How does CAT III technology help flights amid dense fog? - Hindustan Times
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How does CAT III technology help flights amid dense fog?

By | Edited by Aryan Prakash
Dec 27, 2023 06:54 PM IST

On Wednesday morning, various parts of North India, including Delhi were veiled in dense fog, leading to reduced visibility, traffic disruptions, and accidents.

The Delhi airport is experiencing delays impacting around 110 flights – both domestic and international arrivals and departures – due to heavy fog. Specifically, as of 8.30 am on Wednesday, 28 international departures, 15 international arrivals, 42 domestic departures, and 25 domestic arrivals were affected, according to news agency ANI.

An aircraft prepares to take off amid dense fog on a cold winter morning at Indira Gandhi International Airport in New Delhi on December 27, 2023. (Photo by Arun SANKAR / AFP)(AFP)
An aircraft prepares to take off amid dense fog on a cold winter morning at Indira Gandhi International Airport in New Delhi on December 27, 2023. (Photo by Arun SANKAR / AFP)(AFP)

The Delhi Airport Authority has issued a notice stating that flights not meeting CAT III (Category III) standards might encounter disturbances while landing and taking off. CAT III refers to an Instrument Landing System (ILS) allowing flights to land in adverse weather conditions like fog, snow, or rain.

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In a statement posted by X (formerly Twitter), the airport said, “While landings and take offs continue at Delhi Airport, flights that are not CAT III complaint may get affected. Passengers are requested to contact the airline concerned for updated flight information. Any inconvenience caused is deeply regretted.”

On Wednesday morning, various parts of North India, including Delhi, Uttar Pradesh, Punjab, and Haryana, were veiled in dense fog, leading to reduced visibility, traffic disruptions, and accidents.

What is Instrument Landing System (ILS)?

-The Instrument Landing System (ILS) is a precise guidance system for aircraft during runway approaches. According to SKY brary, It employs two radio beams, offering both horizontal and vertical guidance to pilots while landing.

-Within ILS, specific categories are defined for qualified pilots flying equipped aircraft to suitably equipped runways with qualified ILS systems, allowing approaches without acquiring visual references.

-Categories within ILS include:

  • Category I: Standard permits a minimum descent height (DH) of 200 feet above runway threshold elevation (arte) and a Runway Visual Range (RVR) of 550 meters.
  • Category II: Permits a DH not lower than 100 feet and an RVR not less than 300 meters.
  • Category IIIA: Allows a DH below 100 feet and an RVR not below 200 meters.
  • Category IIIB: Permits a DH below 50 feet and an RVR not less than 50 meters.
  • Category IIIC: A full auto-land system providing guidance along the runway centerline without DH or RVR limitations. This category is not widely available due to post-landing ground manoeuvring issues.

-Unique requirements for Category II and III ILS operations encompass aircraft gear, pilot education, and airfield setups. Concerning the airfield, it involves functionality, dependability, and operational protocols.

-Indira Gandhi International (IGI) Airport in Delhi has implemented CAT IIIB ILS, an advanced anti-fog landing system. This technology is also available in Amritsar, Jaipur, and Lucknow, with the Netaji Subhas Chandra Bose International Airport in Kolkata being the latest addition to receive CAT IIIB technology.

More about ILS CAT IIIB and CAT IIIC

ILS CAT III offers precise and dependable guidance to pilots, providing detailed lateral and vertical direction, approach trajectory, and touchdown zone data. This allows pilots to execute accurate landings even without visual cues, substantially minimising the potential for accidents stemming from human error, spatial confusion, or miscalculating landing distances.

A CAT IIIB system facilitates precise approach and landing under specific visibility conditions, typically no less than 50 feet (15m) and a visual range of less than 200 meters, but not below 50 meters. According to The Quint report, the entire process operates automatically, featuring a voice guide that counts down the distance to the runway, indicates when to deploy flaps, and prompts the application of brakes.

For the CAT IIIB system to perform optimally, three key factors require consideration: pilot and co-pilot training on the system, adherence of the aircraft's cockpit to the system's requirements, and compliance of the airport with the system's specifications.

Establishing CAT IIIB system at an airport can incur an initial cost of up to 10 crore, with maintenance expenses averaging around 50 lakh per month, The Quint report said.

CAT IIIC, a more advanced system than CAT IIIB, enables aircraft to land even in situations of zero visibility. Airports equipped with this technology include JFK International Airport in New York and London's Heathrow Airport.

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