Chennai, Aug. 3: A technical snag in the Controller Pilot Data Link Communications (CPDLC) system at the Chennai airport air-traffic control (ATC) on Friday night forced the staff to use voice systems to trace aircraft movements in the oceanic region, instead of the faster and safer CPDLC.

The ATC staff had to tune for aircraft signals along the weaker channels using VHF equipment. “Lucky we did not have any mishaps,” said a senior ATC officer.

“As the CPDLC of Automated Dependent System (ADS) is a back-up tool to trace the aircraft signals from remote oceanic regions where the high frequency voice communication is not possible between the ATC controller and the aircraft pilot. We managed to maintain the traffic through very high frequency and voice communications. CPDLC is exclusively for long distance communication in oceanic control with a data link up to 600- 700 nautical mile,” said the officer.

But the pilots do not seem to be too disturbed about this problem. A senior Air-India pilot told DC that the CPDLC should be activated in oceanic control desk “because it is much faster and safer for the ATC and the pilots to communicate on the correct altitude of the aircraft and its movement.”

The major oceanic routes for monitoring by the Chennai ATC are Singapore, Bangkok and Kuala Lumpur. “There are some pockets in this oceanic region where the ATC cannot make voice contact with the aircraft. True, the CPDLC is not a primary communication link but still, it is very useful during emergencies. Also, it is mainly used in the oceanic region having low network. Its absence could even lead to accidents midair,” said the AI pilot.

When 60-70 per cent oceanic aircraft movements are equipped with CPDLC system, AI sources maintain that none of its flights, except Airbus 777 and 330 models, have the CPDLC. This system is being used for communicating digital messages between the ATC and pilots, especially to trace the aircraft movement in certain regions in the absence of voice communication links.