An apparent mistake by an air traffic controller in Kolkata almost led to a mid-air collision between a United Airways Bangladesh aircraft and a Saudi Arabian Airlines plane in Kolkata on Monday.
Captain Ariful Islam of the United Airways aircraft said his plane came within the “visual distance” of the other aircraft. He had 148 passengers on board his MD 83 flying to Dhaka from Muscat.
“When my plane was about 270 miles off Dhaka and flying at an altitude of 33,000 feet in Kolkata airspace, the Kolkata Air Traffic Control told me to descend to 29,000 feet,” the pilot told this newspaper yesterday.
As he started complying with the directive, the aircraft's TCAS (Traffic Collision Avoidance System) went off and alerted him. The sky was clear and he could see a plane approaching his aircraft just to his left.
“I informed Air Traffic Control that an aircraft was approaching me at the altitude of 32,000 feet. The controller initially said he didn't see any, but moments later he said there was only one aircraft and told me to ascend to 33,000 feet,” mentioned Ariful.
The approaching plane was just 35 seconds away, said Md Kamrul Islam, assistant general manager (marketing support and public relations) of United Airways.
Ariful, who has been with the private airliner for over seven and a half years, said there was another plane, belonging to Emirates, which was flying at a height of 29,000 feet and a Boeing 777 of Biman Bangladesh Airlines flying at 39,000 feet.
Airplanes normally should maintain a height difference of at least 1,000 feet between themselves. No aircraft changes its altitude without the instruction of an air traffic controller.
United Airways official Kamrul said everything had been recorded and the reason for the near-collision would be clear after an investigation.
“We've averted a disaster since our pilot was alert to the danger and our aircraft's TCAS was fully functional,” he added.
Captain Ariful said he had filed a report on the issue with his airliner and the civil aviation regulator of Bangladesh yesterday afternoon.
“The minimum vertical distance between two aircraft should be 1,000 feet whereas the United Airways flight had come as close as 700 feet of the Saudi Airlines aircraft. But for the TCAS, the consequence would have been disastrous," an official at Kolkata ATC told the English daily The Statesman.
The eastern regional executive director of the Airports Authority of India, S Bhaduri, said a probe had been ordered into the incident to find out whether it was the mistake of Kolkata ATC or the United Airways pilot.
On November 12, 1996, a Saudi Arabian Airlines Boeing 747 was involved in a mid-air collision with a Kazakhstan Airlines Ilyushin II to the west of New Delhi. The crash killed all 349 people on board both the planes, making it the world's deadliest mid-air collision. The Kazakh plane had descended further than the ATC had asked it to.
On July 1, 2002, another mid-air collision between a Bashkirian Airlines plane carrying 60 passengers, mostly children, and nine crew, and a DHL aircraft in southern Germany left 71 people dead.