What happened
On May 4, 2003, at approximately 16:42 UTC, a near-miss incident occurred in the LIRKO airspace near Geneva involving two commercial aircraft. The first aircraft, an EasyJet Switzerland Boeing 737-33 (registration HB-IIB), was operating a scheduled flight from Paris Orly to Geneva. Simultaneously, an Air France Boeing 737-35 was climbing from Geneva toward Paris Orly.
The conflict began when the Air France crew read back an incorrect flight level of 190 after being cleared to climb to 180. This error was not identified by the radar controller or the coordinator. Shortly after, the EasyJet aircraft was cleared to descend to flight level 190. As the aircraft descended, the Short Term Conflict Alert (STCA) triggered a proximity warning for the controller. The pilot of the HB-IIB reported that the onboard TCAS had issued a climb resolution advisory. At the closest point of approach, the two aircraft were separated by only 2.1 nautical miles laterally and 700 feet vertically.
The investigation
The investigation by the Swiss Transportation Safety Investigation Board (SUST) focused on the communications and the operational environment at the time of the incident. Investigators examined the radar plots, which confirmed the altitude deviations and the activation of the TCAS resolution advisory. The investigation also reviewed the workload of the air traffic control unit, noting that the INN and INE sectors had been conjoined, meaning two controllers were managing a single, high-density frequency.
Findings
- The primary cause was an incorrect readback of a flight level by the Air France crew, which was not corrected by the controller or the coordinator.
- The monitoring procedure between the two crew members on the Air France flight failed to catch the error.
- The air traffic controllers were experiencing an extremely heavy workload, managing 15 aircraft and 104 radio communications within a 10-minute window—averaging one communication every six seconds.
- The decision to group the INN and INE sectors increased the traffic density to a level that led to a lack of attention from the controllers.
- Standard French phraseology for flight level assignments was not strictly followed by the participants.
Safety action
To prevent a recurrence of such high-workload-induced errors, the investigation concluded with a safety recommendation for the Federal Office for Civil Aviation. It stated that during periods of heavy traffic, different airspace control sectors should not be grouped together to ensure controllers can maintain adequate monitoring and attention.