More fully explaining acquisition and use of CPDLC

Historical background, current and future applications, makers of the equipment, costs of acquisition, installation and training.

Harold Katinszky
FAA Lead Safety Rep,
Aviation Consultant

In addition to being one of the 3 major manufacturers of avionics systems that support CPDLC, Universal Avionics offers formal classroom training on its use. Their instructors employ computer-based simulations and iPads to provide functional representations of flat panel control displays. These can be arranged to replicate the user's configuration for a more life-like learning environment.

Communication in aviation has existed as long as aviation itself. From the moment our ancestors looked skyward wondering how birds flew up to modern jet flight, clear and effective communications have been with us all along from hand signals, to voice, to text. Before radio, brave aviators flew on low frequency A-N radio range and spent hours listening for the correct Morse code signal to keep them on track. That alone was a full time job. A-N was a huge improvement over deduced reckoning.

The world's Air Traffic System (ATS) still uses components defined in the 1940s for air traffic communications such as high frequency (HF) radio. Nearly a century old, HF is still required for most over water operations. Navigation improved greatly with the advent of Selective Calling (SELCAL) in 1957 and waypoint alert to add audio/visual warnings to alert crews to compulsory tasks. Finally, satellite-based positioning systems are another order of magnitude forward, which has ushered in precise GPS approaches.

In efforts to modernize our ATS between pilots and controllers, ICAO introduced Future Aviation Navigation System (FANS) in 1983. In the 1990s, the 1st generation of FANS-1 was introduced by Boeing. Under this FANS umbrella, the evolution of Controller Pilot Data Link Communications (CPDLC) was introduced. Initially CPDLC was implemented by a small airline sector to improve route utilization and fuel economy over water.

Because of the reduction of communication errors caused by human input, CPDLC became the norm in the airline industry. Large airlines could justify the high cost associated with an install, as well afford the considerable equipment space that CPDLC required.


The FANS concept is defined as 3 individual networks integrated to deliver safety of flight:
• Communications (C): Satellite data links with VHF data direct to the pilots.
• Navigation (N): Based on Required Navigation Performance (RNP) with Global Positioning Systems (GPS) or (GNSS).
• Surveillance (S): Uses ADS-C.
Both CPDLC & ADS-C fall under this FANS communication umbrella.


Rockwell Collins screen depicting coast-out route for a North Atlantic crossing. CPDLC greatly simplifies the former difficult transition from VHF to HF and speeds the process of obtaining oceanic clearance. Safety and efficiency is increased with CPDLC as the primary communication mode.

Still in use, the main difference between Aircraft Communication & Reporting System (ACARS), Airborne or Aerodrome Flight Information System, (AFIS) & CPDLC, is that ACARS and AFIS were primarily tools for communication between airlines or companies and their pilots.

Although both ACARS and AFIS can and do provide clearances to crews through ATC when needed, CPDLC is a direct link between pilots and controllers. CPDLC with ADS-C can cover most pilot–ATC communications over water and may someday relegate HF & VHF above all FL180 airspace to a backup form of communication. Hopefully with CPDLC and ADS-C, missing aircraft such as Malaysia Airlines MH370 will be easier to track through the entire flight.

CPDLC implementation

As airspace becomes saturated by aircraft, solutions to better use it requires we move away from ground-based to satellite ATC and navigation systems. A confluence of current issues may reduce the amount of air traffic controllers, possibly putting traffic separation responsibility back on the pilot which will increase flightcrew workload.

While there will still be ground-based communication and navigation, the goal is to have long range enroute navigation performed via satellite. This will make routing more efficient and improve safety when flying over water.

Numerous modifications are improving our airspace system including NextGen, RVSM, CPDLC, ADS-B and ADS-C. CPDLC's greatest asset will be overwater operation coupled with ADS-C. Although phases of flight will not change, CPDLC will be a clearance delivery device on the ground and text communications above FL180 with ADS-C. Aural notifications are inhibited during critical phases of flight.

How CPDLC works

The industry has 3 major manufacturers of CPDLC systems: Honeywell, Rockwell Collins and Universal. All integrated into your flight management system (FMS).

With the units turned on you go through a log on and connect page. When connected, if ATC needs to reach the crew there are audio and visual alerts. When communicating with ATC, the system offers both stored responses (wilco, roger) and free text pages.

When requesting or being directed to an altitude, there are numerous texts to communicate and respond to instructions. Crews must respond with 60 seconds to an up-link message, or respond with standby. If standby is used, ATC expects a response within 10 minutes.

Crews can also make requests to ATC using the free text page. Other requests can include weather deviation requests.
Crews can select an emergency page with several options. Emergency pages also offer mayday or pan pan pan when someone may be ill on board and require medical attention upon landing. Finally crews can also cancel an emergency.

What CPDLC is

Flying over water, CPDLC coupled with ADS-C is a superior option since it reduces numerous errors. Flying over water with HF, pilots relay messages to an HF operator, who transcribes the messages, forwards them to an ATC provider, who then gives a reply to the HF operator, who then relays that message back to the pilots. Delays in response can be so much that aircraft need to be spaced as much as 100 miles apart for safe separation.

Furthermore, HF requires that the signal bounces off the ionosphere – very susceptible to space weather – back to antennas on the ground. There is a myriad of things that can affect HF frequency such as thunderstorms, aircraft components, unauthorized or malicious use, or simply other pilots stepping on each other. Pilots who have flown over water enough times have experienced periods where HF reception is marginal or totally unreadable, so they end up using multiple frequencies to get across the ocean. Some argue Sat phones are the answer. However, Sat phones need to be integrated into your cockpit voice recorder (CVR) and also have busy signals.


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