Datalink Communications
Summary
3/4/2026. Read time: 10 min.
This article originally appeared in POPA Magazine, Summer 2025.
Get used to it; datalink is becoming mainstream. The systems are already in place for Domestic US airspace, European airspace, oceanic airspace, as well as a growing number of other countries. The technology is trickling down to smaller aircraft, and what was once only a training requirement for long-range aircraft is quickly becoming necessary for all business and corporate operators.
Datalink is an umbrella term for an aircraft's capability to send and receive text messages. There are numerous acronyms due to the advancement of equipment over the years and the naming conventions of aircraft avionics manufacturers, but the two primary streams of data are either ACARS or CPDLC. The aircraft hardware is the same; the difference is the network you transmit on and who you talk to.
3/6/2025
Details
ACARS
ACARS (Aircraft Communications, Addressing, and Reporting System) runs on ARINC's network. ARINC is one of the major worldwide Data Service Providers (DSPs). Initially founded by airlines almost 100 years ago, ARINC established non-ATC communications with dispatchers and FBOs and developed ACARS in the 70s. It has evolved and changed hands over the years, beginning as a VHF Digital Link (VDL) and then incorporating SATCOM (Satellite communications). ARINC is now a subsidiary of Rockwell Collins. Rockwell maintains the network and supports Pre-Departure Clearances (PDC), weather reports (TWIP), Oceanic Clearances (RCL), private communication between aircraft, and intra-company messaging.
CPDLC
CPDLC (Controller Pilot Datalink Communications), on the other hand, handles direct ATC communication, both domestically and internationally - including oceanic airspace. ACARS is automatically available on power-up, whereas CPDLC requires logging on to the appropriate ATC controlling agency via a four-letter identifier. Depending on your area of operation, CPDLC may automatically switch to new jurisdictions or require multiple logons.
CPDLC can also support DCL (Datalink Clearance) on the ground at some airports. Once properly logged on (KUSA), ATC can send you your IFR clearance automatically via text instead of voice. It is very similar to ACARS PDC, except better. PDC has limitations on how many clearances you can receive and cannot handle route changes. By looking at the top strip of an airport diagram, you can see what Datalink capabilities are available at the airport.
Airborne CPDLC can be broadly divided into FANS or ATN. The first CPDLC network to know, referred to as FANS (Future of Air Navigation System), connects you to the SITA network (another worldwide DSP). You can connect and communicate via VDL or SATCOM - but that happens seamlessly behind the scenes as long as you are logged on to the correct address (KUSA domestically, for example) and have filed the correct flight plan codes. Depending on your hardware, there are six available means to connect and transmit data to and from the network:
HFDL (High Frequency Datalink - for polar regions)
VDL Mode A/0 (early adopters)
VDL Mode 2 (most systems)
SATCOM INMARSAT (almost global coverage)
SATCOM MTSAT (old)
SATCOM Iridium (global coverage)ATN
The second CPDLC network, NewPENS, is specific to Europe and is called ATN (Aeronautical Telecommunication Network). This is strictly a ground-based VDL system separate from FANS.
CPDLC ATN VDL Mode 2 is required to meet the CPDLC performance specifications and access airspace above FL285 in Europe. Note that you are required to be equipped with the ATN system. Then, there are a growing number of control areas in Europe where it is necessary to log on. There are, however, exemptions to this equipment rule (focusing on GA aircraft):
Any aircraft with a certificate of airworthiness before Jan 1, 1995.
Aircraft with FANS 1/A and an airworthiness certificate before Jan 1, 2018.
Aircraft with 19 or fewer passenger seats, and a MGTOW less than 100,000 lbs, and an airworthiness certificate before Feb 5, 2020.
Aircraft flown for testing, delivery, maintenance, or operating under CPDLC MEL relief.
King Air 90/100/200/300 series aircraft (+1 for Textron lobbying)
And these aircraft with an airworthiness certificate before Feb 5, 2020: GLEX/GL5T, C25C, C56X, F2TH, F900, E50P, E55P, E35L, PC12.
