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  • 1
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    A Family of Well-Clear Boundary Models for the Integration of UAS in the NAS (2014)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The FAA-sponsored Sense and Avoid Workshop for Unmanned Aircraft Systems (UAS) defines the concept of sense and avoid for remote pilots as "the capability of a UAS to remain well clear from and avoid collisions with other airborne traffic." Hence, a rigorous definition of well clear is fundamental to any separation assurance concept for the integration of UAS into civil airspace. This paper presents a family of well-clear boundary models based on the TCAS II Resolution Advisory logic. For these models, algorithms that predict well-clear violations along aircraft current trajectories are provided. These algorithms are analogous to conflict detection algorithms but instead of predicting loss of separation, they predict whether well-clear violations will occur during a given lookahead time interval. Analytical techniques are used to study the properties and relationships satisfied by the models.
    Keywords: Aircraft Communications and Navigation; Air Transportation and Safety
    Type: NF1676L-17779 , AIAA Aviation Technology, Integration and Operations Conference; Jun 16, 2014 - Jun 20, 2014; Atlanta, GA; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    DAIDALUS: Detect and Avoid Alerting Logic for Unmanned Systems (2015)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: This paper presents DAIDALUS (Detect and Avoid Alerting Logic for Unmanned Systems), a reference implementation of a detect and avoid concept intended to support the integration of Unmanned Aircraft Systems into civil airspace. DAIDALUS consists of self-separation and alerting algorithms that provide situational awareness to UAS remote pilots. These algorithms have been formally specified in a mathematical notation and verified for correctness in an interactive theorem prover. The software implementation has been verified against the formal models and validated against multiple stressing cases jointly developed by the US Air Force Research Laboratory, MIT Lincoln Laboratory, and NASA. The DAIDALUS reference implementation is currently under consideration for inclusion in the appendices to the Minimum Operational Performance Standards for Unmanned Aircraft Systems presently being developed by RTCA Special Committee 228.
    Keywords: Air Transportation and Safety
    Type: NF1676L-20901 , 2015 AIAA/IEEE Digital Avionics Systems Conference; Sep 13, 2015 - Sep 17, 2015; Prague; Czechoslovakia
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  • 3
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    Human-In-The-Loop Experimental Research for Detect and Avoid (2015)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: This paper describes a Detect and Avoid (DAA) concept for integration of UAS into the NAS developed by the National Aeronautics and Space Administration (NASA) and provides results from recent human-in-the-loop experiments performed to investigate interoperability and acceptability issues associated with these vehicles and operations. The series of experiments was designed to incrementally assess critical elements of the new concept and the enabling technologies that will be required.
    Keywords: Air Transportation and Safety
    Type: NF1676L-20923 , 2015 IEEE/AIAA Digital Avionics Systems Conference (DASC); Sep 13, 2015 - Sep 17, 2015; Prague; Czechoslovakia
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  • 4
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    Unmanned Aircraft Systems in the National Airspace System: A Formal Methods Perspective (2016)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: As the technological and operational capabilities of unmanned aircraft systems (UAS) have grown, so too have international efforts to integrate UAS into civil airspace. However, one of the major concerns that must be addressed in realizing this integration is that of safety. For example, UAS lack an on-board pilot to comply with the legal requirement that pilots see and avoid other aircraft. This requirement has motivated the development of a detect and avoid (DAA) capability for UAS that provides situational awareness and maneuver guidance to UAS operators to aid them in avoiding and remaining well clear of other aircraft in the airspace. The NASA Langley Research Center Formal Methods group has played a fundamental role in the development of this capability. This article gives a selected survey of the formal methods work conducted in support of the development of a DAA concept for UAS. This work includes specification of low-level and high-level functional requirements, formal verification of algorithms, and rigorous validation of software implementations.
    Keywords: Computer Programming and Software
    Type: NF1676L-24045
    Format: application/pdf
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  • 5
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    Characterizing the Effects of a Vertical Time Threshold for a Class of Well-Clear Definitions (2015)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: A fundamental requirement for the integration of unmanned aircraft into civil airspace is the capability of aircraft to remain well clear of each other and avoid collisions. This requirement has led to a broad recognition of the need for an unambiguous, formal definition of well clear. It is further recognized that any such definition must be interoperable with existing airborne collision avoidance systems (ACAS). A particular class of well-clear definitions uses logic checks of independent distance thresholds as well as independent time thresholds in the vertical and horizontal dimensions to determine if a well-clear violation is predicted to occur within a given time interval. Existing ACAS systems also use independent distance thresholds, however a common time threshold is used for the vertical and horizontal logic checks. The main contribution of this paper is the characterization of the effects of the decoupled vertical time threshold on a well-clear definition in terms of (1) time to well-clear violation, and (2) interoperability with existing ACAS. The paper provides governing equations for both metrics and includes simulation results to illustrate the relationships. In this paper, interoperability implies that the time of well-clear violation is strictly less than the time a resolution advisory is issued by ACAS. The encounter geometries under consideration in this paper are initially well clear and consist of constant-velocity trajectories resulting in near-mid-air collisions.
