The Category II Instrument Landing System (ILS), installed at Calcutta airport in December last year to ensure smooth operation of flights in low visibility, will take a few more months to become operational.

S.P.S. Bakshi, regional executive director, national airport division, hopes it could be activated before monsoon.

A recent survey by the Airports Authority of India has suggested a few technical improvements in the system, which will enable flights to land or take off even when visibility is as low as 350 metre.

The Category I system, now operational on the primary runway of Netaji Subhas Chandra Bose International Airport, fails when the visibility drops below 550 metre.

The Category II ILS has two major components — localiser, which aligns the aircraft to the centreline of the runway, and glide path, which gives the pilot the correct angle for descent.

For proper functioning of the system, the glide path angle needs to be changed so that more accurate data could be provided to the pilot during landing.

The decision height, from where the pilot makes the decision to land, will also be lowered from 60 to 30 metres. “Since both the minimum visibility and decision height have to be lowered, the safety component needs to be upgraded further,” said Bakshi. “Work is being carried out on a war footing and is expected to be over in a month.”

In the Category I system, an aircraft is guided by the glide path to the exact angle up to a height of 200 feet above the touchdown point. Below 200 feet, the pilot operates only with “visual guidance”.

In Category II, this height will be reduced to 42 feet.

“The audit report has pointed out that the glide path equipment and antenna need to be shifted by 58 metre to convey the accurate angle to the pilot,” said an official.

Another major hurdle for activating the new ILS was the tall chimneys and trees in the path of the runway lights. Most of these obstacles are in the Rajarhat and Madhyamgram municipal areas.

“The height of these chimneys have been lowered to the satisfactory level and the report has been sent to the directorate-general of civil aviation in Delhi,” said an official.