Delhi has been experiencing dense fog for the second consecutive day, leading to delays at the Indira Gandhi International Airport. An advisory was issued indicating that flights not compliant with CAT III might face disruptions. On Saturday, as of 8 am, FlightRadar 24 reported an average delay of 37 minutes for departing flights, with around 100 flights delayed and six diverted to other airports. On Friday, the fog led to over 400 flight delays.

CAT III refers to an advanced Instrument Landing System (ILS) that aids aircraft in landing under low visibility, such as fog, snow, or heavy rain. The system uses two radio beams to provide horizontal and vertical guidance to pilots, helping them align with the runway and follow the correct glide path.

There are three levels of CAT III: CAT III A, which allows landings with a Runway Visual Range (RVR) of at least 200 meters; CAT III B, which allows landings with an RVR as low as 50 meters; and CAT III C, which enables landings in zero visibility conditions. Currently, no Indian airport is CAT III C compliant, but it is operational at major international airports like New York’s JFK and London’s Heathrow.

In India, six airports, including Delhi, are certified for CAT III B operations, with Delhi being the first to install CAT III A in 2001. The system at Delhi was upgraded in 2005 to CAT III B, at a cost of Rs 55 crores. The effectiveness of the system depends on both the airport’s equipment and the pilots’ training.