Nº 1 2012 > Aviation
Not your average spectrum user
Technical Officer, International Civil Aviation Organization (ICAO)
The aviation sector is characterized by aeronautical and safety-related factors that distinguish it from other frequency spectrum users. This article discusses three WRC‑12 agenda items which are of major interest to the global aviation community.
Modern airliners travel at speeds of up to 1000 km/h. In busy airspaces, aircraft are separated by distances which are covered in mere seconds. They travel over vast, often intercontinental distances. The equipment carried on board needs to be compatible with the services provided at airports around the world. Every kilo added to the weight of airborne equipment adds to the fuel consumption of the aircraft. For economic reasons, there is little room for redundant equipment.
Today’s commercial aircraft are equipped with two to four VHF radios, voice and digital link. They may also carry two HF radios and a dual-redundant satellite communications link. There are also precision radionavigation and landing systems, radio altimeters, radar transponders, airborne collision avoidance systems, weather radar and so on.
There are approximately 30 antennas or more on an average‑sized modern aircraft; a modern Boeing 747–400 has between 40 and 50 antennas fitted. Needless to say, for global and airborne communications, navigation and surveillance (CNS) operations to work effectively in the confined environment of these aircraft, careful consideration needs to be given to the spectrum used.
The Convention on International Civil Aviation is an international treaty providing the required provisions for flights over the territories of the 191 ICAO Member States and over the high seas. It includes measures to facilitate air navigation, including international standards and recommended practices (SARPs).
The ICAO standards constitute rule of law through the ICAO Convention and form a regulatory framework for aviation, covering personnel licensing, technical requirements for aircraft operations, airworthiness requirements, aerodromes, and CNS systems, as well as other technical and operational requirements.
Aeronautical CNS systems provide functions critical to the safety of aircraft and rely on the continued availability of appropriate frequency spectrum. Civil aviation administrations coordinate their positions on the agenda of world radiocommunication conferences (WRCs) through the development of a common ICAO position catering to the continued and evolving spectrum requirements of CNS services.
Three spectrum concerns have been highlighted as high priority areas for the global aviation community during WRC‑12: unmanned aircraft systems; aeronautical safety allocations; and requirements for the aeronautical mobile satellite (route) service.
Unmanned aircraft systems
The development of a standards framework for unmanned aircraft systems or remotely-piloted aircraft is perhaps the single most challenging standardization task that ICAO has undertaken in a long time.
Consider the following scenario: a remotely-piloted aircraft registered in country A flies over the territory of country B while being managed through a remote pilot station in country C. To make things even more complex, envisage the satellite control link being owned and operated by a satellite operator in country D.
How do you establish the airworthiness of such a composite scenario? In the case of operational problems or even an accident, who is responsible? And to relate to the radio regulatory aspect: how do you safely manage and mitigate an interference problem caused by a satellite operator in country E?
ICAO has recently undertaken the development of the international regulatory framework necessary for unmanned aircraft systems operations in civil airspace. This work will include the development of SARPs for the unmanned aircraft systems command and control link. This is a significant task and will take a number of years to complete.
The development of unmanned aircraft systems standards and recommended practices will always comply with the following fundamental principle: when introducing any new aircraft, system or service to civil airspace, the safety of any other airspace user or property on the ground must not be negatively affected.
Because of the safety aspects inherent in the provision of existing CNS services for the purpose of air traffic management, these services traditionally require appropriate safety allocations, such as the aeronautical mobile (route) service, aeronautical mobile satellite (route) service and aeronautical radionavigation service (as defined in the Radio Regulations).
One additional and unique new aspect required for unmanned aircraft systems is the command and control link used to remotely manage the unmanned aircraft while in flight. As this link provides the sole means to control the unmanned aircraft in real time, it not only requires protection through an appropriate aeronautical safety allocation, but also needs to be exceptionally robust.
Increased flexibility of aeronautical safety allocations to accommodate increased spectrum demands
Aviation is experiencing long-term growth at an annual rate of 4.6 per cent. In order to accommodate this growth, WRC‑07 afforded aviation three new aeronautical mobile (route) service allocations in the frequency bands 112–117.975 MHz, 960–1 164 MHz and 5 091–5 150 MHz. These are to be shared with the existing aeronautical radionavigation service allocations in these bands.
A key to this new and flexible arrangement is the mutual recognition between ICAO and ITU that ICAO ensures compatibility for systems using the new aeronautical mobile (route) service through the development of SARPs for its systems.
The first two allocations were provisional, pending further studies within the ITU Rediocommunication Sector (ITU–R). These studies have now been finalized with a favourable outcome, indicating that sharing with the aeronautical radionavigation service in these bands is feasible.
In addition to the third allocation, the conference invited spectrum administrations and ICAO to assist ITU–R in studying whether aviation’s needs could be fully met within the 5 091–5 150 MHz band. Unfortunately, the outcome of this study appears inconclusive; it has not addressed any of the number of constraints present in this band. No doubt there will be an interesting debate on this subject during WRC‑12.
Long-term spectrum availability and access to meet requirements for the aeronautical mobile satellite (route) service
ITU studies, supported by ICAO, have concluded that long-term aeronautical mobile satellite (route) service spectrum requirements up to the year 2025 can be accommodated within the existing 10 MHz wide 1.5 and 1.6 GHz frequency band allocations available for this service.
ICAO is of the view that further provisions need to be included in the Radio Regulations to clarify and facilitate coordination and assignment to the aeronautical mobile satellite (route) service in these bands, according to the priority given to the service, and to improve transparency in the coordination process.