Continuous vertical guidance is one of the most important tools available to a pilot during the final stages of flight. It ensures the crew can maintain a safe height above terrain and obstacles when approaching a runway. In adverse weather, such as low cloud, they can also descend to a lower altitude before needing to make visual contact with the airport. This continuous vertical guidance decreases the chances of a pilot undertaking a go-around or having to divert, saving both fuel and time.
In Australia, vertical guidance has historically been provided by technology like the ILS and in more recent times, accurate Baro-VNAV, RNP AR and GBAS. However, these recent technologies are usually only found in large aircraft, mostly Boeing and Airbus. A Satellite Based Augmentation System (SBAS) allows regional carriers who fly turboprop and smaller aircraft to reap the same benefits as larger aircraft without the need to install ILS infrastructure.
SBAS test-bed project
Geoscience Australia is currently assessing SBAS technology across Australia using information gathered from trials in multiple sectors including agriculture, mining and aviation. The over 25 SBAS projects will consider the benefits of the highly accurate positioning available using SBAS technology.
Airservices Australia will lead the aviation trial on behalf of the aviation industry to illustrate the safety and efficiency of SBAS to airlines, regional/general aviation, and medivac operations. The project will make use of the Geoscience Australia SBAS test-bed signal to demonstrate the performance of the technology in an aviation context.
The aviation trial, which will run from June, will assess the accuracy and safety of SBAS while ensuring it can be easily implemented using existing avionics. It will test three new technologies, first generation SBAS, second generation SBAS and what is known as Precise Point Positioning.
Several SBAS-enabled approaches will be undertaken with test flights into Mount Hotham, Wagga Wagga, Benalla, and Canberra airports. Airservices will also be measuring SBAS performance using ground equipment in Darwin and Canberra, and recording both current and next generation SBAS on our flight inspection aircraft in partnership with AeroPearl.
Early indications suggest that the business case for SBAS is strong. However, Airservices needs to confirm its safety, reliability and efficiency working with Geoscience and the Australian Strategic ATM Group (ASTRA) over the coming months.
What is SBAS?
A Satellite-Based Augmentation System (SBAS) uses both space-based and ground-based infrastructure to improve the accuracy and integrity of basic Global Navigation Satellite System (GNSS) signals, such as those currently provided by the Global Positioning System (GPS).
SBAS is already well-developed internationally including WAAS in the United States and EGNOS in Europe. For the aviation sector SBAS provides improved navigation and timing over GPS decreasing the likelihood of ‘go-arounds’ and cancellations or diversions due to variable weather.
How does SBAS work?
SBAS works by monitoring signals from GNSS satellites, calculating corrections, and uploading them to a satellite in geostationary orbit for broadcast to aircraft and other users. The test-bed uses Geoscience Australia’s national Continuously Operating Reference Station (CORS) network to monitor the signals. It then sends data to the Lockheed Martin uplink station at Uralla in NSW for processing by software developed by GMV. The corrections are then uploaded to the Inmarsat 4F1 satellite which broadcasts to users in Australia and New Zealand.