You can think of Controller Pilot Data Link Communications as a replacement for your HF when oceanic and VHF over some domestic areas. It is far superior to your HF and has distinct advantages over VHF.
Everything here is from the references shown below, with a few comments in an alternate color.
Figure: CPDLC Contact Message, from Eddie's aircraft.
Here is a CPDLC Checklist in case you need one.
The role CPDLC plays in the Future Air Navigation System is to reduce the time it takes for air traffic control to issue instructions to a pilot and the pilot to acknowledge. In a domestic environment this is rarely a problem. When oceanic, however, it can be a factor. Reducing that time, known as Required Communications Performance (RCP), allows ATC to reduce aircraft spacing.
[ICAO Doc 4444, ¶188.8.131.52.1.6] Lateral separation of aircraft on parallel or non-intersecting tracks or ATS routes. Within designated airspace or on designated routes, lateral separation between aircraft operating on parallel or non-intersecting tracks or ATS routes shall be established in accordance with the following:
You need CPDLC to begin the process of reducing separation standards. This is in your best interests, since the best routes — best winds, shortest distances — will be reserved for those able to fly with reduced separation.
If you have CPDLC and you are in airspace where CPDLC is being used, you should use CPDLC as primary, voice communications as secondary. The general rule of thumb is: if contacted by CPDLC, respond with CPDLC; if contacted by voice, response with voice. When oceanic you still need to check in with HF, get a good SELCAL check, and maintain a listening watch if SELCAL fails.
[ICAO Doc 10037, ¶4.1.2.]
Note.— For aircraft that have CPDLC message printing capabilities, there are constraints associated with the use of the flight deck printer. Printers may not produce an exact copy of the displayed clearance with the required reliability, and should not be used as the primary display for CPDLC. However, in some cases, printed copies may assist the flight crew with clearances and other information that are displayed on more than one page, conditional clearances and crew handover briefings.
[ICAO Doc 10037, ¶4.1.2.]
Note.— ICAO Doc 4444, paragraph 8.3.2, requires that DCPC be established prior to the provision of ATS surveillance services, unless special circumstances, such as emergencies, dictate otherwise. This does not prevent the use of CPDLC for ATC communications, voice being immediately available for intervention and to address non-routine and time critical situations.
Note.— Refer to paragraph 4.6 for guidelines on use of voice and data communications in emergency and non-routine situations.
Note.— For ATN B1 aircraft, emergency message elements are not supported. See Appendix A, paragraph A 4.9 for a list of emergency message elements.
Note.— This will lessen the opportunity for messages to get lost, discarded or unanswered between the ATS unit and the flight crew and cause unintended consequences.
Note.— For FANS 1/A aircraft, some uplink messages do not have a DM 1 UNABLE response. On these aircraft, the flight crew should respond with DM 3 ROGER and then obtain clarification via voice.
It may seem confusing, but you can begin to grasp the problem by understanding not all CPDLC is created equally:
[ICAO Doc 10037, Table 1-1.]
[ICAO Doc 10037, ¶184.108.40.206.]
So, how about all this in English?
[NAS Data Communications Guide, Ch 3] The Controller Pilot Data Link Communication-Departure Clearance (CPDLC DCL) provides automated assistance for delivering initial and revised departure clearances. CPDLC DCL provides the following: flight plan route, initial and requested altitude, beacon code assignment and departure frequency. CPDLC DCL messages are established message sets in Future Air Navigation System (FANS) equipped aircraft. The CPDLC DCL service is designed for use in surface operations and replaces the existing Pre-Departure Clearance (PDC) at Tower Data Link Services (TDLS) sites for participating aircraft.
[NAS Data Communications Guide, Ch 4]
For more about this: PDC vs. DCL.
[NAS Data Communications Guide, Ch 7]
As of late 2020, the CPDLC En Route program in the United States is still in a test phase with limited participation. Contact your manufacturer to see if your participation in the program is possible.
Figure: Different ATSU/Aircraft Interoperable Connectivity, from ICAO Doc 10037, figure 1-2.
EU Regulations are written in a serpentine manner, so this might seem disjointed. But follow from start to finish:
[EU Commission Regulation No 29/2009, Article I, ¶ 3.] This Regulation shall apply to all flights operating as general air traffic in accordance with instrument flight rules within the airspace above FL285 defined in Parts A and B of Annex I.
