Germany planning network of GPS precision approaches

 - January 31, 2007, 5:49 AM

Germany’s air navigation service provider (ANSP), Deutsche Flugsicherung (DFS), is working toward the national implementation of differential GPS-based precision approaches in a program expected to last about two years.

Manfred Dieroff, head of noise abatement, environment and navigation at the DFS, told AIN that the company started developing overlay approaches, effectively copies of the conventional procedures, in the mid-1990s. By 1998 it had published stand-alone GPS procedures, and subsequently it approved the use of GPS for nonprecision approaches (NPAs) without the need for conventional navaids.

Basic area navigation using GPS is also approved in Germany, as it is in other European states, and the ANSP is currently preparing the approval of GPS for standard instrument departures. At the same time, it is in the process of approving the budget for Category I approaches using GPS, a project expected to start this year and take as long as two years.

Pilot Notification
Among the issues the DFS had to address in developing the existing stand-alone procedures, Dieroff said, were the availability of GPS for the approach procedures, a system to notify pilots of any non-availability and alternate means of navigation.

After assessing the safety of the procedures in cooperation with the FAA, the DFS set up a notification system on GPS availability. “The status of GPS as a means of approach operations is calculated and fed into our notam system,” Dieroff explained.

“We currently can offer a service for notification of GPS availability or non-availability through the standard notam, and we cooperate with close to 10 states regarding the use of this notification system. For the hardware there is no difference between calculating availability for 50 or 500 airports; it is just a calculation, and we transmit the results through the aeronautical fixed telecommunications network to our partners,” he added.

The notam information is distributed on the basis of bilateral agreements, but “we make it available to everybody who would like to use it,” Dieroff said. Existing users are all in Europe with the exception of Canada, which uses it only for test purposes. The information is also shared with France, which operates its own GPS notam system.

The regulations require that pilots be made aware of any non-availability during the preparation phase of a flight, Dieroff said. “It is very simple because we have set it up in a way that it is similar to all other navigation systems so if there is a non-available [GPS approach] for the airport chosen there will be a notam about it.”

Aircraft equipment and alternate airport requirements are based on guidance material on the implementation of GPS approaches in the Joint Aviation Authorities’ temporary guidance leaflet three and embodied in national regulations. “One requirement is that the alternate chosen for the flight has to be a non-GPS airport, an airport that can be approached with conventional means,” Dieroff explained. “So for flights to GPS-only airports, you need an alternate for IFR flights and you have to choose a non-GPS approach for the alternate airport.”

Some airports in Germany have chosen to rely on GPS alone, he said, but most have GPS as an additional service alongside conventional approach procedures, typically ILS Category I, II or III. “GPS is well accepted because it is simple to fly.” Whereas the overlay procedures were purely for training and gave no operational benefit, he said, the stand-alone procedures can support simplification and even shortening of the approaches.

So far GPS approach minimums are the same as those for conventional nonprecision approaches, because when the protection areas for GPS were designed in the 1990s they were conservative. Subsequently, though, ICAO has revisited the question and is developing new protection areas that may reduce the minimums for these GPS NPAs. “So there may be an operational advantage as well,” Dieroff predicted.

Program Implementation
“But the most important consideration for the people who use the approaches is the fact that once you are used to operating a GPS receiver or an FMS the procedures are simple to fly, because we tried to develop them in the same manner for all airports, using the T concept so that all procedures look similar,” he added.

For precision approaches, he said, a government-supported research program is under way already, and the DFS is now launching its own operational program to address the implementation of precision approaches.

Germany’s GPS approach strategy differs from France’s. While France plans to use the European geostationary navigation overlay service (EGNOS) space-based augmentation system to support nonprecision approaches with vertical guidance, Germany plans to use differential GPS ground stations–a ground-based augmentation system in ICAO terminology–to support precision approaches: “The step we are taking here is to get into the Category I, II and III business,” Dieroff said.

For the implementation program, the first system will be installed at Bremen Airport in northern Germany, chosen because it is an international airport with a Category III ILS, operated by DFS and used by Lufthansa. DFS had not yet selected a ground station supplier, Dieroff said. The service provider has used a Honeywell ground station for trials at Frankfurt and is using a Thales unit to support certification of GPS-capable multimode receivers at Toulouse, “but there is no idea about the ground station we would set up at Bremen.”

The most difficult aspect of the program is obtaining budget clearance. Dieroff explained, “This is what I am waiting for now; we have done the preparatory work and as soon as the budget is cleared we can then start with the program.”

Germany has led the way in implementing GPS procedures in Europe, and Dieroff said that as a pilot of long standing himself he has seen the system’s benefits. “I have been flying for a long time so I know the advantages and disadvantages of specific navigation systems, and GPS is a real improvement in safety if you can use it correctly. The nonprecision approaches especially are so easy to fly; that’s a real benefit. They all look alike, and once you have loaded them into your flight management computer it works so smoothly; it’s really nice.”

A consequence of being first was that the regulator took a cautious approach, resulting in a long test and inspection phase. One issue was the integrity of the navigation databases supplied by commercial providers. “As an air navigation organization we have no influence on what database providers do with their database or how the coding process is handled,” Dieroff pointed out.