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  • 1
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    Concepts of Integration for UAS Operations in the NAS (2012)
    In:  CASI
    Details
    Publication Date: 2019-07-27
    Description: One of the major challenges facing the integration of Unmanned Aircraft Systems (UAS) in the National Airspace System (NAS) is the lack of an onboard pilot that can comply with the legal requirement identified in the US Code of Federal Regulations (CFR) that pilots see and avoid other aircraft. UAS will be expected to demonstrate the means to perform the function of see and avoid while preserving the safety level of the airspace and the efficiency of the air traffic system. This paper introduces a Sense and Avoid (SAA) concept for integration of UAS into the NAS that is currently being developed by the National Aeronautics and Space Administration (NASA) and identifies areas that require additional experimental evaluation to further inform various elements of the concept. The concept design rests on interoperability principles that take into account both the Air Traffic Control (ATC) environment as well as existing systems such as the Traffic Alert and Collision Avoidance System (TCAS). Specifically, the concept addresses the determination of well clear values that are large enough to avoid issuance of TCAS corrective Resolution Advisories, undue concern by pilots of proximate aircraft and issuance of controller traffic alerts. The concept also addresses appropriate declaration times for projected losses of well clear conditions and maneuvers to regain well clear separation.
    Keywords: Air Transportation and Safety
    Type: NF1676L-13199 , ICAS 2012-28th Congress of the International Council of the Aeronautical Sciences; 23-28 Sept. 2012; Brisbane; Australia
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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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
  • 3
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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
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    A TCAS-II Resolution Advisory Detection Algorithm (2013)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The Traffic Alert and Collision Avoidance System (TCAS) is a family of airborne systems designed to reduce the risk of mid-air collisions between aircraft. TCAS~II, the current generation of TCAS devices, provides resolution advisories that direct pilots to maintain or increase vertical separation when aircraft distance and time parameters are beyond designed system thresholds. This paper presents a mathematical model of the TCAS~II Resolution Advisory (RA) logic that assumes accurate aircraft state information. Based on this model, an algorithm for RA detection is also presented. This algorithm is analogous to a conflict detection algorithm, but instead of predicting loss of separation, it predicts resolution advisories. It has been formally verified that for a kinematic model of aircraft trajectories, this algorithm completely and correctly characterizes all encounter geometries between two aircraft that lead to a resolution advisory within a given lookahead time interval. The RA detection algorithm proposed in this paper is a fundamental component of a NASA sense and avoid concept for the integration of Unmanned Aircraft Systems in civil airspace.
    Keywords: Air Transportation and Safety
    Type: NF1676L-15938 , AIAA Guidance, Navigation, and Control Conference; Aug 19, 2013 - Aug 22, 2013; Boston, MA; United States
    Format: application/pdf
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  • 5
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    The Search for Effective Algorithms for Recovery from Loss of Separation (2012)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Our previous work presented an approach for developing high confidence algorithms for recovering aircraft from loss of separation situations. The correctness theorems for the algorithms relied on several key assumptions, namely that state data for all local aircraft is perfectly known, that resolution maneuvers can be achieved instantaneously, and that all aircraft compute resolutions using exactly the same data. Experiments showed that these assumptions were adequate in cases where the aircraft are far away from losing separation, but are insufficient when the aircraft have already lost separation. This paper describes the results of this experimentation and proposes a new criteria specification for loss of separation recovery that preserves the formal safety properties of the previous criteria while overcoming some key limitations. Candidate algorithms that satisfy the new criteria are presented.
