Winter’s first fog on Monday halted operations for over two hours at the IGI Airport here after runway visibility dropped to below 50 metres, leading to delays and diversions of around 140 flights and causing inconvenience to passengers.

Schedules of around 130 domestic and international flights were delayed from half-an-hour to three hours.

Nine flights had to be diverted to Jaipur, Ahmedabad and Lucknow as visibility at the runway dipped below 50 metres, the minimum required for a CAT-III B compliant plane to land using the instrument landing system (ILS).

Fog started to envelop the airport soon after midnight but it thickened around 6.30 AM. The general visibility was almost zero while the runway visibility dipped below 50 metres, an airport official said.

Nine flights, including an international flight from Amman, scheduled to land between 7 a.m. and 9 a.m. at Delhi airport had to be diverted.

Poor visibility prevailed between 7 a.m. and 9.30 a.m. flight and no planes could either take-off or land at the airport, airport sources said.

“Six flights were diverted to Jaipur, two to Ahmedabad and one to Lucknow. Before being diverted the air traffic control asked them to hover over Delhi for a while but as the planes were running out of fuel, they were asked to divert to these airports,” they said.

The two runways, main (28/10) and third (29/11) of Delhi airport are equipped with CAT-III B ILS, which allows a compliant aircraft to land even when the runway visibility was up to 50 metres.

As soon as visibility increased above 50 metres after 9.20 a.m., flights scheduled to land at Delhi airport were asked to land on the main runway (28/11), using CAT-III B ILS, as the visibility on the third runway was still poor.

“But no flights were allowed to depart as the minimum visibility was around 125 metres and 150 metres, depending upon the size of the aircraft,” the airport sources said, adding during most part of the morning, runway 29/11, remained closed.

Take-offs started around 9.30 a.m. from main runway, after the runway visibility improved to above 125 metres.

As the visibility improved, the airport officials faced huge backlog of flights.

To avoid schedules going haywires due to fog, airport operator DIAL has this year introduced Delhi Airport Collaborative Decision Making (DA-CDM).

The DA-CDM focuses on improving the air traffic flow and capacity management at airports by reducing delays, improving the predictability of events and optimising the utilisation of resources.

Airport operators, airlines, ground handlers and air traffic control (ATC) collaborate and share data through automated system to increase overall airport efficiency, to reduce delays and congestion, and smooth flow of flight information to passengers.

But passengers at the airport terminals complained about having little information about their flights.