An important surveillance equipment was out of order at the airport for 17 hours since Saturday evening.

The Mono Pulse Secondary Surveillance Radar (MPSR), which helps in maintaining the required distance between overflying aircraft within 250 nautical miles (463 km) of Calcutta, started malfunctioning at 7pm on Saturday. It was repaired on Sunday noon.

According to airport authorities, “more than 1,000 aircraft” overfly Calcutta daily, most of them at night. While the radar was out of order, the Air Traffic Control (ATC) had to ask the flight officials in each overflying plane for its position and course to ensure proper separation. The position of an aircraft is automatically displayed on the radar.

“Manual surveillance is quite difficult. A minor mistake in calculation can lead to a disaster,” said an ATC official.

The primary radar — Approach Surveillance Radar (ASR) — was functional through the night. “It has a range of 60 nautical miles or 111.12 km ,” said an official of the Airports Authority of India (AAI). Both the primary and secondary radar were not working from 10am to noon on Sunday because of repairs to the MPSR.

“There were connectivity problems in the secondary radar. It has been sorted out,” said S.P.S. Bakshi, the regional executive director (eastern region) of the AAI.

Upgrade of surveillance system is a long-standing demand of airport employees. They have called for installation of a back-up for the MPSR.

Also, to bring the surveillance standard on a par with Mumbai and Delhi, the employees want an Air Root Surveillance Radar (ARSR), which has a range of 250 nautical miles, to be set up.

“The back-up for the MPSR has recently been sanctioned. The ARSR has not been sanctioned,” said an airport official.

Bakshi said steps were being taken to upgrade the airport’s ATC. “As part of the modernisation plan, the latest equipment will be installed at the ATC. We are trying to make Calcutta the biggest air traffic hub in south-east Asia,” he said.