Recent developments in the LAAS program [GPS

The Federal Aviation Administration (FAA) is investigating the feasibility of using the Global Positioning System (GPS), together with local augmentation as the primary navigation system for the Category II and III precision approach of aircraft. This augmented system would be known as a local area augmentation system (LAAS) because it would place subsystems on the ground at or near an airport to greatly enhance the performance of airborne GPS receivers approaching that airport. The LAAS would complement space-based augmentations of GPS, such as the wide area augmentation system. When complete, the integrated system will meet stringent requirements on accuracy, integrity, continuity, and availability. Indeed, the LAAS will improve the airborne accuracy from approximately 100 m for stand-alone GPS to better than 1 m. This high accuracy is required so that LAAS can guarantee the integrity and continuity of the aircraft guidance during the approach phase of flight. Integrity requires the LAAS to detect any situations which threaten the safety of the landing, and notify the aircraft within 2 s of such a threat. Continuity is a competing consideration-it requires that the total number of alarms, true plus false, sent to the aircraft is very small. High continuity guarantees that the total number of aborted approaches is manageably small. Finally, availability is the fraction of the time during which LAAS is operational-providing position fixes with the specified accuracy, integrity and continuity. This paper describes the LAAS which has been proposed by the FAA. It discusses the fundamental operation of the LAAS.

Some deficiencies of the system of exciting satellite navigation augmentation are analyzed in the application of civil aviation. Since there is no local monitoring in Wide Area Augmentation System (WAAS), the protect level is increased, and the availability is reduced, so it could not satisfy the requirement of the precise approach. Moreover, because the Local Area Augmentation System (LAAS) could not solve the problem brought by ionosphere storms, the LAAS certification becomes complex and expensive. The basic principle of the new satellite navigation augmentation system named Local Airport Monitor (LAM) proposed by Federal Aviation Administration (FAA) is introduced. And the error distribution characteristic of LAM is discussed by sorting three conditions. Moreover, the expressions of LAM protection level and availability are studied. Some conclusions are obtained by simulations. In normal condition, the position accuracy of LAM is better than the one of WAAS and similar to LAAS and the availability of LAM is better than the one of WAAS and worse than LAAS. When there are ionosphere storms, the position precision and availability of LAM and WAAS reduce a little, but the position precision and availability of LAAS reduce 20.5% and 19.3% respectively. Furthermore, the availability of LAM is analyzed and simulated. And some conclusions are obtained: airborne user should first choose satellites whose elevation is lower than 10 degree and bigger than 70 degree. Reference station and airborne should use GAD-A and AAD-B receiver respectively, thus, the availability of LAM could bigger than 99.99%

This paper addresses topics concerning the development of future Unmanned Aerial Vehicles (UAV) so that they can operate safely within the community of the Federal Aviation Administration (FAA) and the International Civil Aviation Organization (ICAO). Studies by the Defense Science Board; the Office of Science and Technology; Government Accountability Office; and the Congressional Research Service: Library of Congress; have all emphasized that soon there will be a significant number of UAVs operating sideby- side with manned civil aircraft in the FAA’s National Airspace System (NAS). It is anticipated that future UAVs will start to perform many of the dull, dirty, and dangerous civilian missions. In 2006, about 600 UAVs are expected to be manufactured in the US alone. Therefore, there is an urgent need for developers of UAVs to understand safety certification for operations in the NAS, and that safety certification starts with the safety requirements; safety design; safe development process; safety verification; and safe operating procedures in the planned operational environment. This paper presents and discusses the experiences and lessons gained by the authors on the development of end-toend aviation safety; from the safety requirements to their final safety certification in the planned operational environment. The authors’ previous and ongoing works include the Global Navigation Satellite Systems (GNSS) systems such as the GPS; WAAS; LAAS; MSAS; GPS III; and different operational environments at different airports such as Incheon International Airport. The FAA started with the two traditional safety certifications processes: airborne system certification and ground system certification; governed mostly by Federal Aviation Regulations (FAR) and FAA’s Acquisition Management System (AMS), respectively. However, when FAA started to implement GNSS, the lines between airborne and ground systems became blurred, and as a result many current Communications, Navigation, Surveillance, and Air Traffic Management (CNS/ATM) systems have to follow both processes. We will also discuss the current Safety Management Systems being developed by both FAA and ICAO as an integrated, systematic, and harmonized approach and process to sort out the differing safety requirements from FAA, SAE-ARP, MIL-STD, RTCA, ASTM, ICAO, etc. to provide the eventual safe operations within the NAS. The discussion will then focus on the real world of institutional, operational, and technical issues for safety certification worldwide. Despite the numerous standards and guidance documents, many past safety analyses and studies were guided by best practices that had been used successfully in the past to streamline the process of providing all the required documentations and verifications. One such area is in the use of the “Integrity Panel of Experts” that had been used successful in the implementation of safety for the FAA’s Wide Area Augmentation System (WAAS) and Local Area Augmentation System (LAAS) programs. In many areas of the world, safety certification from a technical point of view is only the first step to achieving safety certification to fly in their national and sovereign airspace. Finally, we will show the first steps that UAV manufactures need to consider if they want their UAVs to be approved to fly safely in different national civilian airspace.

