Search

Nowadays, there is an increase in the demand for optimized services in urban environments. However, ground transportation in big urban centers has been facing challenges for many years (e.g., resilience and congestion) and new paradigms have been proposed, such as the Urban Air Mobility (UAM) concept. UAM aims to enhance the urban transportation system using manned and unmanned aerial vehicles (i.e., Electric Vertical Takeoff and Landing - eVTOL - vehicles). Although UAM offers many benefits (e.g., cost reduction and increase in transportation capacity), many challenges need to be faced to enable safe and efficient operations. Furthermore, trajectory planning is challenging in the National Airspace System (NAS) and UAM operations due to several factors. Finally, new initiatives concerning UAM trajectory planning can be accelerated with the support of an automatic what-if platform capable of evaluating trajectories feasibility and efficiency. This research aims to propose a simulation platform for enabling trajectory evaluation in UAM operations. This platform, named Trajectory-Based Urban Air Mobility Simulator (TUS), focuses on simulating trajectories in the urban aerial environment. TUS enables users to test new UAM algorithms (e.g., flow management strategies, real-time evaluation of maneuvers effectiveness, airspace configurations) and simulate both manned and unmanned vehicles. Furthermore, TUS operation relies on a set of inputs and evaluates the trajectories generated from efficiency and safety perspectives. This process is performed using a Discrete Event Simulation (DES) approach. The experiments performed showed that TUS can perform a realistic evaluation of UAM trajectories and can be effortlessly used to simulate hundreds of scenarios.

Unmanned aircraft systems (UAS) collaborate with humans to operate in diverse, safety-critical applications. However, assurance technologies need to be integrated into the design process in order to guarantee safe behavior, thereby enabling UAS operations in the National Airspace System (NAS). In this paper, formal methods are integrated with learning-enabled systems representations. The generation and representation of knowledge are captured via monadic second-order logic rules in the cognitive architecture Soar. These rules are translated into timed automata, and a proof of correctness for the translation is provided so that safety and liveness properties can be checked in the formal verification environment Uppaal. This approach is agnostic to the learning mechanism used to generate the learned rules (e.g., chunking, etc.). An example of a fault-tolerant, learning-enabled UAS deciding which of four contingency procedures to execute under a lost link scenario while overflying an urban area is used to illustrate the approach.

In the past few years, there has been a growth in Unmanned Aircraft Systems (UAS) numbers in segregated airspace. However, although there is an interest in integrating large UAS in the National Airspace System (NAS), safety challenges regarding this insertion arise from the inclusion of new ways of reaching unsafe states. Although UAS may be used in different situations and brings several advantages to the airspace (e.g., efficiency), it may bring uncertainties due to the lack of familiarity of Air Traffic Controllers (ATCos) in these operations. Furthermore, the Terminal Maneuvering Area (TMA) is a critical control area generally established at the confluence of Air Traffic Service (ATS) routes in which the aircraft tend to be closer to each other. Besides, defining a final arrival segment for a set of aircraft in a complex environment is challenging. Thereupon, the main objective of this research is to propose a parallel swarm-based method for optimizing final aircraft arrival segment design (i.e., routes that connect the final sector to the Initial Approach Fix - IAF) considering the presence of aircraft of multiple Technology Maturity Levels (TML) - including the UAS. This is conducted from two perspectives: ATCo workload (which is related to safety) and sequencing duration (which is related to efficiency). Furthermore, different phases of UAS integration are considered using the Technology Maturity Levels (TMLs). Finally, the solutions consider airspace restrictions (e.g., minimum separation between aircraft and bad weather conditions). The experiments conducted show that this approach can build safe and efficient solutions, even in situations with many aircraft.

Natural hazards, such as hurricanes and winter storms, computer glitches and technical flaws, and man-made terror or cyber-physical attacks, can lead to localized perturbations of the U.S. national airspace system airport network (NASAN), which can in turn percolate across the interconnected system. Here we develop and demonstrate an approach to quantitatively characterize the robustness of NASAN, defined as loss of critical functions owing to perturbations, and a quantitative framework to select the most efficient and effective post-hazard recovery strategies. The system-level robustness and recovery strategies rely on network science methods and associated attributes. New insights include the central role of network attributes to robustness and optimal recovery sequences. Characterizations of robustness and fragility can inform what-if plans and proactive design, while recovery strategies developed in advance can support systematic, reliable, and timely bounce-back from hazard-related perturbations. The framework can serve as a baseline over which local information or cost optimization can be superposed.

