What happened
On 22 August 2002, a mid-air proximity incident occurred near the TELNO waypoint within the Geneva Upper Area Control (UAC) jurisdiction. The incident involved a Cessna Citation C560, registration HB-VMV, operating a commercial flight from Geneva to Salzburg, and a Deutsche Lufthansa Airbus A319, flight DLH4161, traveling from Nice to Frankfurt.
While climbing through flight level 240, the pilot of HB-VMV received clearance from the Zurich sector radar operator to maintain flight level 260. However, the pilot read back an incorrect flight level of 280. Although the radar operator repeated the route twice, the incorrect altitude was not corrected. Consequently, the aircraft climbed to flight level 274. Simultaneously, the Airbus A319 was cruising at flight level 280. The altitude deviation of the Cessna Citation C560 triggered a Traffic Collision Avoidance System (TCAS) Resolution Advisory (RA) for the Lufthansa crew, as the aircraft came within 600 feet of vertical separation and 1.5 nautical miles of lateral separation.
The investigation
The investigation examined the communications between the aircraft and the Swiss Radar Area West controllers. It established that at the time of the incident, the Zurich sector radar operator and coordinator were trainees working under supervision. The investigation reviewed the sequence of clearances and the specific radio telephony transcripts, noting that the trainee radar operator failed to notice the incorrect altitude readback by the HB-VMCO crew. The investigation also confirmed that the Cessna Citation C560 was not equipped with TCAS, whereas the Airbus A319 was.
Findings
- The primary cause of the incident was an incorrect readback of the assigned flight level by the crew of HB-VMV.
- A contributing factor was the lack of readback verification by the radar operator, who failed to identify the error during the transmission.
- The proximity alert was specifically triggered because the Cessna Citation C560 climbed to flight level 274, encroaching on the flight level 280 occupied by DLH4161.