LAAS integrity study based on internal reliability theory

In order to guarantee integrity of the civil aviation precise approach , Local Area Augmentation System (LAAS) is developed by the U.S. Federal Aviation Administration (FAA). However, the scarcity of the LAAS independent samples available makes it is difficult to accurately establish the fault monitoring models and corresponding checking thresholds, which may cause integrity risk. In the paper, the outliers due to faults are quantitative discussed in the pseudorange domain, basing on internal reliability theory in the case of the unit weight variance factor is known and unknown. The outliers are projected to the position domain and added to the current PL (Protect Level), which is improved for over-bounding the position error due to fault. A new parameter which is not included in current LAAS Signal-in-Space Interface Control Document (ICD) is introduced in the improved PL algorithm. To deal with the data transmission problem caused by the new parameter, a compensating factor is proposed based on the meaning of the redundant measurement element of internal reliability theory, and the transmission of the new parameter is replaced by the amendment of the current parameters. LAAS integrity of the new fault monitoring algorithm is analyzed based on data collected from LAAS test bed on Handan airport by Communication, Navigation, Surveillance/Air Traffic Management (CNS/ATM) Labs, Civil Aviation Administration of China (CAAC) and the Flight Inspection Centre of CAAC. Moreover, the GPS standard constellation and its historical available probabilities are used for the LAAS availability analysis of the new fault monitoring algorithm. These analyses demonstrate that the new fault monitoring algorithm improves the integrity and availability of LAAS.