[EU Commission Regulation No 29/2009, Annex I, Parts A and B] The airspace referred to in [ . . . ] Article 1(3) shall include the airspace above FL 285 within the following Flight Information Regions (FIR) and Upper Flight Information Regions (UIR): Amsterdam FIR, Wien FIR,, Barcelona UIR,, Brindisi UIR,, Brussels UIR,, Canarias UIR,, France UIR,, Hannover UIR,, Lisboa UIR,, London UIR,, Madrid UIR,, Milano UIR,, Rhein UIR,, Roma UIR,, Scottish UIR,, Shannon UIR. — Bratislava FIR,, Bucuresti FIR,, Budapest FIR,, Kobenhavn FIR,, Ljubljana FIR,, Nicosia FIR,, Praha FIR,, Sofia FIR,, Warszawa FIR, Zagreb FIR, Finland UIR south of 61°30′,, Hellas UIR,, Malta UIR,, Riga UIR,, Sweden UIR south of 61°30′,, Tallinn UIR,, Vilnius UIR.
[EU Commission Regulation No 29/2009, Annex IV, Part B] Requirements for air-ground communications based on ATN and VDL Mode 2.
[EU Commission Regulation No 29/2009, Annex III, Part B, Points 2, 3, 4]
[ICAO Annex 10, Volume III, Part I, ¶3.3, 3.4, and 3.6 extracted]
[ICAO Doc 10037, ¶220.127.116.11] The ATN B1 data link system relies on the aeronautical telecommunication network (ATN), which is provided and maintained by various CSPs and/or ANSPs. The ATN was developed by ICAO to support the need for ATS communications. The ATN relies only on VHF (VDL M2) to meet the performance required for the intended operations.
You will need an ATN B1 system to use your CPDLC over domestic European airspace once you've coasted in. FANS 1/A will not work. As of late 2020, you can fly anywhere in Europe without ATN B1, you just can't use data link. Even if you have it, however, you have to get onto a "white list."
The European Data Link Services Mandate aims to restrict noncompliant and non-exempt aircraft to flight below FL285. Some older aircraft will be exempt. The GI, GII, GIII, GIV, G450, G100, G150, and G200, for example are exempt. EuroControl publishes a "Logon List," known as the "White List" to some, Information about the list, getting on the list, and why it does or does not matter: https://ext.eurocontrol.int/WikiLink/index.php/Logon_List.
This is a moving target. The Gulfstream GVII-G500, for example, has ATN B1 but cannot join the White List for a while longer.
Photo: "Confirm Assigned Route" message, from Eddie's aircraft.
When I first heard this a year and a half ago I dismissed it as something I didn't have to worry about since I operate above the tracks. (We can climb right up to 41,000 feet at any weight.) But lo and behold I have been getting this message routinely.
In Gulfstream PlaneView cockpits you are expected to select "REPORT" and then "SEND" without entering any free text. See: Gulfstream CPDLC Confirm Route.
It is said that if they don't hear back from you in sixty seconds, they will consider the communications lost and if a clearance was involved, that clearance is canceled. I've not seen that in writing but the threat is clear: respond within a minute, use "STANDBY" if you must. When dealing with clearances, I usually hit the print button, send the acknowledge, and then read the contents. I figure I can always respond a second time if I have to.
[ICAO Doc 10037, ¶4.3.2.]
Note.— ATN-B1 aircraft use a CPDLC message response timer, which is set at 100 seconds upon receipt of the CPDLC uplink message. If the flight crew has not sent a response within this time:
Note.— For ATN B1 aircraft systems, if the flight crew does not send an operational response within 100 seconds after the RSPD-3 STANDBY was sent, the CPDLC uplink message will time out (refer to paragraph 18.104.22.168).
Note 1.— In the case of a RSPD-3 STANDBY response, the uplink message remains open until the flight crew responds with a RSPD-1 WILCO or RSPD-2 UNABLE. If the closure response is not received within a reasonable period of time, the controller is expected to query the flight crew per paragraph 22.214.171.124.
Note 2.— Transmission times for messages may vary for a number of reasons including the type of transmission media, network loading, or the criteria for transitioning from one media to another (e.g. VHF/Satcom). Operational response times may vary depending on workload and complexity of the instruction or clearance.
You don't have to worry about flying a Strategic Lateral Offset because your FMS will sequence the waypoints even if you are two miles away from the intended course. But if you are further than the tolerance allowed by your FMS, it may not sequence. If that happens, the position report will not be made.
Figure: Waypoint sequencing anomaly, from ICAO Doc 10037, figure 4-6.
[ICAO Doc 10037, ¶126.96.36.199]
As shown in [the figure], when an aircraft passes abeam a waypoint in excess of the defined sequencing parameter (refer to , paragraph F.7) for specific aircraft types), the FMS will not sequence the active waypoint. If the flight crew does not sequence the waypoint, incorrect information will be contained in ADS-C reports, CPDLC position reports and FMC waypoint position reports – the next waypoint in these reports will actually be the waypoint that the aircraft has already passed.
