By PTI

KOLKATA: Two IndiGo planes came too close for comfort before averting a mid-air collision at the border airspace of India and Bangladesh, Airports Authority of India (AAI) officials said Thursday.

With only 45 seconds before the possible collision, it was averted after the Air Traffic Control (ATC) tower in Kolkata instructed one plane to turn right and move away from the other aircraft that had come at the same level on Wednesday.

"Both the aircraft, belonging to low-cost carrier IndiGo, had come on the same level on Wednesday evening and posed a threat to both the aeroplanes," a senior AAI official at the Kolkata airport told PTI over the phone.

"One aircraft was going to Guwahati from Chennai and the other from Guwahati to Kolkata. The planes had come close to each other around 5.10 pm," he said.

At that time, the Kolkata-bound flight was at 36,000 ft in Bangladesh airspace and the other one at 35,000 ft in Indian airspace.

The Bangladesh ATC had asked the Kolkata-bound flight to descend to 35,000 ft and when the aircraft followed the order, it came close to the aircraft which was at 35,000 ft, the official said.

An ATC official in Kolkata saw it and immediately ordered the Chennai-Guwahati flight to make a right turn and move away from the path of the descending aircraft, averting a disaster, he said.

"We have no such information as of now," an IndiGo spokesperson told PTI when contacted.

As per standard procedure, an investigation will be initiated, another AAI official said.

It is not known if the Airborne Collision Avoidance System (ACAS) or the Traffic Alert and Collision Avoidance System (TCAS), which are generally fitted in aircraft, had alerted the pilots or not, the official said, adding that everything will be found out during the investigation.

As per rule, the standard separation gap between two aircraft, both vertical difference and lateral difference, should be a minimum of 1000 ft, said sources at the airport.