“There is no foolproof backup system at Mumbai airport. In the event of a primary radar failure even for a few minutes, there will be absolute chaos here because of the sheer volumes we handle,” said an ATC official. The Chhatrapati Shivaji International Airport (CSIA) is the country’s busiest—it handles over 650 aircraft daily.

“In case of a failure, we have to switch to procedural control and would communicate only via radio for aircraft positions,” the official added. This means controllers will have to rely on visualising aircraft as against a ready radar display with detailed information about altitude, speed, etc.

This would entail larger spacing between aircraft for security reasons. “This means, there would be a gap of at least seven minutes between two arrivals, compared to two minutes currently,” the official said. “In effect, our capacity would be severely cut and we would be able to handle only about 17-18 aircraft per hour, against the 30-odd now.”

“But that’s the best case scenario—a virtual aircraft jam,” the official cautioned, adding “it can be very dangerous if we suddenly aren’t able to see aircraft positions in real time even for a few minutes. The time lag maybe very critical.”

While agreeing operational capacity would be hampered in case of a shutdown, P Anil Kumar, GM (communications, navigation, surveillance) said safety would not be compromised. He also said the Delhi incident was “actually a radar display malfunction rather than a radar malfunction.”

“Such an incident can happen even here, though it doesn’t affect safety and there is nothing worrisome,” he added.

Kumar explained there are two radars at Mumbai—the Approach Surveillance Radar (ASR) and the Route Surveillance Radar (RSR). While the former, also called the S-Band radar, is located at the CSIA and has a range of 60 nautical miles; the latter, also referred to as the L-Band radar, can track aircraft upto 200 nautical miles and is the egg-shaped structure atop the control tower at Juhu aerodrome.

Confirming that the radar at Juhu functioned as a backup, Kumar admitted it was “degraded radar backup, since it cannot be a 100 per cent backup.”

“This is mainly because the Juhu radar has a slower updation rate,” he said referring to the rate at which targets (aircraft) are updated on the system. To simplify, the antenna atop the L-band radar at Juhu clocks five rotations per minute compared to the 15 rotations per minute the S-band radar at CSIA does.

“Each radar consists of 16 modules, with inbuilt redundancies. Even if six modules fail, the radar can work,” Kumar said, but added he didn’t expect “that kind of failure.” The on-site S-band radar is generally shutdown for 5-6 hours annually for preventive maintenance, when the backup radar is used.

SHUTDOWNS WORLDWIDE

* On July 23, a radar outage over the Amazon forced Brazil to close its airspace for nearly three hours, which translated into 10 per cent flight cancellations and over 40 per cent delays.

* Last December, arrivals at Chicago's O'Hare International Airport were slashed to approximately 60 per hour, as against the 96 the airport usually handle. Reason: radar blackout.