- 12 Mar 2021
- Gerrard Cowan
- Avionics for Biz Av
Controller Pilot DataLink Communications is gradually transforming the air traffic control and aircraft operational environment. So is it important to make business aircraft CPDLC-capable? It depends, but in many cases it does make sense. Chris Kjelgaard learns more...Back to Articles
It’s important for business aircraft owners to make sure they understand the role of CPDLC, because it is becoming increasingly important for aircraft operations—particularly on oceanic routes and in upper airspace in congested air traffic environments.
CPDLC, more fully known as controller-pilot data link communications, consists of text messages transmitted between air traffic controllers and the pilots of aircraft in the air and on the ground. Those messages are operational, and communicate departure clearances, flight plan changes, re-routes and weather information, and they help simplify air traffic management tasks.
In many cases they eliminate the need for voice communications between controllers and pilots, says Conrad Theisen, Director of Avionics Sales for Elliott Aviation. Thus, CPDLC messages reduce voice radio-frequency congestion and eliminate potential human error in the form of pilot or controller voice misreads, he adds.
Additionally, by providing a written record of an instruction, either in the form of a paper print out or a readable log file recorded in the flight management system, CPDLC messages give pilots a way to verify after transmissions the ATC instructions they have received.
“This helps reduce pilot workload and improves flight safety,” says Christian Renneissen, Product Manager for Flight Deck Connectivity at Collins Aerospace.
Another benefit of incorporating into a business aircraft's avionics CPDLC capability—in this case digital rather than analogue—is that, by using the ‘Push to Load’ function offered by flight management systems in modern integrated flight decks, pilots can enter into the Flight Management System (FMS) the ATC instructions they receive (after checking them for accuracy), with a single press of a button, according to Adrian Chene, Senior Avionics Sales Representative for Duncan Aviation.
The FMS will then automatically fly the aircraft in compliance with those instructions, reducing pilot workload, and again potentially improving the flight’s margin of safety.
Flight Time Reductions
However, Theisen, Chene and Melissa Raddatz, Regional Sales Manager for Flying Colours Corp., all say the biggest direct cost benefit that owners of business aircraft (rather than pilots) will recognize from giving their aircraft CPDLC capability is the flight-time saving that comes as a result.
“Equipping a business jet with CPDLC will allow the owner or operator to maximize their time, with faster departure clearances (seconds versus minutes), fuel and operational costs savings, all while making the aircraft safer,” says Raddatz.
“The FAA currently has 62 CPDLC departure clearance operational airports—mostly international airports—and continues to grow this list,” she says. “If you are flying at one of these busy international airports you want to receive departure clearance as soon as possible.
“No-one likes sitting on the ground any longer than they have to. Aircraft equipped with CPDLC benefit from being moved more quickly by ATC. The equipped aircraft can be moved at a higher volume than those not equipped.”
For instance, says Chene, late on a typical Friday afternoon there might be a line of 20 business aircraft waiting to depart from Teterboro Airport near New York City.
If for any reason the FAA then announces an upcoming Teterboro departure hold, ATC might well prioritize the CPDLC-equipped aircraft with digitally transmitted text clearance instructions for departure before those whose pilots need to read back voice-transmitted clearances, particularly if the voice frequencies are congested and read-back errors are occurring.
The Three DataLink Types
According to Renneissen, there are three basic kinds of DataLink:
The earliest and most basic form of DataLink is the long-established ACARS capability, by which controllers or companies which operate aircraft can communicate with the aircraft (and vice versa) by sending analogue text messages. These are sent via VHF Digital Link (VDL) Mode A (also called ‘Mode 0’) transceivers mainly used for analogue operations, or VDL Mode 2 digital transceivers used for all-digital operations, but which can also handle ACARS texting.
With digital CPDLC messaging becoming very important, the most widely recognized method internationally is achieved using equipment conforming to ICAO’s FANS 1/A+ standard. While the original Future Air Navigation System (FANS) 1/A navigation-and-communications standard adopted by ICAO for operations worldwide was analogue-based, the later FANS 1/A+ standard subsequently adopted by ICAO uses all-digital communication.
FANS 1/A+ equipage for CPDLC requires VDL Mode A or VDL Mode 2 capability, and (for oceanic operations) HF Data Link capability or satcom transceiver-and-router packages that are able to receive from – and transmit to – Iridium, Inmarsat or MTSAT communications satellites. Nowadays many FANS 1/A+ compliant long-haul aircraft are equipped for all three types of communication, says Chene.