Applications for unmanned aircraft systems (UAS), or “drones,” are increasing rapidly. In order to provide safe and reliable links to integrate UAS into the National Airspace System (NAS), control and nonpayload communication (CNPC) system requirements are being specified. A comprehensive knowledge of the air-to-ground (AG) channels in the bands of interest (C-band and L-band) plays an essential role. The NASA Glenn Research Center has sponsored an AG channel measurement campaign for most of the typical ground site (GS) local environments, including over water [8] , hilly/mountainous [9] , suburban, and near-urban. As a continuation of our prior study, this paper addresses the suburban and near-urban scenarios. Our developed AG channel models include path loss, small-scale fading Ricean K factors, spatial and interfrequency correlations for multiple aircraft antennas, root-mean-square (RMS) delay spread, and wideband tapped delay line (TDL) models. The path loss is described by either log-distance or two-ray models, with small corrections for flight direction. The K factors were 12 (14) dB in L-band and 27.4 (28.5) dB in C-band in near-urban (suburban) environments. The interband signals were uncorrelated, but the intra-band signals were highly correlated, with the median correlation coefficient greater than 0.85. The C-band RMS delay spread was on average 10 to 60 ns, with maximum of approximately 4 μs. The TDL models are composed of the line-of-sight (LOS) component, a ground reflection, and up to seven intermittent multipath components (MPCs). Relative power, phase, occurrence probability, duration, and excess delays for these intermittent MPCs are quantified. An algorithm to simulate the AG channel impulse response (CIR) via the TDL models is provided.

The use of ground-based augmentation systems (GBASs) is increasing in the national airspace system and also in many nations to support aircraft precision approaches and landing. An anomalous ionospheric event if undetected can cause a potential threat to users of single-frequency-based global navigation satellite system augmentation systems. Current GBAS utilize the pre-defined “worst case” ionospheric threat model in their computation of user position errors to consider all possible ionospheric conditions. This could lead to an excessive availability penalty by adding conservatism on the resulting error bounds. This paper proposes a methodology of real-time ionospheric threat adaptation that adjusts the ionospheric threat model in real time instead of always using the same threat model. This is done by using predicted values of space weather indices for determining the corresponding threat model based on an established relationship between space weather indices and ionospheric threats. Since space weather prediction itself is not reliable due to prediction errors, an uncertainty model was derived from 17 years of historical data. When applied to Category I GBAS in the Conterminous United States, this method lowered the upper bound of the current threat model about 95% of the time during the 17 years (from 1995 to 2011) using the bounded prediction value of the disturbance-storm time index.

For over 100 years manned aviation has been based on pilots seeing and avoiding other aircraft. During this time aviation has evolved to a point where there were 37.4 million commercial flights scheduled in 2014 [1]. The national airspace system (NAS) of each country is a complex system-of-systems involving air traffic control, a network of navigation and communication facilities, airports, controlled and uncontrolled airspace, and the associated rules and regulations for each part of this system. It is into this system that we are now introducing unmanned aircraft systems (UAS) for commercial and civilian applications.

Unmanned Aerial Vehicles (UAVs) become promising in different civilian and military applications due to their lower cost and greater flexibility in comparison to manned aircraft. However, the growing diversity of flight makes UAVs vulnerable to mid-air collisions. To ensure the safety for manned aircraft, human pilots are responsible for detecting intruders in airspace and performing appropriate maneuvers to avoid collisions [1]. Unlike manned aircraft with human pilots involved, UAVs must be equipped with Sense and Avoid (SAA) systems to guarantee the flight safety [2]. Thus, SAA systems play an important role in merging UAVs into the National Airspace System. As illustrated in Figure 1, an SAA scheme is composed of four units, which are sensing, conflict detection, collision avoidance, and flight controller, respectively.

Today, unmanned aircraft system (UAS) operations are typically conducted in segregated airspace and in limited combat theaters. In order to integrate UAS into the National Airspace System (NAS), UAS must operate safely, efficiently, and be compatible with existing manned aircraft traffic so that the overall safety and efficiency of the airspace is not degraded [1]. There are many challenges that lie ahead to allow UAS unrestricted access to NAS, but perhaps the greatest technical challenge involves fulfilling the "See and Avoid" requirements (14CFR 91.111 and 91.113).

