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To help pilots combat winter fog, Kolkata airport completes CAT III-B ILS upgrade
The feature allows flights to land in dense fog with visibility as low as 50 metres
The upgrade allows flights to land in dense fog with visibility as low as 50 meters, effective November 27th. (Source: File)
The Netaji Subhas Chandra Bose International Airport in Kolkata is set to boost its operational resilience during fog-prone winter months and heavy rain, with the full installation of the modern Category (CAT) III-B Instrument Landing System (ILS) on both ends of its primary runway.
During winters, widespread flight delays, cancellations and reduced airport capacity are common due to low visibility. While aircraft are designed to fly in extremely cold air at high altitudes, the major problems occur on the ground and during the critical phases of take-off and landing.
“Effective from November 27, the primary runway will be fully equipped with the CAT III-B system. Previously, only the 01R approach (New Town end) featured the CAT III-B ILS, which allows flights to land in dense fog with visibility as low as 50 metres. The other end, 19L (Madhyamgram side), was equipped with the less capable CAT II ILS,” said Airport Director Vikram Singh.
According to officials, in scenarios with fluctuating traffic flow — such as multiple arrivals from the north followed by several from the south — ATC can switch the active runway end (Madhyamgram or Rajarhat/New Town) to allow for shorter approaches. This will not only make runway operations more efficient but also ensure less fuel burn for arriving flights.
“Dual CAT III-B capability will improve the airport’s operational efficiency,” said a senior pilot.
As per airport officials, pilots rely on visual cues. When visibility drops below certain minimums (550 metres for a manual landing), operations must switch to Low Visibility Procedures (LVPs). For very low visibility (around 50 metres), advanced systems like CAT III-B ILS and specially trained pilots are mandatory. Airports without this capability face immediate diversions or cancellations.
ILS is a mechanism that enables aircraft to land safely with the help of guiding systems that add an additional layer of safety and precision over visual approaches. It is divided into three categories, each further divided into three sub-categories (A, B, C). Each level up allows a flight crew to land safely in worse visibility, with Category III enabling safe landing with almost zero visibility, airport officials added.
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The lack of visual cues makes taxiing to and from the runway extremely slow and difficult. Pilots and Air Traffic Control rely on maps and radio, forcing them to use longer holding points and maintain maximum separation between aircraft to prevent runway incursions.
Typically, ATC declares LVP when visibility falls below 800 metres, after which ‘follow-me’ vehicles guide aircraft to their stands. LVP is also activated when the cloud ceiling is below 200 feet.
According to past records, on February 2, 2025, arrivals and departures of 13 flights were delayed at Kolkata airport due to poor visibility caused by fog.
Flight operations at NSCBI Airport were disrupted for three consecutive days from January 23 to 25 due to dense fog, affecting airline schedules and causing inconvenience to passengers. A total of 72 flights were affected on January 23, 34 on January 24, and 53 on January 25 due to low visibility last year.
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