    Keywords: Air Transportation and Safety
    Type: NF1676L-20526
    Format: application/pdf
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  • 6
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    Analysis of Well-Clear Boundary Models for the Integration of UAS in the NAS (2014)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: The FAA-sponsored Sense and Avoid Workshop for Unmanned Aircraft Systems (UAS) defnes the concept of sense and avoid for remote pilots as "the capability of a UAS to remain well clear from and avoid collisions with other airborne traffic." Hence, a rigorous definition of well clear is fundamental to any separation assurance concept for the integration of UAS into civil airspace. This paper presents a family of well-clear boundary models based on the TCAS II Resolution Advisory logic. Analytical techniques are used to study the properties and relationships satisfied by the models. Some of these properties are numerically quantifed using statistical methods.
    Keywords: Air Transportation and Safety
    Type: NASA/TM-2014-218280 , L-20407 , NF1676L-18821
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 7
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    Perspectives on Unmanned Aircraft Classification for Civil Airworthiness Standards (2013)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: The use of unmanned aircraft in the National Airspace System (NAS) has been characterized as the next great step forward in the evolution of civil aviation. Although use of unmanned aircraft systems (UAS) in military and public service operations is proliferating, civil use of UAS remains limited in the United States today. This report focuses on one particular regulatory challenge: classifying UAS to assign airworthiness standards. This paper provides observations related to how the current regulations for classifying manned aircraft could apply to UAS.
    Keywords: Air Transportation and Safety
    Type: NASA/TM-2013-217969 , L-20232 , NF1676L-16131
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  • 8
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    A Well-Clear Volume Based on Time to Entry Point (2014)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: A well-clear volume is a key component of NASA's Separation Assurance concept for the integration of UAS in the NAS. This paper proposes a mathematical definition of the well-clear volume that uses, in addition to distance thresholds, a time threshold based on time to entry point (TEP). The mathematical model that results from this definition is more conservative than other candidate definitions of the wellclear volume that are based on range over closure rate and time to closest point of approach.
    Keywords: Air Transportation and Safety
    Type: NASA/TM-2014-218155 , L-20387 , L-20363 , NF1676L-18401
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  • 9
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    Identifiability of Additive, Time-Varying Actuator and Sensor Faults by State Augmentation (2014)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: Recent work has provided a set of necessary and sucient conditions for identifiability of additive step faults (e.g., lock-in-place actuator faults, constant bias in the sensors) using state augmentation. This paper extends these results to an important class of faults which may affect linear, time-invariant systems. In particular, the faults under consideration are those which vary with time and affect the system dynamics additively. Such faults may manifest themselves in aircraft as, for example, control surface oscillations, control surface runaway, and sensor drift. The set of necessary and sucient conditions presented in this paper are general, and apply when a class of time-varying faults affects arbitrary combinations of actuators and sensors. The results in the main theorems are illustrated by two case studies, which provide some insight into how the conditions may be used to check the theoretical identifiability of fault configurations of interest for a given system. It is shown that while state augmentation can be used to identify certain fault configurations, other fault configurations are theoretically impossible to identify using state augmentation, giving practitioners valuable insight into such situations. That is, the limitations of state augmentation for a given system and configuration of faults are made explicit. Another limitation of model-based methods is that there can be large numbers of fault configurations, thus making identification of all possible configurations impractical. However, the theoretical identifiability of known, credible fault configurations can be tested using the theorems presented in this paper, which can then assist the efforts of fault identification practitioners.
    Keywords: Quality Assurance and Reliability
    Type: NASA/TM-2014-218669 , L-20505 , NF1676L-20305
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  • 10
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    Identifiability of Additive Actuator and Sensor Faults by State Augmentation (2014)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A class of fault detection and identification (FDI) methods for bias-type actuator and sensor faults is explored in detail from the point of view of fault identifiability. The methods use state augmentation along with banks of Kalman-Bucy filters for fault detection, fault pattern determination, and fault value estimation. A complete characterization of conditions for identifiability of bias-type actuator faults, sensor faults, and simultaneous actuator and sensor faults is presented. It is shown that FDI of simultaneous actuator and sensor faults is not possible using these methods when all sensors have unknown biases. The fault identifiability conditions are demonstrated via numerical examples. The analytical and numerical results indicate that caution must be exercised to ensure fault identifiability for different fault patterns when using such methods.
    Keywords: Electronics and Electrical Engineering
    Type: NF1676L-16212 , Journal of Guidance, Control, and DYNAMICS; 37; 3; 941-946
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