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How do aircraft land under zero visibility conditions during dense fog
Poor visibility creates challenges to pilots and hampers flight operations. Aircraft uses a ground-based navigation called the Instrument Landing System (ILS).
As many as 19 flights were diverted, and over 200 flights to and from Delhi's Indira Gandhi International Airport (IGI) were delayed on Saturday as low visibility due to dense fog impacted operations for the second straight day in the city. On Friday, over 400 flights were delayed.
Delhi and its adjoining areas of Noida, Gurugram and Ghaziabad have been witnessing dense fog for the past two days, resulting in an impact on road and train movement also apart from flight operations.
Dense fog creates significant challenges and hampers flight operations as visibility drops, sometimes drastically, impacting movement of aircraft at airports or runways that are not equipped to operate in such weather conditions.
How do aircraft land in dense fog
Aircraft use a ground-based navigation called the Instrument Landing System (ILS).
ILS is a standard International Civil Aviation Organisation (ICAO) precision landing aid that is used to provide directional guidance (azimuth) and descent guidance signals for guidance to aircraft for landing on the runway under normal or adverse weather conditions.
The ILS comprises several components like the localiser, glide path, markers, Distance Measuring Equipment (DME) and runway lighting systems.
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The localiser is the primary component that provides lateral guidance to the pilot. The transmitter and antenna are on the centreline at the opposite end of the runway from the flight's direction of approach.
The Glide path component provides vertical guidance to the pilot, helping to maintain proper descent angle for safe landing.
The DME provides slant distance to the aircraft with respect to touch down point.
In addition to these equipment, lighting systems and visual aids are deployed on the runway for the pilot to see when he/she approaches the decision height or the missed approach point (MAP)
These systems help the pilot to understand how the aircraft is approaching the runway before actually seeing it. Warnings are also sounded when pilots are not meeting the runway's centreline, either undershooting or overshooting it.
Radar instruments are also used with the ILS to ensure stable descent and designated aircraft path despite little or zero visibility.
In addition to these technological support, a pilot's skill and training experience plays a critical role in making real time choices.
Airport infrastructure plays a crucial role in ensuring safe landing. ILS Category 3 certification (CAT 3) is the most significant due to its capability to support landing operations under low visibility conditions, as low as 50 metres. Delhi's Indra Gandhi International (IGI) airport has four CAT 3 compliant runways.
