Controller-Pilot Data-Link communications

Published on Thursday 21 March 2019

DataLink, also named CPDLC (Controller-Pilot DataLink Communications), is an airborne communication technology based on data exchange implemented between 2015 and 2016 in DSNA’s 5 ACCs.

Since May 2016, air traffic controllers are able to provide frequency-transfer instruction by data-link to equipped aircraft over FL 195 (6,000 meters), offering data-link IOC - Initial Operating Capabilities (connection, stuck microphone check, frequency handover) to its customers in all its upper airspace.

On the 1st trimester of 2019, Bordeaux and Brest ACCs step up to  Full Operating Capability (FOC) with the ability to provide ATC clearances to pilots in their airspace through data-link technology.

According to the requirements of the COMMISSION REGULATION (EC) N° 29/2009, revised by (EC) N° 2015/310 lying down requirements for CPDLC services provision, data exchange using the data-link technologies forms the basis of advanced automated functions developed within the European SESAR technology program. With data-link, air traffic management can be safer and more efficient with a reduction of the number of messages to be repeated on the frequency, frequency transfer achieved at the most opportune moment and use of preformatted messages.

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Bordeaux and Brest ACCs have seen the traffic dramatically grow during the summer months and particularly along the South West axis. Combined with other important holiday routes (UK to Italy or Spain, Spain to Italy, etc.), the increase in demand explains most of the delays caused by ATC capacity issues in Bordeaux and Brest ACCs’ control sectors. DSNA has prioritized the implementation of Full Operating Capability Datalink in theses ACCs as an anticipated action to meet seasonal peak in traffic demand. The FOC datalink is a tangible means to deliver capacity improvements.

DataLink FOC phase – ATC clearances to pilots in addition to IOC services already implemented in all 5 French ACCs

What does FOC Datalink consist of (FulI Operating Capability)?

In addition to the 3 DataLink services already accessible to air crew with IOC (Initial Operating Capability), the FOC implements:

  • ACL (ATC Clearance): Allow controllers to issue ATC clearance such as: flight level (CFL), heading, direct route, speed.

Example of CFL clearance

Screenshot of an example of CFL clearance
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If the acknowledge message from the cockpit takes too long to revert to the ATC unit, a “REVERT TO VOICE” alert will appear. The controller will then have to contact the pilot and use a specific phraseology: “[call sign] DISREGARD CPDLC [LEVEL/ROUTE/SPEED] CHANGE MESSAGE, BREAK, [message]”.

DataLink IOC phase – Initial Operating Capability

Three different services are made accessible to air crew via Datalink:

  • DLIC (DataLink initiation capability):  Allows logging on and connecting to the service.
  • AMC (ATC microphone check) :  in case of stuck microphone situations.
  • ACM (ATC communications management) : in clear terms datalink frequency handovers.

On the controller radar screen, a specific icon (lightning symbol) will be displayed on the aircraft label indicating its eligibility to Datalink frequency handover. By simply clicking on it, the following sector and its frequency appear. The controller can decide to send the information over to the aircraft.

A “CONTACT [atsUnit][frequency]” message is sent to the crew and a box surrounds the icon to indicate that the transfer is in progress.

Example of frequency handover

Screenshot of an example of frequency handover
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If the acknowledge message from the cockpit takes too long to revert to the ATC unit, a “REVERT TO VOICE” alert will appear. The controller will then have to contact the pilot and use a specific phraseology: “[call sign] DISREGARD CPDLC FREQUENCY CHANGE MESSAGE, BREAK [message]”.

The Datalink ACM secures and facilitates the transmission of the correct frequency to contact: the digits transmitted are directly displayed into the Radio Management Panel on board.

A simple and consistent procedure

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Benefits for airlines and crews


  • Cuts down on voice traffic and radio frequency congestion,
  • Enables ATCO to focus on its elementary tasks: to provide safe and efficient separations and fluid sequences,
  • Reduces the number of misunderstandings.
  • Secure CFL transmission and the frequency to contact as it is directly available in the radio management panel on board.

More efficient communications

  • Reduces repeated transmissions (no more hearback/readback),
  • Frequency handovers at the optimum time,
  • Simplified communications through predetermined responses.
  • Fatigue reduction of crews and ATCOs by using text message instead of voice.


  • Fast and more accurate communications with ATCOs.
  • 75% CPDLC equipage rate is estimated to generate +11% ATC capacity

What remains of human factor?

Voice communications prevail on any Datalink communications and are at all-time available. Voice remains in any case the primary means of communications.
First line operators (ATCO and pilot) are the only ones that can assess the need to switch back to voice interactions and the moment when the electronic environment will deliver its full potentiality.

The ACM service (Datalink frequency handovers) is to be used in standard air traffic control situations, outside any time pressure and when the following sector is clearly identified and acknowledged as being the right one.

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