Frequently Asked Questions
This page is being updated to add new questions and order / group these FAQs in different categories, such as "For Flight Crew: Ops Use of datalink, Why, ...", "For Operators: FPL related, ...", "General information on datalink".
Recently added FAQs are flagged with "NEW" and FAQs for which the response has been updated with some new information are flagged with "CHANGED".
Within seconds after a check in via voice, pilots receive an instruction by CPDLC. Why would this not be combined since voice contact is made anyway? - NEW
Because: 1) it’s quicker than voice for the controller who needs to make the input anyways to update the system with the given clearance and 2) it avoids further cross-transmissions, misunderstandings and say-again-s.
Within a CPDLC controlled area pilots receive alternating instructions via CPDLC and voice, what is the reasoning behind using voice or CPDLC? - NEW
Because: 1) Pilots might not be aware if a CPDLC-instruction have already timed out due to network delay – one might go through the other might not, all they see is one comes via CPDLC the other via voice, and 2) Time-critical instructions are not supposed to be transmitted via CPDLC – so when ATCO needs the plane down NOW before a traffic in the way in 3-4 minutes, ATCO can’t allow for a timeout or network delay of 2 minutes
Why are there are certain instructions which are not implemented/don’t exist in CPDLC at different ANSPs and the only way to use them is via voice? - NEW
Work is ongoing towards harmonization of the ground messages, so that the same message set will be available and used in all European airspace.
In some cases, part of the instruction is given by voice (turn… to heading…) and within seconds an instruction by CPDLC (climb …). What is the reasoning behind using voice and/or CPDLC for instructions which seemingly could be combined into one or the other? - NEW
ATCOs may need the pilot to turn NOW to get out of the way of traffic and when ATCO sees plane turning, ATCO gives plane the climb which is non-time-critical because there is lateral separation from the traffic via heading. ATCO can’t give a turn and climb together because ATCO can’t guarantee separation until plane actually turned.
In some routes (AMS going south-east, i.e. Rhein Radar upper) there are a multitude of contact/ next/ current messages, followed by actual voice contact. In this case CPDLC is not reducing workload for pilots because 3 CPDLC messages substitute 1 voice message (namely contact…). Why? - NEW
Unfortunately, this can’t change. To the controllers it is still reducing workload, therefore it is increasing capacity and reducing the need for regulations/delays.
Most of the CPDLC messages trigger a pling-plong. Would it be possible to simplify a handover and reduce the number of sound triggers to only instructions? - NEW
This is a valid concern about the HMI. ECTL has already invited AEEC (DLUF) to look at the datalink HMI reported issues and DSG OFG is looking at developing recommendations. Such improvements need to be requested by the airlines to the manufacturers. Also to note that some (new) aircraft don’t warn anymore on system messages which means that system messages (CURRENT ATC UNIT, NEXT DATA AUTHORITY, …) only update the systems and do not cause a “ding”
What should be entered in the flight plan? - CHANGED
A one-page reminder of what to file in the flight plan is available to download here.
Operators of CPDLC capable aircraft, equipped with either FANS 1/A or ATN-B1, shall insert in Item 10 of the ICAO flight plan form, one or more of the following items:
- J1 for CPDLC-ATN-B1 VDLM2
- J2 for CPDLC-FANS 1/A HFDL
- J3 for CPDLC-FANS 1/A VDL MODE A
- J4 for CPDLC-FANS 1/A VDL MODE 2
- J5 for CPDLC-FANS 1/A SATCOM (INMARSAT)
- J6 - Not applicable currently
- J7 for CPDLC-FANS 1/A SATCOM (Iridium)
Operators of CPDLC capable aircraft equipped with FANS 1/A and ATN-B1 shall insert item J1 and one or more of the items J2 to J7, as applicable, in Item 10 of the ICAO flight plan form .
Flights, planning to use CPDLC ATN-B1, shall include in Item 18 of the flight plan the indicator CODE/ followed by the 24-bit aircraft address (expressed in the form of alphanumerical code of six hexadecimal characters). Example: CODE/ F00001
Flight plans should not contain J1 if the crew is not trained and ready to use CPDLC.
Flights, planning to use CPDLC FANS 1/A, shall include in Item 18 of the flight plan the indicator REG/ followed by the nationality or common mark and registration mark of the aircraft, if different from the aircraft identification in Item 7.
