The Category (CAT)-II instrumental landing system (ILS) was used at Calcutta airport for the first time on Monday morning. There were, however, delays as the visibility fell below the CAT-II level, but the flight schedules did not go haywire, despite a thick blanket of fog.
CAT-II ILS can help flights to take off and land with visibility as low as 350 metres. If the visibility is more than 550 metres, CAT-I ILS is enough for planes to operate. The upgraded landing system was commissioned at Netaji Subhas Chandra Bose International Airport in July this year. It did not have to be put to use till Monday.
According to the airport Met department officials, visibility started dropping since dawn. Around 5am, visibility was below 550 metres but flights were taking off with the help of CAT-II. Around 6.45am, the visibility dropped to 300 metres, below the CAT-II level. It took about half an hour for the visibility to reach 350 metres, allowing CAT-II to be used again.
Flights could not take off in between, causing runway congestion. There were delays in take-off because of planes being stranded on the runway. The delays would have been much longer if CAT-II was not operational, said an airport official.
Kingfisher airline officials said five flights to Delhi, Bangalore, Bhubaneswar, Ahmedabad and Raipur were delayed by 20 minutes on an average. Air Indias morning flights were also delayed by 20-40 minutes because of runway congestion, said a spokesperson for the airline.
Met officials warned that CAT-II might not be enough to maintain flight timings this season. The fog this winter is expected to be heavier than last years. The city received heavy rainfall till late in the year. Such showers are usually followed by heavy fog in winter. Visibility at times could drop below 50 metres, said a Met official.
Flight schedules are most affected by fog in January, when visibility often drops below 350 metres from 2am to 7am. According to an official, the airport also needs a surface movement radar to guide aircraft in and out of the runway in low-visibility conditions and to cut down delays.