The Runway Incursion Prevention System (RIPS) program is an ongoing National Aeronautics and Space Administration (NASA) research effort intended to reduce the number of runway incursions at airports throughout the National Airspace System (NAS). The RIPS program flight tests and demonstration of technologies activities at the Dallas/Fort Worth (DFW) International Airport were completed in October 2000. The demonstration involved the application of both airborne and ground based technologies, as well as the integration of these technologies to form a complete runway incursion prevention system. This paper presents information on the research activities conducted at DFW related to the Ohio University Avionics Engineering Center (AEC) installed Global Positioning System (GPS) Local Area Augmentation System (LAAS) ground facility (LGF), it's use, the preliminary results obtained, and observations or conclusions when appropriate. A description of the RTCA DO-247 Surveillance and Guidance Sensor requirements is provided. Details of the DFW LAAS upgrade for NASA RIPS testing, AEC GPS LAAS test van equipage, and the Rockwell Collins Multimode LAAS receiver integration activities are presented. Data analysis activities have just been initiated.

The relationship between range-domain and position-domain errors remains an open issue for GPS augmentation programs, such as the Federal Aviation Administration's Local Area Augmentation System (LAAS). This paper introduces a theorem that guarantees a conservative error bound (overbound) in the position domain given similarly conservative overbounds for broadcast pseudorange statistics. This paired overbound theorem requires that a cumulative distribution function (CDF) be constructed to bound both sides of the range-domain error distribution. The paired overbound theorem holds for arbitrary error distributions, even those that are non-zero mean, asymmetric or multimodal. Two applications of the paired overbound theorem to GPS augmentation are also discussed. First, the theorem is employed to construct an inflation factor for a non-zero mean Gaussian distribution; in the context of a simulation of worst-case satellite geometries for 10 locations in the United States and Europe, the required inflation factor for broadcast sigma is only 1.18, even for biases as large as 10 cm for each satellite. Second, the theorem is applied to bound a bimodal multipath model tightly; the result shaves more than 40% off the previously established inflation factor derived through a more overly conservative analysis.

This paper develops code multipath error budgets for land-based Joint Precision Approach and Landing System (JPALS) ground station receivers. The approach is similar to that used for the civil Local Area Augmentation System (LAAS), with modifications for P(Y)-code tracking and the use of beam-steering antenna arrays. The budget includes two error allocations, one for receiver noise and one for code multipath, both of which are defined as a function of satellite elevation. The noise allocations are based on an analytical model that is fit to JPALS test data, while the multipath allocations are based on test data alone. The results show that JPALS ground stations have some advantages over LAAS ground stations due to antenna differences and the more limited multipath susceptibility of the P(Y)-code. We also investigate code multipath biases by way of simulations. The results indicate that the multipath allocations developed herein capture multipath biases for the expected environments.

Observations of extreme spatial rates of change of ionospheric electron content and the characterization strategy for mitigation applied by the U.S. local area augmentation system are shown. During extreme ionospheric activity, the gradient suffered by a global navigation satellite system user a few kilometers away from a ground reference station may reach as high as 425 mm of delay (at the GPS L1frequency) per km of user separation. The method of data analysis that produced these results is described, and a threat space that parameterizes these possible threats to user integrity is defined. Certain configurations of user, reference station, global navigation satellite system satellite, and ionospheric storm-enhanced density may inhibit detection of the anomalous ionosphere by the reference station.

