SECTION 15 Controller–pilot data link communication (CPDLC) procedures

SERA.15001 Data link initiation and data link initiation failure - Regulation (EU) 2023/1772

1. The logon address associated with an air traffic services unit shall be published in the national aeronautical information publications (AIPs).
2. Upon receipt of a valid data link initiation request from an aircraft approaching or within the data link service area, the air traffic services unit shall accept the request and, if able to correlate it with a flight plan, shall establish a connection with the aircraft.
3. The air traffic services provider shall establish procedures to resolve, as soon as practicable, data link initiation failures.
4. The aircraft operator shall establish procedures to resolve, as soon as practicable, data link initiation failures.

SERA.15005 Establishment of CPDLC - Regulation (EU) 2023/1772

1. CPDLC shall be established in sufficient time in advance to ensure that the aircraft communicates with the appropriate air traffic control unit.
2. Information concerning when and, if applicable, where the air or ground systems should establish CPDLC shall be published in aeronautical information circulars or publications.
3. The pilot shall be able to identify the air traffic control unit that provides the air traffic control service at any time while the service is being provided.

SERA.15010 Transfer of CPDLC - Regulation (EU) 2023/1772

1. When CPDLC is transferred, the transfer of voice communication and CPDLC shall commence concurrently.
2. When an aircraft is transferred from an air traffic control unit where CPDLC is available to an air traffic control unit where CPDLC is not available, the termination of CPDLC shall commence concurrently with the transfer of voice communication.
3. The air traffic controller shall be informed when attempting a transfer of CPDLC resulting in a change in data authority if there are data link messages for which a closure response has not been received. When the air traffic controller decides to transfer the aircraft without receiving pilot responses to the uplink message(s) outstanding, the air traffic controller shall normally revert to voice communication to clarify any ambiguity associated with the uplink message(s) outstanding.

SERA.15015 Construction of CPDLC messages - Regulation (EU) 2023/1772

1. The text of CPDLC messages shall be composed in standard message format, in plain language, or in abbreviations and codes. Plain language shall be avoided when the length of the text can be reduced by using appropriate abbreviations and codes. Non-essential words and phrases, such as expressions of politeness, shall not be used.
2. The air traffic controller and the pilot shall construct CPDLC messages using standard message elements, free text message elements, or a combination of both. The use of free text message elements by air traffic controllers or pilots shall, be avoided.
3. When the implemented CPDLC message set does not provide for specific circumstances, the competent authority may determine, in consultation with operators and other air traffic services providers, that it is acceptable to use free text message elements. In such cases, the competent authority concerned shall define the display format, intended use and attributes for each free text message element.
4. The composition of a CPDLC message shall not exceed five message elements, only two of which may contain the route clearance variable.
5. Construction of multi-element CPDLC messages:
   1. When a multi-element CPDLC message requires a response, the response shall apply to all message elements.
   2. When a single message element clearance or any part of a multi-element clearance message cannot be complied with, the pilot shall send an “UNABLE” response for the whole message.
   3. The controller shall respond with an “UNABLE” message that applies to all elements of the request when no element(s) of a single or multi-element clearance request can be approved. The current clearance(s) shall not be restated.
   4. When a multi-element clearance request can only be partially accommodated, the controller shall respond with an “UNABLE” message applying to all the message elements of the request and, if appropriate, include a reason and/or information on when clearance may be expected.
   5. When all elements of a single or multi-element clearance request can be accommodated, the controller shall respond with clearances corresponding to each element of the request. This response shall be a single uplink message.
   6. When a CPDLC message contains more than one message element and the response attribute for the message is “Y”, when utilised, the single response message shall contain the corresponding number of replies in the same order.

SERA.15020 Responding to CPDLC messages - Regulation (EU) 2023/1772

1. Unless otherwise specified by the competent authority, voice read-back of CPDLC messages shall not be required.
2. Except when correction of the CPDLC message transmitted is needed, when a controller or a pilot communicates via CPDLC, the response shall normally be via CPDLC. When a controller or a pilot communicates via voice, the response shall normally be via voice.

