Michael T. Palmer

Comparison of Ground-Based and Airborne Function Allocation Concepts for NextGen Using Human-In-The-Loop Simulations

Investigation of function allocation for the Next Generation Air Transportation System is being conducted by the National Aeronautics and Space Administration (NASA). To provide insight on comparability of different function allocations for separation assurance, two human-in-the-loop simulation experiments were conducted on homogeneous airborne and ground-based approaches to four-dimensional trajectory-based operations, one referred to as ground-based automated separation assurance (groundbased) and the other as airborne trajectory management with self-separation (airborne). In the coordinated simulations at NASA s Ames and Langley Research Centers, controllers for the ground-based concept at Ames and pilots for the airborne concept at Langley managed the same traffic scenarios using the two different concepts. The common scenarios represented a significant increase in airspace demand over current operations. Using common independent variables, the simulations varied traffic density, scheduling constraints, and the timing of trajectory change events. Common metrics were collected to enable a comparison of relevant results. Where comparisons were possible, no substantial differences in performance or operator acceptability were observed. Mean schedule conformance and flight path deviation were considered adequate for both approaches. Conflict detection warning times and resolution times were mostly adequate, but certain conflict situations were detected too late to be resolved in a timely manner. This led to some situations in which safety was compromised and/or workload was rated as being unacceptable in both experiments. Operators acknowledged these issues in their responses and ratings but gave generally positive assessments of the respective concept and operations they experienced. Future studies will evaluate technical improvements and procedural enhancements to achieve the required level of safety and acceptability and will investigate the integration of airborne and ground-based capabilities within the same airspace to leverage the benefits of each concept.

An evaluation of a real-time fault diagnosis expert system for aircraft applications

Several aspects of the aircraft domain make inflight diagnosis difficult. Many stem from the fact that the aircraft is in operation during and after the occurrence of a fault. These aspects include failure propagation, operator compensation, and lack of complete information. Still other aspects include responding rapidly to a failure, recognizing multiple failures, and predicting the effect of the failure on the aircraft. To address these concerns, a fault monitoring and diagnosis expert system called Faultfinder was conceived and developed to detect and diagnose inflight failures in an aircraft. Faultfinder is an automated intelligent aid whose purpose is to assist the flight crew in fault monitoring, fault diagnosis, and recovery planning. The present implementation of this concept performs monitoring and diagnosis for a generic aircrafts propulsion and hydraulic subsystems. This implementation is capable of detecting and diagnosing failures of known and unknown (i.e., unforeseeable) type in a real-time environment. Faultfinder uses both rule-based and model-based reasoning strategies which operate on causal, temporal, and qualitative information. This paper describes a preliminary evaluation of the diagnostic concepts implemented in Faultfinder. The evaluation used actual aircraft accident and incident cases which were simulated to assess the effectiveness of Faultfinder in detecting and diagnosing failures. Results of this evaluation, together with the description of the current Faultfinder implementation, are presented.

A HIGH-PERFORMANCE SIMULATED ON-BOARD AVIONICS ARCHITECTURE TO SUPPORT TRAFFIC OPERATIONS RESEARCH

This paper describes the conceptual design and prototype development of a high-performance simulated avionics architecture that supports the exploration of new air traffic management concepts and technologies in a medium-fidelity computer workstation-based simulation. This simulated avionics architecture serves as the inter-process communications backbone of the Aircraft Simulation for Traffic Operations Research (ASTOR), which is the piloted simulation NASA Langley Research Center uses for examining the feasibility of new prototype airborne traffic conflict detection and resolution tools. The architecture chosen for ASTOR is that of an enhanced avionics data bus that achieves conceptual compatibility, rather than hardware compatibility, with existing avionics standards. It does this by making use of the data word and equipment channel definitions inherent in the ARINC 429 standard (and its accompanying ARINC 700series system characteristic documents), but also by not making use of any of the bit-level data encoding, hardware, or electrical signal characteristics of a physical ARINC 429 bus. This type of use of welldocumented communications standards for existing avionics components has aided the development of ASTOR by providing a common understanding of the conceptual data flows in the simulation, and also by supporting the evolutionary extension of current avionics capabilities to include new data sources and technologies.

Prototype flight management capabilities to explore temporal RNP concepts

Next generation air transportation system (NextGen) concepts of operation may require aircraft to fly planned trajectories in four dimensions - three spatial dimensions and time. A prototype 4D flight management capability is being developed by NASA to facilitate the development of these concepts. New trajectory generation functions extend todaypsilas flight management system (FMS) capabilities that meet a single required time of arrival (RTA) to trajectory solutions that comply with multiple RTA constraints. When a solution is not possible, a constraint management capability relaxes constraints to achieve a trajectory solution that meets the most important constraints as specified by candidate NextGen concepts. New flight guidance functions provide continuous guidance to the aircraftpsilas flight control system to enable it to fly specified 4D trajectories. Guidance options developed for research investigations include a moving time window with varying tolerances that are a function of proximity to imposed constraints, and guidance that recalculates the aircraftpsilas planned trajectory as a function of the estimation of current compliance. Compliance tolerances are related to required navigation performance (RNP) through the extension of existing RNP concepts for lateral containment. A conceptual temporal RNP implementation and prototype display symbology are proposed.

Autonomous aircraft operations using RTCA guidelines for airborne conflict management

A human-in-the-loop experiment was performed at the NASA Langley Research Center to study the feasibility of DAG-TM autonomous aircraft operations in highly constrained airspace. The airspace was constrained by a pair of special-use airspace (SUA) regions on either side of the pilots planned route. Traffic flow management (TFM) constraints were imposed as a required time of arrival and crossing altitude at an en route fix. Key guidelines from the RTCA airborne conflict management (ACM) concept were applied to autonomous aircraft operations for this experiment. These concepts included the RTCA ACM definitions of distinct conflict detection and collision avoidance zones, and the use of a graded system of conflict alerts for the flight crew. Three studies were conducted in the course of the experiment. The first study investigated the effect of hazard proximity upon pilot ability to meet constraints and solve conflict situations. The second study investigated pilot use of the airborne tools when faced with an unexpected loss of separation (LOS). The third study explored pilot interactions in an over-constrained conflict situation, with and without priority rules dictating who should move first. Detailed results from these studies were presented at the 5th USA/Europe Air Traffic management R&D Seminar (ATM2003). This overview paper focuses on the integration of the RTCA ACM concept into autonomous aircraft operations in highly constrained situations, and provides an overview of the results presented at the ATM2003 seminar. These results, together with previously reported studies, continue to support the feasibility of autonomous aircraft operations.

Airborne Conflict Resolution for Flow-Restricted Transition Airspace

An airborne conflict detection and resolution approach is presented for application to flights subject to metering constraints on descent. Conflict resolution (CR) is an extension of an existing genetic algorithm previously developed for the Autonomous Operations Planner (AOP). This approach provides for the avoidance of both traffic and area hazards simultaneously while meeting flight plan constraints.

Implementation of a research prototype onboard fault monitoring and diagnosis system

Due to the dynamic and complex nature of in-flight fault monitoring and diagnosis, a research effort was undertaken at NASA Langley Research Center to investigate the application of artificial intelligence techniques for improved situational awareness. Under this research effort, concepts were developed and a software architecture was designed to address the complexities of onboard monitoring and diagnosis. This paper describes the implementation of these concepts in a computer program called FaultFinder. The implementation of the monitoring, diagnosis, and interface functions as separate modules is discussed, as well as the blackboard designed for the communication of these modules. Some related issues concerning the future installation of FaultFinder in an aircraft are also discussed.