What happened
On February 28, 2005, at approximately 09:44 UTC, a serious airprox incident occurred near the PERAK waypoint, 17 NM southwest of the Geneva DVOR. The incident involved two commercial flights: CFG 444, a Boeing 757-300 operated by Condor Flugdienst GmbH, and AZA 9117, a Boeing 747-200 operated by Atlas Air for Alitalia.
Both aircraft were initially cruising at flight level 330. To maintain separation, air traffic controllers instructed the Atlas Air flight to descend to flight level 320. However, shortly after being transferred to a different radar sector, the Boeing 747-200 (N536MC) unexpectedly began climbing, passing flight level 324. This unplanned ascent placed the aircraft on a collision course with the Condor flight.
As the aircraft converged, the TCAS system on the Boeing 757-300 (D-ABOB) issued a Resolution Advisory (RA) to climb. The pilot of CFG 444 complied, climbing to flight level 340. At the closest point of approach, the two aircraft were separated by only 4.1 NM horizontally and 500 ft vertically.
The investigation
The investigation focused on why the Boeing 747-200 climbed while under instructions to descend. While the pilot of the Atlas Air flight reported receiving a Traffic Advisory (TA), the investigation examined the flight instruments and cockpit environment.
Investigators utilized Eurocontrol's InCAS simulation tool to reconstruct the flight paths and the likely TCAS alarms. The investigation also reviewed the functionality of the aircraft's altimetry systems and the role of air traffic control in managing the conflicting trajectories.