New Delhi, Dec 23 (PTI): Over 100 flights were affected today due to this winter's first dense fog which engulfed the IGI airport here disrupting air operation and causing inconvenience to passengers.

Flight operations virtually remained suspended for about two hours, between 7 AM and 9 AM, after dense fog descended at the airport. Runway visibility dropped suddenly from 700 m to less than 50 m on all three runways.

With runway visibility being far less than the required minimum limit of 125 m (for smaller aircraft) and 150 m (for bigger aircraft), no flights were taking off, an airline official said, forcing the airline to hold back flight departures.

As flight operations remained standstill for two hours, it led to delay in schedule of over 40 flights which had a cascading effect on the schedule of other flights. Over 100 flights, during the day were delayed, three flights including an international were diverted while three flights were cancelled, airport sources said.

Situation started to improve after 8.30 AM when visibility rose to 300 m. The general visibility on the main runway (which is the most preferred runway during foggy days) was 50 m while the runway visibility was 75 m.

At one time, the runway visibility dropped to zero at one end of the third runway. "Delhi airport witnessed dense fog from 3.30 AM till 10 AM today. All the runway had CAT-IIIB and CAT-IIIC dense fog at 7 AM when runway visual range suddenly dropped from 775-900 m to just 75 m. It improved at 9 AM when the visibility on main runway first to 330 m and on third runway to 100 m at around 10 AM," Airport MeT in-charge R K Jenamani said.

Fog cover, however, remained over the airport and city all through the day as more fog advanced from eastern side. "It was a very sudden transition as till yesterday Delhi was not having any fog. Even shallow fog or smog were missing for last 42 days due to strong winds," Jenamani said.

Dense fog conditions is likely to start midnight tonight and visibility dip below 50 m at around 3 AM, he added. Airport operator Delhi International Airport Limited (DIAL), alongwith all stakeholders like airlines, air traffic control, ground handling staff and others, has taken a host of measures to meet any situation arising due to fog.

Some of the measures include ATC scheduling slots for departure of flights in advance based on the MeT forecast and airlines prioritising their flights and plan boarding as per the slot, which would reduce inconvenience to passengers.

DIAL and airlines has made adequate arrangement for food and drinks to stranded passengers.