Preliminary data based on the notification from the Bulgarian authorities :
On 8 September 2016 at 15:02 UTC in the controlled airspace of the Republic of Bulgaria, family sector Sofia-East, an infringement of the minimum standards of the safe radar separation between aircrafts transiting the upper airspace of Bulgaria was committed. Airbus A321-211 aircraft, reg. marks TC-ATF, of 'Atlasjet' performing flight with flight number KKK8YJ from LSZH to LTBA and Boeing 737-8F2 aircraft, reg. marks TC-JVS of 'Turkish Airlines', performing flight with flight number THY4AV from EGKK to LTBA, passed by each other at a minimal horizontal distance of 1,2 nm at FL 363 without vertical separation. The occurrence was realized due to an unexpected climb of the aircraft, reg. marks TC-ATF, to unknown FL, instead of the clearance to descend given by the ATCO and confirmed by the pilot in command (PIC). The ATCO issued instructions for descending to the aircraft, reg. marks TC-ATF, from FL 350 to 310 and to the aircraft, reg. marks TC-JVS from FL 370 to 330. In attempt to resolve the conflict, the ATCO issued instructions to the aircraft, reg. marks TC-ATF to turn left and to the aircraft, reg. marks TC-JVS to turn right. After the safe separation between the aircrafts was recovered, the PIC of aircraft reg. marks TC-ATF reported a technical problem and PIC of the aircraft reg. marks TC-JVS reported “TCAS RA”.