About 20 flights were delayed because of low visibility caused by dense fog at the Calcutta airport on Sunday morning, an airport official said.

“Hundreds of passengers were inconvenienced because the fog triggered a chain of delays,” said an official.

“A GoAir flight from Singapore had to be diverted to Nagpur. The rest were all outgoing flights, bound for Hyderabad, Delhi, Bagdogra, Port Blair and Guwahati, among other places. Their departure was delayed.”

The disruptions took place between 5am and 8am. At one point, the visibility had dipped to 50 metres, sources said.

This was the first disruption caused by fog at the Calcutta airport this winter.

The airport has the Category III-B Instrument Landing System, which allows an aircraft to land safely when the visibility is as low as 50 metres. The system was installed in January last year.

“For the system to function at its optimum level, pilots have to be trained in it as well. Some of the pilots flying today were not CAT III-B complaint and that led to the delays,” said the official.

Sherpa Sangay was booked on a flight to Bagdogra that was to leave at 6am. He had turned up at the airport an hour before.

Around 9am he told Metro: “I don’t know when the flight will take off.”