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Radar due for key repair
- Manual surveillance on flights during shutdown period

Flight operations in the city will be risk-prone for a week this month, as the radar system at Netaji Subhas Chandra Bose International Airport will undergo “major repairs”.

More than 250 flights take off from and land at Calcutta airport and another 1,000 fly over daily. During the repair period — the dates are yet to be fixed — these flights will have to be guided manually by the Air Traffic Control (ATC) personnel.

“Handling flights manually is problematic and often risky,” warned an ATC official.

When the radar remains functional, the “minimum horizontal separation” between two aircraft should be five nautical miles (9.26 km) within 60 nautical miles (111.12 km) of the radar coverage. Beyond that, it should be 10 nautical miles (18.52 km).

But during manual surveillance, there should either be a gap of 10 minutes or 80 nautical miles (148.16 km) between two aircraft to avoid collision in the air.

To ensure the minimum distance during manual surveillance, the ATC has to depend on the flight position data provided by the pilot. “The pilot can err in reporting his position or the ATC officials, who get overworked in such situations, can issue wrong directions. This can result in two aircraft coming dangerously close to each other,” said a senior ATC official.

“Besides, to ensure the minimum separation, there will be long delays in take off and landing,” the official added.

This is the first time since the new radar was installed in 1998 that such a major maintenance work — to cost Rs 2 crore — is being taken up.

“Engineers of the company which will carry out the repairs will visit the sites this week and finalise the dates for shutdown. The repairs will take around a week,” said an airport official.

The city airport has a primary and a secondary radar. Only the secondary radar will be shut down for repairs, but since the antennae of both radar are in the same system, the primary radar, too, will remain non-functional.

The secondary radar has 35 radiatic columns which transmit data between an aircraft and the ATC. “For 10 years, there have been no major repairs. Prolonged exposure to wind and rain has damaged some columns,” the official said.

Calcutta’s radar system often malfunctions. Last Thursday, it stopped functioning for two hours because of operational reasons. In 2005, the radar did not function for eight days following a lightning strike.

The airport is to have a new radar system in another year and a half.

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