What happened
On 5 February 2018, a Saudi Arabian Airlines Boeing 772, registration HZ-AKW, was operating a scheduled flight from Jeddah to Lahore. While cruising at FL370 on route G214, the aircraft was cleared by Lahore ATC to descend to FL330 via the LAMOM 2 ALPHA arrival. During the descent, the aircraft was re-cleared to stop the descent at FL350 while passing FL367.
During this phase of flight, the aircraft's rate of descent increased significantly, reaching approximately 3,168 fpm. As the aircraft passed through FL351, it encountered a Traffic Advisory (TCAS-TA) followed by a Resolution Advisory (TCAS-RA). The advisory was triggered by reciprocal traffic, a Pakistan International Airlines Airbus A320, registration AP-BLS, which was maintaining FL340 on the same route.
The investigation
The Safety Investigation Board (SIB) examined radar records, ATC audio tapes, and flight data. The investigation focused on the coordination between Karachi and Lahore Air Traffic Control (ATC) units, as well as the descent profile of the aircraft. The board reviewed the loss of radar contact with the aircraft in the Karachi FIR and the subsequent handover to Lahore ATC.
Findings
- The primary cause of the incident was an excessive rate of descent by the crew of HZ-AKW during the final 1,000 feet of the descent to FL350.
- A lack of situational awareness by the Lahore Area Procedure Controller contributed to the event, as the controller failed to identify and communicate the presence of the reciprocal AP-BLS traffic to the crew.
- Karachi ATC did not provide information regarding potential conflicts in their sector and failed to coordinate the early descent with Lahore ATC prior to the aircraft crossing the transfer point.
- Procedural lapses were noted in the management of flight progress strips and the unauthorized use of radar phraseology by a controller not qualified for radar services.
- Technical limitations, specifically the loss of radar data in the Rojhan SSR coverage area, hindered effective surveillance.