Lesley A. Weitz

Considerations for Interval Management Operations in a Mixed-Equipage Environment

Interval Management (IM) encompasses an evolving set of applications that enable more precise and consistent spacing between aircraft to yield increased throughput and efficiency in the National Airspace System. Most IM applications contain relative (flightdeck) and absolute (ground-based) components. Relative spacing relates the position of an aircraft in a stream to its preceding aircraft and is different from absolute spacing, where spacing is achieved by independently controlling aircraft to a specified point-inspace at a desired time. The flight-deck component consists of avionics that provide speeds to the flight crew to achieve and maintain a desired spacing interval relative to a target aircraft. The ground-based component helps controllers initiate the flight-deck operation and also provides air traffic controllers with speed advisories to manage the unequipped aircraft to absolute scheduled times of arrival at a specified point. In a mixed-equipage IM environment, where both of these components are used to manage the spacing of equipped and unequipped aircraft, the relative spacing flight-deck component and absolute spacing concept for the ground-based component are combined into a single operation. This paper addresses some of the challenges and considerations for the mixed-equipage operation, including performance differences in the two concepts and scheduling considerations that could be developed to increase system benefits. The results of this paper may help to drive decision-making for implementing IM in a mixed-equipage operation. Results also suggest that in many cases the relative spacing concept provides operational throughput benefits over the absolute spacing concept.

Modeling Delay and Delivery Accuracy for Mixed Absolute and Relative Spacing Operations

Interval Management (IM) is a future airborne spacing concept that aims to provide more precise inter-aircraft spacing to yield throughput improvements and greater use of fuel-efficient trajectories for arrival and approach operations. To participate in an IM operation, an aircraft must be equipped with avionics that provide speeds to achieve and maintain an assigned spacing interval relative to another aircraft. It is not expected that all aircraft will be equipped with the necessary avionics, but rather that IM fits into a larger arrival management concept developed to support the broader mixed-equipage environment. Arrival management concepts are comprised of three parts: a ground-based sequencing and scheduling function to develop an overall arrival strategy, ground-based tools to support the management of aircraft to that schedule, and the IM tools necessary for the IM operation (i.e., ground-based set-up, initiation, and monitoring, and the flightdeck tools to conduct the IM operation). The Federal Aviation Administration is deploying a near-term ground-automation system to support metering operations in the National Airspace System, which falls within the first two components of the arrival management concept. This paper develops a methodology for determining the required delivery precision at controlled meter points for aircraft that are being managed to a schedule and aircraft being managed to a relative spacing interval in order to achieve desired flow rates and adequate separation at the meter points.

Multi-Purpose Cockpit Display of Traffic Information: Overview and Development of Performance Requirements

This paper describes a Multi-Purpose Cockpit Display of Trac Information (MPCDTI), which integrates core functional capabilities that can be combined in various ways to perform ADS-B In applications in the NextGen environment. The MPCDTI is dierent from other CDTIs in that it packages the capability to manage multiple applications within a single piece of equipment. Four key elements of the MPCDTI have been dened: elemental functions, simultaneous enablement, automatic algorithm selection, and output arbitration. These elements allow compatible functions to be enabled and prevent the MPCDTI from outputting infeasible or conicting guidance to the ight crew. The objectives of this paper are to present the key features of the MPCDTI and also to suggest a functional approach for developing MPCDTI and future application performance requirements.

Investigating the Performance of Two Interval Management Algorithms in a Fast-Time Simulation Environment

Interval Management (IM) is a future air traffic management concept that enables aircraft to achieve and maintain precise spacing intervals relative to other aircraft. Air traffic controllers (ATC) will initiate an IM operation by identifying candidate aircraft pairs and providing an IM Aircraft with a clearance to space relative to a Target Aircraft with a desired spacing interval. Flight-deck Interval Management (FIM) avionics, onboard the IM Aircraft, will calculate speeds to achieve and maintain the desired spacing interval. IM operations are envisioned in a range of environments, where more precise spacing will help ATC to achieve air traffic objectives. In an arrival and approach operation, a string of aircraft may be formed with each aircraft spacing relative to its preceding aircraft. This paper investigates the performance of two different IM speed control algorithms, which are candidate algorithms for the FIM avionics, and the interoperability of those algorithms. The speed control algorithms are described, and a fast-time simulation environment is presented. Simulation results for an aircraft string that is comprised of aircraft using different algorithms in their FIM avionics are presented to reveal the achieved inter-aircraft spacing and the growth or decay of spacing errors along the string. The effects of a mix of aircraft types, different wind conditions, and surveillance errors are investigated, and recommendations to improve algorithm performance are made.

