Delhi had up-to-date radar but had not installed it. Consequently, instead of continuously seeing an aircraft’s altitude on the blip on their screen, air traffic controllers had to rely on what pilots told them and could not see changes as they happened.
Kazakhstan Airlines Flight 1907/ Saudia Flight 763, November 12, 1996
Besides having archaic radar, Delhi Airport operated under difficult conditions, because the Indian Air Force had appropriated much of the airspace, and both incoming and outgoing airliners were funneled along the same narrow path, thus greatly increasing the possibility of a midair collision. The midair collision over Lake Constance we describe later in this chapter was similarly in part due to funneling, because the Swiss Air Force had restricted the airspace for civilian flights.
The Saudia (Saudi Arabian Airlines) flight, a Boeing 747-100 with 289 passengers and 23 crew, had taken off at 18:32 local time from Delhi, bound for Dhahran, Saudi Arabia. Coming the other way on its approach to Delhi Airport was a Kazakhstan Airlines charter flight, an Ilyushin IL-76TD, with 27 passengers and 10 crew. Both aircraft were being handled by the same approach controller.
The first-generation Saudia 747 had 3 aircrew, 2 pilots and a flight engineer, with the pilots handling communications with air traffic control.
The Kazakhstan Ilyushin had 2 pilots, a captain and first officer, but since it was originally a military aircraft it had a dedicated radio operator sitting at post behind the pilots without any flying instruments. Handling communications with air traffic control, the operator had to lean toward the pilots’ shoulders to check the heading and altitude. Complicating matters further, controllers at Delhi found working with aircrew used to flying only in the old Soviet Union difficult, as they were used to dealing in meters rather than feet, and their understanding of English left much to be desired. Though no one has suggested it, the fluent Indian English used by the controllers may not have helped.
Both aircraft were in the same corridor, coming in opposite directions. The Ilyushin wanted to descend to land at Delhi, while the Saudia 747 wanted to climb to its cruising height. To be safe, the approach controller decided to let them pass each other before proceeding. He therefore allowed the Kazakhstan Ilyushin to descend to 15,000 feet and maintain that altitude, and allowed the Saudia 747 to climb to 14,000 feet, a 1,000-foot separation being recognized there as an adequate safety margin. The Kazakhstan radio operator reported they were at 15,000 feet when in fact they were at 14,500 and still descending.
Even though not in theory necessary, the approach controller warned the Kazakhstan aircraft of the presence of the 747:
Identified traffic twelve o’clock, reciprocal Saudia Boeing 747, ten nautical miles. Report in sight.
He got no reply.
For some reason that has not been established—possibly the pilots misunderstood, bearing in mind they were not talking directly to the controller—the Kazakhstan Ilyushin continued to descend and found itself unwittingly below the 747, in which case, although not intended, it should have passed safely underneath.
By a stroke of very bad luck, it was then that the radio operator noticed their altitude was wrong. The captain applied full power to climb, and as they rose their tail clipped the left wing of the 747, shearing both off. The 747 spiraled downward, the remains of the wing on fire, breaking up before hitting the ground at over 700 mph.
The Ilyushin did not break up but was uncontrollable, hitting the ground with such force that no one survived, though four people with fatal injuries were found alive. At that stage in the flight the passengers had probably undone their seat belts. Two passengers strapped in their seats were found alive on the 747 but later succumbed to their internal injuries.
The total death toll was 349.