What happened
On August 17, 2011, a high-risk airprox occurred in the Geneva TMA, approximately 2.9 NM southwest of the St-Prex VOR. The incident involved an Airbus A320, operating as flight SWR 194W, and a Cessna Citation C56X, operating as AUF 331.
At the time, the Geneva approach sector was being managed by a trainee controller under the supervision of an instructor. The instructor was monitoring the trainee from an adjacent, unoccupied position known as the FIN position. While the trainee was guiding the Cessna Citation C56X onto the ILS approach for runway 23, the instructor observed a potential conflict between that aircraft and the Airbus A32 and descending from Barcelona.
Believing the trainee's separation method was inadequate, the instructor took control of the frequency from the FIN position and ordered the Airbus A320 to turn left to avoid the Cessna Citation C56X. However, this maneuver inadvertently placed the Airbus A320 on a collision course with the Cessna Citation C56X, which was already established on the approach axis. The aircraft reached a minimum lateral separation of 0.7 NM and a vertical separation of only 375 ft before the conflict was identified and resolved.
The investigation
The investigation examined radar tracks, Mode S data, and radio communications. It established that while the trainee and the primary controller (APC) were aware of the conflict, the instructor—operating from the FIN position—was not alerted by the system. The investigation found that the FIN position was not receiving flight plan data, which prevented the Short Term Conflict Alert (STCA) from appearing on the instructor's console. Furthermore, the STCA audible alerts were only broadcast through speakers at the primary workstations and were not transmitted to the controllers' headsets.
Findings
- The primary cause was the risk of collision between two IFR aircraft following the instructor's takeover of control.
- The trainee controller utilized a separation concept that the instructor deemed insufficient, prompting the intervention.
- The instructor experienced tunnel vision due to the stress of managing the initial conflict, which prevented them from noticing the secondary conflict being created.
- The instructor's workstation (FIN) lacked the same data parameters and visual/audible STCA alerts as the trainee's position.
- The STCA audible alerts were not audible through the controllers' headsets.
Safety action
Following the investigation, a safety recommendation was issued to the relevant aviation authorities to implement technical adaptations ensuring that STCA alerts are distributed to all active control positions. Additionally, a safety letter was published by the air navigation service provider to remind controllers of the technical limitations regarding STCA alerts at the FIN position.