A possible mid-air collision involving an IndiGo aircraft -- bound for Guwahati from Dibrugarh with 179 passengers onboard -- was averted due to an alert by the Air Traffic Control that there was an 'intruder' aircraft at 30,000 feet.
IndiGo said the flight had an advisory triggered by the Traffic Collision Avoidance System.
"IndiGo flight 6E - 206 with 179 passengers onboard en route from Dibrugarh to Kolkata had a Resolution Advisory triggered by TCAS. Resolution Advisory was triggered while descending at 1507 pm," the airline said in a statement.
TCAS is an on-board equipment that advises pilots about the traffic in the proximity of the aircraft and also tells pilots the avoidance action (Resolution Advisory) to maintain desired separation between the aircraft.
The incident was reported to Tezpur radar and thereafter normal flight was resumed, it said.
However, ATC sources said the the advisory was issued to the Indigo flight due to a defence exercise going on there.
"Some defence exercise involving fighter jets was going on due to which the advisory was issued to the pilot," said ATC sources.