Why fogs disrupt flights in India every year and how to fix it

Severe fog has been disrupting flights across North India. (Hindustan Times/Vipin Kumar)
Severe fog has been disrupting flights across North India. (Hindustan Times/Vipin Kumar)


  • Once again, dense fog has grounded flights in northern India, leaving thousands stranded, frustrated and angry. Mint explains why poor visibility hobbles most flights from taking off or landing, even at airports that have anti-fog CAT IIIB Instrument Landing System (ILS).

What’s the latest trigger?

On 14 January, visibility dipped to near zero, leading to more than 300 flights being delayed and over 80 being cancelled as a dense fog engulfed New Delhi’s Indira Gandhi International (IGI) airport for nearly 11 hours. The disruption, coupled with lack of proper communication from airline staff and food falling short, incensed thousands of stranded passengers, and even resulted in an IndiGo pilot being assaulted by a passenger when announcing the delay on board. With such dense fogs likely to persist, the delays will have a cascading effect on airline networks in other parts of the country too.

But we have hi-tech airports, don’t we?

Most airports use the instrument landing system (ILS) radio navigation. Costing a little over 10 crore, it has two radio signals—a Localizer that offers left or right guidance, and a Glide Slope for up or down signals. Airports typically apply the Category II (CAT-II) procedure for flights and pilots when visibility is 275-550 metres, and CAT-III below 275 metres, down to 50 metres. Only CAT-III B certified pilots can land when the visibility is about 50 metres. CAT III C can land on auto-pilot even in zero visibility and is currently used at airports like New York’s JFK International Airport and London’s Heathrow airport.

Why do fogs create such disruption?

Delhi airport has four runways but only two are compliant with ILS CAT IIIB standards. Of the two non-compliant runways, one has been non-operational for weeks. Of the compliant runways, one was reportedly downgraded to CAT 1 due to nearby building work but was made operational again on 16 January. Plus, flights cannot depart unless visibility is at least 125 metres, so planes pile up on bays

What are the other hurdles?

Claiming airports were shut as flights can’t operate in zero-visibility, the government has asked the Delhi Airport authorities to “immediately expedite the operationalization of the CAT III-enabled 4th runway (in addition to the existing CAT III-enabled runway)". This, however, will be subject to clearance from the Directorate General of Civil Aviation (DGCA). Yet, the fact is that airlines will have to train more pilots to be CAT-III B compliant, and the cost is estimated to be around 7 lakh per pilot.

What’s the way forward?

Some airlines are experimenting with the global position system (GPS) as alternatives to ILS. Airbus has integrated these new technologies with an ILS look-alike interface, which can help pilots to perform “straight-in" approaches using satellite positioning, even in low-visibility conditions. But GPS signals can be affected by atmospheric conditions, interference or jamming. The Microwave Landing System, which uses microwave frequencies, is very precise but has higher costs.

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