Two IndiGo aircraft carrying nearly 330 passengers came in very close proximity of each other on Tuesday night but were able to avert a mid-air collision after alarms went off, PTI reported. The incident took place over Bengaluru airspace.

The Coimbatore-Hyderabad aircraft had 162 passengers while the Bengaluru-Kochi plane had 166 passengers. A vertical distance of only about 200 feet separated the two planes at one point, unidentified people told PTI.

Confirming the incident, the airline said, “The TCAS [Traffic Collision Avoidance System] Resolution Advisory system was triggered on two of our aircraft operating Coimbatore-Hyderabad and Bangalore-Cochin routes, respectively, on July 10, 2018. Following normal procedure, this has been reported to the regulator [Directorate General of Civil Aviation].”

The Traffic Collision Avoidance System monitors the airspace around a plane for other aircraft to warn pilots of possible collision risks.

The Aircraft Accident Investigation Board has started an investigation into the incident, PTI reported.