**Active Final Approach Spacing Tool (AFAST)**

# Overview Description

# January 31, 2002

# NAS2-98005

# Technical Research in Advanced Air Transportation Technologies

Final

Overview Description

Active Final Approach Spacing Tool (aFAST)

CDRL Item 5b

# Prepared under

# RTO -- 62

# AATT Operational Concept for ATM -- Year 2002 Update

#### January 31, 2002

#### Prepared For: NASA Ames Research Center

#### Moffett Field, CA 94035-1000

#### Prepared By: Titan Systems Corporation -- SRC Division

#### Billerica, MA 01821-4134

![](media/image1.jpeg){width="5.416666666666667in" height="0.75in"}

**ACKNOWLEDGEMENT**

The majority of the descriptions presented in this document have been
taken directly from NASA documents shown in the bibliography. Minor
modifications have been made to the text to provide readability. The
aFAST Flow chart has however been independently developed for this
description. This approach to the development of this document was taken
in order to remain faithful to the efforts that are presently being
undertaken by the NASA AATT Project Office, the aFAST Tool Developers
and the associated NASA AATT contractors.

**Table of Contents**

1.  **Description 1**

2.  **Operational Concept 2**

3.  **Functional Flow 3**

4.  **Bibliography 5**

# List of Figures

1.  **aFAST System Overview 3**

2.  **aFAST Functional Flow 4**

## AATT ACTIVE FINAL APPROACH SPACING TOOL (aFAST)

## OVERVIEW DESCRIPTION

**1. DESCRIPTION**

**Purpose**

-   Help terminal area controllers optimize traffic flow to runways to
    minimize delay and increase throughput.

-   Compute an efficient landing sequence, approach spacing and runway
    assignment for arrival aircraft.

**Users**

-   Terminal area air traffic controllers

-   Terminal area traffic management coordinators (TMCs)

**Operational Results**

-   In operational testing at DFW, passive FAST increased landing rates
    by 9-13%.

-   The FAA estimates that passive FAST saves airlines US\$10 million
    per year at DFW.

-   aFAST is not operational however benefits analysis indicates a
    potential savings of over \$300 M/year for 10 major airports (see
    #35 Bibliography).

**Overview**

The Final Approach Spacing Tool (FAST) is a decision support tool for
terminal area (TRACON) air traffic controllers. The TRACON typically
encompasses the airspace within approximately 40 miles of a major
airport. TRACON air traffic controllers manage arrival aircraft which
enter their airspace from adjacent ATC facilities or internal airports.
The controllers are responsible for assigning an appropriate runway and
landing sequence to each aircraft and maintaining safe separation.

FAST assists air traffic controllers by providing its advisory
information on the radar planview displays. Additionally, FAST assists
traffic management coordinators by providing schedule information on
auxiliary timeline displays.

In general, arrival aircraft are vectored from en-route airspace into
terminal airspace over metering fixes. Aircraft are assigned to a
default runway, which is typically the closest runway to their
respective metering fix. A controller occasionally reassigns aircraft to
alternate runways to reduce delay on a particular runway or to balance
delay and aircraft among multiple runways. Ideally, a controller would
prefer to finalize an aircraft\'s runway assignment as early as possible
(i.e. near the metering fix), but uncertainties in the traffic situation
often require later reassignments.

During each scheduling cycle, FAST builds a trajectory for each aircraft
from its current position to the runway threshold. The FAST sequencing
algorithm uses these trajectories to systematically order aircraft on
common trajectory paths and to merge aircraft on different trajectory
paths. Using the relative sequences of aircraft on each trajectory path,
FAST performs conflict prediction and resolution in order to achieve a
conflict-free arrival plan. When a conflict is predicted, it is resolved
by adding delay to the aircraft\'s trajectories in the form of vectoring
and speed control.

**2. OPERATIONAL CONCEPT**

Active FAST is designed to deal with the complexities of inter-arrival
spacing within the TRACON (particularly on the final approach path).
Active FAST generates "control instruction" level advisories whereby
controllers issue specific speed and heading instructions based upon the
advisories. Advisories will be displayed to controllers via their
standard terminal color displays. Dedicated aFAST displays will be
provided for TMCs in the ARTCC and TRACON. These displays will be used
for strategic planning. Displays will also be available for ATCSs in the
Tower. The Tower displays will provide enhanced situational awareness.

As arrivals enter the TRACON, they are assigned a runway and sequence
number. Active FAST builds a plan for these arrivals based on aircraft
performance characteristics, airspace constraints, and separation
requirements. A trajectory for each aircraft is created and adjusted
based on real time radar updates. These trajectory calculations include
identification of when and where each aircraft should receive speed
adjustments or headings. These speeds and headings will eventually be
able to be incorporated into future technologies such as Datalink.
However, in the near term operational environment, these advisories will
be displayed in logical increments (e.g. speeds of 210 knots and 180
knots, headings in 10 degree increments) to the TRACON arrival
controller so that they can be issued as control instructions. Active
FAST continues to monitor and update the plan based upon radar track
updates. The plan is modified when necessary, and ultimately leads to an
optimized delivery of aircraft to the runway threshold.

