Sending e-mail to ATC via CPDLC

Controller pilot datalink communications are the future of international flying—and they may soon be mandatory.

By Peter Berendsen
ATP/CFII. Boeing 747, MD11

Views of Greenland, such as the eastern coast seen here, are a highlight of any ocean crossing—and even more enjoyable with CPDLC established.

Almost since the beginning of long-range navigation, the crackle and hissing sounds of high-frequency (HF) communication radios have been as much a part of ocean crossings as fatigue, coffee and glorious sunrises after a long night over the Atlantic.

The procedure has not changed in decades, and is still the same for most flights—somewhere east of Newfoundland, Gander Center loses radar contact of Europe-bound flights and instructs crews to contact Gander Radio on a primary and secondary HF frequency.

These are selected from a family of frequencies according to the time of day, as the position of the sun influences the reflectivity of the ionosphere and therefore HF transmission range. The person talking to you on HF at Gander Radio is not the actual controller but a radio operator who acts as an intermediary between pilot and controller.

Every 10 degrees of longitude, flightcrews transmit position reports to Gander Radio and, after passing 30° W, to Shanwick, the oceanic control center responsible for the eastern half of the North Atlantic. Shanwick transmits through antennas at SNN (Shannon, Ireland) and is actually located at PIK (Prestwick, Scotland).

Shortly before landfall, a new squawk is assigned, and communications revert to a normal VHF radar environment. Most airline flights leave North America in the afternoon or evening to arrive in Europe the next morning. From Europe, flights leave around lunchtime to arrive in the US gateways in the early afternoon and evening.

This means that there are two big waves of traffic—one eastbound and one westbound. The North Atlantic Organized Track System, which changes twice a day, tries to channel this traffic on predetermined routes while taking advantage of the wind situation of the day. Executive jets and freighters that leave the US in the morning and return from Europe at night fly in opposite directions to the main traffic flow and may have limited flight levels and routings available to them.

Origins of CPDLC

Today’s traffic volume would be almost impossible to handle with just HF position reports. Therefore, a number of years ago, controller pilot datalink communication (CPDLC) was introduced. CPDLC is an ATC communications system based on the exchange of datalink text messages via satellite.

Combined with automatic dependent surveillance (ADS), communications errors are reduced while the need for manpower at the radio and control centers is also reduced. The fee structure of Gander and Shan­wick encourages the use of CPDLC, and it may well be required in the future.

On May 24, 2004, the first business jet using future air navigation system (FANS) technology crossed the Atlantic and communicated with air traffic controllers via digital messaging. The aircraft was a Boeing BBJ, and the flight—from GYY (Gary IN) to GVA (Geneva, Switzerland)—was part of a trial being conducted by the FANS Central Monitoring Agency (FCMA).

New ATC index page on the FMS gives access to various CPDLC functions.

BBJs now come standard with CPDLC/FANS equipment—the customer has to supply the satellite link. In Nov 2008, Gulfstream Senior Intl Captains Sean Sheldon and Ron Newton flew a Gulfstream G450 test aircraft under FANS procedures from SAV (Savannah GA) to LTN (Luton, London, England) and back across the Atlantic using CPDLC and ADS.

The aircraft, which featured an integrated PlaneView avionics package with triple flight management systems (FMSs) operating in synchronous mode, used CPDLC/ADS for oceanic communication and position reporting. Dassault’s large Falcon jets offer CPDLC, and Embraer’s Legacy 650 comes with the Honeywell Primus Elite avionics system, which is also certified for FANS 1/A CPDLC.

CPDLC is being introduced in more and more areas of the world, and is mandatory on some trunk routes used mostly by airlines. In addition to Gander and Shanwick, New York Oceanic, Santa Maria and Recife/Atlantico on the South Atlantic offer CPDLC facilities. The Pacific is covered as well.

Some airways in Asia such as the L888 airway from Almaty in Kazak­stan to Chengdu, China via the highlands of Tibet, as well as several airways in the Bay of Bengal south of Calcutta, India are CPDLC only. Even some countries in Africa, such as Senegal have embraced CPDLC for their oceanic airspace. There are more than 34 FIRs supporting CPDLC/FANS worldwide.

Avionics upgrade to FANS/CPDLC

For most operators, only frequent ocean crossings will justify the installation of CPDLC today. FAA has announced its datalink communications service and estimates a mandate in the 2016 time frame.

ATC LOGON/STATUS page shows current CPDLC and ADS status as well as active center.

But starting in 2011, the European Union plans to make CPDLC mandatory in several steps in upper European airspace. Trials have been conducted since 2006 in Maastricht airspace over Holland, Belgium and northern Germany.

By 2015, all aircraft must be equipped if using core EU airspace. CPDLC involves modifications to the FMC CDUs and the ACARS. ACARS via satcom is required as HF datalink installations may not be certified.

After modification, a new “ATC” button on the FMC CDU allows access to the CPDLC messaging interface, while ACARS is used to request and receive the oceanic clearance as well as other reports such as weather. The business jet community has been slow to embrace CPDLC/ FANS on its intercontinental aircraft, but the benefits become quite apparent now.

FANS routings offer reduced fuel burn and flight time, increased payload and sometimes reduced ATC user fees. Honeywell says that the basic hardware building blocks for FANS are found on many of the newer long-range business jets today. In most cases, the upgrade to FANS involves loading only the FANS software in the FMS, if satellite communications are installed already.

The ideal candidate long-range business jet will have the FMS, GPS, CMU/DMU, satcom and VHF data radio installed already. Only the FMS software (and possibly DMU software) will need to be upgraded.


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