GNSS-based curved landing approaches with a virtual receiver

The civil aviation of the future should be ecological, economical, and safe. The citizens in metropolises have on the one hand the need to travel efficiently between airports near the city. On the other hand they, do not want to suffer from noise and emission of airplanes starting and landing at airports close to cities. Consequently, the future airplane should harmonize these needs. In order to fulfill these requirements new concepts for departure and approach procedures are mandatory. Curved approaches are one solution since critical regions can be omitted. These complex maneuvers can only be carried out with the help of satellite navigation systems. One major challenge of curved approaches is the changing obstruction of satellite signals due to shadowing effects by the aircraft itself during curved approaches. Existing GPS landing systems suffer therefore degraded performance (continuity, availability, integrity and accuracy) during curved approaches, especially with higher roll angles and at high and low latitudes. To avoid this problem and to meet the requirements of integrity, accuracy, continuity and availability for future GNSS landing systems, the concept of the so called "virtual receiver" has been developed in the framework of the research project "Biirgernahes Flugzeug" (Metropolitan Aircraft). The main idea is to avoid obstruction by combining GNSS observations of few antennae, optimally instaUed on the airplane and computing one common aircraft position solution. This paper presents the mathematical concept of the virtual receiver. The benefits in terms of continuity, precision and reliability are evaluated based on a simulation study and from the analysis of real data from a test flight with the research aircraft D-mUF, a Dornier 128-6 from the Institut of Flight Guidance (TV Braunschweig). It will be shown, that virtual receiver outperforms a single antenna solution concerning the precision (DOP-values are reduced by 30 %) and the reliability (MDBs are reduced by 10 % on average).