What happened
On December 6, 2005, an Airbus A320-212 operating a scheduled flight from Berlin to Cologne was cruising at flight level 320. At approximately 21:23 local time, air traffic control cleared the aircraft to descend to flight level 250, with the instruction to maintain this new altitude until reaching the PODER waypoint. Following the initiation of the descent, the controller instructed the crew to switch to a new radio frequency for the next sector. This frequency change was not performed.
Simultually, a Boeing 747-312M(SF), flying a scheduled service from Amsterdam to Dubai, was cruising at flight level 310. During the descent of the A320, the Traffic Collision Avoidance System (TCAS) on the A320 generated a climb instruction, while the crew of the Boeing 747 reported receiving a TCAS descent instruction.
Radar data confirmed that both flight crews followed the TCAS resolution advisories. The flight paths of the two aircraft crossed with a horizontal separation of 1.2 NM and a vertical separation of only 600 ft, placing the A320 behind and above the Boeing 747. Both aircraft continued their flights and landed safely at their destinations with no injuries and no damage to the aircraft.
The investigation
The BFU examined radar recordings, radio communications, and flight data to reconstruct the encounter. The investigation reviewed the air traffic controller's credentials, noting the controller had held a license since 2000 and had been on duty since 15:00 that day. Meteorological conditions at the time of the event were reported as visual meteorological conditions (VMC) above a continuous cloud layer.
Findings
- The required separation standards in this airspace were 5 NM horizontally or 1000 ft vertically.
- The aircraft were operating with a vertical separation of only 600 ft and a horizontal separation of 1.2 NM.
- The TCAS resolution advisories were successfully executed by both crews, preventing a loss of separation.
- The A320 crew did not complete the instructed frequency change to the next sector prior to the TCAS event.