What happened
On November 7, 2018, at approximately 03:12 UTC, two commercial aircraft experienced a serious airprox incident near waypoint GIVEK in Mumbai airspace. The first aircraft, a Jet Airways Boeing 777 (registration VT-JLJ), was climbing through FL338 toward FL350 on a flight from Mumbai to Bangkok. Simultaneously, an Air India Airbus 319 (registration VT-SCP) was cruising at FL340 on a flight from Bhopal to Mumbai.
During the encounter, the standard separation of 1000 feet and 10 nautical miles was breached, with the vertical distance between the two aircraft dropping to just 200 feet and lateral separation reducing to 3NM. The conflict triggered Resolution Advisories (RA) in both cockpits, instructing the Boeing 777 to descend and the Airbus 319 to climb. The incident was eventually resolved on the controller's display at 03:15 UTC.
The investigation
The AAIB India investigation focused on the performance of the Mumbai Radar (RSR(N)) controller and the functionality of the surveillance systems. Investigators established that the Short Term Conflict Alert (STCA) had first been triggered at 02:58 UTC, but the controller did not take corrective action.
Crucially, the investigation found that the Mode C information (altitude data) for VT-JLJ became intermittently unavailable on the radar screen during the approach to the conflict. Despite the flight block turning red to indicate a confirmed violation of separation, the controller proceeded to terminate radar service for VT-JLX and transfer control to Nagpur Radar without verifying the aircraft's altitude or resolving the active conflict. Furthermore, the investigation noted that the Air India crew attempted to contact Mumbai ATC twice without receiving a response, and the Jet Airways crew attempted to report the conflict after the fact, but their calls went unacknowledged.
Findings
- The Radar Controller ignored the initial STCA for over 11 minutes.
- The Controller failed to monitor critical radar data parameters, specifically the loss of Mode C altitude information.
- The controller transferred aircraft control to another sector while a confirmed conflict warning was active on the screen.
- The aircraft were not in two-way communication with either Mumbai or Nagpur ATC at the time of the airprox.
- The controller failed to comply with established Air Traffic Services (MATS) procedures regarding separation and service termination.
Safety action
- The Radar Controller is to receive corrective training regarding surveillance techniques, STCA procedures, and handling aircraft during emergencies.
- The Airports Authority of India (AAI) is advised to improve VHF coverage reliability up to the transfer of control points on all routes.