What happened
On June 30, 2005, at approximately 17:18 UTC, a serious airprox incident occurred near MEDAM, roughly 71 nautical miles southwest of Geneva. The incident involved an Embraer E145, registration F-GRGL, operated by Régional, and an Airbus A321-231, registration TC-OAE, operated by Onur Air.
At the time, the Onur Air flight was descending from flight level 300 to 280. Simultaneously, the Régional flight was cruising at flight level 280. Due to a technical issue during a transponder code change, the F-GRGL disappeared from the radar screens of the Geneva control center for over five minutes. While the controller was unaware of the aircraft's exact position, the TC-OAE was cleared to descend into the same flight level occupied by the undetected Embraer. The conflict was only identified when the crew of the F-GRLE initiated a climb following a TCAS RA (Resolution Advisory) alert, revealing that the two aircraft had come within approximately 1.1 nautical miles of each other and a vertical separation of nearly zero feet.
The investigation
The investigation examined radar tracks, radio communications, and the technical performance of the aircraft's onboard systems. Investigators focused on why the F-GRGL vanished from radar and why the air traffic controllers did not detect the loss of correlation. The investigation also reviewed the transition period of the