For flights, conducted wholly or partly in the EUR CPDLC airspace specified in 3.3.1.1 (of Doc 7030/5), and not equipped with CPDLC ATN-B1, but which have been granted an exemption, either automatic or by EC Decision, should include the letter “Z” in item 10 and the indicator “DAT/CPDLCX” in item 18 of the flight plan. (Note this answer used to say RMK/CPDLCX but has been amended to align with the EASA SIB 2020-03 regarding exemptions). This also applies to aircraft that are operating with inoperative data link equipment which is under conditions specified in an applicable MEL. For flights needing to file both 1FANS1PDC as well as CPDLCX it is recommended to enter the 'DAT/' only once e.g. DAT/CPDLCX 1FANS2PDC although the NM systems will accept entries with mulitple '/DAT' entries e.g. DAT/1FANS2PDC DAT/CPDLCX.
Flights made by aircraft that are both exempt and equipped should file J1 and the aircraft code as described above if they intend to use CPDLC or file Z and DAT/CPDLCX as described above if they do not intend to use CPDLC, but not both.
To avoid an automatic rejection of the logon/notification, the pilot should ensure that the Flight Number and Destination/Arrival parameters contained in the logon message are exactly the same as the Flight Number and Destination/Arrival parameters filed in the flight plan.
Listed below are some typical scenarios and an illustration of what should be filed for an aircraft with the ICAO code ‘1CA0DE’:
* The aircraft is CPDLC/ATN equipped and the crew are trained
File ‘J1’ in field 10 and ‘CODE/1CA0DE’ in field 18
* The aircraft is CPDLC/ATN equipped but the crew are not trained
Nothing should be filed for CPDLC/ATN. This flight is in contravention of the regulation.
* The aircraft is not exempt and is not capable of CPDLC over the ATN
Nothing should be filed for CPDLC/ATN. This flight is in contravention of the regulation.
* The aircraft is exempt
File ‘Z’ in field 10 and ‘DAT/CPDLCX’ in field 18
* The aircraft is exempt but capable of CPDLC over FANS 1/A
File the appropriate J codes for FANS1/A capability and ‘Z’ in field 10 and ‘DAT/CPDLCX’ in field 18
* The aircraft is exempt but capable of CPDLC over the ATN
File either i) ‘J1’ in field 10 and ‘CODE/1CA0DE’ in field 18 or ii) ‘Z’ in field 10 and ‘DAT/CPDLCX’ in field 18, depending on whether or not the crew intend to use CPDLC/ATN on this particular flight
* The aircraft is generally CPDLC/ATN equipped but for a given flight has a CPDLC equipment, which is temporarily inoperative
Per the EASA guidance, "in accordance with Article 3(3) flights with equipment temporarily inoperative may continue to operate within the applicable airspace. However, these operations are to be within the limits and conditions of the MEL (Minimum Equipment List), and the flight plan should also reflect that the aircraft is exempt during this temporary inoperative period. If the operator decides to declare its CPDLC exempt status, flight plan should reflect that the aircraft is exempted by including letter “Z” in item 10 and the indicator “DAT/CPDLCX” in item 18 of each flight plan." (extracted from the EASA datalink FAQs)
What will the NM do when an airline files a flight plan with a route above FL285 in data link airspace but does not file ‘J1’ to indicate it is capable of performing CPDLC over the ATN or ‘DAT/CPDLCX’ to indicate that it is exempt from the data link regulation?
NM expects aircraft operators to comply with the regulation, but flight plans are not be rejected at this stage. NM will monitor the situation and will take action as needed at the request of ANSPs or competent authorities.
If my aircraft are not on the Logon List are they still considered compliant with the data link regulation and will they suffer any restrictions?
The Logon List is an operational response by some ANSPs to improve the performance of datalink operations by not allowing aircraft that are observed to perform poorly from logging on. Whether or not an aircraft is on the Logon list does not effect whether an aircraft is considered compliant with the regulation. Aircraft not on the Logon list will still be considered compliant with the regulation if they are equipped in accordance with the regulation. However aircraft not on the Logon list are not permitted to logon to use data link by the ANSPs that implement the Logon List. There are currently no plans from the Logon List ANSPs to apply any restrictions to aircraft not on the Logon List, other than not allowing those aircraft to logon to data link.
Is my aircraft exempt?
All queries about the exemption status of an aircraft should be addressed to EASA at the following email address: [email protected]
Is there an EASA FAQ for data link?