Synthetic vision has the potential to improve safety in aviation through better pilot situational awareness and enhanced navigational guidance. The technological advances enabling synthetic vision are GPS based navigation (position and attitude) systems and efficient graphical systems for rendering 3D displays in the cockpit. A benefit for military, commercial, and general aviation platforms alike is the relentless drive to miniaturize computer subsystems. Processors, data storage, graphical and digital signal processing chips, RF circuitry, and bus architectures are at or out-pacing Moore's Law with the transition to mobile computing and embedded systems. The tandem of fundamental GPS navigation services such as the US FAA's Wide Area and Local Area Augmentation Systems (WAAS) and commercially viable mobile rendering systems puts synthetic vision well with the the technological reach of general aviation. Given the appropriate navigational inputs, low cost and power efficient graphics solutions are capable of rendering a pilot's out-the-window view into visual databases with photo-specific imagery and geo-specific elevation and feature content. Looking beyond the single airframe, proposed aviation technologies such as ADS-B would provide a communication channel for bringing traffic information on-board and into the cockpit visually via the 3D display for additional pilot awareness. This paper gives a view of current 3D graphics system capability suitable for general aviation and presents a potential road map following the current trends.

Predictability is a necessity in today's commercial flight operations if delays are to be minimized. Possible mitigations, such as the implementation of continuous descent arrivals (CDAs), may help generate the required procedural predictability to curtail these delays. However, on the basis of its individual avionics suite, each aircraft follows a different barometric vertical descent path; furthermore, the aircraft may be given additional level-off segments by air traffic control to compensate for possible deviations in the vertical profile. Therefore, aircraft flying the current descent profiles are too unpredictable and thus the procedures cannot be implemented in complex airspace structures or when traffic is moderate to high. This study introduces a mitigation to this problem by taking the global positioning system (GPS) one step further by integrating the GPS-based ground-based augmentation system (GBAS) into the new optimized continuous decent arrival procedure, subsequently, allowing for the introduction of a geometrical vertical guidance, namely, the GBASCDA, which will make the aircraft flying the descent profile predictable. With the increase in availability of GBAS aircraft equipage, specifically the GPS landing system (GLS), and the approaching amendment of the Appendix E of the Minimum Operational Performance Standards for GPS Local Area Augmentation System Airborne Equipment–RTCA DO-253D, this idea of the integration of the GBAS on the arrival/descent segment as a viable solution may be finally coming within reach.

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. This paper will explain the use of GBAS for taxi guidance. It presents, how the required navigation performance for automatic taxiing can be provided using GBAS. Besides the highly precision position service provided via Differential GPS, the Terminal Area Path (TAP) messages will be used to provide the aircraft with accurate and reliable information about the taxi route. Taxi trials with DLR's A320 research aircraft ATRA (Advanced Technology Research Aircraft) and the GBAS ground station at airport Braunschweig-Wolfsburg (EDVE) showed that over the whole maneuvering area the received VHF signal level was adequate for transmitting such a “Ground-TAP”. These tests were performed with an antenna on the aircraft located at a height of 8ft, which is lower than the actual required coverage minimum of 12ft defined in ICAO Annex 10. Together with a redefined voice communication structure and a list of predefined routes the use of GBAS for taxi routing functionalities of an Advanced Surface Movement Guidance & Control System (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.

This paper develops a single-frequency filter for smoothing GPS code measurements using a nonlinear method. The method zeroes steady-state divergence errors caused by ionospheric storms. The filter has significant potential to improve the availability of safety-critical differential GPS systems such as Ground-Based Augmentation Systems (GBAS). These systems, of which the Local Area Augmented System (LAAS) is one example, typically rely on a Hatch Filter for code smoothing. Although the Hatch filter offers excellent noise reduction and ease of implement under nominal conditions, the filter amplifies ionosphere errors under rare, anomalous storm conditions. Our method generalizes the Hatch Filter by adding a correction term which is computed through a nonlinear process. The nonlinear process detects high ionosphere-delay gradients and estimates the appropriate correction term for the Hatch Filter. Experimental trials indicate that the nonlinear filter not only zeroes steady-state divergence but also reduces maximum transient errors by 0-25% relative to the Hatch Filter without impacting filter noise under nominal conditions.

