What happened
On June 5, 1999, at approximately 13:03 UTC, a Beech 1900D, registration F-GTKJ, operating as an Air France flight, was descending through flight level 170 near Saint Rémy de Maurienne. The aircraft was flying under IFR procedures, transitioning from Milan Control to Marseille Control, after receiving clearance to descend to flight level 120.
Simultaneously, a Rolladen Schneider LS4 glider, registration F-CEIE, was operating under VFR in the same area, having been lifted to flight level 170 by orographic waves. The two aircraft were on converging paths with a closing speed of approximately 270 knots.
The pilot of the Beech 1900D spotted the glider at a distance of roughly 300 meters. The commander immediately disconnected the autopilot and executed a right-hand avoidance maneuver. The pilot of the LS4 only became aware of the approaching aircraft after hearing the sound of the engines, at which point the horizontal separation was estimated at only 20 meters and vertical separation was negligible.
The investigation
The investigation focused on the trajectories of both aircraft and the airspace regulations in effect. Data from the Beech 1900D flight data recorder (FDR) confirmed that the aircraft's trajectory did not significantly change during the first two seconds after the autopilot was disconnected, meaning the avoidance maneuver was initiated very late.
The investigation also examined the airspace classification. While the Beech 1900D was operating in Class E airspace, the crew believed they were in Class D airspace. This discrepancy was attributed to the use of Jeppesen charts by the crew, which did not clearly indicate the specific boundaries of the Class E airspace in that sector, unlike the official SIA documentation.
Findings
- The primary cause of the incident was the insufficient application of the 'see and avoid' principle, as the glider pilot did not perceive the approaching aircraft until it was too late to maneuver, and the Beech 1900D pilot had insufficient time to execute an effective avoidance maneuver after detecting the glider.
- The Beech 1900D was not equipped with a TCAS, and the LS4 glider was not equipped with a transponder.
- The crew of the Beech 1900D was unaware they were operating in Class E airspace due to inaccuracies in their navigation documentation.
- The high closing speed of 270 knots left a window of only about two seconds for the flight crew to react once the glider was spotted.