The EASA FAQs regarding datalink can be found here.
Who do I need to notify that my aircraft is exempt?
EASA recommends the operators to notify their Competent Authorities.
Considering that the DLS IR mandates the provision of CPDLC above FL285, what are the rules for use of CPDLC below FL285? - CHANGED
A number of States in addition to complying with the DLS IR, have implemented and operationally use CPDLC below FL285. The flight level above which datalink services are offered is published in the national AIPs. In general the procedures to use CPDLC are the same in all airspaces identified in the AIPs as datalink airspace and any local operating procedures, if the case, will be detailed in the relevant AIPs.
What are the provisions for execution of instructions that I receive via CPDLC? - CHANGED
Briefly put, the flight crew should first send the appropriate CPDLC response to the instruction, and afterwards execute the instruction immediately. Section 8.13 of the LINK2000+ Flight Crew Operational Guidance document contains detailed information on this subject.
What is the exact meaning of “MESSAGE NOT SUPPORTED BY THIS ATS UNIT”?
The ACC/UAC controlling you at the moment does not support usage of the particular request that you have downlinked. This will typically be the case in States that have decided to implement only those messages that are required as a minimum.
Where can I find information about the data needed for a manual re-logon to the same ACC/UAC for which the CPDLC connection has been unexpectedly terminated, if necessary?
The message archiving/logging function of your HMI should contain the necessary information in the latest UM183 message - CURRENT ATC UNIT [facility designation], [facility name], facility function] that you received.
What should I do if my downlinked request times out?
You will receive an error message from the ground. At the same time the controller will be notified and may possibly handle your request via voice. All depending on the nature of your request you may also decide to restate your request via CPDLC.
Can I send downlink requests as soon as I have established the CPDLC connection (CDA)?
No, you should wait until you have received the UM 183 message - CURRENT ATC UNIT [facility designation], [facility name], facility function]. Note: Technically speaking – you could send downlink requests earlier, but operationally it wouldn’t be acceptable as you would be still under the control of the previous controller (ATC) – on voice. Your ‘first’ CPDLC connection will normally happen some time before you are under control of the first CPDLC-equipped ACC/UAC in the DLS IR airspace, any requests that you might downlink will result in the following error message from the ground system: CPDLC TRANSFER NOT COMPLETED – REPEAT REQUEST.
How do I know which ACC/UAC I have to manually log on to? - CHANGED
Your flight planning department will normally make this information available to you, but in general terms it will always be the first ACC/UAC of the airspace covered by the DLS IR that your flight encounters. A European map with the four letter ICAO codes of these datalink operational centres is provided in the "Deployment Status" page of this wiki to support the flight crew identifying which centres they need to manually log on for the first time or re-log on, after a failed automatic forward of the logon by the ground.
Do I have to manually log on to each ACC as I move along? - CHANGED
In general, you should only need to log on to the first ACC/UAC of the airspace covered by the DLS IR that your flight passes. Ground system automation will ensure that relevant details are forwarded between the ACCs concerned as your flight progresses.
However, there are still some centres, in which the automatic forwarding of the logon information (LOF/NAN) is not working. In these cases, the crew will have to log on again to the new downstream centre. The European map in the "Deployment Status" page of this wiki identifies the centres where datalink is operational and also the centres where the automatic forward of the logon information (LOF/NAN) is not working.
How do I know that I am within VDL2/ATN coverage and what is the right time to manually logon to an ACC?
The VDL2/ATN air-ground network covers the geographical area of the Implementing Rule. When the aircraft is in sight of a VDL2/ATN signal, an indication is provided on the aircraft’s HMI and is implementation specific (e.g. “ATN is available”). The appropriate time to initiate a manual log-on request, prior to entering the DLS IR airspace may vary, but will generally be between 10 and 20 minutes.
Note: There are still some areas where the CPDLC coverage may necessitate one or more re-logons as the flight progresses. ECTL monitors the full operational use of the logon information automatic forwarding by the ground and the status is current status is depicted in the "Deployment Status" page in this wiki.
If there is an aircraft change at the last minute, will this have to be disseminated through a CHG message, indicating the changed 24bit address of the replacement aircraft?
Yes, absolutely. Failure to do so will prevent you from logging on successfully to the ground system since your logon will simply be rejected. In the event of a mismatch between the 24-bit aircraft address in the flight plan and that of the aircraft trying to log on, the logon is rejected. This ground system behaviour was designed for safety reasons to ensure that data link exchanges only take place with the intended aircraft.