SERA.15025 Correction to CPDLC messages - Regulation (EU) 2023/1772

1. When a correction to a CPDLC message is deemed necessary or when the contents of such a message need to be clarified, the air traffic controller and the pilot shall use the most appropriate means available for issuing the correct details or for providing the necessary clarification.
2. When voice communication is used to correct a CPDLC message for which no operational response has yet been received, the controller’s or the pilot’s voice transmission shall be prefaced by the phrase: “DISREGARD CPDLC (message type) MESSAGE, BREAK” – followed by the correct clearance, instruction, information or request.
3. When referring to and identifying the CPDLC message to be disregarded, caution shall be exercised in its phrasing so as to avoid any ambiguity with the issue of the correction to the clearance, instruction, information or request.
4. If a CPDLC message that requires an operational response is subsequently negotiated via voice, an appropriate CPDLC message closure response shall be sent to ensure proper synchronisation of the CPDLC dialogue. This may be achieved either by explicitly instructing the recipient of the message via voice to close the dialogue or by allowing the system to automatically close the dialogue.

SERA.15030 Controller data link communication procedures for emergencies, hazards, and CPDLC equipment failure - Regulation (EU) 2023/1772

1. When an air traffic controller or a pilot is alerted that a single controller–pilot data link communication message has failed, the air traffic controller or the pilot shall take one of the following actions, as appropriate:
   1. via voice, confirm the actions that will be taken with respect to the related dialogue, prefacing the information with the phrase: “CPDLC MESSAGE FAILURE”;
   2. via controller–pilot data link communication, reissue the controller–pilot data link communication message that failed.
2. Air traffic controllers that are required to transmit information concerning a complete controller–pilot data link communication ground system failure to all stations likely to intercept should preface such a transmission by the general call: “ALL STATIONS CPDLC FAILURE” – followed by the identification of the calling station.
3. When controller–pilot data link communication fail and the communication reverts to voice, all CPDLC messages outstanding shall be considered not delivered and the entire dialogue involving the messages outstanding shall be recommenced by voice.
4. When controller–pilot data link communication fails but is restored prior to a need to revert to voice communication, all messages outstanding shall be considered not delivered and the entire dialogue involving the messages outstanding shall be recommenced via CPDLC.

SERA.15035 Intentional shutdown of CPDLC system - Regulation (EU) 2023/1772

1. When a system shutdown of the communications network or the CPDLC ground system is planned, a NOTAM shall be published to inform all affected parties of the shutdown period and, if necessary, the details of the voice communication frequencies to be used.
2. Aircraft in communication with the ATC units shall be informed by voice or CPDLC of any imminent loss of the CPDLC service.

SERA.15040 Discontinuation of the use of CPDLC requests - Regulation (EU) 2023/1772

1. When a controller requires all stations or a specific flight to avoid sending CPDLC requests for a limited period of time, the following phrase shall be used: ((call sign) or ALL STATIONS) STOP SENDING CPDLC REQUESTS [UNTIL ADVISED] [(reason)].
2. The resumption of the normal use of CPDLC shall be advised by using the following phrase: ((call sign) or ALL STATIONS) RESUME NORMAL CPDLC OPERATIONS

SERA.15045 Use of CPDLC in the event of air–ground voice communication failure - Regulation (EU) 2023/1772

The existence of a CPDLC connection between an air traffic services unit and an aircraft should not prevent the pilot and the air traffic controller concerned from initiating and performing all the required actions in the event of air–ground voice communication failure.

SERA.15050 Testing of CPDLC - Regulation (EU) 2023/1772

Where the testing of CPDLC with an aircraft could affect the air traffic services being provided to the aircraft, coordination shall be effected prior to such testing.