The third type of DataLink messaging, also digital, is the protocol developed for the Aeronautical Communications Network (ATN) 1-Broadcast (1B) standard by Eurocontrol under its Link 2000+ initiative. The ATN 1B CPDLC technical protocol is different from that used by FANS 1/A+, but operates similarly, says Renneissen.
Where is CPDLC Equipage Mandatory?
While CPDLC equipage is not mandatory in most areas of the world, it is now mandatory for operations in two very highly used areas of upper airspace. Here, the CPDLC equipage must be digital, but the two mandated areas require different digital protocols, according to Renneissen.
One of the areas is the entire volume of airspace between flight levels 290 and 410 (all of the most preferred cruise altitudes) in the North Atlantic Mandate Area. This area includes almost all North Atlantic airspace south of Iceland and Greenland.
Aircraft flying at any mandated cruise level in the area must be equipped for CPDLC to the FANS 1/A+ standard.
The two air navigation service providers managing that airspace, Nav Canada and the UK’s NATS, previously allowed aircraft not equipped for CPDLC to cruise through the North Atlantic Mandate Area at altitudes above flight level 410.
However, the problem of managing those aircraft as they climb and descend through the flight levels between FL290 and FL410 is now making controllers insist the aircraft are equipped for CPDLC, says Chene.
According to Chene, the North Atlantic mandate effectively means that all aircraft not equipped with CPDLC can only fly through North Atlantic airspace at altitudes which are generally sub-optimal for fuel-efficiency (and may have a higher chance of encountering bad weather), or else on longer transatlantic routings which are generally to the north of the mandate area, over Iceland and Greenland.
Those routes include the various ‘Blue Spruce’ routes designated by ATC to allow aircraft which aren’t FANS 1/A+-equipped to cross the Atlantic.
For non-equipped aircraft, particularly those flying westbound through the jet stream headwinds, the difference in routing distance could well make an intermediate fuel stop necessary, adding more time to the flight itinerary, says Chene.
The second very important area of airspace in which CPDLC equipage is mandatory is all airspace above flight level 285 in the Eurocontrol area. That represents all of the upper airspace above western Europe, including all of the airways transiting between western and southern Europe and western and eastern Europe.
Since all flights between western Europe and Asia and western Europe and Africa also route via airways in the mandated area, those flights must be CPDLC-equipped too, unless they fly at sub-optimal cruise altitudes below 28,500 feet.
The EU allows some exceptions to the mandatory equipage, but most modern business jets are not excepted. What is mandatory, however, is that all aircraft equipped to the ATN-1B standard use VDL Mode 2 radios to receive and transmit CPDLC messages, says Renneissen.
CPDLC use in the United States
While CPDLC equipage isn’t mandatory in any other areas of airspace yet, that doesn’t mean it isn’t in wide use by ATC elsewhere to improve the efficiency of flight operations and airspace usage.
For instance, notes Renneissen, the FAA offers departure clearances at 62 major US airports via two types of CPDLC, one – the digital-CPDLC method – offering rather more operational flexibility than the older, analogue method.
That older method is called FAA Pre-Departure Clearance (PDC), transmitted to either the operator of the aircraft (which then prints out the clearance for the pilots), or directly to the flight deck, via an ACARS message or by means of an e-mail or text delivered to a PED through a dispatch-subscription service such as Jeppesen/Boeing’s ForeFlight service or Garmin’s Fltplan.com.
While very useful, PDC is relatively inflexible in that the FAA cannot deliver any subsequent revision of the departure clearance by text again to the same aircraft at the same airport within a 12-18 hour period. Any subsequent revisions are transmitted by voice.
The FAA’s newer, digital departure clearance method is known as CPDLC Departure Clearance, or DCL.
The FAA offers the service to aircraft equipped to the FANS 1/A+ CPDLC standard and using either VDL Mode A or VDL Mode 2 rather than satcom transmission, according to Renneissen.
DCL text clearances can easily be obtained by pilots by logging on via FANS to KUSA and requesting the service. A big advantage DCL has over PDC (which it does not replace) is that controllers can transmit revisions to the original DLC clearance digitally to the flightdeck via an updated DCL, any time before the flight departs.
Slightly confusingly, there is also another text-based departure clearance service, also known as DCL, available at 120 airports throughout the world, notes Renneissen.
