29D2, lightly damaged and with its pilot concussed, landed back at Montricher airfield.