What happened
On 1 October 2002, at approximately 16:28 UTC, an airprox incident occurred 10.5 NM from the runway 05 axis at Geneva airport. The incident involved an Embraer ERJ145, flight SAS615, and a private DR221, registration F-BPKI.
Due to heavy arrival traffic, the Geneva Terminal (TMA) frequency was temporarily closed, and the DELTA control frequency was coupled with the TMA frequency to manage the workload. The pilot of F-BPKI initially contacted the coupled frequency to request a route that avoided the Geneva TMA. However, during the flight, the pilot entered the controlled airspace (CTR) without proper clearance.
As the Embraer ERJ145 was on its final approach to runway 05, it intercepted the path of the DR221. The pilot of SAS615 received a TCAS Resolution Advisory (RA) and was forced to climb to avoid the conflict. The two aircraft eventually crossed with a minimum separation of 0.6 NM and 600 ft.
The investigation
SUST examined the operational procedures and technical logs at Geneva airport. The investigation established that the DELTA controller was managing the TMA frequency without specific authorization, as the operational coupling of the two frequencies was not a standard or provided procedure.
Furthermore, a programming error occurred when the controller assigned a transponder code to F-BPKI, which incorrectly correlated the aircraft in the system as F-GUKI. This error remained uncorrected throughout the flight. The investigation also found that the Short Term Conflict Alert (STCA) failed to trigger because the system was not active for aircraft below 4,000 ft.