Potential for the use of GBAS at close-by airports

Abstract

This paper presents the results of a feasibility study to use GBAS for approaches to secondary airports in the vicinity of the prime airport where the system is located. The evaluations are based on a maximum vertical error at a desired decision height (e.g. 200ft which corresponds to the CAT-I minimum) which may not be exceeded with a certain probability. This is taken as a starting point to ensure that no collisions with terrain or obstacles can occur. The tolerable vertical error is mainly determined by four parameters: the obstacle clearance surface, the total system error including navigation sensor and flight technical error, the glide path angle of the approach and the ionospheric threat model. In this paper we investigate the influence of all those parameters on the possibility to provide approaches down to the CAT-I limit at close-by airports. The main concern for such an application is the influence of possible undetected ionospheric gradients. For all other effects no significant decorrelation of errors over several kilometers which is not accounted for can be expected. Results show that such operations can be feasible at airports within about 24km of the GBAS under the German iono threat model and with an assumed glide path angle of 3°.