Recent advances in sensing and computing technology has made unmanned aerial vehicles/systems (UAV/UAS) low cost but still increasingly capable of executing complex missions in challenging environments. They have gained popularity in a vast range of civilian applications, including search and rescue, disaster relief, and filming. Recently, the Federal Aviation Administration (FAA) has issued the Notice of Proposed Rulemaking (NPRM) on UAS certifications [1], indicating that a large number of UAS will be present in the National Airspace System (NAS) in the near future. The NASA UTM project is an effort on enabling low-altitude UAS flights [2]. Big value envisaged by Amazon Prime Air [3] happens only when the drone is able to fly itself tens of miles from the distribution center to people’s homes autonomously. One prerequisite for such flights is collision avoidance. Our research aims at drones that travel in class G airspace. This article is an exploration of the drone collision avoidance problem in urban areas. The main contribution is a safety control framework that enables a UAS to perform collision avoidance with manned aircraft during autonomous navigation.

Recent advances in unmanned and autonomous vehicle technology are accelerating the push to integrate these vehicles into environments, such as the National Airspace System, the national highway system, and many manufacturing environments. These environments will require close collaboration between humans and vehicles, and their large scales mean that real-world field trials may be difficult to execute due to concerns of cost, availability, and technological maturity. This paper describes the use of an agent-based model to explore the system-level effects of unmanned vehicle implementation on the performance of these collaborative human–vehicle environments. In particular, this paper explores the introduction of three different unmanned vehicle control architectures into aircraft carrier flight deck operations. The different control architectures are tested under an example mission scenario using 22 aircraft. Results show that certain control architectures can improve the rate of launches, but these improvements are limited by the structure of flight deck operations and nature of the launch task (which is defined independently of vehicles). Until the launch task is improved, the effects of unmanned vehicle control architectures on flight deck performance will be limited.

Automatic dependent surveillance-broadcast (ADS-B) is one of the fundamental surveillance technologies to improve the safety, capacity, and efficiency of the national airspace system. ADS-B shares its frequency band with current radar systems that use the same 1,090 MHz band. The coexistence of radar systems and ADS-B systems is a key issue to detect and resolve conflicts in the next generation air transportation system (NextGen). This paper focuses on the performance evaluation of ADS-B with existing radar systems and performance optimization of ADS-B systems to improve the safety and efficiency of conflict detection and resolution in NextGen. We have developed a simulation environment which models the complex interplay among the air traffic load, the radar systems, the ADS-B systems, and the wireless channel. A simple model is used to derive an analytical expression for a performance metric of ADS-B. This model is then used to design an adaptive ADS-B protocol for maximizing the information coverage while guaranteeing reliable and timely communication in air traffic surveillance networks. Simulation results show that the effect of ADS-B interference on the current radar system is negligible. The operational ability of ADS-B meets the performance requirements of conflict detection and resolution in air traffic control. However, upgrades are required in the current radar system for operation within an ADS-B environment since the current radars can significantly degrade the ADS-B performance. Numerical results indicate that the proposed adaptive protocol has the potential to improve the performance of conflict detection and resolution in air traffic control.

Unmanned aircraft systems (UAS) are expected to be used in greatly increasing numbers in the near future. To safely integrate them into the National Airspace System (NAS) [1] requires highly reliable communication links for control and nonpayload communications (CNPC) [2]. Although spectrum allocations for UAS appear to be in place, UAS missions can differ markedly from those of conventional piloted aircraft, and new challenges will appear. One of these challenges is the potential detrimental effects of the air-ground (AG) channel [3]. For past systems that used elevated ground site (GS) antennas in open areas, multipath propagation was minimal. Data rates and bandwidths of past systems were also small, rendering the multipath issue either inconsequential or easily overcome by (sometimes large) transmit power increases or longer latencies. Legacy voice communication systems are also comparatively low rate and forgiving of delay and can usually resort to repetition to improve reliability.

