What happened
On May 21, 2018, an airprox incident occurred within the Chennai Area Control Centre (ACC) jurisdiction involving two jet-powered aircraft. The first, HK053, an Indian Navy aircraft, was performing a practice diversion and touch-and-go maneuver at Vijaywada before returning to Vizag. The second, IGO647, a commercial flight traveling from Vizag to Bangalore, was cruising at FL240.
As HK0SB climbed through FL238 toward its assigned FL250, it intercepted the path of IGO647. The vertical separation between the two aircraft plummeted to a mere 200 feet with no horizontal separation maintained. This proximity triggered Traffic Advisory (TA) and subsequent Resolution Advisory (RA) alerts on both aircraft. The crew of IGO647 performed emergency maneuvers, including a rapid descent and a subsequent climb, to avoid the collision. Following the conflict, the crew of IGO647 maintained FL245 because they were unable to receive clear instructions from Air Traffic Control (ATC).
The investigation
The investigation by AAIB India focused on the coordination between various ATC units and the performance of the Chennai automation system. Investigators examined the handover process between Vizag, Vijaywada, and Chennai controllers. It was noted that while the Chennai Planning Controller had approved the climb to FL250, there was a fundamental misunderstanding regarding the aircraft's flight profile.
Furthermore, the investigation scrutinized the surveillance capabilities during the event. The aircraft HK053 was initially displayed as a synthetic track based on flight plan data rather than a real-time surveillance track. The investigation also reviewed the impact of high traffic density caused by the temporary merging of the UMM North and South sectors, which increased radio frequency congestion and communication difficulties.