The positioning accuracy and integrity of the Ground-Based Augmentation System (GBAS) are impacted by the abnormal troposphere and ionosphere conditions resulting from extreme weather and intense radiation. Non-nominal troposphere error will increase the residual tropospheric uncertainty between the GBAS ground facility and aircraft. The plasma bubbles may induce signal scintillations while passing across a signal path, which could result in a loss of lock or a cycle slip. However, existing methods cannot deal with the threats caused by abnormal meteorological conditions. To reduce the impact of these conditions on GBAS, this paper describes an optimization method. By reassessing the weight matrix W in the calculation of the Vertical Protection Level (VPL), satellites that suffer from bigger pseudorange errors are assigned less importance in the positioning solution. Therefore, the positioning accuracy and integrity of GBAS are improved. Initially, we evaluate the Geometric Dilution of Precision and VPL for both single GPS and GPS+BDS constellations under abnormal meteorological conditions. The performance of different orbiting satellites in such conditions is then evaluated to further analyze their benefits in future Multi-Constellation Dual Frequency (MCDF) GBAS. The results show that the proposed optimization method can effectively reduce the influence of abnormal meteorological conditions and improve the positioning accuracy and integrity of MCDF GBAS. Moreover, mixed orbiting satellites provide more robustness against abnormal meteorological conditions and can significantly enhance the performance of MCDF GBAS.

The ground-based augmentation system (GBAS) is the cornerstone for enabling automated landings without the instrument landing system (ILS). Currently, GBAS is evolving to GBAS approach service type-D (GAST-D) for category III landings. This development toward GBAS GAST-D extends GBAS via the use of multiple frequencies (L1/L2 and L5) and the use of multiple global navigation satellite system constellations. GBAS requires correction data to be broadcast to aircraft, which is currently handled via the VHF data broadcast (VDB) datalink. However, VDB has several known shortcomings: 1) low throughput, 2) small area of operation, and 3) no cyber-security measures. In this article, we propose the use of the L-band digital aeronautical communications system (LDACS) for broadcasting GBAS correction data to address these shortcomings. In flight experiments conducted in 2019, we set up an experimental GBAS installation using LDACS. Broadcast data are secured using the timed efficient stream loss-tolerant authentication (TESLA) broadcast authentication protocol. Our results indicate that cryptographically secured GBAS data via LDACS can provide GAST-C and GAST-D services with high availability if cryptographic parameters are chosen appropriately.

The Ground-Based Augmentation System (GBAS) is a navigation system for aircraft designed to be used for precision approaches and landings. GBAS improves the accuracy of the satellite navigation system significantly. However, some flight accidents still occur occasionally due to lack of availability and it makes more stringent requirements on availability that CAT II/III precise approach is trying to introduce GBAS. Therefore, it is necessary to find an effective prediction algorithm for GBAS. The protection level is a key parameter in the process of evaluating the availability. There are three relevant parameters: quantile K represents the fault-free missed detection multiplier; projection matrix S is the vertical projection factor in the along-track coordinate system; variance of measurement noise is the standard deviation of the uncertainties of the residual differential error, which consists of the root sum square of uncertainties introduced through ionospheric and tropospheric decorrelation as well as the contribution of the ground and airborne multipath and noise. Some researchers have found that the model for the standard deviation of GBAS pseudo-range correction error is conservative, which causes decline of prediction accuracy. However, it is hard to explicitly model this parameter. We made a reevaluation based on support vector machine and improved the prediction algorithm for availability. We developed the simulation software and make practical measurement. Considering the influence of different distributions of based stations of GBAS, the availabilities of EWR, GIG and IAH are evaluated, and the results were compared with the actual values. The result shows that the prediction errors are 3.17%, 1.96% and 0.98% respectively.

Augmentation System (GBAS) in equatorial and low latitude regions. The ionosphere affects the propagation of GPS signals and can reduce the positioning accuracy in the equatorial and low-latitude regions. Auxiliary systems have been developed to meet the safety requirements of aviation. In this context, GBAS provide higher accuracy for differential corrections. To evaluate the performance of a GBAS, a simulation model of the GPS L1 signal-in-space has been developed, considering ionospheric delay based on statistical distributions of vertical Total Electron Content residuals obtained from IRI model and Rede Brasileira de Monitoramento Contnuo estimates, in combination with amplitude ionospheric scintillation simulated based on - probability distributions, as well as phase scintillation, generated according to empirical relationships between the indices 4 and . The GPS L1 signal model also considers clock and random errors, tropospheric delays, ambiguity, and multipath, for a complete description.