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AIR TRAFFIC CONTROLLERS ASKING FOR CPDLC LOG-ON 22

While repeating this process over and over again, we listen to radio calls and transmit at the same time. Even while we
are transmitting, we are usually already thinking about the next transmission. When it reaches a point of handling
approximately 20 or more aircraft in a complex traffic situation, controllers can be running out of time to think, especially
if there is someone who’s not listening or has some other trouble.
Active CPDLC can give us minutes of valuable thinking time, which we can then use to provide better service to pilots.
During the summer, despite the efforts of flow control, controllers are more often overwhelmed by the traffic (not
necessarily higher in numbers, but in complexity). At this time it is a huge relief to be able to deal with some aircraft on
CPDLC, while using the voice to solve other problems. Controllers at Maastricht UAC understand that it’s a hassle for
most pilots to log on, especially if, in the end for one reason or another, the system is not even used.

PAST AND FUTURE
Some time ago, CPDLC reliability was so low that we were considering completely suspending its use. Fortunately,
times have changed, service providers have improved their communications capacity by multi frequency deployment and
the situation is improving. However, the problems in the past have unfortunately created some distrust in the system by
some controllers, who are still hesitant to use CPDLC, which in turn further discourages pilots to log on. This naturally
results in the next controller not being able to use the system and getting frustrated as well. The process becomes an
old-fashioned catch-22.
We are trying our best to educate even these hesitating controllers to the benefits of the system. We ask everyone at
Maastricht UAC to use it as much as possible for the provided mutual benefit. It will take time, but we can only achieve it
if we work together on both sides. Due to the eventual timeout in the CPDLC system, controllers operating in small sectors
or under time pressure tend not to use CPDLC in the interest of safety. They can’t allow a message to time out because it
can cause all their plans to go down the drain.
We are constantly working on enhancing CPDLC for our controllers by implementing new messages and fixing bugs.
In the past year we’ve implemented the first batch of conditional clearances “CLIMB/DESCEND FLXXX RCH BY FIX”,
which will be extended with distance to/from point and time parameters as well. This will enable an even higher rate of
usage from the controllers’ side. Certain functions that have long been automated, such as squawk changes in the
Maastricht UIR, are automatically uplinked without controller interaction, which reduces controller workload as well.

BENEFITS FOR PILOTS
Pilots can see the benefits of the system in the possibility of recalling messages, better
understanding or having to talk less on the frequency with the controllers. Requests for
level changes and directs are more likely to be granted in a busy environment if they’re
transmitted via CPDLC. Although these benefits might seem very small, the main benefit
of better ATC service should not be forgotten.

KNOWN ISSUES
Controllers understand the possibility that certain crews are not trained or the aircraft
is not capable of using CPDLC on certain flights. If a crew in a similar position receives a
request to log on, they can simply say “Unable CPDLC” and controllers won’t ask for any
details. We have faced many challenges and we try to mitigate the built-in limitations of the CPDLC system which can
cause safety issues, (e.g., FANS 1A aircraft receiving messages which are not actual anymore).
Some aircraft still can’t log on to our network, particularly from the ATN (EQPMT: J1) group. This is because
Maastricht UAC and SkyGuide had to introduce a so-called “whitelist” filtering, due to the high number of aircraft with
“bad” avionics or outdated avionics software versions, which caused amongst others most of the so-called Provider Aborts.
Now, we require aircraft operators wanting to use ATN CPDLC to register their aircraft through Eurocontrol CRO, and if
they meet the requirements (minimum performance) they will be included in the whitelist with the next AIRAC update
and they’ll be able to use ATN CPDLC.
Due to this ATN whitelist filtering we have a present issue with dual stack airframes as B748, B788/789 and A359
aircraft which are often equipped with both systems. The airborne system prefers to log on the more secure ATN, while
some companies are not aware of the abovementioned whitelisting requirement which results in log-on failures, unless
the pilot knows how to select the mode of connection to FANS 1A. Unfortunately, we can’t solve this issue from our side,
we can only encourage airlines to register their ATN capable aircraft with us, and then we can use CPDLC without any
special procedures.
We do prefer the ATN system due to its higher reliability and considerably lower latency. FANS 1A aircraft regularly
take more than 1.5 minutes for a message turnaround, which is often too long in our environment (operational timeout
is 2 minutes). Nevertheless, having an aircraft on FANS CPDLC is much better than not having the possibility of CPDLC
at all. We thank you for helping us, thank you for using CPDLC!

InterPilot | The Safety and Technical Journal of IFALPA ISSUE 3 | 2017