What happened
On March 23, 2003, at approximately 20:00 UTC, two Air France aircraft were involved in a serious in-flight incident near Montélimar, France. The first aircraft, an Airbus A319-113 with registration F-GPMF, was climbing from flight level 190 toward flight level 260. Simultaneously, an Airbus A3 320-211, registration F-GHQA, was descending from flight level 270 toward flight level 260.
As the F-GPMF climbed through flight level 243, its Traffic Collision Avoidance System (TCAS) issued a Traffic Advisory. Shortly thereafter, the system issued an "Adjust Vertical Speed" Resolution Advisory (RA), instructing the crew to reduce their rate of climb. The crew responded by increasing the aircraft's pitch.
On the opposing aircraft, F-GHQA, a "Climb" RA was issued approximately ten seconds after the initial advisory on the first aircraft. During the encounter, the crews of both aircraft visually identified the other aircraft. Flight data indicates that the minimum lateral separation was approximately 0.8 NM and the minimum vertical separation was approximately 300 ft.
The investigation
The BEA investigation examined the flight data recorder (FDR) and cockpit voice recorder (CVR) from both aircraft, as well as radar recordings and air traffic control (ATC) communications. The investigators analyzed the sequence of TCAS alerts, the flight profiles of both aircraft, and the specific maneuvers performed by the crews in response to the Resolution Advisories. The investigation also reviewed the ATC instructions provided by Marseille Control, which had cleared the climbing aircraft to flight level 260 and advised the descending aircraft to maintain level 270 until the crossing was complete.
Findings
- The primary cause of the incident was the TCAS RA command which prompted the climbing aircraft to alter its vertical profile in a manner that led to a loss of separation.
- The climbing aircraft (F-Gimf) followed the "Adjust Vertical Speed" RA by increasing pitch, which temporarily increased its vertical speed before it could stabilize.
- The descending aircraft (F-GHQA) followed a "Climb" RA, which contributed to the reduction in vertical separation.
- Air traffic controllers had provided appropriate separation instructions prior to the TCAS intervention, but the automated systems triggered conflicting maneuvers between the two aircraft.