Cables cut, air surveillance down for 13 hours in east India

KOLKATA: Crude axing of two optic fibre cables near Birati in north Kolkata downed a newly installed hi-tech air traffic service, blanked out radar surveillance across eastern India, and left thousands of passengers vulnerable as planes travelled through communication black holes in the sky that lasted 13 hours.
Kolkata airport handles 300 flights daily and its ATC also has to monitor 700-800 overflying aircraft every day.
State-owned telecom service provider BSNL, which carries data from radars and other surveillance gadgets to the airport, cried sabotage and hinted at foul play by a private operator. But sources said the culprit could well be a labourer planting bamboo poles for Kali Puja pandals. Airports Authority of India (AAI), which believed its integrated radar system was foolproof, now has a problem on its hands as the link failure exposed its vulnerability.
The regular night shift at the Kolkata ATC turned into a pressure-cooker situation after data from six radar stations and eight automatic dependant surveillance-broadcast (ADS-B) units disappeared suddenly at 10.49pm on Friday. Only two patches in the sky, each of 350 nautical mile radius around Kolkata and Behrampore, remained under radar surveillance.

Passengers at NSCBI Airport in Kolkat. ((PTI Photo)
"The integration of radars that happened when Aircon 200 automation system was commissioned a few days ago allowed area controllers an overview of the sky on a single monitor. For example, if a flight took off from Chennai and was flying to Kolkata, controllers at Kolkata had it under radar coverage all through. But on Friday night, once the radar links failed, controllers could not get the live position of the planes till they were within 350 nautical miles of Kolkata airport," an aviation industry insider told TOI.
After an initial bout of panic, controllers fell back on the antiquated yet time-tested radio communication with pilots to locate their position and flight speed. Fears of a possible crash or collision ebbed as calls to other stations revealed the radars were working fine. Engineers then zeroed in on the BSNL modem. The signal was gone, pointing to a link failure.
"The problem was clearly in an area under the local telephone exchange. Closer to the airport, all the data from various radar heads converge and are carried by a pair of optical fibre cables. Had one cable been severed, the other could have taken over. But both were cut, leading to the link failure," an engineer explained.
At the ATC, the separation between flights beyond radar coverage was increased from 10 nautical miles to 80-120 nautical miles. What added to the problem was disruption in telecom services as well. Controllers had to use cellphones to communicate with Dhaka, Yangon, Chennai and neighbouring ATCs to hand over planes flying into these regions from Kolkata and vice-versa.
Flight disruption though was minimal as radars at Kolkata remained operational. So did the radars at Badu and Behrampore that are linked by a different pair of cables as well as microwave. When link was restored at 11.49am on Saturday, controllers were able to again access to radars at Varanasi, Nagpur, Guwahati, Katihar and Jharsuguda along with eight ADS-B ground receivers.
Interestingly, during the training for the new system by Spanish firm Indra, controllers and engineers at Kolkata had identified this very weakness. "It is a fantastic technology that is used in both developed and developing economies. But while probing its robustness, we did spot this possible weakness in the last-mile router or link failure. When we asked the Indra team, they didn't have a solution as a communication link failure between the radar head and the receiving station is unheard of. But since it has happened now, we have to look at ways to address the lacunae," an engineer said.