A mid-air disaster was averted in the Mumbai airspace when a Vistara aircraft came perilously close to an Air India plane, prompting the Aircraft Accident Investigation Bureau (AAIB) to launch a probe.

On February 7, the Vistara’s UK 997 Pune-bound aircraft from Delhi, carrying 152 passengers, was just 100 feet away from the Air India’s AI 631 flight for Bhopal which had 109 passengers on board.

The AI flight captain has written in her resolution advisory report that the aircraft was just 100 feet away when it was taken to a safer distance.

The collision was averted after an automatic warning alerted the pilots of the two planes of being in close proximity to each other, an official said.

The commander of the Air India flight acted swiftly on the instrument warning and steered the aircraft to a safer distance, a senior official of the airline said.

The two pilots of the Vistara flight have been grounded, pending investigation, while the Air India pilots have been cleared for flying by the AAIB for not being at fault, the official added.

Vistara confirmed the incident and said both its pilots have been taken off flying duty, pending investigation.

"In this particular incident, the resolution advisory (by the Traffic Collision Avoidance System or TCAS) got triggered due to conflicting traffic. Our pilot followed the standard operating procedure to avoid it and carried out an uneventful landing. The matter is under investigation by the relevant authority," a spokesperson of the Vistara said.

TCAS is an onboard equipment that advises pilots regarding the traffic in the proximity of the aircraft and also prescribes what action a pilot can take to maintain the desired separation between the aircraft.

"The Air India aircraft was going as per the ATC instructions. There was no confusion. But it seems that something had gone wrong between the Vistara pilot and the ATC as the Vistara aircraft kept descending while the ATC was giving different instructions. There was some kind of an argument between them," the Air India official said.

"The Vistara aircraft continued descending. So, finally, when our pilot saw the warning (the Vistara aircraft breaching the mandatory separation) on board, she just took the corrective action and turned the aircraft from the collision point," the airline said.

The Air India pilot’s action was perfect as she followed the resolution advisory and steered the aircraft to a safer distance, it added.

"The AAIB has cleared our pilot for flying," the Air India official said while lauding her timely action.

"It was a close shave," he said.