Towards Higher Levels of Automation in Taxi Guidance: Using GBAS Terminal Area Path (TAP) Messages for Transmitting Taxi Routes

Kurzfassung

Abstract According to Sheridan and Verplank’s classification of levels of automation, taxiing on an airport still has a very low automation level. Key element for increased automation in taxi guidance is a precise and reliable navigation capability. As a Ground Based Augmentation System (GBAS) can fulfill the stringent requirements for a precision approach, it can play an important role in providing the required navigation performance during taxiing as well GBAS is a safety critical system designed to meet the requirements for both precision approach and landing, and departure operations in various visibility conditions. Consequently, the capabilities and availability of such a system give the motivation for developing new applications intended to support higher level surface operations within a local airport environment. One future application for instance, could be the use of Terminal Area Path (TAP) technique to provide routing information. TAP is the RTCA concept to enable advanced or complex procedures with GBAS. This incorporates the support of complex (i.e. laterally and vertically guided) approach, missed approach as well as departure procedures. TAP’s are incorporated in the latest RTCA LAAS ICD DO-246D and will be broadcasted by the GBAS ground station through the VHF data broadcast message type 4. These messages will be processed in the aircraft’s GBAS avionics system and the guidance information will be computed there. This eliminates the need for an on-board database to support these operations. The idea is to use these TAPs also for transmitting information which allows aircraft performing taxi operations. In contrast to Final Approach Segment (FAS) data blocks, TAPs will have variable lengths depending on the type of defined legs. Normally TAPs define initial fix (IF), track to fix (TF), and radius to fix (RF) legs, compatible with [1]. A TAP consists of an IF leg followed by one or more legs of other leg types. Similar to the path definition for an approach, these legs can also define a route on ground. Such a set of IF, TF, and RF are able to define a taxi route and could be transmitted via VHF broadcast on ground. Taxi trials with DLR’s A320 research aircraft ATRA and the GBAS ground station at airport Braunschweig-Wolfsburg showed that over the whole maneuvering area the VHF signal level was adequate for transmitting such a “Ground-TAP”. These tests were performed with an antenna on the aircraft in a height of 8ft, which is lower than the actual required coverage minimum defined in ICAO Annex 10. Together with a re-defined voice communication structure and a list of predefined routes the use of GBAS for taxi routing functionalities of an A-SMGCS is feasible. Due to the independency from an on-board database the combination of such a message broadcast and the GNSS based positioning can be the key enabler for a future auto taxiing functionality.