Numerous factors influence the operational performance of the National Airspace System (NAS). In particular, the traffic efficiency is affected by uncertainties such as weather, navigation accuracy, aircraft performance and operational procedures, and air traffic management (ATM) actions. This study focuses on identifying various air traffic uncertainty sources and deriving the associated mathematical models of service time distributions. These models provide the distributions given air traffic uncertainties through analytical expressions without resorting to computationally expensive Monte-Carlo simulations.

The system of air-ground communications is one of the most fundamental elements of air traffic control in the National Airspace System (NAS). The current air-ground voice communications systems are using the more than 50-year-old analog voice transmission technology in the licensed air traffic management VHF spectrum band. The limited spectrum is allocated statically based on air traffic control organization and geographic locations. With the increasing use of data applications for air-ground communications, the demand to effectively use the limited spectrum has increased. There are several proposed approaches to solve the projected saturated spectrum in the future. However, these approaches do not address the current practice of static spectrum allocation, which this author anticipates will be a major bottleneck for effective use of the limited spectrum. The current static channel assignment creates inefficient use of the limited spectrum. Regardless of whether a channel is used, it is permanently assigned to the particular geographical areas and organizations. This prevents other users from using the channels when the channels are idle. Also, this static allocation of the spectrum constrains the reassignment of channels and creates a long transition period for moving the existing analog system to a new digital system. The emerging Cognitive Radio (CR) technology provides the opportunity to address the static allocation of spectrum issue and offer a more flexible transition approach for updating the legacy air-ground radio system. The emerging CR technology provides the sensing of surrounding environment, allowing the radio to adapt to the environment accordingly. Built on software-defined radio (SDR) technology, CR is able to employ these features with the cognitive engine and the aid of several sensors. The cognitive engine carries out these tasks by obtaining all available information from sources such as sensors, protocol layers, a policy engine, and its own hardware, and then interprets, reasons, and makes the optimum decision to adapt. Integrated with ground radio stations and centralized management systems, the CR can dynamically use the available channels based on its actual location, environment condition, and, therefore, maximize the use of the limited spectrum.

This addresses topics concerning the development of future Unmanned Aerial Vehicles (UAV) so 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 side-by-side with manned civil aircraft in the FAA's National Airspace System (NAS). It is anticipated that future UAVs will perform many of the dull, dirty, and dangerous civilian missions. In 2006, about 600 UAVs were 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 safety requirements, safety design, safe development processes, safety verification, and safe operating procedures in the planned operational environment.

The problem of regulating air traffic in the en route airspace of the National Airspace System is studied using a Eulerian network model to describe air traffic flow. The evolution of traffic on each edge of the network is modeled by a modified Lighthill-Whitham-Richards partial differential equation. The equation is transformed with a variable change, which makes it linear and enables us to use linear finite difference schemes to discretize the problem. We pose the problem of optimal traffic flow regulation as a continuous optimization program in which the partial differential equation appears in the constraints. We propose a discrete formulation of this problem, which makes all constraints (the discretized partial differential equations, boundary, and initial conditions) linear. Corresponding linear programming and quadratic programming based solutions to this convex optimization program yield globally optimal solutions to various air traffic management objectives. The proposed method is applied to the maximization of aircraft arrivals and minimization of delays in the arrival airspace due to exogenous capacity reductions. The corresponding linear and quadratic programs are solved numerically using CPLEX for a benchmark scenario in the Oakland Air Route Traffic Control Center. Several computational aspects of the method are assessed-in particular, accuracy of the numerical discretization, computational time, and storage space required by the method.

Traffic flow management (TFM) allocates the various airport, airspace, and other resources to maintain an efficient traffic flow consistent with safety. TFM is a complex area of research involving the disciplines of operations research, guidance and control, human factors, and software engineering. Hundreds of human operators make TFM decisions that involve tens of thousands of aircraft, en route air traffic control centers, the Federal Aviation Administration's System Command Center, and many airline operation centers. This paper provides an overview of how TFM decisions are made today and challenges facing the system in the future, and reviews modeling and optimization approaches for facilitating system-wide modeling, performance assessments, and system-level optimization of the national airspace system in the presence of both en route and airport capacity constraints.

