Flight operations were disrupted at the Indira Gandhi International Airport (IGIA) after dense fog set in early on Friday.
About 50 flights, mostly early morning departures, were affected after visibility at the airport went down to 150 metres.
Five flights, three international and two domestic, were diverted to other airports.
Flights were delayed from half an hour to three hours while four flights had to be cancelled and five were rescheduled. The runway visibility was around 150 to 275 metres for both the runways in the morning and flight operations were being carried out using the CAT-III B instrument landing system.
Software supplier summoned
The Air Traffic Control (ATC) system at IGI airport, which crashed at 5.45 pm on Thursday, started functioning normally by late evening.
Airports Authority of India (AAI), which manages air traffic at IGIA, called Raytheon, the US based company that had supplied the ATC software, to inspect the system and find out the reasons for its crash.
The radar screens at the ATC tower had gone blank on Thursday evening after the automated computer system - AutoTrac II - crashed.
The system processes the signals received by the radars and calculates flight coordinates.
“There are three layers of the system so that if one fails, there are two backups. On Thursday, all three systems failed,” said an AAI spokesman. “This is a very serious issue and we are investigating what went wrong.”
The Directorate General of Civil Aviation too has an ordered a probe in the incident.
“There is a problem with the maintenance of the system and that is why it crashed,” said a senior air traffic controller who didn’t wish to be identified. “This is not the first time it developed a problem but in earlier incidents, the glitch had not persisted for so long.”