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NASA NTRS2004

Preliminary Validation of the Small Aircraft Transportation System Higher Volume Operations (SATS HVO) Concept

This document provides a preliminary validation of the Small Aircraft Transportation System (SATS) Higher Volume Operations (HVO) concept for normal conditions. Initial results reveal that the concept provides reduced air traffic delays when compared to current operations without increasing pilot workload. Characteristic to the SATS HVO concept is the establishment of a newly defined area of flight operations called a Self-Controlled Area (SCA) which would be activated by air traffic control (ATC) around designated non-towered, non-radar airports. During periods of poor visibility, SATS pilots would take responsibility for separation assurance between their aircraft and other similarly equipped aircraft in the SCA. Using onboard equipment and simple instrument flight procedures, they would then be better able to approach and land at the airport or depart from it. This concept would also require a new, ground-based automation system, typically located at the airport that would provide appropriate sequencing information to the arriving aircraft. Further validation of the SATS HVO concept is required and is the subject of ongoing research and subsequent publications.

Williams, Daniel↗
NASA NTRS2004

Small Aircraft Transportation System, Higher Volume Operations Concept: Normal Operations

This document defines the Small Aircraft Transportation System (SATS), Higher Volume Operations (HVO) concept for normal conditions. In this concept, a block of airspace would be established around designated non-towered, non-radar airports during periods of poor weather. Within this new airspace, pilots would take responsibility for separation assurance between their aircraft and other similarly equipped aircraft. Using onboard equipment and procedures, they would then approach and land at the airport. Departures would be handled in a similar fashion. The details for this operational concept are provided in this document.

Abbott, Terence S.↗
NASA NTRS2004

ADS-B within a Multi-Aircraft Simulation for Distributed Air-Ground Traffic Management

Automatic Dependent Surveillance Broadcast (ADS-B) is an enabling technology for NASA s Distributed Air-Ground Traffic Management (DAG-TM) concept. DAG-TM has the goal of significantly increasing capacity within the National Airspace System, while maintaining or improving safety. Under DAG-TM, aircraft exchange state and intent information over ADS-B with other aircraft and ground stations. This information supports various surveillance functions including conflict detection and resolution, scheduling, and conformance monitoring. To conduct more rigorous concept feasibility studies, NASA Langley Research Center s PC-based Air Traffic Operations Simulation models a 1090 MHz ADS-B communication structure, based on industry standards for message content, range, and reception probability. The current ADS-B model reflects a mature operating environment and message interference effects are limited to Mode S transponder replies and ADS-B squitters. This model was recently evaluated in a Joint DAG-TM Air/Ground Coordination Experiment with NASA Ames Research Center. Message probability of reception vs. range was lower at higher traffic levels. The highest message collision probability occurred near the meter fix serving as the confluence for two arrival streams. Even the highest traffic level encountered in the experiment was significantly less than the industry standard "LA Basin 2020" scenario. Future studies will account for Mode A and C message interference (a major effect in several industry studies) and will include Mode A and C aircraft in the simulation, thereby increasing the total traffic level. These changes will support ongoing enhancements to separation assurance functions that focus on accommodating longer ADS-B information update intervals.

Barhydt, Richard↗
NASA NTRS2004

Design of a Multi-mode Flight Deck Decision Support System for Airborne Conflict Management

NASA Langley has developed a multi-mode decision support system for pilots operating in a Distributed Air-Ground Traffic Management (DAG-TM) environment. An Autonomous Operations Planner (AOP) assists pilots in performing separation assurance functions, including conflict detection, prevention, and resolution. Ongoing AOP design has been based on a comprehensive human factors analysis and evaluation results from previous human-in-the-loop experiments with airline pilot test subjects. AOP considers complex flight mode interactions and provides flight guidance to pilots consistent with the current aircraft control state. Pilots communicate goals to AOP by setting system preferences and actively probing potential trajectories for conflicts. To minimize training requirements and improve operational use, AOP design leverages existing alerting philosophies, displays, and crew interfaces common on commercial aircraft. Future work will consider trajectory prediction uncertainties, integration with the TCAS collision avoidance system, and will incorporate enhancements based on an upcoming air-ground coordination experiment.

