Bad Vöslau as the first test location
AOPA Austria has been working for several years to practically test Universal Access Transceivers, or UAT for short, in Austria as well.
The first ground station is to be established at Bad Vöslau airfield. The location is ideal because installation, maintenance and accessibility are comparatively straightforward, and the airfield management is willing to provide the appropriate infrastructure.
The project is still going through the approval process. Two points are currently dominating the discussion.
Possible DME fault is being investigated
The District Authority of Baden has raised the question of whether the planned UAT transmitter could interfere with the DME at Vienna Airport.
UAT operates on 978 MHz, which places it in a frequency range in the vicinity of which aeronautical navigation systems are also operated. For a new ground station, it must therefore be demonstrated that no safety-critical interference occurs.
AOPA Austria has submitted technical documentation and experience from Finland, where comparable UAT installations are already in operation. Information from the device manufacturer is also intended to demonstrate that interference-free operation is possible.
A final official assessment is still pending.
TIS-B is crucial for the utility of the system
The second outstanding issue concerns TIS-B, which is Traffic Information Service – Broadcast.
This particular service is crucial for the practical idea behind the project. Via TIS-B, ground stations can transmit traffic data to appropriately equipped aircraft.
The American UAT system shows how this can work: the FAA also feeds in radar targets of aircraft that do not themselves transmit a compatible ADS-B signal. This allows a pilot to obtain a significantly more complete traffic situation picture on their cockpit display than exclusively via direct ADS-B air-to-air signals.
However, approval for the transmission of corresponding traffic data has not yet been granted for the Austrian test facility.
AOPA Austria therefore suggests using data from Austro Control for this purpose. Initial talks are said to have been generally positive; the responsible specialist department is now to examine the issue in more detail.
Why ADS-B alone does not make all aircraft visible
The challenge becomes particularly clear when one looks at today's technical landscape of general aviation.
An ADS-B-in receiver can directly display other aircraft equipped with ADS-B out. However, many aircraft continue to transmit only Mode C or Mode S without ADS-B position data.
These aircraft are frequently visible to ATC, but cannot automatically appear directly on another aircraft's ADS-B In display.
TIS-B could partially close precisely this gap: the ground infrastructure receives the traffic information from air traffic control and transmits it on to appropriately equipped pilots.
This corresponds to the basic principle of the American system, which has been established for years.
FLARM remains another parallel universe
The situation is made even more complex by FLARM.
The system is particularly widespread in gliding and is also used by microlights and other light aircraft. It is very well suited for collision warning within its own technical infrastructure.
However, FLARM is not automatically fully interoperable with traditional ADS-B and Mode-S traffic.
This results in several technical worlds co-existing in Europe. A pilot can see part of the traffic via ADS-B, another via FLARM, and might only detect other aircraft visually or through traffic information from the flight information service.
Achieving as complete a cockpit traffic picture as possible therefore remains one of the major challenges.
UAT could carry more than just traffic
The real advantage of UAT lies in the available data capacity.
In the USA, UAT operates on 978 MHz. Over this, the FAA provides not only TIS-B, but also FIS-B.
Equipped aircraft can receive weather and aeronautical information via FIS-B. This includes, for example, weather products, METARs, TAFs, as well as selected NOTAMs and airspace information.
The data is transmitted from ground stations and can be received without a cellular connection.
This is particularly interesting for light GA aircraft.
Mobile communication is not a reliable solution in the air
Many pilots today use tablets or smartphones for navigation. As long as there is mobile phone reception, weather, NOTAMs or other information can be updated.
However, as flight altitude increases, the connection frequently becomes unreliable.
The mobile network is primarily designed for users on the ground. Although an aircraft may still have data reception at a few thousand feet, you should not rely on it.
An aviation-specific broadcast service has a decisive advantage here: information is broadcast specifically into the airspace and is available to all suitable receivers within the coverage area.
Satellite services are available, but expensive
Satellite-based solutions already exist for weather information.
Systems from Garmin or Golze Engineering, for example, can receive weather data via Iridium and then forward it to a tablet or avionics.
Technically, this also works reliably at higher altitudes.
However, costs for hardware and ongoing data subscriptions arise. Furthermore, such systems focus primarily on weather information.
A UAT network, on the other hand, could combine multiple services on a shared data channel.
The American model
In the USA, UAT has been part of the ADS-B infrastructure for many years.
There are two technical ADS-B paths available there: 1090ES and 978 MHz UAT. Aircraft below FL180 can generally use UAT within the relevant US regulations, while above FL180 1090ES is required.
For ADS-B-In users, UAT offers an additional benefit: FIS-B weather information is broadcast on 978 MHz.
TIS-B, in turn, can also provide traffic information about aircraft that are themselves only equipped with a transponder, provided they are detected by ground surveillance.
Precisely this principle makes UAT interesting for European general aviation.
No substitute for see and avoid
As attractive as a comprehensive traffic situation display in the cockpit may be, it remains a support system.
Not all traffic is necessarily displayed. Gliders, aircraft without a switched-on or functioning transponder, drones or other airspace users may still be missing.
Visual scanning of the airspace therefore remains indispensable for VFR pilots.
The FAA also points out in its ADS-B In services that the information displayed is for situational awareness and its technical limitations must be understood.
Europe's problem is less the technology than the regulation
UAT is not a new experimental radio technology. The standard is established and has been widely used in the USA for years.
The challenge for Europe lies rather in integrating him into existing frequency plans, approval structures and air traffic control systems.
This raises questions regarding spectrum usage, liability, data quality, and the provision of ATC traffic data.
Precisely why the pilot plant in Bad Vöslau is interesting. It is intended not only to show that a transmitter works technically, but also how such a system could be operated under European regulatory conditions.
Conclusion
The ADS-B/UAT project in Bad Vöslau could become an important test case for the digitalisation of general aviation in Europe.
The goal is an attractive one: to transmit traffic, weather, NOTAMs and temporary airspace restrictions directly into the cockpit via a shared data channel – independently of the mobile phone network and using comparatively simple receiving equipment.
Technically, a proven model for this already exists with UAT. The decisive hurdles at present are frequency licensing, potential interference with other navigation systems, and above all, the provision of TIS-B traffic data.
If AOPA Austria and the authorities involved manage to find a viable solution for this, Bad Vöslau could become much more than just a single test installation. The airfield could become the starting point for a new data infrastructure for European general aviation.
Source references:
Flieger.News
