In a spine-chilling incident that could have resulted in hundreds of deaths, three passenger planes of foreign carriers are known to have come extremely close to one another in Delhi and a collision was averted after repeated auto generated warnings and alerts from the Air Traffic Control.
The incident took place on December 23, when three aircraft of Dutch carrier KLM, Taiwan's Eva Air and the US-based National Airlines came extremely close to each other. The National Airlines' flight NCR 840 was enroute to Hong Kong from Afghanistan and Eva Air flight was flying to Vienna from Bangkok. The third aircraft KLM was on the way to Bangkok from Amsterdam.
Speaking of the incident, an official told the Press Trust of India thus: "First it was NCR 840, which was flying at flight level 310 (31,000 ft) and EVA 061 at flight level 320 (32,000 ft) which breached mandatory separation. The pilots of both the aircraft were alerted by the onboard TCAS warning system." He went on to explain that at this time, the KLM flight was at a height of 33,000 feet.
After the warning, the pilot of the NCR 840 reportedly sought permission from the ATC to climb to 35,000 ft, but was told to remain at 31,000 ft until given further directions.
"However, when the air traffic controller (ATC) observed it climbing, it was immediately asked to take a left turn. In the meantime, EVA also continued climbing at flight level 330, a level at which KLM was already flying, and at this time, another TCAS warning went off, alerting the pilots to steer the aircraft to a safer distance," the official added.
Once the NCR 840 received the orders to stay at 31,000 ft, it once again descended, coming precariously close to the EVA flight, triggering another alarm.
The Aircraft Accident Investigation Bureau (AAIB) has now started a probe into the incident.
In a similar incident, two IndiGo aircraft were said to have averted a mid-air collision on October 31. The two planes were flying in the airspace over the India-Bangladesh border. The aircraft were only 45 seconds apart and the collision was averted when the ATC tower in Kolkata asked one of the planes to change its path.
"Both the aircraft, belonging to low cost carrier IndiGo, had come on the same level on Wednesday evening and posed a threat to both the aeroplanes," a senior AAI official at the Kolkata airport told PTI.
While one was a Chennai-Guwahati flight, at 35,000 ft in the Indian airspace, the other one was flying to Kolkata from Guwahati at 36,000 ft in the Bangladesh airspace. The Bangladesh ATC is then said to have asked the Kolkata-bound flight at 36,000 ft to descend to 35,000 ft and that is when the two aircraft came close.
Noticing that the planes were just 45 seconds apart at around 5.10 pm, an official of the Kolkata ATC instructed the Guwahati-Kolkata flight to turn right and move away.