Hi-tech instrument landing system in place in times of fog

To assist aircraft operations in reduced visibility and to mitigate the impact of fog on flight operations, the Indira Gandhi International Airport here has equipped itself with a number of facilities to ensure that aircraft receive maximum help through visual and non-visual aids.

Application of the instrument landing system (ILS) and implementation of low visibility procedures are some of the steps taken in times of fog.

The instrument landing system through electronic signals guides the pilot on a number of aspects while landing.

The ILS performs a host of functions including guiding the aircraft along the extended central line of the runway, guiding the aircraft along the right slope on which it should land and provides the distance to touch-down and helps checking height at that distance.

The four categories of ILS applicable to the IGI airport are CAT I, CAT-II, CAT-IIIA and CAT IIIB according to the relevant runway visual range (RVR).

When the RVR is less than 550 metres, low visibility procedures are implemented. They consist of protection of the ILS sensitive area, clearing it of any other aircraft, vehicles and persons as well as special runway and taxiway lighting.

For all navigation facilities and lighting systems, power is supplied through generators to ensure disruption-free operation.

In cases when the RVR is only 100 metres, “follow-me” jeeps guide aircraft during ground movement. RVR measuring instruments on the runway and special ground lighting systems also provide assistance.

The IGI airport has three CAT IIIB instrument landing systems and two of the CAT-I ILS variety. These systems have been purchased from countries such as Japan, England, Norway and Germany and the cost of each system is around Rs.1.6 crore .

Owing to reduced visibility on the runway due to fog, air traffic controllers occasionally cannot detect the movement of the aircraft through the naked eye.

In this case, advanced surface movement ground control systems and surface movement radar are utilised to make the aircraft visible on the monitoring screens of the air traffic controllers.


  • Special runway, taxiway lighting when visibility is less than 550 m.
  • “Follow-me” jeeps to guide aircraft during ground movement

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