 "Delhi smog disrupts flights: Can CAT III technology help land planes in low visibility?")
It is the story of every winter: Delhi’s toxic smog has left its residents breathless. North India has been reeling from poor air quality, as a dense layer of fog engulfs most of the region.
The hazardous smog has led to the closure of in-person classes at schools and a ban on all construction activities in Delhi-NCR as Stage IV of the Graded Response Action Plan (GRAP) came into effect on Monday (November 18).
Hundreds of flights were disrupted as Delhi’s air quality plunged to a new low yesterday, with the Air Quality Index (AQI) touching 1,500 at 3 pm, according to the tech company IQAir.
Let’s take a look at how Delhi’s air pollution has impacted its flight movement.
Flights cancelled, delayed in India
As Delhi witnessed the season’s worst smog Monday, reducing visibility, at least 15 flights were diverted and over 100 were delayed at the Indira Gandhi International (IGI) Airport.
An official said that 13 flights were diverted to the Jaipur airport, one to Dehradun and one to Lucknow.
Reports say the diversions were made as some pilots were not trained in CAT III operations.
“Some diversions were necessitated as certain pilots lacked training in CAT III operations, required for managing flights under extremely low visibility conditions,” the official was quoted as saying by The New Indian Express (TNIE).
According to the flight-tracking website Flightradar24, over 600 flights, including arrivals and departures, faced delays and 21 were cancelled at the Delhi airport on Monday.
Six flights scheduled for Tuesday were also cancelled.
Impact Shorts
More ShortsDelhi International Airport Ltd (DIAL) warned on X yesterday that “low visibility procedures are still in progress and flight operations may be affected”.
Kind attention to all flyers!#Fog #FogAlert #DelhiAirport pic.twitter.com/FzggP0Rnou
— Delhi Airport (@DelhiAirport) November 18, 2024
The India Meteorological Department (IMD) predicts that Delhi will continue to witness “dense fog” conditions until November 21.
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 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 until 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.
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.
ALSO READ: In Graphics | Why does Delhi's air quality deteriorate in winter?
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.
As dense fog covered North India in the past few days, the DGCA “advised” airlines to deploy CAT II/III-compliant aircraft.
“The DGCA has not issued a directive, but an advisory to airlines for deploying aircraft and crew that can land in low visibility for late evening to morning flights. Airlines have been advised to do so at CAT II/III- compliant airports currently witnessing low visibility,” an official told Times of India (TOI).
This is probably the first time that such an advisory had to be issued so early in winter.
With inputs from agencies
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