FANS 1/A
There's more! FANS and ATN CPDLC are half of "FANS 1/A," the other half being ADS-C (keep reading). FANS 1/A (1 for Boeing, A for Airbus) is the performance specification required for ATC datalink communication, met by both FANS and ATN. Yes, it's a confusing way to name things. FANS 1/A is the minimum requirement; newer, more capable systems may be called FANS 1/A+ or FANS B or C in your aircraft.
FANS 1/A can have one of two latencies: RCP400/RSP400 or RCP240/RSP180. These stand for Required Communication Performance and Required Surveillance Performance, respectively. The numbers refer to the seconds required for receiving and transmitting data.
While both qualify as FANS 1/A systems, RCP240/RSP180 is the specification required to access the PBCS Tracks (most efficient, tightest spaced tracks) in the North Atlantic. The 400 specs are generally early avionics iterations, and most have moved to tighter standards.
ADS-C
Then there is the previously mentioned ADS-C, the second half of FANS 1/A. CPDLC is communication, and ADS-C is surveillance. ADS-C can send the same data as ADS-B, but on demand. The C means "contract," but it's easier to think of it as "contact." ATC pings your aircraft via satellite or VDL. Then, your aircraft sends the data back to them directly. CPDLC communicates with the pilots, whereas ADS-C communicates with the aircraft. Of the FANS 1/A RCP 400/240 and RSP 400/180 specifications, the RCP values refer to your CPDLC communication capabilities, whereas RSP values refer to your ADS-C surveillance capabilities.
Aviate
So, what do you do with this information?
Start with your AFM to determine what your aircraft is capable of: ACARS, FANS, and/or ATN.
Let's assume you have it all. ACARS, you can begin to use as soon as you update your ICAO flight plan equipment codes appropriately (E1, E2, and/or E3). Everything else requires, you guessed it, paperwork.
Domestic CPDLC (FANS) requires FANS 1/A or FANS 1/A+ over VDL Mode 2 equipment, the common spec being TSO-C160a. You can do DCL with VDL Mode 0/A. Getting started involves applying for access via L3 Harris - a full write-up on Domestic CPDLC is available here. You submit the specific hardware part numbers and revisions found in your maintenance manual, and once approved, update your flight plan codes:
Item 10a: J4, E3
Item 10b: D1
Item 18: DAT/1FANSE2PDC or DAT/1FANSER2PDC, CODE/"six digit HEX code"
Oceanic and International CPDLC (FANS) has the same specification as domestic CPDLC with an asterisk; accessing PBCS routes in the North Atlantic requires FANS 1/A+ (meaning it is RCP240/RSP180 capable). On top of that, you need LOA A056 Datalink Communications and all the bells and whistles that go along with an LOA: operator training and manuals. And if you give a mouse a cookie, you will want to get a host of other LOAs to go along with it:
B036 RNP 4 and/or 10
B039 North Atlantic High Level Airspace
B046 RVSM
D195 MEL
With LOA A056 in hand, update your flight plan codes:
10a: J1-J7 (depending on your equipment), P1 or P2 (RCP400 or RCP240)
10b: D1 (ADS-C FANS)
18: DAT/1FANSE2PDC -or- /1FANSER2PDC, SUR/260B RSP180
ATN CPDLC is more similar to the Domestic CPDLC process. The difference is in some areas, logon is not optional. First, make sure you have ATN equipment: CPDLC ATN VDL Mode 2.
Then, register for ATN use in Europe by contacting the Eurocontrol Datalink team (ectl_nm_datalink_team@eurocontrol.int) to request access to the ATN CPDLC Login List dashboard. Enter the specific part numbers and software revisions (found on the hardware) via the dashboard. Once approved, you are ready to logon where required. Don't forget G1 (ADS-C ATN) and J1 in box 10b and CODE/"six digit HEX code" in box 18.
Lastly, if you have datalink, adopt it and use it. This is not a technology you want to avoid because you don't think you need it. It's becoming required in more and more places and a necessary means of ATC communication- this trend is going to continue. Datalink is not part of basic training. You usually are not exposed to it until you are already flying an aircraft with the equipment capability, which puts you behind the eight ball. If you've got it, take advantage, practice domestically, and become proficient.