In today's National Airspace System (NAS), when an application requires information from another application, a custom application-to-application interface is built. This results in an increasingly complex system, where applications are tightly coupled and expensive to develop and maintain. System-Wide Information Management (SWIM) addresses these shortfalls by implementing a shared infrastructure for managing NAS information. SWIM is based on a service-oriented architecture, a fast growing trend in information technology. It will help the Federal Aviation Administration (FAA) meet the information-sharing needs of the Next Generation Air Traffic System (NGATS) and the federal government's E-government Initiative. SWIM will reduce the cost, complexity, and cycle time for building new applications and help the FAA implement SWIM-enabled applications that increase FAA and user productivity.

The authors present the Communication System Architecture for Air Traffic Management and Weather Information Dissemination as viewed within the context of the overall National Airspace System (NAS) and the services it provides. This paper presents the architecture in the 2015 time frame when the final phases of transition take place from analog voice to digital data exchange of common data via integrated networks. The results of this transition are an integrated collection of systems and procedures that efficiently use the capacity of the NAS while balancing access to all user classes and maintaining the highest levels of safety. Efficient collaboration among users is built on a foundation of common data. This information base provides common situational awareness to all participants. All users are accommodated and will receive benefits commensurate with equipage level. This architecture development provides a technical framework for decision-making, research, and analysis of communication technologies.

An Eulerian network model for air traffic flow in the National Airspace System is developed and used to design flow control schemes which could be used by Air Traffic Controllers to optimize traffic flow. The model relies on a modified version of the Lighthill-Whitham-Richards (LWR) partial differential equation (PDE), which contains a velocity control term inside the divergence operator. This PDE can be related to aircraft count, which is a key metric in air traffic control. An analytical solution to the LWR PDE is constructed for a benchmark problem, to assess the gridsize required to compute a numerical solution at a prescribed accuracy. The Jameson-Schmidt-Turkel (JST) scheme is selected among other numerical schemes to perform simulations, and evidence of numerical convergence is assessed against this analytical solution. Linear numerical schemes are discarded because of their poor performance. The model is validated against actual air traffic data (ETMS data), by showing that the Eulerian description enables good aircraft count predictions, provided a good choice of numerical parameters is made. This model is then embedded as the key constraint in an optimization problem, that of maximizing the throughput at a destination airport while maintaining aircraft density below a legal threshold in a set of sectors of the airspace. The optimization problem is solved by constructing the adjoint problem of the linearized network control problem, which provides an explicit formula for the gradient. Constraints are enforced using a logarithmic barrier. Simulations of actual air traffic data and control scenarios involving several airports between Chicago and the U.S. East Coast demonstrate the feasibility of the method

The National Institute of Standards and Technology has proposed using the common criteria and system-level protection profiles (SLPPs) to specify security requirements in large systems, such as those used in air traffic management. This article summarizes experience with SLPP and security targets for the US Federal Aviation Administration's National Airspace System. The authors review the FAA efforts, highlight the problems encountered, and offer suggestions for future work, calling for more research on linking systems, software, and security requirements engineering with SLPP; clearer ties between security specifications and system certification; and better guidance on the appropriate use of SLPP as a prerequisite to widespread use

The acceptance and implementation of advanced digital avionics and flight control systems is dependent on the successful integration of these systems into the current and future National Airspace System (NAS). This paper describes a digital avionics systems research facility known as the Digital Information Facility (DIF) developed to provide researchers with the ground systems and air-to-ground interfaces needed to conduct and document experiments involving a mix of new technologies within the existing NAS infrastructure. The DIF supports four NAS functions: Controller Pilot Data Link Communications (CPDLC), Flight Information Services (FIS), Differential Global Positioning System (DGPS) navigation, and Automatic Dependent Surveillance-Broadcast (ADS-B). The DIF also includes the capability to record pilot and air traffic management interactions and document research participant observations. The DIF capability includes connectivity to flight test and simulated aircraft in a fully immersive Communications, Navigation, and Surveillance (CNS) environment.

The unstructured traffic environment that is gradually evolving in the National Airspace System may necessitate decision aiding tools to help controllers manage aircraft traffic efficiently and within acceptable safety and workload levels. An experiment was designed to assess the effect of conflict detection and trial planning resolution aids and traffic conditions on the performance of controllers and the efficiency of flight. Twelve controllers participated in a high-fidelity simulation study in the Indianapolis Center dynamic simulation facility using the user request evaluation tool (URET). Study results indicated that URET clearly improves the acceptability of operations and may enhance safety, particularly in the unstructured environment. In addition, the study findings strongly support a shift toward more strategic air traffic control with conflict probe as well as a significant increase in the contribution of the D controller to the primary sector tasks. Because of study limitations, it was not possible to associate any quantitative estimates of airspace user benefits with the potentially more efficient resolution strategies. The results and experimental approach are discussed in terms of their contribution to measurement methods and issues in the evolutionary progression toward a free flight-based air traffic system.

