What stood between Delhi and a disaster on Thursday were the air traffic controllers at the Indira Gandhi International Airport (IGIA).
At 5.45 pm on Thursday, the radar screens at the airport's air traffic control tower, which show position of aircraft across north India, went blank without warning.
The air traffic control officials (ATCO) at Delhi airport not only handle aircraft landing and taking off from IGIA but also all airborne civil aircraft in Delhi air space.
The Delhi air space stretches from Pakistan and Afghanistan border to Nepal border and from Srinagar to Varanasi.
“At any given point of time, there are some 70 aircraft flying over this area,” said a senior air traffic control official, who didn’t wish to be named.
“The radar screen went blank and we couldn’t see plane positions,” he said. “The radars were working but the data they were sending couldn’t be seen as the software that processes the information had collapsed.”
There were 15 senior ATCOs who were handling all the aircraft at that time, apart from other support staff.
All ATCOs are trained to handle a situation like this but such a situation rarely occurs. As the automated computer system failed, it was left to the ATCOs to save the day.
“We gave our best and the stress level at the tower for two hours was immense as any error could have led to a mishap,” he said.
The ATC tower switched to a different procedure immediately and all details not available on the computer were obtained by talking to pilots over radio.
The system slightly normalised by 6.45 pm but normal take offs and landings began after 7.30 pm.
The congestion and delays were huge because all departing flights were asked to wait and only a few landings took place.
There were no flight diversions in this period.
“While usually the distance between airborne planes are kept at 10 nautical miles, it was increased to 80 nautical miles to avoid any chance of them getting close,” said an official.
“Aircraft approaching Delhi were asked to orbit till asked to land.”