Two AI aircraft come close to midair collision

New Delhi: Over 500 people had a close shave when two wide-body aircraft of Air India came perilously close to each other while flying into the city. Timely action by pilots of the two Boeing 787s averted a tragedy, close to the site of the midair collision that took place at Charkhi Dadri two decades ago.
One of the flights was coming in from Paris and the other from Vienna. A source told TOI: “One flight was at 22,000 feet and slightly ahead of the other, which was at 21,000 feet.The aircraft were about 75 miles from IGI Airport.” The Delhi ATC asked the pilot of the plane flying above to descend, which meant crossing the level of the aircraft slightly behind it, the source added. As the first pilot wasn’t aware of the plane below his, the two aircraft came dangerously close, said multiple sources. At one point, the distance between the two planes was as less a mile.
“The traffic collision avoidance system (TCAS) alarms went off in the cockpit of both planes. The pilot of the plane above immediately pulled up and the one below virtually dived to avoid a collision. Both the 256-seater Dreamliners were nearly packed to capacity,” said one of the sources quoted above.
After landing, the pilots of AI 142 (from Paris) and AI 154 (from Vienna) filed a report with the airline, and the Directorate General of Civil Aviation was informed.
Confirming the near-miss, a senior AAI official said: “The air-proximity took place on Thursday in Delhi and was reported by the controller. It was due to wrong call sign used by the controller. The controller involved has been derostered from ATC duties and a preliminary inquiry has started.”
DGCA is learnt to have asked the ATC to give exact details of the incident by plotting the whereabouts of the planes on the radar. The regulator wants to know the vertical and horizontal separation between the two planes at the time of the incident. If the breach in vertical separation was less than 250 feet, the case would be referred to the Aircraft Accident Investigation Board, which handles the most serious safety breaches or accidents.
Modern aircraft have airborne collision avoidance system equipment that issue two types of advisories to pilots: traffic advisories and resolution advisories. As the first step, a TA is issued to give an advance warning to the crew of two planes that they are headed in the same direction. In the second stage, an RA is issued that asks the crew to take evasive action.
“Usually, TA goes off first in the cockpit when the planes are approaching each other and are at a safe distance. Pilots accordingly take steps. But in Thursday’s near-miss, the TA and the RA went off almost simultaneously, which gave only seconds for the pilots to react. They showed great presence of mind and saved the day,” said a source.
On November 12, 1996, the outskirts of Delhi had witnessed the worst-ever mid-air collision when a Saudi Arabian Boeing 747, which had taken off from IGI, collided with a Kazakhstan Airlines Ilyushin-76 that was flying into the capital, at Charkhi Dadri, killing all 349 people on board the two planes.