What happened
On 11 December 2016, a serious air proximity incident occurred at Kolkata's Netaji Subhash Chandra Bose International Airport involving two scheduled commercial flights. The first aircraft, an Inter-globe A320-232 with registration VT-IEM, was preparing for departure to Shamshabad. Simultaneously, a Silk Air B737-800, registration 9VMGH, was on final approach from Singapore.
During the sequence, the tower controller attempted to expedite two departures before the arrival of the Silk Air flight. A heavy Boeing 777 was cleared for an intersection takeoff, and the Inter-globe A320-232 was instructed to backtrack the full length of Runway 19L. As the Inter-globe aircraft commenced its takeoff roll, the Silk Air B737-800 was crossing the runway threshold. This resulted in a critical reduction of separation, with lateral distance dropping to approximately 0.6 NM and vertical separation reaching zero feet. The situation was resolved when the Silk Air crew initiated a go-around, and the controller provided divergent headings to both aircraft.
The investigation
An AAIB India inquiry examined radar data, ATC transcripts, and flight recorder information. The investigation focused on the tower controller's management of the runway sequence and the use of non-standard departure procedures. Investigators looked into the timing of takeoff clearances and the controller's failure to monitor the speed of the arriving aircraft. The inquiry also reviewed the impact of a heavy aircraft's presence on the runway and the controller's adherence to separation standards defined in ICAO Doc-4444.
Findings
- The tower controller utilized a non-standard procedure by allowing one aircraft to backtrack while another prepared for an intersection departure.
- The controller attempted to expedite departures without properly accounting for the arrival of the Silk Air flight.
- The tower controller failed to comply with standard operating procedures regarding separation between arriving and departing aircraft.
- The controller did not adequately consider wake turbulence constraints when releasing the second departure.
- The controller issued speed reduction instructions to the arriving aircraft despite not being radar-rated.
- The go-around by the Silk Air crew was unanticipated by the tower controller.