Wednesday, November 29, 2017

CAT's eye for fog landings: Calcutta airport set to switch on advanced instrument landing system this winter

Dum Dum: Calcutta airport is ready to beat the fog this winter with its new Category III-B Instrument Landing System that enables a pilot to land an aircraft safely in low visibility up to 50 metres. 

An inspection on Tuesday by a two-member team from the Directorate General of Civil Aviation (DGCA) completed the final round of clearance for CAT III-B ILS to be switched on.

"The inspection of the runway lights, a crucial part of CAT III-B ILS, has been done and we expect to make it operational soon," airport director Atul Dixit said on Wednesday.

The number of lights on the centreline of the primary runway have been doubled as part of the upgrade from CAT-II to III-B. In the existing system, the lower visibility limit for a safe landing is 350 metres.

CAT III-B has been installed on the southern side of the primary runway because the wind blows from north to south in Calcutta during winter. This means aircraft landing from the southern side are doing so against the wind, which is the norm. A tailwind would increase the possibility of an aircraft overshooting the runway while landing.

The change in wind direction is the reason why, air traffic control officials said, residents of Ballygunge get to see more planes in winter than they do during the rest of the air.

In summer, aircraft mostly land from the northern side of the runway, which is why people living in Barasat and Madhyamgram see more flights arriving.

The CAT III-B system, which has been installed at a cost of Rs 130 crore, includes an advanced signalling mechanism and more lights on and near the runway and taxiways. In CAT II, there are approach lights along the threshold and centreline lights on the runway.

The gap between two lights along the centreline of the runway is 50 feet in the CAT II system. This gap is halved in the switch to CAT III-B.

The airport's primary runway is 11,900 feet in length. Centreline lights on the taxiways will guide pilots till the parking bays after landing.

Two units of a signalling instrument called runway visual range transmissometer have been installed on the primary runway. These instruments send signals to a receiver in the aircraft, guiding it to the runway.

In the CAT II system, a pilot is guided by the signalling system till 100 feet above the ground, when the runway isn't in sight. In CAT III-B, an aircraft can descend till 50 feet above the ground because of the advanced signalling system. Then the pilot would see the approach and touchdown zone-lighting system.

In Calcutta, flight schedules are usually disrupted most in December and January, when fog strikes.

CAT III-B is the second-most advanced instrument landing system available. No airport has CAT III-C yet.

Most airlines operating in India already have pilots who are CAT III-B compliant.

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