CNS/ATM resource kit – Chapter 2: Communication

Note: The information contained in this kit was correct at the time of publishing but has not been updated since the flight operations rules commenced in December 2021. It includes references to repealed regulations.

The communications element of communication, navigation, and surveillance in air traffic management (CNS/ATM) is evolving with technology. Although emerging communication technology means more use is being made of data link communications, most operations will still use very high frequency (VHF) and high frequency (HF) voice communication.

This chapter will look at emerging trends in communication, en route radio navigation, controller-pilot data link communications (CPDLC), satellite communications (SATCOM) voice and operations in North Atlantic high level airspace.

Voice and data communication

Airborne radio has been used in Australia for nearly 100 years, and voice communication on VHF and HF remains a vital part of air-to-ground and air-to-air communication. UHF voice is used by the military.

However, there is an increasing emphasis in both civil and military on the transfer of messages via digital codes. These screen-based messages use services such as the controller-pilot data link communication (CPDLC), a technology which emerged in the late 1990s.

As Australian aviation transitions from ground- to satellite-based navigation, communication and surveillance will be transformed by the introduction of four dimensional (4D) trajectories. When fully implemented, air traffic controllers (ATCs) will be able to plot the precise flight path an aircraft will take before an aircraft takes off. This will allow them to map out the projected trajectories of all flights in Australian airspace.

OneSKY Australia program

By 2021, Australia is aiming to provide air traffic control services using one of the most advanced and integrated air traffic control systems in the world. In collaboration with the Department of Defence, Airservices Australia aims to provide a single flight information region for Australian skies under an intergrated air traffic management system. The current civilian system, known as The Australian Advanced Air Traffic System (TAAATS) built in the 1990s and commissioned in 2000, will be retired.

One of the key operational and safety benefits from the new system is that an air traffic controller (ATC) at any of the 200 consoles across Australia will be able to access the same flight information simultaneously, reducing the risk of sharing incorrect information. It will place Airservices and the Department of Defence in a position to manage the forecast growth of air traffic movement in Australia.

Operations with controller-pilot data link communications (CPDLC)

CPDLC has been used in Australia since 1998. It uses a two-way data link, instead of voice, to transmit non-urgent information between air traffic control (ATC) and pilots. CPDLC can be used to issue clearances, such as weather deviations, altitude clearances, amended route clearances, speed instructions, as well as secondary surveillance radar (SSR) codes and frequency transfers.

CPDLC is used in a range of operations, including:

  • oceanic airspace—instead of the unreliable and interference-prone high frequency (HF) radio
  • other airspace at the discretion of the controller.

CPDLC functionality is integrated with the flight data record (FDR). When a CPDLC clearance is uplinked to an aircraft, the FDR is updated on receipt of the ‘will comply’ (WILCO) response from the flight crew. The controller accesses CPDLC message elements via the CPDLC editor.

SATCOM voice

In the 1990s, ICAO determined that future primary long-range communications with aircraft would be by HF or SATCOM data link, and at the time made no provision for satellite voice (SATVOICE). Under ICAO Standards and Recommended Practices (SARPs), SATVOICE is not recognised as an acceptable means of communication for air traffic services (ATS) purposes.

However, the transition to data link communications has not happened as envisioned, and HF voice communication remains a primary means of long-range communication.

Some countries have allowed SATVOICE to be used in lieu of a second HF communications system, providing the aircraft installation and ground segments of the system meet performance standards.

Status in Australia

SATVOICE is not authorised for ATS use in Australia because the Airservices Australia communications infrastructure does not support SATVOICE operations.

However, SATVOICE in North Atlantic high level airspace (NAT HLA) is permitted when authorised by CASA. About 3000 aircraft fly across the North Atlantic airspace daily, with approvals to operate in the ICAO NAT region airspace based on ICAO NAT DOC 007.

For unrestricted operations in the NAT region, operators must have fully functioning HF communications equipment. While SATVOICE and datalink communications are gradually being introduced into NAT operations, operators may still need HF datalink as back-up.

Operators who can demonstrate compliance with the ICAO satellite voice guidance material (SVGM) requirements may be authorised by CASA to use SATVOICE in the NAT HLA region. Aircraft must meet installation requirements and operational procedures must be appropriate.

In transitioning to performance-based navigation (PBN) requirements in this airspace by 30 January 2020, North Atlantic minimum navigation performance specification (NAT MNPS) was redesignated as the North Atlantic high level airspace (NAT HLA).


Aircraft operating in North Atlantic high level airspace require a CASA issued navigation authorisation until 30 January 2020, to coincide with the transition to PBN.

Key points

  • Communication and surveillance are being transformed by the introduction of four dimensional trajectories which allow air traffic controllers (ATCs) to plot the precise flight path an aircraft will take before an aircraft takes off, allowing them to map out the projected trajectories of all flights in Australian airspace.
  • CPDLC, used in Australia since 1998, is a means of communication between ATC and pilot, using a data link instead of voice. Its main advantages include reduced congestion of voice channels, fewer communication errors and reduced workload for pilots and controllers.
  • Aircraft operating in North Atlantic high level airspace require a CASA issued navigation authorisation until 30 January 2020, to coincide with the transition to PBN.


Further reading

  • Airservices Australia (2016). OneSKY Australia program. Retrieved April 2017


Published date: 23 June 2021
Online version available at:
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