FLIGHTDECK IMPROVEMENTS

CPDLC update: receiving accurate printed instructions makes sense

Controller Pilot Datalink Communication is growing rapidly in overseas usage and may become a requirement for business jets flying internationally.

By Peter Berendsen
ATP/CFII. Boeing 747, MD11


This screenshot from Rockwell Collins CPDLC implementation shows that an ATC clearance from Maastricht Center (EDYY Netherlands, Belgium, northern Germany) was received and accepted. The wording is similar to the spoken clearance.

Those of us who are flying over oceans, deserts or other remote areas of this planet consider the crackle and static of shortwave HF communication radios part of the experience.

It used to be that position reports, weather information, communication with the aircraft operator and telephone calls all had to be channelled through HF frequencies when long distances had to be covered. And even today the use of HF radios is still a daily routine on transoceanic and intercontinental flights.

But as flightdeck technology continues to evolve, HF is serving more and more as a backup. Satellite calls and automated controller-pilot datalink communication (CPDLC) are becoming the main air traffic control communication tools in flight operations all over world. Business jet operators that dispatch to international destinations need to be aware of the changing ATC environment as CPDLC becomes a recommendation or requirement, even just north of the border, in Canada.

Origins of CPDLC

The need for a different way to control oceanic airspace initially arose from increasing traffic volumes and a limited number of optimum tracks and flight levels. The North Atlantic is a vast ocean with lots of airspace but has no meaningful civil radar coverage. Most airlines schedule their flights to leave US gateways in the afternoon or evening and return from Europe the following afternoon.

These 2 traffic waves, 1 going east and 1 going west, have been channelled through the North Atlantic organized track system for many decades. Freighter and business jet traffic going in opposite directions always had limited routes and levels available, mostly very low or very high.

With the increase in traffic, communication and control became important constraints. HF radio operators could only handle so many calls, and separation between aircraft had to be spacious to prevent collisions.

Having 10 minutes in trail separation and 60 nm lateral separation between aircraft eats up a lot of airspace quickly. ATC units on both sides of the Atlantic looked for a communications system based on the exchange of datalink text messages via satellite and real-time virtual traffic situation displays based on ADS (Automatic Dependent Surveillance) position reports.

On the drawing board, this was called FANS (Future Air Navigation System) and is today known as CPDLC. On the North Atlantic and in many other parts of the world, trunk routes that pass over remote areas are increasingly controlled via CPDLC. Examples are the North Pacific routes to Japan and China, routes to South America over the South Atlantic, the famous L888 airways across the high plateau of Tibet and the Himalayas in China and airspace over central Africa.

ATC units see the advantages of CPDLC even over inhabited terrain

Actual photo from a recent B747-400 oceanic flight. After logon, this automated message confirms CPDLC contact with Gander Oceanic. The pilot has not yet acknowledged the message (status open).

Nav Canada, Eurocontrol, and the UK's NATS service have all implemented programs to widen the use of CPDLC. Currently operators are encouraged to declare their CPDLC equipment on the flightplan and to use CPDLC while enroute by the fee structure which gives substantial credits for use of this technology.

But in the near future CPDLC will be mandatory and some desirable routes may be off limits to aircraft without this capability.

Already some airways across India and the Bay of Bengal require the use of CPDLC. The L888 route over Tibet and the Himalayas is also now CPDLC only. While these routes are not of great importance to most US non-airline operators, the North Atlantic is. Since February 2013 the 2 most central and optimal tracks across the Atlantic are CPDLC only.

They are separated by 60 nm laterally. Between them a new track with only 30 nm separation will be established for CPDLC aircraft only between FL360 and FL390. After 2015, larger parts of the NAT MNPS area—like the airspace where most Atlantic crossing take place—will be CPDLC only.

Again the theme is clear: As airlines push for more capacity on optimum routes in the best flight levels, aircraft that do not have the new equipment get squeezed out. Currently 40 to 50% of aircraft use CPDLC in the NAT airspace.

Nav Canada has been using CPDLC in the North Atlantic airspace since 2002. In December 2011 the Montreal Flight Information Region (FIR) was the first Canadian ATC unit to implement CPDLC domestically. Today it is in use in 6 of 7 domestic FIRs controlled by Nav Canada, representing over 90% of Canada's domestic airspace.

While you can still fly in this airspace without CPDLC equipment at this time, in the future this might be either more expensive or restricted or both. And in Ireland and the UK as well as Maastricht (Eurocontrol), overflying airliners are strongly encouraged to participate in CPDLC. Business jets are currently exempt.

Not designed for terminal use but very helpful enroute

It is important to realize that CPDLC/ADS is an enroute ATC system. It is not designed for terminal areas with heavy traffic such as approach control. Only direct ATC voice communication with the pilots is able to cope with the ever changing dynamic traffic environment of an approach or departure sector. But enroute it works very well and eliminates the need for a lot of routine voice transmissions. It also helps those pilots and ATC units that have some difficulty communicating in English, as all messages are canned in the aircraft and ATC computers already.

How CPDLC actually works for the pilot is best illustrated by joining the flightdeck crew of a nonstop US-Europe flight as they cross into Canada and get ready for the oceanic portion of the flight. The first big difference to traditional voice communications is that the oceanic clearance is requested and received by datalink. It may be printed out on the cockpit printer.

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