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Sources said “inadequate network” of the airport’s Very High Frequency Omni Range communication system has turned 1,000 nautical miles — 1,852km — on various routes covering Kolkata into blank zones.
The Airports Authority of India is aware of the problem and has asked the Kolkata ATC to identify the zones. “The study is almost complete and we are expecting a report soon,” said an AAI official.
“Once we fly into a blank zone, the voice communication with the ATC is snapped abruptly. Attempts to communicate through other higher frequencies, too, don’t work,” said a senior Air India pilot. “During emergencies like sudden bad weather, we try to communicate through other aircraft which are in the coverage area,” he said.
Pilots in a blank zone also face “severe problems” in changing altitude or direction. “With the ATC out of bounds, there is no one to guide us if we need to go down or fly up. In such situations we take a call based on our interactions with adjacent aircraft,” a pilot pointed out.
The problem is most acute on the Kolkata -Port Blair route as almost the entire 500 nautical miles (926km) of the stretch fall in a blank zone. On the Kolkata -Bagdogra route, flights have no communication link with the airport on a 100-nautical mile stretch (185.2km) between Katihar and Bagdogra.
Similarly, around 250 nautical miles (463km) on the Kathmandu route and 100 nautical miles on the Mumbai route are beyond the Kolkata ATC’s communication link.
Overflying flights between Europe and south-east Asia face the problem on eight routes over the Bay of Bengal.
“The problem has been persisting for several years and is a major safety concern for us,” said an airport official.
A senior AAI official in Delhi said the power of the two “very high frequency” transmitters at the airport was being increased in an attempt to solve the problem. There are similar transmitters in the Andamans, Visakhapatnam and Berhampore. But sources said the Andamans transmitter had not been functioning properly while the other two could not be accessed by aircraft flying over land.
Three new Remote Control Air Ground transmitters have been installed at Katihar (Bihar), Jharsuguda (Orissa) and Shillong (Meghalaya) but they are yet to be functional.