Barhydt, Richard↗
NASA NTRS2000

FACET: Future ATM Concepts Evaluation Tool

FACET (Future ATM Concepts Evaluation Tool) is an Air Traffic Management research tool being developed at the NASA Ames Research Center. This paper describes the design, architecture and functionalities of FACET. The purpose of FACET is to provide E simulation environment for exploration, development and evaluation of advanced ATM concepts. Examples of these concepts include new ATM paradigms such as Distributed Air-Ground Traffic Management, airspace redesign and new Decision Support Tools (DSTs) for controllers working within the operational procedures of the existing air traffic control system. FACET is currently capable of modeling system-wide en route airspace operations over the contiguous United States. Airspace models (e.g., Center/sector boundaries, airways, locations of navigation aids and airports) are available from databases. A core capability of FACET is the modeling of aircraft trajectories. Using round-earth kinematic equations, aircraft can be flown along flight plan routes or great circle routes as they climb, cruise and descend according to their individual aircraft-type performance models. Performance parameters (e.g., climb/descent rates and speeds, cruise speeds) are obtained from data table lookups. Heading, airspeed and altitude-rate dynamics are also modeled. Additional functionalities will be added as necessary for specific applications. FACET software is written in Java and C programming languages. It is platform-independent, and can be run on a variety of computers. FACET has been designed with a modular software architecture to enable rapid integration of research prototype implementations of new ATM concepts. There are several advanced ATM concepts that are currently being implemented in FACET airborne separation assurance, dynamic density predictions, airspace redesign (re-sectorization), benefits of a controller DST for direct-routing, and the integration of commercial space transportation system operations into the U.S. National Airspace System (NAS).

Bilmoria, Karl D.↗
NASA NTRS2005

Analysis of Aircraft Clusters to Measure Sector-Independent Airspace Congestion

The Distributed Air/Ground Traffic Management (DAG-TM) concept of operations* permits appropriately equipped aircraft to conduct Free Maneuvering operations. These independent aircraft have the freedom to optimize their trajectories in real time according to user preferences; however, they also take on the responsibility to separate themselves from other aircraft while conforming to any local Traffic Flow Management (TFM) constraints imposed by the air traffic service provider (ATSP). Examples of local-TFM constraints include temporal constraints such as a required time of arrival (RTA), as well as spatial constraints such as regions of convective weather, special use airspace, and congested airspace. Under current operations, congested airspace typically refers to a sector(s) that cannot accept additional aircraft due to controller workload limitations; hence Dynamic Density (a metric that is indicative of controller workload) can be used to quantify airspace congestion. However, for Free Maneuvering operations under DAG-TM, an additional metric is needed to quantify the airspace congestion problem from the perspective of independent aircraft. Such a metric would enable the ATSP to prevent independent aircraft from entering any local areas of congestion in which the flight deck based systems and procedures may not be able to ensure separation. This new metric, called Gaggle Density, offers the ATSP a mode of control to regulate normal operations and to ensure safety and stability during rare-normal or off-normal situations (e.g., system failures). It may be difficult to certify Free Maneuvering systems for unrestricted operations, but it may be easier to certify systems and procedures for specified levels of Gaggle Density that could be monitored by the ATSP, and maintained through relatively minor flow-rate (RTA type) restrictions. Since flight deck based separation assurance is airspace independent, the challenge is to measure congestion independent of sector boundaries. Figure 1 , reproduced from Ref. 1, depicts an example traffic situation. When the situation is analyzed by sector boundaries (left side of figure), a Dynamic Density metric would identify excessive congestion in the central sector. When the same traffic situation is analyzed independent of sector boundaries (right side of figure), a Gaggle Density metric would identify congestion in two dynamically defined areas covering portions of several sectors. The first step towards measuring airspace-independent congestion is to identify aircraft clusters, i.e., groups of closely spaced aircraft. The objective of this work is to develop techniques to detect and classify clusters of aircraft.

Bilimoria, Karl D.↗
NASA NTRS2005

Small Aircraft Transportation System, Higher Volume Operations Concept: Off-Nominal Operations

This document expands the Small Aircraft Transportation System, (SATS) Higher Volume Operations (HVO) concept to include off-nominal conditions. The general philosophy underlying the HVO concept is the establishment of a newly defined area of flight operations called a Self-Controlled Area (SCA). During periods of poor weather, a block of airspace would be established around designated non-towered, non-radar airports. Aircraft flying enroute to a SATS airport would be on a standard instrument flight rules flight clearance with Air Traffic Control providing separation services. Within the SCA, pilots would take responsibility for separation assurance between their aircraft and other similarly equipped aircraft. Previous work developed the procedures for normal HVO operations. This document provides details for off-nominal and emergency procedures for situations that could be expected to occur in a future SCA.

