Nav Canada is close to completing the nationwide rollout of a controller-pilot data link communications (CPDLC) system that is among the most advanced uses of this technology in any domestic airspace.

After deploying CPDLC to six out of seven of its domestic flight information regions (FIR) under a phased introduction, Nav Canada is progressively broadening the message sets to cover a greater range of operational needs. At the same time, the company is seeing a steady increase in airline usage and CPDLC equipage rates as carriers recognize its benefits.

CPDLC allows the exchange of many routine air-ground communications to occur via digital text message rather than voice. Not only does this improve the accuracy of messaging and decrease error rates it also reduces frequency congestion and eases workloads in the cockpit and control rooms.

“People have been talking about CPDLC for at least 30 years, and now we have actually implemented it,” Nav Canada Chief Technology Officer Sid Koslow says. The company's strategy of deploying it in small increments, one FIR at a time, has been one of the reasons for its wide acceptance by the airline industry, says Koslow. He believes that CPDLC—and the introduction of a medium-term conflict-detection tool—“will put us in a really good position to improve the efficiency of the [domestic] airspace” over the next few years.

Nav Canada introduced CPDLC in its oceanic airspace in 2002 and it is now mandatory for aircraft to be equipped with FANS 1/A—which includes CPDLC capability—between Flight Levels 360-390 on core tracks.

CPDLC's use in high-altitude domestic airspace began in December 2011 with its deployment at the Montreal area control center, which was followed by five other centers through 2012 and 2013. Although rollout was expected at the Toronto center last year, it is now preparing for initial deployment this year. CPDLC is used with the Canadian automated air traffic system (CAATS).

Nav Canada plans to gradually ramp up the capability of CPDLC in four phases, says Bill Crawley, director for air traffic system integration. Six of the seven centers are now at the third phase of deployment, and when all are at this point it will likely mark the most advanced stage of CPDLC use across a large domestic airspace.

The first phase allowed pilots to request altitude and speed changes via data link, but controllers still had to issue clearances by voice. In the second phase, controllers used CPDLC to transmit radio-frequency changes as aircraft crossed sector boundaries. The third phase allows controllers to repeat back and to clear altitude and speed changes using data link. “Direct to” requests have also been added to the message set, clearing aircraft to proceed to certain waypoints.

The fourth phase of CPDLC capability is yet to be defined, Crawley says. Discussions are being held with airlines—particularly Air Canada—about what should be added to the message sets. Requirements for other planned ATM initiatives also will be a factor in the planning for Phase 4.

Nav Canada is pleased with the rate of acceptance by controllers and pilots, says Crawley. By December 2013—about a year after CPDLC was introduced at most of the en route centers—42% of domestic flights were equipped for CPDLC. Equipage rates are far higher for oceanic airspace, where CPDLC has been in use much longer.

During December 2013, 180,000 messages were exchanged using the system, and the monthly total of CPDLC contacts nearly doubled from the start of the year to the end.

Equipage rates vary dramatically between domestic FIRs. The rate is 79% for the Gander domestic sector, 68% for Moncton and 51% for Montreal, which are the three eastern sectors. In the three western sectors, the rate is 27% for Edmonton, 28% for Winnipeg and 29% for Vancouver. The eastern sectors have higher rates because they receive more transatlantic traffic, which has greater equipage.

There are currently no plans to introduce an equipage mandate for domestic airspace.

Nav Canada is talking to airlines about the business case for retrofitting their aircraft for CPDLC, says Crawley. The safety and efficiency business case is obviously much more apparent for airspace that does not have VHF coverage, but there is also a strong argument for CPDLC where VHF is available, he says.

For example, route changes required for vectoring around storm cells and severe weather can be cleared more quickly via CPDLC than radio. And some route change requests that would be too cumbersome to make over VHF would be viable with CPDLC.

Pedro Vicente, Nav Canada's manager for CAATS integration, says controllers have been quick to realize the benefits of CPDLC because it means there is very little chance of communication errors with pilots, or a message being heard by the wrong pilot.

CPDLC is reducing the time needed to exchange and verify routine messages, particularly when English is not the pilot's first language.

Controllers also can send a message and then turn to other tasks while they wait for the response, Vicente says. Another collateral benefit is quieter control rooms.