What happened
On June 9, 2017, at approximately 15:16 UTC, a serious air proximity incident occurred in the EMRAK holding pattern near Mumbai. A Jet Airways B737-800, registration VT-JFM, was descending through the holding pattern toward Mumbai. Simultaneously, a Go Air A320-214, registration VT-WAK, was descending from Delhi toward Pune.
During the descent, the Lower Area Control (LAC) controller issued a series of step-down instructions to the Go Air crew. Although the automation system generated Predicted Conflict Warnings (PCW) and the controller explicitly advised the crew to maintain FL210 due to traffic, the controller subsequently cleared the Go Air aircraft to descend to FL100. This clearance was issued while the Jet Airways aircraft was passing through FL178 on its way to FL160. This resulted in a breach of standard separation, with the two aircraft reaching a vertical separation of only 100 feet and a lateral separation of 2.8 NM.
The investigation
The investigation by AAIB India examined ATC recordings, flight data recorder (DFDR) information, and crew statements. The inquiry found that both aircraft's TCAS systems triggered Resolution Advisories (RA), and both crews followed the instructions. The investigation also noted that the LAC controller had been performing minimal duties in the specific radar unit (ASR) during the preceding months and was managing high traffic density, including surveillance of five simultaneous holds.
Findings
- The primary cause was the inadvertent issuance of a descent clearance to FL100 to the Go Air aircraft, which directed it through the flight level occupied by the Jet Airways aircraft.
- The Go Air crew failed to maintain situational awareness; despite receiving multiple warnings regarding traffic and being given unusual step-descend instructions, they did not seek clarification from ATC regarding whether they were clear of the other aircraft.
- High traffic density and the controller's limited recent experience in that specific radar sector contributed to the loss of separation.
- The investigation also noted that neither airline successfully preserved or downloaded the Cockpit Voice Recorder (CVR) data following the incident.
Safety action
- It is recommended that the LAC controller undergo corrective training focusing on separation, surveillance, and managing TCAS RA situations.
- A recommendation was made for AAI to explore sectorizing the lower area control to reduce the number of holds managed by a single controller.
- The Go Air crew should undergo training regarding Crew Resource Management (CRM) and situational awareness when responding to ATC instructions.