Abbott, Terence S.↗
NASA NTRS2006

Small Aircraft Transportation System Higher Volume Operations Concept

This document defines the Small Aircraft Transportation System (SATS) Higher Volume Operations concept. The general philosophy underlying this concept is the establishment of a newly defined area of flight operations called a Self-Controlled Area (SCA). Within the SCA, pilots would take responsibility for separation assurance between their aircraft and other similarly equipped aircraft. This document also provides details for a number of off-nominal and emergency procedures which address situations that could be expected to occur in a future SCA. The details for this operational concept along with a description of candidate aircraft systems to support this concept are provided.

Abbott, Terence S.↗
NASA NTRS2008

Proceedings of the Sixth NASA Langley Formal Methods (LFM) Workshop

Today's verification techniques are hard-pressed to scale with the ever-increasing complexity of safety critical systems. Within the field of aeronautics alone, we find the need for verification of algorithms for separation assurance, air traffic control, auto-pilot, Unmanned Aerial Vehicles (UAVs), adaptive avionics, automated decision authority, and much more. Recent advances in formal methods have made verifying more of these problems realistic. Thus we need to continually re-assess what we can solve now and identify the next barriers to overcome. Only through an exchange of ideas between theoreticians and practitioners from academia to industry can we extend formal methods for the verification of ever more challenging problem domains. This volume contains the extended abstracts of the talks presented at LFM 2008: The Sixth NASA Langley Formal Methods Workshop held on April 30 - May 2, 2008 in Newport News, Virginia, USA. The topics of interest that were listed in the call for abstracts were: advances in formal verification techniques; formal models of distributed computing; planning and scheduling; automated air traffic management; fault tolerance; hybrid systems/hybrid automata; embedded systems; safety critical applications; safety cases; accident/safety analysis.

Rozier, Kristin Yvonne↗
NASA NTRS2009

Feasibility of Mixed Equipage Operations in the Same Airspace

This study used a human-in-the-loop simulation to examine the feasibility of mixed equipage operations in an automated separation assurance environment under higher traffic densities. The study involved two aircraft equipage alternatives with and without data link and four traffic conditions. In all traffic conditions the unequipped traffic count was increased linearly throughout the scenario from approximately 5 to 20 aircraft. Condition One consisted solely of this unequipped traffic, while the remaining three conditions also included a constant number of equipped aircraft operating within the same airspace: 15 equipped aircraft in condition two, 30 in condition three, and 45 in condition four. If traffic load became excessive during any run, participants were instructed to refuse sector entry to inbound unequipped aircraft until sector load became manageable. Results showed a progressively higher number of unequipped aircraft turned away under the second, third, and fourth scenario conditions. Controller workload also increased progressively. Participants rated the mixed operations concept as acceptable, with some qualifications about procedures and information displays. These results showed that mixed operations might be feasible in the same airspace, if unequipped aircraft count is held to a workable level. This level will decrease with increasing complexity. The results imply that integrated airspace configuration is feasible to a limit. The results also indicate that the conflict detection and resolution automation, equipage, and traffic density are important factors that will need to be considered for airspace configuration.

Kopardekar, Parimal↗
NASA NTRS2010

Formal Verification of Air Traffic Conflict Prevention Bands Algorithms

In air traffic management, a pairwise conflict is a predicted loss of separation between two aircraft, referred to as the ownship and the intruder. A conflict prevention bands system computes ranges of maneuvers for the ownship that characterize regions in the airspace that are either conflict-free or 'don't go' zones that the ownship has to avoid. Conflict prevention bands are surprisingly difficult to define and analyze. Errors in the calculation of prevention bands may result in incorrect separation assurance information being displayed to pilots or air traffic controllers. This paper presents provably correct 3-dimensional prevention bands algorithms for ranges of track angle; ground speed, and vertical speed maneuvers. The algorithms have been mechanically verified in the Prototype Verification System (PVS). The verification presented in this paper extends in a non-trivial way that of previously published 2-dimensional algorithms.

