Close shave: 2 IndiGo planes came dangerously close over Delhi airport in November; probe on

“At the time of the closest vertical separation (400 feet), lateral separation was 1.2 NM (nautical miles). At the time of the closest lateral separation (0.2 NM), vertical separation was 800 feet. There was no injury to any of the occupant on board in both aircraft. There was no damage,” the AAIB said in its preliminary incident report. It is worth noting that as per norms, aircraft must maintain a minimum vertical separation of 1,000 feet and lateral separation of 5 nautical miles while airborne. IndiGo has not yet commented on the incident or the AAIB investigation.

According t0 AAIB’s report, the A321 departed from IGI Airport’s Runway 27 at 12:31 PM on November 17, and was cleared by the air traffic controller to climb to 8,000 feet. However, the aircraft “was observed turning left toward the takeoff path of RWY 29R (Runway 29 Right)” instead. At the same time, the A320 operating the Delhi-Raipur flight received departure clearance and took off from Runway 29 Right.

“During this sequence, a breach of separation occurred…triggering a Current Conflict alert,” the AAIB said, adding that both aircraft received TCAS-RAs (Traffic Alert and Collision Avoidance System-Resolution Advisory). TCAS-RAs are specific instructions provided by the Traffic Alert and Collision Avoidance System, or TCAS, to pilots on how to avoid conflict with air traffic, and could include directions to descend, climb, or adjust vertical speed of the aircraft. TCAS is a critical safety system in aircraft to avoid mid-air collisions.

However, the preliminary probe report did not provide a timeline for the ongoing investigation. The AAIB obtained the data for the probe from the aircraft’s cockpit voice recorders and flight data recorders, manuals related to operations the airline and airport, and recordings of radar data and Air Traffic Control tape recordings, among others. The aviation incidents probe agency has also recorded the initial statements from the concerned flight crew and air traffic controllers.