How do I indicate that I am exempted from the DLS IR – and do I have to?
If you are exempted from the DLS IR (either automatically by virtue of one of the cases listed in Article 3, para 4 of the rule itself or by approval obtained through application) you must indicate this by inserting the letter Z in Item 10a of the FPL, and then inserting the indicator DAT/ followed by the descriptor CPDLCX in Item 18, resulting in: DAT/CPDLCX. A 2009 amendment to ICAO Regional Supplementary Procedures (SUPPs) – Doc 7030/5 (Serial No.: EUR/NAT-S 09/03-EUR 2-4 and 3-2) contains the relevant provisions.
Where can I find Contact Management (CM) address information?
The Registry of the ATN NSAP (CM) addresses is maintained by the European ICAO EUR Planning group of the AST TF (Aeronautical Fixed Service To SWIM Transition Task Force). The document can be downloaded from the ICAO Paris Office and information on the operational ATN NSAP addresses is provided in the Deployment Status page of this wiki.
Where can I obtain information about the data link service provisions and procedures of each individual ACC/UAC?
Each State publishes the data link provisions, starting date of data link operations and relevant operational information by means of an Aeronautical Information Circular (AIC) or Aeronautical Information Publication (AIP). An AIC is an advanced notice of changes to the AIP.
Note: Information on harmonized procedures can be found in the LINK2000+ ATC and Flight Crew Operational Guidance documents.
What parameters should the ANSPs monitor to monitor the quality of service?
A proposed set of metrics for ANSPs to use as the basis for reporting the quality of service to their regulators is available here .
What's the difference between the DPMG and the DSG? -CHANGED
Both DPMG and DSG ae addressing datalink (as their name replies) aspects. However, the two groups are complementary and do not overlap and datalink stakeholders are encouraged to attend and follow both groups.
DPMG is a group established by EUROCONTROL/NM following the request and mandate by the EC aiming to support performance monitoring and reporting (Datalink Performance Monitoring Function/DPMF). A key task for DPMG is to monitor the datalink performance in Europe and develop reports in coordination with the concerned stakeholders, for the use of the stakeholders themselves but also for other bodies such as EASA, EC NM Board etc. More information on the DPMF/DPMG is available in the DPMG OST at https://ost.eurocontrol.int/sites/DPMF
DSG is a group established by EASA, EUROCONTROL and SDM, aiming to push for solutions to identified/pending/new problems encountered by stakeholders in the datalink implementation. DSG brings together all relevant datalink stakeholders (Users: Controllers and Pilots, CSPs, industry), EASA, NSAs, …) aiming to collectively work on identifying and implementing solutions to datalink problems. Participation in/following of DSG should benefit all stakeholders who are implementing datalink with the aim to identify solutions to their existing problems and benefit from awareness of problems encountered by other stakeholders. More information on the DSG is available in the DSG OST at https://ost.eurocontrol.int/sites/DSG.
How was the target PA rate of 1 PA per 100 hours derived?
Initially the PA rate was measured as the percentage of CPDLC sessions that ended with a Provider Abort. However since the length of CPDLC sessions can vary quite significantly between different centres and the probability of suffering a PA is related to the length of a CPDLC session, it was decided that a PA rate related to the duration of CPDLC sessions was a better metric for making comparisons between different ATC centres. Since there is no acceptable PA rate defined in the industry standards a target value was derived from the ED120 requirement for Continuity as described below, based on the assumption that a PA represents a loss of communication for 6 minutes.
The continuity requirement states that 99.9% of transactions must complete before the expiration timer. So if we assume 10 transactions per hour (as ED120 does when assessing risk), then a single PA in an hour would result in the loss of one transaction i.e. given 10 transactions in 60 minutes then in the six minute period of the PA we would expect one transaction to fail. So each PA per hour would imply a 10% reduction in continuity, hence in order to achieve the desired continuity of 99.9% a PA rate of 1 PA per 100 hours is required and this is the target PA rate that has been adopted.
How should an ANSP provide the datalink logs (LISAT data) data to NM?
The DPM uses the CM and CPDLC application level logs from the ANSPs in order to support its performance monitoring tasks. The LISAT data need to provided in a specific XML format and they uploaded to a specific FTP site or send to NM via newPENS. More details is provided in a the file. ANSPs are invited to contact the NM datalink team.