Frequently Asked Questions (FAQ) on CPDLC

Are different CPDLC technologies supported at Maastricht?

Yes. Maastricht operates a multi-stack system, allowing it to communicate with both ATN- (Aeronautical Telecommunications Network) and FANS 1/A+ - (Future Air Navigation Systems Plus with latency timer) equipped aircraft. In continental airspace, CPDLC via ATN over VDL Mode 2 is the technology of choice.

How many aircraft exchange CPDLC messages with the Maastricht Upper Area Control Centre?

IN Q1 2017 more than 21% of the traffic crossing the Maastricht airspace use CPDLC on a daily basis and  due to the operational benefits CPDLC usage keeps increasing quickly.

Is the fact that CPDLC is slower than voice communications a problem?

Although CPDLC communication is not primarily intended for tactical communication but rather for strategic messages, speedy replies of air crews to all Data Link instructions are essential for the safe and efficient usage. Important issue is to always WILCO the Up-Link instructions!

What are Controller-Pilot Data-Link Communications (CPDLC) ?

Controller-Pilot Data-Link Communications (CPDLC) is an air/ground data-link application operated at the Maastricht Upper Area Control Centre, which enables the exchange of text messages between controllers and pilots. CPDLC complements traditional voice communications, providing pilots and controllers with an additional communications medium. The objective of CPDLC is to improve the safety and efficiency of air traffic management.

What are the expected benefits of CPDLC implementation in continental airspace?

Frequency congestion on sector frequencies is a well-known constraint. Voice communication tasks represent between 35% and 50% of the tactical (executive) controller’s overall workload.

The use of a supplementary communication medium like CPDLC offers the potential to relieve some congestion, enhancing existing communications between the air and the ground, and offering unambiguous transmission of routine messages between controllers and pilots. In addition, shortcomings such as stuck microphones, blocking of frequencies or simultaneous transmissions are avoided, contributing to the overall safety of the ATC system. CPDLC contributes to reducing the pilot's and the air traffic controller's communication workload, and allows them to concentrate on other essential tasks.

What does the controller CPDLC interface look like?

The actual CPDLC capabilities (white listing) are displayed beside connectivity status to the air traffic controllers at the Maastricht Upper Area Control Centre, thus aircrews can expect to be asked to LOG-ON  in line with AIP procedures if not done already when entering MUAC airspace.

At least when the frequency is busy, flight crews should ensure that they are LOGGED-ON.

What is CPDLC used for?

CPLDC is used to exchange routine, non-time-critical messages at strategic level between aircrews and controllers. If urgent messages need to be exchanged at tactical level, traditional voice communications are used.

This is why air crews cannot always expect to get CPDLC clearances when LOGGED ON.

What types of CPDLC messages are exchanged at Maastricht?

The operational use of CPDLC in Maastricht allows for the exchange of the following ground originated messages:

  • Check stuck microphone
  • Squawk SSR code/ident
  • Contact frequency
  • Proceed Direct flight to a point
  • Cleared to a point via several points
  • Cleared via a complete route clearance
  • Maintain Speed or less/greater
  • When can you accept FL
  • State preferred FL/Top of Descent
  • Climb or Decent to a FL to reach by

Aircrew are also able to answer ATC instructions by data link and request routings from ATC.

Which airlines participate?

An Aeronautical Telecommunications Network (ATN) is used by approximately 50 airlines while around 200 airlines LOG-ON to FANS 1/A+ (Future Air navigation Systems Plus with latency timer) in MUAC’s airspace. In the following table we have listed the biggest users of each CPDLC technology.


EZY/EZS EasyJet UK/EasyJet Switzerland 31,7%
SAS Scandinavian Airlines 17,6%
DLH/EWG/GWI Lufthansa/Eurowings/Germanwings 16%
IBK/NAX Norwegian Air Shuttle/Norwegian Air International 12%
FIN Finnair 4%
SWR/UAE Swiss/Emirates/Others 3%



KLM > 9,8%
DLH Lufthansa 9,6%
BAW British Airways 9%
UAE Emirates 8,5%
UAL United Airlines 5%
AFR Air France 4%
BER, QTR, ETD, CPA Pacific Air Berlin, Quatar Airways, Etihad, Cathay each 3%


Why do we need Controller-Pilot Data-Link Communications (CPDLC)?
  1. Capacity: One of the biggest constraints in air traffic control today is the saturation of voice communication channels. CPDLC helps alleviate this saturation and congestion by providing an additional communications medium for aircrews and controllers.
  2. Safety: All equipped and white listed Aircraft are requested to LOG-ON to CPDLC as secondary means of communication to enhance COM safety during excess traffic load, severe weather or to mitigate loss of communication.