In an effort to accommodate the predicted growth in air traffic, the Federal Aviation Administration (FAA) and the aviation community have developed a concept of operations for the National Airspace System (NAS) called Free Flight. This operational concept has been developed for the midterm time frame (nominally a period of time that centers around 2005). The Center for Advanced Aviation System Development (CAASD) at The MITRE Corporation developed the concept and has conducted laboratory exercises to validate the portion of the concept that applies to the en route domain. The paper describes CAASD's laboratory efforts to begin validating the en route portion of the concept by examining the operational issues associated with the concept and the functional issues related to its evolution to the midterm. The laboratory validation exercises described examine the functionality of possible capability enhancements, but do not address associated detailed human factors issues. Favorable results from CAASD's initial qualitative validation efforts support the need for further quantitative validation activities that include more detailed analyses, further development of operational procedures and computer-human interfaces, and more rigorous exercises involving FAA field controllers.

Initiatives in air traffic management both in the United States and in Europe are aimed at providing air traffic controllers with automation tools to separate traffic, meet time constraints required for traffic flow and accommodate route preferences of users such as airlines. These efforts are expected to result in removal of restrictions on users preferred routes without compromising safety. Thus, aircraft will be able to fly optimal routes such as great circle and wind-optimal routes. NASA has developed the design for a new automation tool, referred to as the direct-to tool, which advises the controller on direct time-saving routes for any aircraft irrespective of levels of equipage. In contrast to earlier studies on the potential benefits of direct routes in the National Airspace System, the objective of the paper is to evaluate the benefits based on a controller tool. The paper describes the benefits of applying this algorithm to the 20 air route traffic control centers within the United States. Benefits are measured in terms of the total time savings accrued by flying the direct route. Results are described for three different implementations dependent on the search region bounding each air route traffic control center. The first region exactly encloses the air route traffic control center airspace, the second is the smallest rectangular bounding region while the third is a bigger rectangular bounding region approximately twice as large as the second region. It is shown that the application of the direct-to routing algorithm does not significantly alter the number of conflicts and their spatial distribution compared to the case in which the aircraft fly along the airways. The results presented in the paper suggest that the direct-to routing algorithm can provide significant cost savings to the users without adversely impacting the air traffic management functions.

This paper proposes an application of the Total Airspace and Airport Modeller (TAAM)/sup 2/ tool for determining the impact of new Communications, Navigation, and Surveillance (CNS) ground-based and avionics technology on the efficiency of the National Airspace System (NAS). TAAM presents an opportunity to attack this problem by simulating aircraft movements using rules that mimic actual operations. The rules can be tailored to represent local procedures, restrictions, and conflict resolution strategies, producing a realistic picture of aircraft movement. This paper describes a novel method for manipulating TAAM output to produce a measure of the voice channel occupancy (VCO) in a sector. This method can be applied for current conditions, where all communications use the voice channel, and for the future case in which Controller-Pilot Data Link Communications (CPDLC) is used to issue controller/pilot instructions. TAAM could then be used to examine the benefits of CPDLC in terms of relieving restrictions or reducing vectoring and holding. Overall system benefits such as reduction in delays or distance traveled could be estimated from the TAAM results.

