Controller-pilot datalink communications at our Maastricht UAC

At EUROCONTROL's Maastricht Upper Area Control Centre (MUAC), we have been operating controller-pilot datalink communications (CPDLC) since 2003 to help mitigate the shortcomings of traditional voice communication.

CPDLC - an air/ground datalink application - offers the benefit of an additional, independent and secure channel, which reduces the strain on busy VHF sector frequencies, transmitting clear messages with no risk of misunderstandings. Use of the system increases capacity and safety; it improves the day-to-day efficiency of communications between controllers and pilots.

Currently, more than 50% of the traffic crossing the MUAC airspace receives some CPDLC clearances. We use it as a secondary communications medium, complementing VHF voice communications, which remains the primary means for tactical communication.

Additionally, since 2022, MUAC also supports ADS-C connections. ADS-C enables aircraft to automatically log on and downlink key aircraft intent flight management system information (e.g. the extended projected profile) to the MUAC system, which can be displayed on controllers’ screens.

As of February 2020, with some exemptions, CPDLC is required to operate above FL285 in Europe. In MUAC airspace, as indicated in AIP, every aircraft included in a log-on list is expected to log-on if technically capable.

To operate CPDLC with MUAC you need to have state of the art aeronautical telecommunications network (ATN) datalink avionics on-board your aircraft.

The MUAC CPDLC log-on address (EDYY) offers datalink services 24/7 to all aircraft equipped with the appropriate CPDLC avionics in the upper airspace (above FL 245) of:

• the Brussels Upper Flight Information Region (EBUR UIR),
• the Hannover Upper Flight Information Region (EDVV UIR), and
• the Amsterdam Flight Information Region (EHAA FIR).

Our CPDLC operations support the following message types:

• Datalink integration capability (DLIC)
  Log-on is a prerequisite for operational datalink services via the exchange of address information in order to establish flight plan/address associations in the ATC system, ensuring correct message delivery.
• Air traffic control clearance (ACL)
  ACL enables the air traffic controller to issue climb/descent clearances, direct clearances, turns and headings and SSR instructions, or to reply to aircrew requests. The ACL service also enables the aircrew to make operational requests and to respond to ATC clearances and instructions.
• Air traffic control communication management (ACM)
  ACM supports automated controller/aircrew communications hand-off, via both R/T and datalink, from one sector/centre to another.
• Air traffic control microphone check (AMC)
  AMC provides air traffic controllers with the capability to uplink an instruction to check that pilots are not inadvertently blocking a voice frequency/channel with a “stuck microphone switch”.

Follow this procedure to ensure proper operations:

• Flight-plan information
  CODE/... [ATN] must be provided in Field 18 of the flight plan, to ensure the correlation of datalink messages. ATN datalink ('J1') capability should be indicated in Field 10. If the aircraft does not have the ATN CPDLC capability, but it is exempted from the obligation, DAT/CPDLCX should be included in Field 18.
• Initiation
  Logging on to the system is a prerequisite in order to establish the aircraft’s flight plan and ensure correct message delivery. The aircraft can already log on 10 to 15 minutes before entering the airspace of MUAC, if not logged on already to the upstream ANSP. The ground system then initiates a CPDLC connection and the aircraft responds to the ground system with a message which is automatically generated by the airborne avionics.
• Initiation time
  After completion of the CPDLC initiation, the ground system attempts CPDLC connection some 10 minutes before the aircraft enters the airspace. For aircraft departing from an airport located close to the airspace managed by MUAC, the CPDLC connection will only occur above FL 150, to support sterile cockpit operations below FL100.
• Current data authority (CDA)
  Following confirmation of the CPDLC connection, the ground system automatically receives a current data authority (CDA) notification, informing ATC that the aircraft is ready to conduct CPDLC. During the log-on phase, the CPDLC connection and CDA sequence are normally conducted outside the MUAC airspace. Aircraft must be under the control of a controller in Maastricht before any actual CPDLC exchanges can occur. Besides the voice trigger of the instruction to "Contact Maastricht on ...", aircrew can also tell from the CDA change that they have come under the control of MUAC.

To maximise service delivery in congested airspace, we apply, together with Skyguide and DFS, CPDLC logon list filtering.

This ensures that avionics showing a high failure rate as defined in the CPDLC Safety Case will be blocked in order to improve end-to-end datalink performance for the other users. Configurations with such a high failure rates are identified by the EUROCONTROL Network Manager Data Link Performance Monitoring Function (DPMF).

These ongoing performance issues are one of the reasons why up-links for CONTACT instructions are used only two-thirds of the time - in less critical cases which, however, alleviating the frequency load considerably.