Narkawicz, Anthony J.↗
NASA NTRS2010

UAS Integration into the NAS Project

The goal of the UAS Integration in the NAS Project is to contribute capabilities that reduce technical barriers related to the safety and operational challenges associated with enabling routine UAS access to the NAS This goal will be accomplished through a two-phased approach of system-level integration of key concepts, technologies and/or procedures, and demonstrations of integrated capabilities in an operationally relevant environment. Technical objectives include: PHASE 1: a) Validating the key technical areas identified by this project. System-level analyses, a State of the Art Analysis (SOAA), and a ConOps will identify the challenges and barriers preventing routine UAS access to the NAS. b) Developing a national roadmap and gap analysis identifying specific deliverables in the area of operations, procedures, and technologies that will impact future policy decisions. PHASE 2: a) Provide regulators with a methodology for developing airworthiness requirements for UAS and data to support development of certifications standards and regulatory guidance. b) Provide systems-level integrated testing of concepts and/or capabilities that address barriers to routine access to the NAS. Through simulation and flight testing, address issues including separation assurance, communications requirements, and Pilot Aircraft Interfaces (PAIs) in operationally relevant environments

Bauer, Jeff↗
NASA NTRS2010

Human in the Loop Simulation Measures of Pilot Response Delay in a Self-Separation Concept of Operations

A human-in-the-loop (HITL) simulation experiment was conducted by the National Aeronautics and Space Administration (NASA) to assess airline transport pilots performance and reported acceptance of the use of procedures relying on airborne separation assistance and trajectory management tools. This study was part of a larger effort involving two NASA centers that includes multiple HITL experiments planned over the next few years to evaluate the use of automated separation assurance (SA) tools by both air traffic controllers and pilots. This paper presents results of measured pilot response delay that subject pilots incurred when interacting with cockpit tools for SA and discusses possible implications for future concept and procedures design.

Consiglio, Maria C.↗
NASA NTRS2010

Identification and Characterization of Key Human Performance Issues and Research in the Next Generation Air Transportation System (NextGen)

This report identifies key human-performance-related issues associated with Next Generation Air Transportation System (NextGen) research in the NASA NextGen-Airspace Project. Four Research Focus Areas (RFAs) in the NextGen-Airspace Project - namely Separation Assurance (SA), Airspace Super Density Operations (ASDO), Traffic Flow Management (TFM), and Dynamic Airspace Configuration (DAC) - were examined closely. In the course of the research, it was determined that the identified human performance issues needed to be analyzed in the context of NextGen operations rather than through basic human factors research. The main gaps in human factors research in NextGen were found in the need for accurate identification of key human-systems related issues within the context of specific NextGen concepts and better design of the operational requirements for those concepts. By focusing on human-system related issues for individual concepts, key human performance issues for the four RFAs were identified and described in this report. In addition, mixed equipage airspace with components of two RFAs were characterized to illustrate potential human performance issues that arise from the integration of multiple concepts.

