Airprox Serious incident Airbus A319-112 D-AKNK, Friday 10 June 2011

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Date:	Friday 10 June 2011
Time:	08:38 UTC
Type:	Airbus A319-112
Owner/operator:	Germanwings
Registration:	D-AKNK
MSN:	1077
Year of manufacture:	1999
Engine model:	CFMI CFM56-5B6/P
Fatalities:	Fatalities: 0 / Occupants:
Other fatalities:	0
Aircraft damage:	None
Category:	Serious incident
Location:	18 NM NE FRI VOR - Switzerland
Phase:	En route
Nature:	Passenger - Non-Scheduled/charter/Air Taxi
Departure airport:	Barcelona-El Prat Josep Tarradellas Airport (BCN/LEBL)
Destination airport:	Stuttgart-Echterdingen Airport (STR/EDDS)
Investigating agency:	STSB
Confidence Rating:	Accident investigation report completed and information captured

Narrative:
Germanwings flight 2529, an Airbus A319-112 (D-AKNK), which was descending, was cleared to flight level FL 250 by the Geneva area control centre (ACC). Geneva area control centre then handed the aircraft over to Zurich ACC. There was an agreement in existence between Geneva and Zurich which provided for such a handover at FL 280 without further coordination. The Geneva ACC air traffic controller entered FL 280 into the system as the cleared altitude but had given the A319 clearance to FL 250 over the radio. At the same time the Hahn Air Raytheon 390 D-IAGG aircraft which had taken off from Zurich was climbing to its cruising altitude on an opposite heading and had been cleared to FL 270 by Geneva ACC. When the descending A319 had passed FL 280 and the climbing Raytheon 390 was converging on a virtually opposite flight path, both the Geneva ACC air traffic controllers and the Zurich ACC controllers noticed the conflict and tried to influence the flight path of the aircraft which was on their frequency. When the traffic alert and collision avoidance system (TCAS) of the two aircraft responded, the crews immediately followed the corresponding resolution advisories (RA). During the RA, the air traffic controller gave an instruction to the crew of the Raytheon 390 to descend immediately. The crew of the Raytheon 390 followed this instruction and no longer followed the TCAS advisory; this led to a further reduction in the separation of the two aircraft at the crossing point.
According to the radar recording, at the crossing point the lateral separation was 1.3 NM and the altitude difference was 75 ft.

Causes
The serious incident is attributable to the fact that air traffic control gave clearance to an aircraft which led to a hazardous convergence with another aircraft. The fact that one of the flight crews then followed the resolution advisories of the traffic alert and collision avoidance systems (TCAS) only initially and instead followed the instructions of air traffic control meant that the convergence involved had a high risk of collision.
The following factors have been identified as causative for the serious incident:
- The air traffic controller entered the flight level prescribed for this flight as a clearance into the air traffic control system, but gave a different clearance to descend by radio.
- None of the five air traffic controllers who were involved in managing the aircraft concerned noticed the discrepancy between the descent clearance in the system and the radio message.
- The crew of the aircraft followed the instructions of air traffic control instead of continuing to follow the diverging resolution advisory of the TCAS.

The following factors contributed to the genesis of the serious incident:
- An Air Force exercise led to an increased workload and a more difficult overview for civil air traffic control.
- The use of a non-standard phraseology by air traffic control.

The following factors contributed systemically to the occurrence of the serious incident:
- Air traffic control had no safety net at their disposal which would have been able to detect the working error of an air traffic controller at an early stage.
- Working processes in air traffic control which made it difficult to detect routine working errors.

Accident investigation: