Satellite technology gains ground

Global Navigation Satellite Systems (GNSS) using ground-based augmentation are considered the future solution for precision approaches at airports. Airlines, Air Navigation Service Providers (ANSPs) and manufacturers have been collaborating on a worldwide scale to expand the technology’s capabilities. EUROCONTROL’s SESAR and the FAA’s NextGen programmes are working towards replacing Instrument Landing Systems (ILS) with groundbased augmentation systems (GBAS).

According to a market intelligence report conducted by the business media provider ATC Global, GBAS may provide considerable cost-savings. What’s more: GBAS has a high potential for maximising capacity at airports and allows flexible operational use. The German ANSP, Deutsche Flugsicherung (DFS), was the first in the world to operate GBAS for Category I precision approaches in regular operations at an airport. DFS plans to set up a GBAS trial installation for Category II and III operations by 2013/2014.

The system boosts the accuracy and integrity of GPS by transmitting corrections to aircraft via a Very High Frequency (VHF) radio data link from a transmitter on the ground. It focuses on the airport area covering approximately a 40km radius. For an airport, even with multiple runways, only one ground station, comprising four GPS antennas, a computer and a VHF transmitter, is necessary.

DFS installed its GBAS ground station, manufactured by Honeywell, at Bremen Airport in 2007. Specific test tools and performance intensive ground and flight tests were used to test the system. Then, test operations under instrument meteorological conditions down to minimum descent altitudes were conducted with two airlines, TUIfly and Air Berlin. In 2011, the German Federal Supervisory Authority for Air Navigation Services (BAF) certified the GBAS station as a primary landing system. In February 2012, it received approval for Category I operations. In the near future, DFS is considering implementing more GBAS CAT I installations as additional landing systems together with interested airports.

Numerous advantages

The aviation industry has embraced GBAS as the future technology for precision landings because of its many advantages. Although it is currently in an early-production stage, installing a GBAS station is much more cost-effective than installing several ILS. One GBAS station serves all runway ends of an airport and requires significantly less maintenance. The system does not need to be checked periodically by flight inspection as is necessary for an ILS. Normally, a ground inspection is required just once a year.

More important than savings on infra – structure, are the benefits for airports and airlines that are expected from more efficient operations: GBAS does not require protection areas close to the runways, as is necessary with ILS. Consequently, approaching aircraft do not need to wait until other aircraft on the ground have left the protection areas. It is expected that in this way, GBAS will contribute to capacity enhancement and the reduction of delays.

Captain and Head of the Boeing fleet at our co-operation partner Air Berlin, Marc Altenscheidt, commented: “We have invested in GBAS technology and are participating in the DFS project because, in the long run, we see a high potential in GBAS to fly more efficient landings, and increase flight safety and reliability even under low visibility conditions. In this way, we will also save fuel and costs. Generally, it is part of our strategy to have the whole fleet equipped with the latest technology.”

An important factor for airport development is that the GBAS signal is less susceptible to signal reflections. Neither weather nor obstacles, such as terminal buildings and large aircraft hangars, have much impact on a GBAS installation.

Another striking advantage of GBAS can be found in its flexibility; the technology can easily be updated to new procedures via file upload. Currently, with just one GBAS station, 49 variable approaches in the vertical domain are possible. This means that the independent use of several glide path angles is possible. In the future, this could help disseminate air traffic around an airport and in this way reduce aircraft noise in densely populated conurbations. Different approach procedures during day and night times are also conceivable. Furthermore, GBAS may one day permit the use of laterally displaced approach paths. Then, curved approaches, for example at airports in mountainous areas, will be possible. In the future, all available constellations and requencies, for example via GLONASS and GALILEO, are to be used. The technology is also to be deployed for departure procedures and terminal area operations.

The full potential of GBAS has not yet been completely exploited. This will be the case though when it has achieved CAT II and III capability. Many advantages of the technology are, however, already evident under CAT I conditions.

Global co-operation

To enhance GBAS deployment, co-operation between air navigation service providers and the aviation industry around the globe is currently in full swing. Apart from the German project, there are other projects underway. The FAA in the US, Airservices Australia, CECEA in Brazil, and AENA in Spain have all installed systems for CAT I approaches. Russia has also established a considerable number of facilities.

A crucial step in the transition from ILS to GBAS as the primary landing system is the onboard technology. Some aircraft types are already equipped with GBAS receivers as standard or an option, such as the Boeing 747-8 and the 787, or the Airbus 380 as well as the 320 family. Air Berlin, for example, has equipped its Boeing 737 next generation fleet with GBAS on-board receivers. It will, however, take time before all aircraft dispose of GBAS avionics worldwide.

The next milestone in GBAS deployment will be to enable CAT II and III precision approach performance. The first GBAS CAT II/III trial ground station developed by Thales was installed in May 2012 at Toulouse Blagnac Airport for research within the framework of SESAR. DFS will also contribute to SESAR with the technical evaluation of a trial installation for CAT II and III approaches at Frankfurt Airport in 2013/14. The knowledge gained will help establish international standards.

Common approval practice, the use of common test cases and tools, and the develop – ment of ICAO standards and specifications will be invaluable for the implementation of GBAS CAT II/III around the world.

About the authors

Stefan Naerlich is the Head of Navigation Services at DFS. He has been with the company since 1996 and is responsible for the technical implementation of satellite naviga – tion and development projects such as GBAS and EGNOS. After his studies, the control engineer worked on the development of control and navigation systems at Honeywell in Germany, where he was head of the navigation systems and gyroscope department.

Hans-Jochen Kreher is the Head of the Satellite Navigation Depart – ment at DFS. From 2003 to 2005, the electrical and automation engineer was the national expert for satellite navigation at the European Commission in Brussels. Before that he led the EGNOS project at DFS. Previously, he had been involved with the development of navigation and flight control systems for DASA (now EADS).