Lee, Paul U.↗
NASA NTRS2009

Convective Weather Avoidance with Uncertain Weather Forecasts

Convective weather events have a disruptive impact on air traffic both in terminal area and in en-route airspaces. In order to make sure that the national air transportation system is safe and efficient, it is essential to respond to convective weather events effectively. Traffic flow control initiatives in response to convective weather include ground delay, airborne delay, miles-in-trail restrictions as well as tactical and strategic rerouting. The rerouting initiatives can potentially increase traffic density and complexity in regions neighboring the convective weather activity. There is a need to perform rerouting in an intelligent and efficient way such that the disruptive effects of rerouting are minimized. An important area of research is to study the interaction of in-flight rerouting with traffic congestion or complexity and developing methods that quantitatively measure this interaction. Furthermore, it is necessary to find rerouting solutions that account for uncertainties in weather forecasts. These are important steps toward managing complexity during rerouting operations, and the paper is motivated by these research questions. An automated system is developed for rerouting air traffic in order to avoid convective weather regions during the 20- minute - 2-hour time horizon. Such a system is envisioned to work in concert with separation assurance (0 - 20-minute time horizon), and longer term air traffic management (2-hours and beyond) to provide a more comprehensive solution to complexity and safety management. In this study, weather is dynamic and uncertain; it is represented as regions of airspace that pilots are likely to avoid. Algorithms are implemented in an air traffic simulation environment to support the research study. The algorithms used are deterministic but periodically revise reroutes to account for weather forecast updates. In contrast to previous studies, in this study convective weather is represented as regions of airspace that pilots are likely to avoid. The automated system periodically updates forecasts and reassesses rerouting decisions in order to account for changing weather predictions. The main objectives are to reroute flights to avoid convective weather regions and determine the resulting complexity due to rerouting. The eventual goal is to control and reduce complexity while rerouting flights during the 20 minute - 2 hour planning period. A three-hour simulation is conducted using 4800 flights in the national airspace. The study compares several metrics against a baseline scenario using the same traffic and weather but with rerouting disabled. The results show that rerouting can have a negative impact on congestion in some sectors, as expected. The rerouting system provides accurate measurements of the resulting complexity in the congested sectors. Furthermore, although rerouting is performed only in the 20-minute - 2-hour range, it results in a 30% reduction in encounters with nowcast weather polygons (100% being the ideal for perfectly predictable and accurate weather). In the simulations, rerouting was performed for the 20-minute - 2-hour flight time horizon, and for the en-route segment of air traffic. The implementation uses CWAM, a set of polygons that represent probabilities of pilot deviation around weather. The algorithms were implemented in a software-based air traffic simulation system. Initial results of the system's performance and effectiveness were encouraging. Simulation results showed that when flights were rerouted in the 20-minute - 2-hour flight time horizon of air traffic, there were fewer weather encounters in the first 20 minutes than for flights that were not rerouted. Some preliminary results were also obtained that showed that rerouting will also increase complexity. More simulations will be conducted in order to report conclusive results on the effects of rerouting on complexity. Thus, the use of the 20-minute - 2-hour flight time horizon weather avoidance teniques performed in the simulation is expected to provide benefits for short-term weather avoidance.

Karahan, Sinan↗
NASA NTRS2009

Feasibility of Mixed Equipage Operations in the Same Airspace

This study used a human-in-the-loop simulation to examine the feasibility of mixed equipage operations in an automated separation assurance environment under higher traffic densities. The study involved two aircraft equipage alternatives - with and without data link- and four traffic conditions. In all traffic conditions the unequipped traffic count was increased linearly throughout the scenario from approximately 5 to 20 aircraft. Condition One consisted solely of this unequipped traffic, while the remaining three conditions also included a constant number of equipped aircraft operating within the same airspace: 15 equipped aircraft in condition two, 30 in condition three, and 45 in condition four. If traffic load became excessive during any run, participants were instructed to refuse sector entry to inbound unequipped aircraft until sector load became manageable. Results showed a progressively higher number of unequipped aircraft turned away under the second, third, and fourth scenario conditions. Controller workload also increased progressively. Participants rated the mixed operations concept as acceptable, with some qualifications about procedures and information displays. These results showed that mixed operations might be feasible in the same airspace, if unequipped aircraft count is held to a workable level. This level will decrease with increasing complexity. The results imply that integrated airspace configuration is feasible to a limit. The results also indicate that the conflict detection and resolution automation, equipage, and traffic density are important factors that will need to be considered for airspace configuration.

Kopardekar, Parimal↗
NASA NTRS2011

Complexity Management Using Metrics for Trajectory Flexibility Preservation and Constraint Minimization

The growing demand for air travel is increasing the need for mitigating air traffic congestion and complexity problems, which are already at high levels. At the same time new surveillance, navigation, and communication technologies are enabling major transformations in the air traffic management system, including net-based information sharing and collaboration, performance-based access to airspace resources, and trajectory-based rather than clearance-based operations. The new system will feature different schemes for allocating tasks and responsibilities between the ground and airborne agents and between the human and automation, with potential capacity and cost benefits. Therefore, complexity management requires new metrics and methods that can support these new schemes. This paper presents metrics and methods for preserving trajectory flexibility that have been proposed to support a trajectory-based approach for complexity management by airborne or ground-based systems. It presents extensions to these metrics as well as to the initial research conducted to investigate the hypothesis that using these metrics to guide user and service provider actions will naturally mitigate traffic complexity. The analysis showed promising results in that: (1) Trajectory flexibility preservation mitigated traffic complexity as indicated by inducing self-organization in the traffic patterns and lowering traffic complexity indicators such as dynamic density and traffic entropy. (2)Trajectory flexibility preservation reduced the potential for secondary conflicts in separation assurance. (3) Trajectory flexibility metrics showed potential application to support user and service provider negotiations for minimizing the constraints imposed on trajectories without jeopardizing their objectives.

Idris, Husni↗