Trajectory Planning for the Cooperative Manipulation of a Flexible Structure by Two Differentially-Driven Robots

In this paper we explore cooperative manipulation of a flexible structure using a team of two nonholonomically-constrained, differentially-driven robots. Cooperative manipulation is achieved by tracking relative trajectories that are designed for both the nonholonomic nature of the platforms and path constraints limiting the deformation of the flexible structure. The relative trajectories are designed by transforming an optimal-trajectory problem to a nonlinear programming problem. A tracking control law is also designed for the nonholonomic nature of the platforms with consideration for the challenges in cooperative manipulation. Results are presented for a simulation example, and a hardware demonstration for a simple case is used to demonstrate the feasibility of the approach.

Comparing Interval Management Control Laws for Steady-State Errors and String Stability

Interval Management (IM) is a future airborne spacing concept that leverages avionics to provide speed guidance to an aircraft to achieve and maintain a specified spacing interval from another aircraft. The design of a speed control law to achieve the spacing goal is a key aspect in the research and development of the IM concept. In this paper, two control laws that are used in much of the contemporary IM research are analyzed and compared to characterize steady-state errors and string stability. Numerical results are used to illustrate how the choice of control laws gains impacts the size of steady-state errors and string performance and the potential trade-offs between those performance characteristics.

Defining an Error Budget for Required Interval Management Performance

Interval Management (IM) is the capability to delegate the task of achieving or maintaining a relative spacing interval behind another aircraft using ADS-B In surveillance. The spacing interval is managed along common or merging Area Navigation (RNAV) or Required Navigation Performance (RNP) route structures. The IM requirements on the longitudinal spacing accuracy can be considered analogous to the lateral path conformance requirements in RNP. As with RNP, the performance of IM depends on accurate calculations and reduced uncertainty. In the case of IM, accurate knowledge of the spacing interval, which in turn depends on an accurate description of the horizontal path and associated computations, drives the construction of an error budget.

Modeling Uncertainty in Inter-aircraft Spacing Between the Final Approach Fix and the Runway Threshold

Interval Management (IM) is a NextGen concept that includes an avionics capability that provides flight crews with speed guidance to precisely achieve and maintain an Assigned Spacing Goal, specified in either time or distance, relative to a preceding aircraft. The use of IM for arrival and approach operations aims to increase the accuracy of inter-arrival spacing, leading to increases in runway throughput. However, flight crews must discontinue following IM speed guidance prior to landing (typically when within five nautical miles of the landing runway) so that aircraft may fly safe, stabilized approaches. Variations in aircraft flight profiles and environmental conditions contribute to the uncertainty in inter-arrival spacing at the runway threshold. The potential, therefore, exists for some of the accuracy achieved prior to the termination of IM speed guidance to be lost in the last few miles of the approach. In this paper, the total uncertainty in the spacing interval between the point at which speed guidance is discontinued and the runway threshold is quantified taking into account uncertainties related to aircraft performance, automation systems, operating procedures, and environmental conditions. Further, this paper proposes that the spacing goal at the point where IM speed guidance is discontinued be computed such that the most significant factors contributing to the spacing uncertainty are mitigated. This proposal provides a means to define error budgets on those significant factors.

Communication of Target Trajectory and Wind Information to Improve Airborne Interval Management Spacing Performance

Interval Management (IM) is an ADS-B-enabled NextGen concept that will lead to more precise inter-aircraft spacing between an IM Aircraft and a Target Aircraft, in order to increase runway throughput. This paper describes the integration of IM operations with time-based metering operations and the related ground automation, which will support air traffic controllers in managing mixed operations (i.e., some aircraft are equipped with IM avionics and some are not). There are several considerations when determining how IM operations should be integrated into the time-based metering environment, including the initiation location and the information that must be communicated to the IM avionics to conduct the IM operation. This paper examines some performance trade-offs between where to initiate IM and the extent to which communication of supporting trajectory and wind information is needed. Starting the IM operation far from the destination runway requires more information about the environment in order to ensure that the desired spacing precision can be met, but is less sensitive to the pre-conditioning of the traffic at initiation. Conversely, initiating IM closer to the runway requires less information to be provided to the IM Aircraft; however, it requires more consistent traffic pre-conditioning prior to initiation. The performance trade-offs discussed here will be used as input to the development of Data Communications messages, which can enable the transfer of more complex operational and environmental information between air traffic control and flight crews and/or avionics to improve IM performance.