Flight schedules at Calcutta airport went haywire on Monday morning because of fog, which brought down the runway visibility at one point to as low as 50 metres.

Twentyfour domestic and international flights were left stranded for nearly three hours on an average, while an IndiGo flight had to hover over the airport for 30 minutes before it could land.

There is good news, though, for Tuesday, as the weather office has ruled out “dense fog” in the next 24 hours. “There is no possibility of dense fog, but there can be some mist,” said G.C. Debnath, of Regional Meteorological Centre, Alipore.

The Met officials have also predicted a cold Tuesday, with the North Wind sweeping across Calcutta and the rest of Gangetic Bengal.

The airport had been under a thick blanket of fog since late on Sunday. Lufthansa’s Calcutta-Frankfurt flight, which was scheduled to take off at 2.50am on Monday, could hit the runway only around 3am. “But it had to finally return to the parking bay because of poor visibility,” said an airport official.

Visibility was at its worst at 4.30am, when it dropped to 50 metres. The situation improved briefly at 5.10am, enabling the Lufthansa flight to take off. From 6.10am to 7.30am, visibility was back to 50 metres.

The airport’s CAT II instrumental landing system, installed last year to ensure smooth flight operations, fails to function when visibility drops below 350 metres.

Jet Airways’ Delhi-bound flight took off at 7.45am. The Air India Express flight to Singapore, scheduled to take off at 7am, finally left at 8.50am.

Jet Airways’ Port Blair-bound flight left at 7.40am, instead of 5am. Air India’s flights for Guwahati and Port Blair were delayed by hours.

Incoming flights, too, were delayed by 30 minutes to an hour.