Delhi: Dense fog delays flights, power demand at a high

An airport official said despite the dense fog, no flight was diverted or cancelled. However, passengers were asked to check flight timings for delays.

The Capital recorded dense fog for nearly six hours from 3am ro 9am on Thursday, leading to visibility dipping to 25 metres at Palam and 50 metres at Safdarjung, disrupting both flight and rail operations. While no flight diversion was reported during this dense fog spell, over 50 flights were delayed at Indira Gandhi International Airport. Trains were also impacted, with at least 12 trains to or from the Capital running late by over two hours, while two Delhi-bound trains had to be rescheduled due to the weather, officials said.

Visibility dipping to 25 metres at Palam and 50 metres at Safdarjung, disrupting both flight and rail operations (PTI)

The India Meteorological Department (IMD) classifies fog as “shallow” when visibility dips below 1,000 metres, as “moderate” when visibility is between 200 and 500 metres and as “dense” when it is below 200 metres. It is “very dense” when visibility is below 50 metres.

A Met official said Delhi reported shallow fog at Palam from 11pm, with visibility dipping to 400 metres by 2.30am, to 100 metres by 3am and to a low of 25 metres by 3.30am, after which it largely remained below 200 metres till around 9am. Even by noon, visibility was still around 600 metres before gradually improving to over 1,000 metres after 1pm, officials said.

“The impact was seen both at Palam and Safdarjung after 2.30am and the lowest visibility at Palam was 25 metres between 3am and 3.30am. Safdarjung reported a visibility of 50 metres around the same time,” said the official, adding even during the day, the sun did not come out completely, and visibility hovered between 500 and 1,500 metres in parts of the Capital.

An airport official said despite the dense fog, no flight was diverted or cancelled. However, passengers were asked to check flight timings for delays.

“Low visibility procedures are in progress at Delhi Airport. All flight operations are presently normal. Passengers are requested to contact the airline concerned for updated flight information.” the Delhi airport tweeted at 6.15am

The airport initiates low visibility procedures (LVP) -- measures aimed at making landing for flights easier, when visibility dips below 800 metres. During this period, CAT-I procedures are in place, which is the most basic set of precautions to guide pilots in landing. Only flights and pilots that are CAT-II compliant are allowed to land when visibility is less than 550 metres, while CAT-III A pilots can land when visibility is between 175 and 300 metres. CAT-III B is the most stringent set of qualifications for a pilot to land a flight, allowing them to land even when visibility is 50 metres.

While flights can still land at the airport when visibility is 50 metres, no flight is allowed to depart unless runway visibility range (RVR) is 125 metres, leading to flight delays. A departure of over 15 minutes from the scheduled time of arrival or departure is classified as a ‘delay’.

A northern railway official meanwhile said at least 12 trains either going to or from the Capital, were delayed by over two hours because of the fog. In case of dense fog, trains reduce their speed in order to navigate safely, travelling below 50kmph at times.

The IMD currently has a yellow alert in place for the Capital for the next three days, warning of moderate to dense fog to continue over Delhi till January 8. A yellow alert is generally issued to warn the general public about an upcoming weather phenomenon.