A320 / B738, en-route, north northwest of Sofia Bulgaria, 2016

A320 / B738, en-route, north northwest of Sofia Bulgaria, 2016

Summary

On 4 June 2016, a Boeing 737-800 instructed to climb from FL340 to FL380 by the controller of one sector in Bulgarian upper airspace came into sufficiently close proximity to an Airbus A320 under the control of a different sector controller to trigger co-ordinated TCAS RAs. Separation was eventually restored after the 737 followed its RA despite the A320, which had already deviated from its clearance on the basis of a prior TCAS TA without informing ATC, ignoring their RA. The Investigation found that the root cause of the conflict had been inadequate coordination between two vertically separated ATC sectors.

Description

On 4 June 2016, an Airbus A320 (TC-ATK) being operated by Atlasjet on a scheduled international passenger flight from Dusseldorf to Istanbul under callsign KKK5LP and cleared to maintain FL370 lost prescribed separation in day VMC against a Boeing 737-800 (TC-JGF) being operated by Turkish Airlines on an international passenger flight from Istanbul to Rome Fiumicino under callsign THY7FX whilst both aircraft were on crossing tracks and the 737 was climbing from FL340 to FL380. Both aircraft received TCAS RAs but only the 737 followed it, the A320 having already begun to deviate from its clearance on receiving a prior TA. The (lateral) Closest Point of Approach (CPA) of 2.75 nm and 575 feet vertically occurred after the RAs had ceased.

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