Serious incident Airbus A320-232 TC-ATK,
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ASN Wikibase Occurrence # 200093
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Date:Saturday 4 June 2016
Time:15:18 UTC
Type:Silhouette image of generic A320 model; specific model in this crash may look slightly different    
Airbus A320-232
Registration: TC-ATK
MSN: 2747
Engine model:IAE V2527-A5
Fatalities:Fatalities: 0 / Occupants:
Aircraft damage: None
Category:Serious incident
Location:15 NM East of DOLAP -   Bulgaria
Phase: En route
Nature:Passenger - Scheduled
Departure airport:Düsseldorf International Airport (DUS/EDDL)
Destination airport:Istanbul-Atatürk International Airport (IST/LTBA)
Investigating agency: AAIU Bulgaria
Confidence Rating: Accident investigation report completed and information captured
An Airbus A320-232 operated by AtlasJet as KKK5LP from Düsseldorf to Istanbul and a Turkish Airlines Boeing 737-800, flight THY7FX from Istanbul to Rome were involved in a loss of minimum separation incident in the controlled airspace of Bulgaria, sector "Sofia-West".
Both aircraft passed each other with a minimal horizontal distance of 2,6 nm and 500 ft. vertical separation.
Flight THY7FX entered Bulgarian airspace at 14:53 UTC at FL320 via L615. At 15:10 flight KKK5LP entered Bulgarian air space at FL370. Both aircraft were flying in opposite directions on different airways that cross over northwestern Bulgaria.
At 15:15 the controller of the SCL sector of Sofia ACC issued instructions to THY7FX for climbing to FL380 and turning 10°. At that time KKK5LP is 52NM away, and under control of the SCU sector of Sofia ACC.
One minute later, as THY7FX is climbing, a Medium Term Conflict Detection (MTCD) warning betweeen the two flights is generated as THY7FX would be crossing KKK5LP's flight level. The potential conflict is not completely visualized in the two SCU and SCL sectors, as is in both the sectors one red dot for conflict is shown only, without displaying the related second red dot in the radar label of the other aircraft. The distance between the two aircraft is 34.1 NM.
The distance is still 14.1 NM as THY7FX crosses FL370 while climbing with vertical speed of 600 ft/min.
Now a Short-term conflict alert (STCA) was triggered and ddisplayed at both the working positions of SCU and SCL sectors. The distance between the two aircraft was 12,8 NM. In order to avoid further conflicht, the SCU sector controller issued instructions to the flight crew of KKK5LP for an immediate "turn left heading 060". The flight crew did not confirm the instructions.
At 15:18 the flight crew of KKK5LP disconnected the autopilot while receiving a TCAS Traffic advisory (TA) indication and began to climb.
The SCL sector controller then issued instructions to the flight crew of THY7FX to turn 40° left. The flight crew did not respond to this instruction.
Subsequently KKK5LP now received a TCAS Resolution advisory (RA): DON'T CLIMB. At the same time THY7FX received a TCAS RA 'CLIMB', after which the flight crew disconnect the autopilot.
Contrary to the TCAS RA and without informing ATC, flight KKK5LP starts climbing. The distance between the two aircraft is 7.1 NM.
The SCL sector controller repeated the instructions to the aircraft: "THY7FX turn immediately 40° to the left". This was confirmed: "Roger, turn left, we have TCAS RA". At the time, KKK5LP was still climbing and now chaning the heading according to previous instructions.
At 15:18:53, the horizontal distance between THY7FX and KKK5LP is 2.6 NM and vertical separation is 500 ft. Fifteen seconds later KKK5LP starts descending to FL370 without reporting to the controller of this change and still without reporting the TCAS RA received.
Both aircraft then proceeded to their respective destinations uneventfully.

Main cause:
Incorrect assessment of the air situation and issuing of permission for changing the trajectory of A/C THY7FX without carrying out relevant coordination by the ATCO of sector SCL with the ATCO of sector SCU, uncommanded climb of A/C KKK5LP and no response to TCAS RA by the crew of A/C KKK5LP.
Contributing cause:
Inefficient performance of coordination procedures between ATCOs of SCL and SCU sectors, ACC-Sofia, upon work in vertically separated sectors in accordance with Part 2 of the Manual on Air Traffic Services of the ACC-Sofia.


Accident investigation:
Investigating agency: AAIU Bulgaria
Report number: 
Status: Investigation completed
Download report: Final report


Revision history:

01-Oct-2017 18:22 harro Added
01-Oct-2017 19:26 harro Updated [Narrative]
01-Oct-2017 19:34 harro Updated [Photo, ]
01-Oct-2017 19:34 harro Updated [Photo, ]

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