How bad is the Delhi smog? So bad that even Prime Minister Narendra Modi’s flight to Oman was delayed by an hour on Monday morning. PM Modi was not the only one whose schedule was disrupted.
Poor visibility across the National Capital Region triggered several cancellations and delays at Delhi’s Indira Gandhi International Airport. At least 100 flights were cancelled, and over 300 were delayed, as airlines were forced to adjust their schedules. The operations are currently being conducted under CAT III conditions.
How Delhi airport was hit by smog
The disruptions meant the Ministry of Civil Aviation had to step in. It issued a heavy fog alert for north India, saying that Delhi and other airports in the region were experiencing dense fog that severely affected visibility. “Safety is our priority,” it assured.
Heavy Fog Alert for Northern India
Delhi (DEL) & other airports in Northern India are experiencing dense fog, severely affecting visibility.
For Passengers:
Before heading to the airport, please check the latest flight status with your airline.
Check flight information on the…— MoCA_GoI (@MoCA_GoI) December 15, 2025
Airlines, including IndiGo and Air India, also warned flyers of possible delays, urging them to stay updated on their flight status.
In an advisory issued around 9 am, IndiGo said visibility had drastically reduced due to dense fog, impacting flight operations. It warned that some flights may be proactively cancelled during the day to prioritise safety and avoid extended waiting at the airport.
Passengers were also informed they could rebook or claim refunds online in case of cancellations.
Travel Advisory
Due to dense fog in Delhi this morning, visibility has reduced drastically, impacting flight operations. As a precaution, some flights may be proactively cancelled through the day to prioritise safety and help minimise extended waiting at the airport.
We…
— IndiGo (@IndiGo6E) December 15, 2025
Delhi airport reiterated that poor visibility meant operations were taking place under CAT III protocols.
Why does fog affect flights?
Smog affects visibility. Even a short spell of smog can slow down landing, take off and taxing at the airport.
With pilots having fewer visual cues during approach, landing, and ground movement, operations tend to slow down. Airlines often pre-emptively delay or cancel flights to maintain safety margins, and runway spacing increases because aircraft need more time between landings, according to a report in CNN-News18.
These slowdowns take place even when an airport is operating under CAT III procedures.
What is CAT III?
CAT III (Category III) is an Instrument Landing System (ILS) that enables pilots to land aircraft in poor visibility conditions such as dense fog. ILS is a guidance system that allows a plane to land in poor visibility conditions using radio signals, along with high-intensity lighting arrays sometimes, as per The Quint report.
Low visibility makes it difficult for pilots to land aircraft, increasing the risk of accidents during touchdown. Today, modern aircraft and runways are equipped with technology that helps the landing of planes in poor or zero visibility, reported The Indian Express.
According to SKYbrary, the ILS uses two radio beams – localiser and glideslope – to equip pilots with vertical and horizontal guidance during landing. ILS is divided into four categories based on decision height (DH) and runway visual range (RVR).
DH is defined as the lowest altitude during the descent at which pilots can rely on the ILS. RVR is the distance over which the pilot can see the lights or markings on the runway, as per the Indian Express report.
Landing has to be aborted if the RVR is below a certain threshold at the decision height.
Here is how ILS is categorised:
Category I of ILS: When DH is not lower than 200 feet and a runway visual range of 550 metres or more.
Category II: DH should not be lower than 100 feet, and an RVR of not less than 300 metres.
Category IIIA: DH is below 100 ft, and an RVR is not under 200 metres.
Category IIIB: DH is below 50 ft and an RVR not less than 50 metres.
CAT IIIC: When no DH or RVR applies.
In India, six airports, including Delhi, Lucknow, Jaipur, Amritsar, Bengaluru and Kolkata, are equipped with CAT IIIB operations.
The CAT IIIC system that allows plane landing even at zero visibility is supported only at a handful of airports, including New York’s John F Kennedy Airport and London Heathrow Airport.
How do flights, pilots become CAT III compliant?
An airline must have its flights equipped with CAT IIIB and pilots trained to operate the technology to get the CAT IIIB certification.
Flights which do not comply with the technology are not allowed to operate in inclement weather conditions with reduced visibility.
For Indian airlines, one of the main challenges is to educate the pilots to operate CAT IIIB-equipped planes.
“Not all pilots flying domestic airplanes are trained to land on the CAT IIIB system. Presently, the DGCA [Directorate General of Civil Aviation] is very strict about pilot training with regard to CAT IIIB system, but some domestic airlines tend to avoid this. It is an expensive affair too as the training can cost nearly Rs 10 lakh per pilot,” VP Agrawal, former chairman of Airport Authority of India, had told Scroll in 2016.
Why are winter landings tricky?
Landing is said to be the riskiest phase in a flight. According to research from Boeing, the final descent and landing occupy about four per cent of total flight time, yet 49 per cent of fatal accidents occur in this window.
Low visibility due to fog only makes the process more complex, as pilots cannot use external references to make a judgment during landing. While the ILS provides precise radio-based cues, it can only be put in place when the aircraft, crew, and runway are certified for such an operation.
With inputs from agencies
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