A mid-air disaster was averted last week when an IndiGo plane which was on a collision course with an Indian Air Force (IAF) jet in Chennai airspace steered away to safety following an auto-generated warning.

The two aircraft were just "300 ft" away from each other at the time of the incident on May 21 which set off a Resolution Advisory (RA) for the IndiGo pilot to steer the aircraft to a safer distance, sources said.

Resolution Advisory is an auto-generated warning in the cockpit for the pilot to manoeuvre the aircraft and avoid a collision.

IndiGo confirmed the incident, which is now being investigated by aviation regulator Directorate General of Civil Aviation. There was no response from the IAF.

"IndiGo aircraft VT-ITW operating on the Visakhapatnam-Bengaluru route and an Indian Air Force jet were on a collision course as the two aircraft were at a distance of just 300 ft from each other. The planes were at an altitude of 24,000 ft in Chennai airspace. IndiGo Airbus A320 flight was on the climb," sources said. The mishap was averted at 9.49 pm on May 21.

"An IndiGo flight 6E- 647 (Vizag-Bengaluru) was involved in a resolution advisory at flight level 240, on May 21," IndiGo said in a statement.

"Pilot followed the laid standard operating procedures," the statement said, adding this matter was immediately brought to the notice of the regulator as per the prescribed protocol.

The incident is being investigated by the DGCA, it said.