Effective and clear communication between aircraft pilots and air traffic controllers at terrestrial stations is key to maintaining mistake-free operations during domestic or international civil air routes, especially when lives are on the line.
Within the framework of the International Telecommunications Union Radio Regulations, the VHF frequency band 117.975-137 MHz is currently allocated on a primary basis to the Aeronautical Mobile (Route) Service, which is reserved for communications relating to the safety and regularity of flights along national or international civil air routes. This frequency band is used for critical air-ground, ground-air, and air-to-air voice communications, as well as data communications services for air traffic management and operational control of airlines throughout the world.
During the World Radiocommunication Conference (WRC-23), held in Dubai, United Arab Emirates, from 20 November to 15 December 2023, the ITU Member States agreed on the identification of an important new allocation for the aeronautical mobile-satellite (R) service (AMS(R)S) in the VHF frequency band 117.975-137 MHz.
With this allocation, attained after active deliberations by various administrations, the aviation industry worldwide will be able to supplement existing VHF terrestrial coverage by using Low Earth Orbit satellites to relay air traffic control messages between aircraft pilots and traffic controllers over remote airspace and oceanic areas.
Regarding the use of the new service in practice, an important element must be highlighted: the space segment will be able to receive and transmit to standard VHF radios already installed onboard aircraft. This means that no changes are necessary to an aircraft’s avionics equipment. The use of space segment will allow a larger footprint than that currently provided by traditional terrestrial towers of the aeronautical mobile service.
As the area to be covered by the space-based VHF system will depend on non-geostationary satellite systems, the new allocation to the AMS(R)S will be subject to the architecture and design of the satellite constellations used. In this sense, the area can be limited to one or several Flight Information Regions (FIRs), which can be regional or even global. The space-based VHF system is mainly intended to cover oceanic and distant areas where terrestrial service is not available. In addition, it could be used as a backup for terrestrial stations in case they are affected by any destructive event or during emergencies.
No operational impact is expected with the use of the new allocation, as the latency ranges from the systems of the new Aeronautical Mobile Satellite (R) Service are compatible with existing aeronautical VHF systems.
With respect to the outcomes of WRC-23, a new Resolution was approved reinforcing that “the optimization of air traffic management (ATM) over oceanic and remote areas necessitates appropriate aeronautical surveillance and communication means, to meet the required communication performance for reduced separation minima”.
Likewise, the new Resolution highlights the role of the International Civil Aviation Organization (ICAO), taking into consideration its current Standards and Recommended Practices (SARPs).
Regarding the protection of existing systems operating within frequency band 117.975-137 MHz, as well as in adjacent frequency bands under primary allocation, WRC-23 successfully identified technical and operational conditions to ensure protection from possible interference after the introduction of the new AMS(R)S allocation.
Overall, through the new allocation agreed by ITU Member States during WRC-23, the aviation industry worldwide has successfully enhanced the connectivity of voice and VHF Data Link between aircraft pilots and air traffic controllers over oceanic and distant areas where current terrestrial service is not available. This will allow any aircraft to connect to ATC via a non-geostationary satellite.