Collision en vol entre Elfe S4 et IS-29D près de Montricher, Suisse

Le 22 avril 1978, un Elfe S4 et un IS-29D sont entrés en collision en vol près de Montricher, Suisse. L'Elfe S4 était en train de spiraler dans une ascendance thermique lorsque l'IS-29D, venant de se larguer de son remorquage, a tenté de rejoindre l'ascendance. La collision a entraîné la perte de l'empennage de l'Elfe S4, obligeant le pilote à sauter en parachute pour se mettre en sécurité, tandis que l'IS-29D a atterri sans problème sur l'aérodrome de Montricher. Les deux pilotes ont subi des blessures légères et l'Elfe S4 a été détruit. Le rapport officiel a cité une observation insuffisante de l'espace aérien par le pilote de l'IS-29D comme cause.

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.