What happened
On May 3, 2001, at approximately 06:25 UTC, a near-collision occurred in the Geneva area control centre airspace. The incident involved a Lufthansa CRJ1, operating flight DLH5818 from Düsseldorf to Lyon, and an Oyonair BE9L, operating flight F-GNMA from Lyon to Pardubice.
While descending through the INI NORD sector, the crew of DLH5818 was instructed by the radar controller to descend to flight level 190. However, the pilot twice acknowledged a descent to flight level 180. The controller did not correct this erroneous readback. Shortly thereafter, the aircraft crossed paths 4 nautical miles north of the MILPA waypoint. At the moment of crossing, the two aircraft had a horizontal separation of 1.6 nautical miles and a vertical separation of 0 ft.
The investigation
An investigation by the Aircraft Accident Investigation Bureau established that the radar controller had recently undergone a change of personnel just five minutes prior to the incident. The investigation examined radio transcripts, which revealed that while the Lufthansa crew communicated in English, the Oyonair crew was communicating in French.
The investigation also noted that the BE9L aircraft was not equipped with a Traffic Collision Avoid to Avoidance System (TCAS), whereas the CRJ1 was. The investigation confirmed that the pilot of DLH5818 reported a TCAS Resolution Advisory (RA) alert immediately following the close encounter. Despite the alert, the crew of DLH5818 did not alter their heading or altitude.
Findings
- The primary cause of the incident was two erroneous acknowledgements between the DLH5818 crew and the radar controller regarding the assigned flight level.
- The radar controller failed to identify and correct the pilot's incorrect readback of flight level 180.
- The controller and the coordinator did not draw attention to the discrepancy when the pilot explicitly announced the descent to level 180.
- The aircraft F-GNMA lacked TCAS capability, which prevented the system from providing a resolution advisory to both aircraft involved.