Around 20 flights were delayed while two were cancelled as the fog enveloped the airport suddenly around 7 AM, sources said.
Operations were normal despite a shallow fog in the morning and the runway visibility was above 200 metres but suddenly around 7 AM dense fog descended at the airport and runway visibility dropped to zero at one end of the runway 29/11 (the third runway), while it was below 50 metres on the other end.
The general visibility on the main runway (28/11 which is the most preferred runway by the airlines during the foggy days) was 50 metres while the runway visibility was 75 metres.
The runway visibility being far less than the required minimum limit of 125 metres (for smaller aircraft) and 150 metres (for bigger aircraft), no flights were taking off, an airline official said, forcing the airlines to hold back the departure of flights.
Situation started to improve after 8.30 AM when visibility rose to 300 metres.