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Air India plane crash: Recalling the Charkhi Dadri collision, one of the worst aviation disasters in history
A London-bound Air India Boeing 787 Dreamliner crashed into a residential neighbourhood in Ahmedabad last week, killing at least 249 people.
The aviation disaster — one of the worst in decades — came 29 years after the Charkhi Dadri mid-air collision of Saudia Flight 763 which was going from Delhi to Saudi Arabia's Dhahran, and Kazakh Flight 1907 which was travelling from Kazakhstan's Chimkent (now Shymkent) to Delhi. The accident led to the death of all 349 people on board both planes.
Here is a look at what led to the Charkhi Dadri accident, which is considered the deadliest mid-air collision in aviation history of the world.
The incident
On November 12, 1996, around 6.40 pm, the Saudia Flight 763 took off from Delhi to Dhahran, carrying many Indian workers to their jobs in the Middle East and with Captain Khalid al-Shubaily in the cockpit.
Around the same time, Kazakh Flight 1907, which had Captain Alexander Cherepanov in the cockpit, was about to land in Delhi.
Suddenly, as the narrator in the popular air crash documentary show, Mayday (Air Crash Investigations), puts it, 'the early evening sky ignites into a fireball… flaming wreckage falls from the sky'.
Tim Place, the pilot of a United States Air Force cargo plane, in the vicinity, first witnessed the incident. 'This cloud just lit up… felt like you could feel the heat,' he said. All three planes were in contact with air traffic controller V K Dutta.
The massive jets plunged into the mustard fields below, in two wreckage fields seven kilometres apart, in Charkhi Dadri, around 120 km away from Delhi.
The cause of the crash
Kazakh Flight 1907 was flying at 23,000 ft, about 74 nautical miles from Delhi airport when its crew first contacted Dutta. He cleared the flight to descend and maintain 15,000 ft, according to a recent report by The Indian Express. Saudi Flight 763 was first cleared to fly at 10,000 ft and then at 14,000 ft. Dutta instructed the crew to maintain 14,000 ft and stand by for permission to climb higher.
This was done to ensure a mandatory 1,000-ft separation between the jets when they crossed paths. Working with only a primary radar, the only one available around that time, Dutta depended on the pilots of the Kazakh 1907 and Saudi 763 to know their altitudes. Both crews acknowledged Dutta's instructions to maintain 15,000 ft and 14,000 ft, respectively. 'Saudi seven six three (will) maintain one four zero (14,000 ft),' the Saudi crew acknowledged. This was their last transmission to the ATC.
Following the crash, the government set up a Court of Inquiry. The investigation did not find any fault with Dutta and said he had given correct instructions to both flight crew. It held that the mid-air collision happened because the Kazakh pilots did not maintain their assigned altitude of 15,000 ft and descended to 14,000 ft, according to The Indian Express report.
Another possible reason for the Kazakh jet deviating from its assigned altitude, investigators felt, could be the pilot's poor proficiency in English, who may have misunderstood the altitude assigned to the Saudi jet as his own.
The accident led to several corrective steps, including equipping major airports with SSRs (Secondary Surveillance Radar) and separate air corridors for arriving and departing aircraft besides the installation of a Traffic Alert and Collision Avoidance System (TCAS) in the aircraft. India has not witnessed any mid-air collision ever since.