    Keywords: Air Transportation and Safety
    Type: NF1676L-14472 , 31st Digital Avionics Systems Conference; Oct 14, 2012 - Oct 18, 2012; Williamsburg, VA; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 6
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    A Mathematical Analysis of Air Traffic Priority Rules (2012)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: This paper analyzes priority rules, such as those in Part 91.113 of the Federal Aviation Regulations. Such rules determine which of two aircraft should maneuver in a given conflict scenario. While the rules in 91.113 are well accepted, other concepts of operation for NextGen, such as self separation, may allow for different priority rules. A mathematical framework is presented that can be used to analyze a general set of priority rules and enables proofs of important properties. Specific properties considered in this paper include safety, effectiveness, and stability. A set of rules is said to be safe if it ensures that it is never the case that both aircraft have priority. They are effective if exactly one aircraft has priority in every situation. Finally, a set of rules is called stable if it produces compatible results even under small changes to input data.
    Keywords: Air Transportation and Safety
    Type: NF1676L-14144 , 12th AIAA Aviation Technology, Integration, and Operations (ATIO) Conference; Sep 17, 2012 - Sep 19, 2012; Indianapolis, IN; United States
    Format: application/pdf
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  • 7
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    Formal Verification of Safety Buffers for Sate-Based Conflict Detection and Resolution (2010)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The information provided by global positioning systems is never totally exact, and there are always errors when measuring position and velocity of moving objects such as aircraft. This paper studies the effects of these errors in the actual separation of aircraft in the context of state-based conflict detection and resolution. Assuming that the state information is uncertain but that bounds on the errors are known, this paper provides an analytical definition of a safety buffer and sufficient conditions under which this buffer guarantees that actual conflicts are detected and solved. The results are presented as theorems, which were formally proven using a mechanical theorem prover.
    Keywords: Air Transportation and Safety
    Type: NF1676L-9213 , 27th International Congress of the Aeronautical Sciences (ICAS 2010); Sep 19, 2010 - Sep 24, 2010; Nice; France
    Format: application/pdf
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  • 8
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    Formal Verification of Air Traffic Conflict Prevention Bands Algorithms (2010)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: 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.
    Keywords: Air Transportation and Safety
    Type: NASA/TM-2010-216706 , L-19881 , NF1676L-10778
    Format: application/pdf
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  • 9
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    Time of Closest Approach in Three-Dimensional Airspace (2010)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: In air traffic management, the aircraft separation requirement is defined by a minimum horizontal distance and a minimum vertical distance that the aircraft have to maintain. Since this requirement defines a cylinder around each aircraft rather than a sphere, the three-dimensional Euclidean distance does not provide an appropriate basis for the definition of time of closest approach. For instance, conflicting aircraft are not necessarily in loss of separation at the time of closest three-dimensional Euclidean distance. This paper proposes a definition of time of closest approach that characterizes conflicts in a three-dimensional airspace. The proposed time is defined as the time that minimizes a distance metric called cylindrical norm. An algorithm that computes the time of closest approach between two aircraft is provided and the formal verification of its main properties is reported.
    Keywords: Air Transportation and Safety
    Type: NASA/TM-2010-216857 , L-19933 , NF1676L-11570
    Format: application/pdf
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  • 10
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    A Criteria Standard for Conflict Resolution: A Vision for Guaranteeing the Safety of Self-Separation in NextGen (2010)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: Distributed approaches for conflict resolution rely on analyzing the behavior of each aircraft to ensure that system-wide safety properties are maintained. This paper presents the criteria method, which increases the quality and efficiency of a safety assurance analysis for distributed air traffic concepts. The criteria standard is shown to provide two key safety properties: safe separation when only one aircraft maneuvers and safe separation when both aircraft maneuver at the same time. This approach is complemented with strong guarantees of correct operation through formal verification. To show that an algorithm is correct, i.e., that it always meets its specified safety property, one must only show that the algorithm satisfies the criteria. Once this is done, then the algorithm inherits the safety properties of the criteria. An important consequence of this approach is that there is no requirement that both aircraft execute the same conflict resolution algorithm. Therefore, the criteria approach allows different avionics manufacturers or even different airlines to use different algorithms, each optimized according to their own proprietary concerns.
    Keywords: Air Transportation and Safety
    Type: NASA/TM-2010-216862 , L-19932 , NF1676L-11543
    Format: application/pdf
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