Ronald Braff

A Method of Over Bounding Ground Based Augmentation System (GBAS) Heavy Tail Error Distributions

The purpose of this paper is to describe a statistical method of modeling and accounting for the heavy tail fault-free error distributions that have been encountered in the Local Area Augmentation System (LAAS), the FAA’s version of a ground-based augmentation system (GBAS) for GPS. The method uses the Normal Inverse Gaussian (NIG) family of distributions to describe a heaviest tail distribution, and to select a suitable NIG family member as a model distribution based upon a statistical observability criterion applied to the FAA’s LAAS prototype error data. Since the independent sample size of the data is limited to several thousand and the tail probability of interest is of the order of 10-9, there is a chance of mismodeling. A position domain monitor (PDM) is shown to provide significant mitigation of mismodeling, even for the heaviest tail that could be encountered, if it can meet certain stringent accuracy and threshold requirements. Aside from its application to GBAS, this paper should be of general interest because it describes a different approach to navigation error modeling and introduces the application of the NIG distribution to navigation error analysis.

Analysis of Stand-alone Differential GPS for Precision Approach

Recently, there has been wide-spread interest in the use of the Global Positioning System (GPS) for precision approaches in a civil aviation environment. However, most of the work to date in Europe and North America has treated a GPS/inertial reference system (IRS) combination as the source of guidance for this phase of flight. Since the US has a very large general aviation population, the FAA is very interested in determining the role of a stand-alone implementation of differential GPS (DGPS) as a navigation sensor for precision approaches. This paper has two parts: a summary of the analysis of this application of DGPS; and a discussion of the navigation satellite test bed that is under development at the FAAs Technical Center. The first part contains proposed accuracy, integrity and availability operational requirements, and their air traffic implications. A stand-alone DGPS concept is developed, and analysed. The major results of the analysis indicate that stand-alone DGPS may not fully meet Category I (CAT I) accuracy requirements. The results of the analysis are then used to provide the rationale for the major recommendation: that FAA pursue an implementation of a wide-area DGPS (WADGPS) to achieve a Near CAT I precision approach capability. The second part of the paper discusses the three-phase navigation satellite experimental programme that is being developed to acquire the data to validate the enhancements to GPS, including a GPS Integrity Channel (GIC) and WADGPS. The objectives of each of the experimental phases are presented and discussed. Then the experiments of Phase I that address GIC/WADGPS are discussed.

Recent developments in the LAAS program [GPS]

The Local Area Augmentation System (LAAS) is the Federal Aviation Administrations ground-based augmentation system (GBAS) for local-area differential Global Positioning System (DGPS). It will support all categories of precision approach. LAAS is currently under advanced development and specification. The purpose of this paper is to provide an update on the LAAS program strategy and a technical description of the LAAS. The LAAS program involves a government-industry partnership, specification of the Ground Segment, and FAA in-house development of a test prototype containing all of the LAAS features. The technical section contains both top-level and intermediate-level descriptions of LAAS, with emphasis on the Ground Segment. Three distinguishing advances are described in more detail: multipath limiting antenna, airport pseudolite, and a method for transforming integrity parameters from the pseudorange domain to the position domain.

THE FAA'S LOCAL AREA AUGMENTATION SYSTEM (LAAS)

The Federal Aviation Administration (FAA) is developing the Local Area Augmentation System (LAAS) as a public use local area differential GPS system. The LAAS is required to support all categories of precision approach navigation. The purpose of this paper is to summarize the FAAs LAAS technical activities and programme plans. First, the complementary roles of the Wide Area Augmentation System (WAAS) and LAAS are summarized. Then technical activities are discussed, including requirements, system architecture, and flight tests. The paper concludes with a summary of the FAAs plans for LAAS, including the planned schedule of major programme activities.

FAA's DGPS CAT III feasibility program: update and test methodology

The FAA has established a program to evaluate the technical feasibility of using guidance from the satellite-based Global Positioning System (GPS) for Category III (CAT III) precision approaches. A combination of flight tests, analyses and simulations will be used to evaluate differential GPS (DGPS) and associated monitoring techniques for CAT III application. Emphasis will be placed on meeting accuracy and integrity requirements for a complete DGPS-based CAT III autoland capability. Contractors will be required to provide the ground and airborne equipment for computing DGPS-based aircraft position and velocity. Contractors will also provide a demonstration aircraft completely equipped with a DGPS-based capability. Feasibility will be demonstrated by meeting either sensor accuracy requirements for CAT III applications or total system accuracy requirements. It is expected that meeting total system accuracy requirements would place less demand on the accuracy of the DGPS-based sensor than meeting sensor requirements, but more demand on automatic total system performance monitoring in the aircraft. This paper presents an updated schedule of program activities and describes the test methodology in detail.<<ETX>>

Impact of navigation accuracy on the intervention rate in a highly automated air traffic control system

Progress in navigation technology is expected to bring about a lower air traffic control (ATC) intervention rate than the rate that could be expected based upon todays navigation and flight control capabilities. The extent to which this may occur is quantified, and additional possible benefits, such as increasing air traffic throughput and intervening earlier in potential loss of separation between aircraft, are discussed. A prototypic aircraft-aircraft encounter is defined. It includes a simple intervention-decision rule which attempts to capture the prudence practiced by todays air traffic controllers, and which typifies one type of decision rule presently under consideration for use in a future automated ATC system such as AERA 3. This rule is applied to an operational environment where GPS (Global Positioning System) is employed to navigate user-preferred routes.<<ETX>>

Performance study of a new crosslink-aided User Range Accuracy (URA) integrity monitor algorithm for LPV-200

A new algorithm for the GPS satellite User Range Accuracy (URA) integrity monitor that incorporates the satellite ranging measurements taken at ground monitor stations, aided by the crosslink ranging measurements taken between the GPS satellites, is presented. The new algorithm provides improved performance and eliminates the need for a key assumption of a previous algorithm that used ground and crosslink measurements. The performance of the new algorithm is analyzed and measured by the values of the minimum monitorable URA (MMU) for the satellites in the constellation. The availability of LPV-200 operations for an aviation GPS receiver that uses the MMU values as URAs to derive its integrity assured navigation position solution is also analyzed. The LPV- 200 availabilities at representative US and worldwide airport locations are presented. Improved performance of the new algorithm is shown as a reduction of the MMU value and an increase of the LPV-200 availability.

TECHNICAL AND PROGRAMMATIC FEATURES OF THE FAA'S LAAS

The US Federal Aviation Administration (FAA) is developing and planning to field the Local Area Augmentation System (LAAS). LAAS is a Ground-Based Augmentation System (GBAS) to GPS, and is designed to serve all categories of precision approach. The purpose of this paper is to provide the latest technical and status information on the LAAS programme. The technical aspects of the LAAS specification are discussed, followed by a description of specification validation field testing and results. Institutional and programmatic aspects are then summarized along with a chronology of events leading up to the Government Industry Partnership (GIP) for the initial development and fielding of LAAS.