GBAS CAT II/III Business Aircraft Flight Trials and Validation – Phase 1

J. Dvorska, L. Podivin, M. Musil, L. Zaviralova, M. Kren

Abstract: The development of new GNSS based technologies that will enable precision approaches down to CAT II/III minima is currently in the operational validation phase. After years of technical feasibility assessments by the community of the GPS L1 based augmentation system, operational validation focusing on specific solutions is at its final stages. The objective of this paper is to describe the activities conducted with respect to the validation of the GBAS CAT II/III concept for business aircraft, the results from flight trials and feedback on feasibility of requirements from the airborne perspective. The focus is on the avionics receiver prototype (providing equivalent functionality to the Multi-mode receiver known from air transport aircraft) upgraded to GBAS CAT II/III (GAST D) capability. The paper focuses on Phase 1 of validation activities starting with the integration into Honeywell experimental business aircraft, Falcon F900EX. The test setup includes prototype avionics receiver with GBAS GAST D capability coupled with the autopilot of the aircraft to enable autonomous approaches to CAT II minima. Additional multi-mode receiver is placed on board of the experimental aircraft, to check for interoperability and consistency of results of two GBAS capable receivers. Dual-frequency Novatel receiver, connected to the same antenna as the other two receivers, provides centimeter level accuracy after post processing with another Novatel receiver based on ground with surveyed antenna location, to provide the truth to which the performance of the system is compared. In order to verify the VDB transmission from the ground station, as well as airborne reception (i.e. with respect to number of CRC errors) a Telerad receiver is placed on board and connected to the same VHF antenna as the other two GBAS capable receivers. The recording equipment enables to record all the aircraft data relevant for validation of models, as well as data from all the receivers (both ARINC 429, as well as internal data including GBAS specific monitors status) needed for verification and validation of the overall GBAS CAT II/III concept based on GPS L1. An experimental display which can overlay the primary flight display on one pilots’ side and which can be turned on and off, subject to pilots’ needs, was updated to provide status of the GBAS solution (supported modes GBAS CAT I or CAT II/III, as well as information on service downgrade). Deviations based on the outputs of the tested receiver were displayed together will all the usual information based on legacy display. The successful flight trial campaign, described in the paper, occurred in September and early October of 2013. It included total of 56 approaches, over 5 airports in US and Europe and flights were conducted with 4 experimental GBAS GAST D ground stations from 4 different manufacturers (US as well as European) and Honeywell certified GBAS GAST C ground station. The testing included a wide range of validation exercises focusing on important aspects for GAST D as well as GAST C. Ground station interoperability tests, multipath data collections while stationary and during taxi in order to conduct validation of multipath airborne model were performed. GAST D as well as GAST C straight-in approaches from outside of Dmax (distance after which augmentation and integrity data from ground station cannot be used for precision approach) at 23 nautical miles, were performed together with approaches from PAR (precision approach region at 10 nautical miles). Also number of regression tests was performed to check for correct behavior of the overall system (e.g. jumps that could be caused by difference in solution for GAST C and GAST D). One type of tests included injection of an error to the airborne receiver in GAST D mode that caused its regression to GAST C, for both outside and inside PAR. Further testing included ground station aspects, turn off of one reference receiver measurement units which either causes a downgrade to GAST C or different level performance depending on the number of reference receivers used in the installation. VHF data broadcast inhibit from the ground station was tested as well. Data analysis was performed in several categories to capture all the important aspects of the airborne subsystem validation. Performance analysis for nominal approaches in GAST C and GAST D was done with respect to the NSE (navigation sensor error), and TSE (total system error) which are important inputs into the concept validation as well as validation of simulations for the proof of concept. Performance during the injected faults was also evaluated. GAST D monitors (Dual solution ionospheric gradient monitor, Difference correction magnitude check, Fault detection, Carrier code divergence, Bias approach monitor, Loss of approach guidance, Reference receiver monitor) were evaluated with respect to correct setting of applicable thresholds, number of alarms, and possible false alarms and their impact. Further data analyses focused on investigating the reasons for service type downgrades when unintentional and SV exclusions.
Published in: Proceedings of the 27th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2014)
September 8 - 12, 2014
Tampa Convention Center
Tampa, Florida
Pages: 822 - 834
Cite this article: Dvorska, J., Podivin, L., Musil, M., Zaviralova, L., Kren, M., "GBAS CAT II/III Business Aircraft Flight Trials and Validation – Phase 1," Proceedings of the 27th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2014), Tampa, Florida, September 2014, pp. 822-834.
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