Some manufacturers published misinformation about latency timers that you should take note of it your CPDLC does not include such a device.
[NAT OPS Bulletin 2018-002, ¶2.1] The intention of the message latency monitor function is to prevent pilots from acting on a CPDLC uplink message that has been delayed in the network. The most serious of such cases would be the pilot executing a clearance that was no longer valid.
There have been instances with airlines and business jets receiving ATC instructions to climb via CPDLC that did not get delivered to the crew until the following flight. In at least one case the crew executed the climb causing a possible loss of separation.
[NAT OPS Bulletin 2018-002, ¶2.1] When the pilot receives the uplink CPDLC message SET MAX UPLINK DELAY VALUE TO [delayed message parameter] SECONDS he/she shall:
a) Send a positive response to ATC as prompted by the avionics (ACCEPT [ROGER]) regardless of whether the aircraft supports the latency monitor.
b) If the aircraft is equipped with a correctly functioning message latency monitor, enter the specified uplink delay into the avionics in accordance with the aircraft procedures. Some avionics will automatically set the delay value in accordance with the uplink message and do not allow for a manual input.
Refer to your aircraft manuals for specific responses. Three particular Gulfstreams provide examples of three possible reponses:
You can only have one active CPDLC connection, think of it as your actual air traffic control contact. But you can have two connections, usually the active connection and the "next."
[ICAO Doc 10037, ¶188.8.131.52.1.] An aircraft can have a maximum of two CPDLC connections established concurrently, each with a different ATSU. Only one CPDLC connection can be active at any given time; any second connection is inactive.
[ICAO Doc 10037, ¶ 184.108.40.206.2.] An ATSU system may request multiple simultaneous ADS contracts to a single aircraft, including one periodic and one event contract, which may be supplemented by any number of demand contracts. Up to five separate ground systems may request ADS contracts with a single aircraft.
When do you need to do a CPDLC position report? It depends! ADS-C might have you covered but some ATSU's want them anyway. The only way to know for sure is to check Appendix B of ICAO Doc 10037. For example, position reports with Gander Oceanic are not required because they don't ask for them in Appendix B:
Figure: Gander Oceanic Remarks, from ICAO Doc 10037, Appendix B.
Position reports are required with Mauritus because they do ask for them in Appendix B. (CDA is the "Current Data Authority")
Figure: Gander Oceanic Remarks, from ICAO Doc 10037, Appendix B.
[ICAO Doc 10037, ¶220.127.116.11] When using CPDLC to provide position information, the flight crew should report unnamed waypoints (latitudes/longitudes) using the ICAO format of nn[N/S]nnn[E/W] or, if both degrees and minutes are required, nnnn[N/S]nnnnn[E/W].
Note.— The flight crew and flight operations officers/dispatchers should not use the ARINC 424 format. ARINC 424 describes a 5-character latitude/longitude format for aircraft navigation databases (e.g. 10N40 describes a lat/long of 10N140W). The ATS unit may reject or be unable to process any downlink message containing waypoint names in the ARINC 424 format.
[Oakland Center Guidance, ¶3] Oakland OCA/FIR (KZAK) cannot accept position reports containing latitude and longitude (Lat/Long) in the ARINC 424 format, which is limited to five characters (e.g. 40N50). Position reports in the KZAK CPDLC service area containing Lat/Long waypoints will be accepted in complete latitude and longitude format only. Flights unable to send position reports in complete latitude and longitude format must accomplish position reporting via HF voice communications.
This holds true everywhere in the world. Air Traffic Control does not understand what you mean by "40N50" even if your FMS does. In that case, 40N050W would be called for.
[ICAO Doc 10037, ¶18.104.22.168]
[ICAO Doc 10037, ¶22.214.171.124]
Note.— In an ADS-C environment, the flight crew should not provide position reports or revised waypoint estimates by CPDLC or voice, unless otherwise instructed or under conditions in certain airspace as stipulated in AIP (or other appropriate publication)
Note.— Some ANSPs require a single CPDLC position report, even when in an ADS-C environment, to provide the controlling ATS unit confirmation that it is the CDA and the only ATS unit able to communicate with the aircraft via CPDLC (refer to Appendix B).
In general you should not provide position reports or revised waypoint estimates by CPDLC or voice unless you see something that tells you to do so. Append B can be misleading. The subject is only brought up in the North Atlantic region where you are explicitly told "For ADS-C flights, the flight crew should not submit position reports via voice to reduce frequency congestion, unless requested by aeronautical radio operator." Makes sense, but don't let that talk you into thinking now you need to do so in other regions because the same phrase is missing.
