How flights land safely in zero visibility conditions

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Delhi is witnessing dense fog for the second consecutive day on Saturday, prompting the airport to state in an advisory that flights that are not CAT III compliant might get affected. At the Indira Gandhi International Airport, departure delays of an average of 37 minutes were witnessed as on 8 am, as per FlightRadar 24. Almost 100 flights were delayed, while six Delhi-bound flights were diverted. On Friday, more than 400 flights were delayed due to bad weather conditions at the airport.

What Is CAT III

CAT III is an Instrument Landing System (ILS) which aids planes in landing in extremely poor visibility conditions, providing pilots ground-based radio navigation about the aircraft's runway alignment and glide path. The system employs two radio beams that offer horizontal and vertical assistance during landing.


CAT III A system permits landing of aircraft upto Runway Visual Range (RVR) not less than 200 meters. CAT III B permits landing of aircraft when RVR is less than 200 meters but not less than 50 meters, while CAT III C allows landing in zero visibility conditions. These conditions include those arising out of snow, rain, or in Delhi's case, fog.

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Apart from horizontal and vertical guidance, CAT III also provides data on approach trajectory and touchdown zone. Further, guidance is also given regarding the distance left to the runway, when to deploy flaps and apply brakes.


The CAT II system guides the aircraft in the event that the RVR is not less than 350 metres, while a CAT I system assists landing for a RVR of over 550 metres. The RVR is the distance till which the pilot can see the runway's lights or markers.

Which Indian Airports Are CAT III Compliant?

There are six airports in India where the runways are certified for CAT III B operations - Delhi, Lucknow, Jaipur, Amritsar, Bengaluru and Kolkata.


CAT III A system was first installed on runway 28 at Delhi's Indira Gandhi International airport in year 2001 and was upgraded to CAT III B ILS with Advanced Surface Movement Guidance and Control Systems (ASMGCS) in 2005 at a cost of Rs 55 crores.


Apart from an airport runway being compliant to a CAT category, landing under the said category is also dependent on flight equipment and pilot training.


No Indian airport is CAT III C complaint yet. The system is in application at New York's John F Kennedy International Airport and London's Heathrow Airport.