In air traffic control, the traffic flow management (TFM) function seeks to optimize the flow of air traffic. A flow is a movement of air traffic, considered as a rate or a cluster, not as individual aircraft. The National Airspace System (NAS) is a complex, interdependent network of airports, airspace, and aircraft. It is observed that a TFM congestion problem at one place in the NAS has air traffic flow effects elsewhere in the system. It is also observed that TFM congestion problems do not necessarily occur singularly, they are frequently coincident. This work investigates whether multiple, coincident TFM problems interact, i.e., whether unanticipated combination effects arise when multiple problems occur simultaneously. The National Airspace System Performance Analysis Capability (NASPAC) simulation model is used. >

The general architecture of the US National Airspace System (NAS) is presented. Background on the overall air traffic control (ATC) system's history is given as prologue to descriptions of the major elements of the NAS Plan, the US Federal Aviation Administration's current effort to upgrade and modernize the ATC system. Technologies central to achieving the planned end-state configuration for each element are characterized in terms of their functional impact and potential benefit. Communications, navigation aids, weather support, surveillance, and maintenance systems are all undergoing significant technology upgrade. Digital processing capabilities and communications technology lead the way in permitting this modernization program to become reality. Significant consolidation efforts are yielding a much more cost-effective, responsive, and flexible ATC environment. >

The current edition of the US Federal Radionavigation Plan, issued in 1984, presents a consolidated federal plane on the management of those radionavigation systems which are used by both the civilian and military sectors. It states the US Dept. of Defense (DoD) goal to phase out the use of TACAN, VOR/DME, OMEGA, LORAN C, and TRANSIT in military platforms and for Global Positioning System (GPS) to become the standard radionavigation system for DoD. This would eliminate all the current sole-means air navigation systems (TACAN and VOR/DME) aboard military aircraft. Instrument Flight Rule (IFR) operations within controlled airspace requires an operating sole-means air navigation system to be aboard the aircraft. The authors investigate the requirements for GPS certification as a sole means air navigation system in the US National Airspace System (NAS); discuss the implication for GPS user equipment (UE) hardware and software; describe the actual UE implementation; and discuss approaches for UE integration with flight instruments on US Navy aircraft. >

The future applicability of the Global Positioning System (GPS) to the National Airspace System (NAS) for user navigation and landing support is discussed. Functional characteristics and performance estimates are presented for several GPS enhancements, including the use of a geostationary satellite L-band repeater, a CONUS calibration network, and pseudolites. Analysis results indicate that an enhanced GPS system can meet US Federal Aviation Administration (FAA) enroute/terminal area navigation and nonprecision approach requirements under conditions which include accuracy degradation due to worst-case satellite failure, selective availability, and signal integrity. Similarly, it is shown that a Category I precision approach and landing requirement is essentially met using two pseudolites per airport. Additional analysis and extensive testing are required to validate the Category I findings. >

The Federal Aviation Administration plans to independently monitor signals in space from the Global Positioning System (GPS) for the purpose of providing immediate awareness to civil aviation users of the operational status of GPS when it is used in the National Airspace System. The operational status will be disseminated to Air Traffic Control and will possibly be broadcast from ground monitoring stations to GPS aviation users via a dedicated integrity channel. An algorithm is described that measures the coverage of a configuration of ground monitoring station locations, and is applied to several different configurations of ground monitoring stations to compare the coverage provided. Also included are the resulting ground monitoring station configurations that give the best coverage of GPS signals for several specific geographical areas, the conterminous United States (CONUS), Canada, and Alaska.

The US Federal Aviation Administration (FAA) has undertaken an effort to model and analyze the performance of the National Airspace System (NAS), a system that encompasses the nationwide airport and airspace network in the United States. This effort and the resulting capability, called the National Airspace System Performance Analysis Capability (NASPAC), are based on operations research and computer-modeling techniques. The authors provide a detailed description of a discrete-event simulation model of the NAS developed as part of the NASPAC project. Special emphasis is placed on the model's representation of the airport and airspace entities that constitute the NAS and the airspace user demand. The authors present the results of an initial analysis of the possible impact of a proposed new airport at Denver, CO, and conclude with a discussion of the potential future direction of NASPAC. >

Tbe important integrity and reliability peformance considerations for both landing and en route radionavigation in the National Airspace System are discussed and analyzed. The integrity and reliability of the present systems are described in detail to develop a better understanding of the performance that should be expected of alternative radionavigation systems. NAVSTAR GPS is then analyzed and suggestions are made as to how it could be enhanced to provide increased levels of integrity and reliability.

Consideration is given to the calculation of stereographic representations of airborne targets from observations of slant range, azimuth, amd altitude in a multiple radar tracking system. Emphasis is placed upon the translation of the accuracy of the surveillance information into the stereographic plane. Applications include air traffic control operations in which calculations must be performed repeatedly in real time for numerous targets without overtaxing available computational resources.