Factual Information
On 28 February 2005 at 09:44 UTC, a serious incident (AIRPROX) occurred near waypoint PERAK, 17 NM southwest of the DVOR of Geneva (GVA). The aircraft involved were:
- CFG 444: a Boeing B757-300, registration D-ABOB, operated by Condor Flugdienst GmbH, on a scheduled IFR flight from Munich (EDDM) to Palma de Mallorca (LEPA).
- AZA 9117: a Boeing B747-200, registration N536MC, operated by Atlas Air on behalf of Alitalia, on a scheduled IFR flight from New York Kennedy (KJFK) to Milan Malpensa (LIMC).
Air traffic services were provided by Swiss Radar Upper Area West (UAC). The airspace was class A.
Sequence of Events
At 09:30:32 UTC, the crew of CFG 444 contacted the K3/L3 sector controller on frequency 134.315 MHz, reporting flight level (FL) 330. The controller identified the aircraft and cleared it to maintain FL 330 on route BENOT-BALSI.
At 09:34:46 UTC, the crew of AZA 9117 contacted the same sector on coupled frequency 124.030 MHz, also at FL 330. The controller identified the aircraft and cleared it to maintain FL 330 on route GVA-TOP (Geneva-Torino). Approximately 7 minutes later, the controller instructed AZA 9117 to descend to FL 320, which was acknowledged. The controller then requested a minimum rate of descent of 1000 ft/min and advised of traffic crossing within the next two minutes.
At 09:42:37 UTC, the controller instructed AZA 9117 to maintain FL 320 and transferred it to the L2 sector on frequency 126.050 MHz. At 09:43:00 UTC, the AZA 9117 crew reported maintaining FL 320. The L2 controller identified the aircraft and instructed it to descend to FL 250 (the exit level coordinated with Milan Control). The instruction was acknowledged.
At 09:43:29 UTC, radar data showed AZA 9117 suddenly climbing through FL 324, creating a potential loss of separation with converging CFG 444. The K3/L3 controller immediately detected the danger and instructed CFG 444 (the only aircraft on his frequency involved in the conflict) to climb to FL 340. The crew replied: 'already on TCAS climb now climbing level three four zero, we have the traffic in sight'. At that moment, the aircraft were approximately 5 NM from the crossing point of their routes, with a vertical separation of about 600 ft.
At 09:43:40 UTC, the Short Term Conflict Alert (STCA) activated. The aircraft were 3 NM from the crossing point with 500 ft vertical separation.
At 09:43:43 UTC, the L2 controller called AZA 9117, noting the aircraft was climbing through FL 325 instead of descending as instructed. The crew replied they had received a traffic advisory (TA). The controller instructed them to descend to FL 250 and asked if they had the traffic in sight; they replied negatively. The controller expressed confusion about the TCAS climb indication, as the conflicting traffic was above at FL 330. The crew responded that they apparently had traffic below on the right and added: 'this is a, one of those jurassic jets'.
During the incident, the commander of AZA 9117 had left the cockpit for personal needs and heard the spoken alarms. As he returned, he saw on the variometer the end of a corrective resolution advisory (RA) to descend. He later observed the threat in red at +1800 ft and made visual contact. He noted that the copilot's altimeter was 'a little erratic' at the time. The flight engineer reported that during descent to Milan, the crew reacted to a false RA, likely due to 'malfunction of the copilot's altimeter', which was sticking and oscillating. The commander shared this view.
At 09:44:04 UTC, the aircraft crossed with a vertical separation of 1700 ft. The K3/L3 controller informed CFG 444 that the conflicting traffic was back at FL 320 and it could descend to FL 330. The pilot replied they were currently overflying and wanted to wait 30 seconds. At 09:44:17 UTC, they reported reaching FL 330.
The minimum distances recorded on radar between AZA 9117 and CFG 444 were 4.1 NM horizontally and 500 ft vertically.
Additional Information
Weather conditions at the time: Geneva weather at 09:20 UTC reported wind 040 degrees at 19 kt, max 31 kt, variable between 340 and 070 degrees, visibility 10 km, scattered clouds at 3500 ft, temperature -06°C, dew point -11°C, QNH 1014 hPa. Upper wind forecasts for the area were provided by Skyguide.
According to the Air Traffic Manual Geneva, chapter 4-6, aircraft destined for Milan (Malpensa, Linate) must be at maximum FL 250 at waypoint VEROB, 30 NM northwest of TOP VOR.
A simulation using Eurocontrol's InCAS tool reconstructed the aircraft trajectories and probable TCAS alerts.
A technical communication from the Swiss Federal Office for Civil Aviation (OFAC) regarding transponder periodic tests noted that high-frequency emissions should be avoided during altitude coding system tests to prevent false ACAS avoidance maneuvers.