The radar at the city airport will not function for most part of the day for at least a week from April 30 because of repairs.

“The secondary radar will not function for the entire duration of the repairs, while the primary radar will be operated from 6pm to 10am,” said P.K. Singhal, the regional executive director (eastern India) of the Airports Authority of India (AAI).

So, for eight hours each day the air traffic control (ATC) will have to manually guide aircraft within its range, which officials fear will be “problematic and risky”.

The Rs 30-lakh repairs — the biggest since the system was installed 10 years ago — will continue for at least a week. “We may extend the duration if required,” added Singhal.

The primary radar helps the ATC keep a tab on aircraft movement within 60 nautical miles. The secondary radar has a range of 200 nautical miles.

Initially, it was planned that both the primary and secondary radar will be shut down during the repairs. But ATC officials requested the airport authorities to operate the primary radar in the evening and at night.

During manual surveillance, the ATC will have to ensure a “minimum horizontal separation” of 10 minutes or 80 nautical miles (148.16 km) to avoid a mid-air collision. “This will delay take-off and landing,” said an official.

When the radar remains functional, the gap could be five nautical miles (9.26km) within 60 nautical miles (111.12 km) and 10 nautical miles (18.52 km) beyond that.

“There has not been any overhaul of the radar since its installation 10 years ago. Following prolonged exposure to rain and sun, the antennae have developed cracks,” explained Singhal.

A team from the company which will carry out the repairs recently visited the site.