Note.— If the flight crew inserts non-ATC waypoints (e.g. mid-points) into the aircraft active flight plan and activates the change, the aircraft system may trigger an ADS-C waypoint change event report at the non-ATC waypoint, or include information about the non-ATC waypoint in the predicted route group, as well as the intermediate and fixed projected intent groups. As a result, the ADS-C report will include information about the non-ATC waypoint, which is not expected by the ATC ground system.
Note.— If the flight crew activates a non-ATC cleared route into the aircraft system, the ADS-C reports will include information that will indicate the aircraft is flying a route that is deviating from the cleared route.
If you have an ARINCDirect account, simply log on to "ARDC" or "ARDD" and wait. It should log you in for five minutes, just as if you were oceanic.
If you need to deviate for weather while using CPDLC, it pays to know Chapter 4 of ICAO Doc 10037. Be careful you ask for a weather deviation versus an offset.
Figure: Offset and weather deviation, from ICAO Doc 10037, Figure 4-2.
[ICAO Doc 10037 ¶126.96.36.199]
Note.— CPDLC offers timely coordination of weather deviation clearances. However, the flight crew may deviate due to weather under the provisions of ICAO Doc 4444, paragraph 15.2.3. The extent to which weather deviations are conducted may be a consideration when applying reduced separations.
Note.— The difference between a weather deviation and an offset affects how ATC separate aircraft.
You have to stay on your offset course precisely; you can "meander" as necessary up to your cleared distance when cleared for a weather deviation.
[ICAO Doc 10037 ¶188.8.131.52]
Figure: Weather deviation clearance up to 20 nm, from ICAO Doc 10037l, Figure 4-3.
Figure: Subsequent weather deviation up to 20nm left, from ICAO Doc 10037, Figure 4-4.
Figure: Subsequent weather deviation up to 30nm right, from ICAO Doc 10037, Figure 4-5.
Note.— The ATSU applies the appropriate separation standards during the maneuvers.
[ICAO Doc 10037 ¶184.108.40.206.1] When requesting a deviation on either side of route, the flight crew should request a weather deviation left and right of route using LATD-2 REQUEST WEATHER DEVIATION UP TO (lateral deviation) OF ROUTE.
[ICAO Doc 10037, ¶220.127.116.11.1] When the flight crew no longer needs the deviation clearance and is back on the cleared route, the flight crew should send a LATD-4 BACK ON ROUTE report.
Note.— If a LATD-4 BACK ON ROUTE report is received while the aircraft is still off route, the incorrect information provided to ATC may affect the separation standards in use. Alternatively, the flight crew may consider requesting a clearance direct to the waypoint – on receipt of the uplink clearance, the procedure specified in item a) above applies.
If you've taken a formal class in CPDLC you will have been told all about the ICAO Gold Manual and how to find out what your CPDLC and ADS-C obligations are anywhere in the world. You really should have the manual but if you don't, the information is in JeppFD. The problem is that it is buried deep!
The definitive answer is Appendix B of ICAO Doc 10037, also known as the "GOLD" manual because of its name, the Global Operations Data Link manual. In case you don't have that, you can also look on JeppFD where it is buried where you are least likely to find it. It used to take me 10 minutes or more to find it, so I did a series of screen grabs.
Let's say you are flying from EGLF to KHPN and want to look up the CPDLC codes. Select the "publications" icon on the left bar:
That should bring up some information about the route. Select "Pubs" instead:
Here's where I usually go wrong when flying over the Atlantic by selecting Atlantic. Don't do that, there is no En Route Data for the Atlantic there, you need to select Europe if you want Atlantic en route data. In other parts of the world it is more straightforward:
Now select the applicable airway manual. This should be obvious, but in the case of the Atlantic, you need to select Europe:
Now select the appropriate En Route Data page:
Now you should see a "CPDLC Coverage" page. If you don't, try a nearby region instead:
Now you should see the coverage map and below that a table with each sector.
EU Commission Regulation No 29/2009, 16 January 2009
ICAO Annex 10 - Vol III - Aeronautical Communications, Communications Systems, International Standards and Recommended Practices, Annex 10 to the Convention on International Civil Aviation, Vol III, Second Edition, July 2007
ICAO Doc 4444 - Air Traffic Management, 16th Edition, Procedures for Air Navigation Services, International Civil Aviation Organization, October 2016
ICAO Doc 4444, Amendment 9 to the PANS-ATM, 15 June 2020
ICAO Document 10037 - Global Operational Data Link (GOLD) Manual, First Edition, 2017
NAS Data Communications Guide, FAA, May 15, 2019
NAT OPS Bulletin 2018-02, Latency Monitor, Rev 01, 4 June 2018
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