GBAS research station in braunschweig - Five years of successful GBAS operations

In December 2008 the Institute of Flight Guidance of the German Aerospace Center (DLR) installed a Ground Based Augmentation System (GBAS) manufactured by Thales Air Systems at the research airport Braunschweig-Wolfsburg in Germany. Since then, the Institute of Flight Guidance and other users have conducted many comprehensive experiments with this ground station throughout the GBAS research area. The ground station is part of the DLR air traffic validation center. It is not certified for official operations but is designed and developed according to all applicable specifications. In this setup, different flight inspection techniques were investigated with the station and new operational procedures were tested. Different aircraft were used for flight inspection as well as for operational procedure trials. This includes an Airbus A320 research aircraft, a King Air 350 flight inspection aircraft as well as a Boeing 737 standard airliner or a Do-128 research aircraft of the Technical University of Braunschweig. For a novel approach of verifying the contents of the GBAS message broadcast and the VHF coverage of the ground station, a helicopter (Bo-105) was used for flight tests. Over the years, different upgrades of the GBAS ground stations were realized. This includes hardware upgrades as well as software upgrades. In terms of hardware, different GPS receivers were used as well different processor boards. The software was upgraded to not only support straight-in “ILS-look-alike” Category I operations but also Terminal Area Paths (TAP), a functionality that allows curved path segments. In addition, prototypical software was installed to support Category II/III, so called GBAS Approach Service Type D (GAST-D) operations. Furthermore, the TAP functionality can be used to transmit “Ground-TAPs” to provide a highly accurate guidance for taxi operations during low visibility operations. Through Ground-TAPs taxi guidance is possible especially for pilots who are unfamiliar with the given airport or during operations in adverse weather conditions. Different trials are planned to verify this idea in 2014. In this paper, a short overview about the different upgrades of the ground station as well as the operational GBAS research with the ground station will be given. In addition, different performance reports of the station regarding position accuracy and VHF availability will be presented. Furthermore, the results of the helicopter flight trials regarding the VHF coverage with the low cost instrumentation will be shown and discussed in this work. To reduce integration costs, the onboard VHF receiving equipment was integrated into a crate that was hooked as sling load to the helicopter's cargo hook. A VHF antenna was fitted onto the crate and the receiver equipment was battery powered inside the crate. With this setup, the VHF reception in the terminal area of the research airport was investigated. The VHF coverage was tested along the defined approach paths as well as symmetrically around the VHF Data Broadcast (VDB) antenna of the ground station.