History of Flight
On 7 January 2020, Pakistan International Airlines flight PIA301 (B77L, registration APBGY) was operating from Islamabad to Karachi. Emirates Airline flight UAE516 (B77W, registration A6EPS) was operating from Dubai to Delhi. Both aircraft were under the control of Karachi Area Control Centre.
At 07:26:57 UTC, PIA301 contacted ATC Karachi (Area Radar Controller East) maintaining FL400 and was cleared for the Nawabshah 2A STAR. At 07:32:14 UTC, UAE516 contacted ATC reporting FL350, proceeding direct to waypoint BADUL.
At 07:39:30 UTC, ATC instructed PIA301 to descend to FL180 at pilot discretion, contrary to the SATI phraseology. This clearance was given with traffic PIA588 (ATR72) at FL170 in mind. A Flight Plan Alert was generated but not acted upon.
Conflict and TCAS-RA
At 07:44:22 UTC, PIA301 vacated FL400 descending for FL180 while northeast of Nawabshah, with UAE516 southwest of Nawabshah at FL350, 70.52 NM apart. By 07:46:30, PIA301 was passing FL374 and UAE516 at FL350, 36 NM apart. At 07:47:48, separation reduced to 15 NM with PIA301 at FL359.
At 07:47:52, Short Term Conflict Alert (STCA) Violation Phase activated (Prediction Phase did not). Both aircraft were 13.69 NM apart. At 07:48:05, ATC instructed UAE516 to turn left 10 degrees for spacing; UAE516 acknowledged and reported TCAS-RA. At 07:48:18, ATC instructed PIA301 to turn left 10 degrees.
At 07:48:19, PIA301 was passing FL354 and UAE516 at FL350, 6.9 NM apart. At 07:48:21, PIA301 initiated climb (passing FL355, vertical speed +2592 ft/min) and UAE516 initiated descent (passing FL349), due to TCAS-RA. At 07:48:28, PIA301 passed FL358 and UAE516 FL347, 4.1 NM apart, vertical separation exceeding 1000 ft. At 07:48:43, aircraft crossed with lateral separation 0.54 NM and vertical separation 1800 ft (PIA301 at FL366, UAE516 at FL348).
Aftermath
At 07:48:47, UAE516 reported clear of conflict and resumed FL350. At 07:49:09, PIA301 reported TCAS-RA and requested direct to MAKLI. At 07:49:17, PIA301 stated no traffic information was given. ATC then cleared PIA301 to FL100. No damage to aircraft or injuries to passengers/crew were reported. The minimum vertical separation was 400 ft at 6.91 NM lateral distance.
Findings and Cause
The investigation concluded that the incident occurred due to lack of situational awareness on the part of ATC Karachi (Area Radar Controller East). The STCA Prediction Phase did not activate, which would have provided a caution about 120 seconds prior to the Violation Phase.