Unlike the FAA’s digital DCL service, however, global DCL is transmitted by ACARS or AFIS only to aircraft equipped to the analogue ARINC 623 ACARS aeronautical operational control standard. Pilots must request these clearances on their multi-function display units.
The FAA isn’t likely to make CPDLC equipage mandatory for business aircraft flying in US airspace, Chene reckons, not least because thousands of smaller business aircraft remain unequipped and may never need the technology if they don’t fly in upper airspace.
However, the FAA offers another CPDLC service specifically to VDL Mode 2-equipped aircraft: en route CPDLC, a service which offers flexible updating of flight plans, re-routes and weather updates.
Renneissen says that, under its ‘Waterfall’ plan, the FAA planned to complete rolling out en route CPDLC at all its Air Route Traffic Control Centers (ARTCCs) by the end of 2020, but the onset of the Covid-19 pandemic hindered the roll-out greatly.
For now, the FAA is offering en route CPDLC at its Washington DC, Indianapolis and Kansas City ARTCCs, which allows a contiguous corridor of en route CPDLC capability across approximately half the area of the mid-Atlantic and mid-western US.
CPDLC Availability Grows Worldwide
While the FAA hasn’t yet been able to roll out en route CPDLC at all of its ARTCCs – and thus provide nationwide coverage for the service – Renneissen says Nav Canada’s Enroute CPDLC service for FANS 1/A+-equipped aircraft using VDL Mode 2 radios already covers all of Canada’s domestic airspace.
Like the FAA, however, Nav Canada has not made CPDLC equipage mandatory for flights in Canadian domestic airspace, except for those which are also routing through the North Atlantic Mandate Area at flight levels between 290 and 410.
Elsewhere in the Americas, another huge area of busy domestic airspace might soon also see en route CPDLC coverage.
Renneissen says Brazil is planning to implement domestic en route CPDLC for VDL Mode 2-equipped aircraft in the fairly near future, under its ‘Landell Project’.
Additionally, while CPDLC equipage isn’t mandatory anywhere else in the world, the capability is widely used by FANS 1/A+-equipped aircraft flying in major areas of oceanic airspace such as the Oakland FIR, which controls most Pacific airspace and which Renneissen says is completely covered for en route CPDLC service.
The increasing coverage of CPDLC service worldwide for important air traffic control functions – such as en route real-time updating of flight plans and push-to-load reroutes – makes CPDLC equipage worth considering for owners of business aircraft who fly in areas of oceanic and upper airspace, as well as from airports which offer text-based departure clearances.
However, there are just as clearly other cases where installing CPDLC capability might not make so much sense.
For instance, there remain thousands of jet, turboprop and piston-powered business aircraft flying in domestic US airspace, which neither regularly operate to any of the 62 airports at which the FAA offers its DCL service, nor fly in oceanic or European upper airspace.
It might never make much sense to equip many of those aircraft for CPDLC capability, particularly if—as Theisen suggests—their legacy avionics installations could make installation of the incremental capability very expensive.
What CPDLC Equipage Costs
As a rule of thumb, CPDLC equipage is likely to be much cheaper in aircraft which already have modern integrated flight decks such as those in Collins’ Fusion or Proline ranges, or in Garmin’s G5000 range, says Theisen.
They either already have optional CPDLC capability built in (CPDLC can be activated simply by purchasing a software upgrade or an encrypted activation code) or any additional hardware and software required can be installed relatively cheaply.
The total cost to the owner of CPDLC equipage in such aircraft could be as low as $50k-$100k, according to Theisen. However, an older aircraft with a legacy avionics suite might require a much more customized, extensive avionics update to enjoy CPDLC capability, with costs soaring to as much as $600k or $700k, Theisen and Renneissen estimate.
Another factor bearing on an owner’s decision whether or not to invest in CPDLC capability is whether the owner wants to maximize the chances of the aircraft selling quickly, and for a premium price, says Chene. Aircraft not equipped may well take much longer to sell.
Ultimately, Raddatz and Chene argue, much depends on where, and how often, the owner wants to operate the aircraft, and the flight profiles it will typically fly. If resale considerations and expedited clearances aren’t important, then CPDLC equipage may well make less sense.
What does make sense is for owners to discuss their plans and requirements with their trusted avionics sales representative, including their envisaged resale strategies. “Having a well-maintained aircraft with updated avionics is rarely a drawback in terms of selling your aircraft,” concludes Raddatz.