Safety Studies on GNSS Instrument Approach at Žilina Airport

The purpose of this paper is the familiarization with the Global Navigation Satellite System (GNSS), its utilization in aviation and analysis of safety, mainly during instrument approach procedures. Further, the system description is presented and on its basis hazards and risks are identified and later analysed. The main objective of this paper is to review the safety of the system during multiple instrument approaches and to refer to the future potential of GNSS. Today a variety of systems are installed on-board of commercial airliners for navigation during the different phases of flight. Ground-based radio navigation aids, such as VOR/DME or NDB, are used for continental en-route and non-precision approach operations. For precision approaches an instrument landing system (ILS) is necessary. These systems have their limitations; aircraft must follow pre-defined air traffic routes which has an unfavourable effect on the capabilities of Air Traffic Flow Management. The Free Route Airspace is currently used in Europe. It is a specified airspace in which users can freely plan a route between a defined entry point and a defined exit point. Nowadays, the air traffic develops rapidly which causes delays. This is one of the reasons why a system such as GNSS is so essential. Ultimately, GNSS could replace all traditional radio navigation aids, even though there are still technical, operational and institutional issues to be resolved before reaching this goal. Our paper describes the safety evaluation of GNSS based instrument approaches at the Zilina airport (LZZI). GNSS has many sub-systems, which are known as augmentation systems. Each of them has their potential, advantages and disadvantages. We will focus mostly on the EGNOS+GPS core satellite system usage at LZZI. Since we have been evaluating the safety of the instrument approach on a concrete airport we will have to consider all sub-systems which take part in performing the procedure, for example airport systems, ATC, aircraft equipment, flight crew and the GNSS system itself. The methodology or guidance used for this paper is derived from the CAP 760 by the UK Civil Aviation Authority. The risk assessment and mitigation process will be presented through steps logically excepted from the CAP 760 seven-step process.