The primary users of the aFAST advisories are the TRACON arrival
controllers. However, many other users can benefit from the information.
Other controllers within the TRACON can view the aFAST advisories to
better understand the arrival controller's plan (e.g. a departure
controller may want to know whether or not an arrival may be instructed
to slow down or turn). TMCs in the TRACON can use the aFAST information
to make dynamic runway changes for aircraft near the TRACON boundary.
The information displayed on the Planview Graphical User Interface
(PGUI) can also help the TMCs in the TRACON and ARTCC better understand
the traffic situation inside the TRACON. Controllers in the ATCT can
also benefit from the PGUI by observing where gaps will occur in the
arrival stream (for runway crossings or departure slots).

As shown in Figure 1, the aFAST system uses aircraft flight plans and
position data from FAA computers, inputs from TRACON arrival controllers
and traffic managers, and current weather information, to produce
advisories to assist controllers in managing and controlling arrival
traffic. The weather information is provided either by the Rapid Update
Cycle (RUC), or by the Integrated Terminal Weather System (ITWS). RUC
provides a weather forecast every 3 hours (80 km grid). ITWS provides a
weather forecast every 5 minutes (2 km grid).

![](media/image2.png){width="6.460416666666666in"
height="5.232638888888889in"}

Figure 1 aFAST System Overview

TRACON arrival controllers interact with aFAST, both receiving
advisories and providing inputs, through standard FAA hardware. The
aFAST advisories will be displayed to TRACON controllers on FAA TRACON
display systems. Controller inputs will be made through message entry
devices. Traffic managers interact with aFAST through dedicated aFAST
displays. They provide inputs such as runway spacing requirements,
airport configuration, and airport acceptance rates. Traffic managers in
both the ARTCC and TRACON may monitor aFAST timelines to gain a more
accurate picture of the real-time operation in the TRACON.

3.  **FUNCTIONAL FLOW**

Figure 2 illustrates the detailed functional flow of aFAST operating in
the TRACON and depicts the functional interfaces with external data
sources. The input/output sources, appearing in double boxes, are shown
in the figure. The major functions within aFAST are:

-   Data Acquisition and Processing

-   Data Formatting and Distribution

-   Trajectory Generation

-   Arrival Planning

-   Advisory Generation

-   Conflict Detection

-   Display Message Processing

![](media/image3.wmf){width="7.625in" height="4.402777777777778in"}

**Figure 2 aFAST Functional Flow**

The external interfaces required for aFAST include:

-   Host Computer System - To receive flight data and radar tracks from
    the ARTCC\'s HCS via an interface device.

-   Terminal Automation System -- To receive flight data, radar tracks,
    and controller entries from the Terminal Automation System via an
    interface device. This includes interfacing with the terminal color
    display hardware.

The additional external interfaces that are preferred for aFAST include:

-   Integrated Terminal Weather System (ITWS) - To receive low altitude
    wind and storm motion data from ITWS via an interface device.

-   Surface Decision Support Tools -- To exchange information with
    surface decision support tools in order to optimize the queuing of
    departures.

-   Other atmospheric data - To receive high altitude wind, temperature,
    and air pressure data as a function of position and altitude.

**4. BIBLIOGRAPHY**

1.  **National Aeronautics and Space Administration**; *Decision Support
    Tools of the Advanced Air Transportation Technologies Project*; May
    2000

2.  **Federal Aviation Administration, US Department of Transportation,
    Washington DC**; *National Airspace System Architecture Version
    4.0*; January 1999

3.  **National Aeronautics and Space Administration, Ames Research
    Center**; *CTAS - Final Approach Spacing Tool (FAST)*; July 2000
    <http://ctas.arc.nasa.gov/project_description/fast.html>

4.  **National Aeronautics and Space Administration, Ames Research
    Center**; [*Center TRACON Automation System -- FAST Fact
    Sheet*](../NASA/FAST_FS.pdf); April 2000

5.  **Robinson III, J. E., D. R. Isaacson**; [*A Concurrent Sequencing,
    and Deconfliction Algorithm for Terminal Area Air Traffic
    Control*](../CTAS/robinson_08_00.pdf); AIAA Guidance, Navigation,
    and Control Conference, Denver, CO; August 2000

6.  **Quinn, C., J. E. Robinson III**; [*A Human Factors Evaluation of
    Active Final Approach Spacing Tool
    Concepts*](../CTAS/quinn_06_00.pdf); 3rd USA/Europe Air Traffic
    Management R&D Seminar, Napoli, Italy; June 2000

7.  **Mueller, K. T., J. E. Robinson III**; *[Final Approach Spacing
    Tool (FAST) Velocity Accuracy Performance
    Analysis](../CTAS/mueller_08_98.pdf),* AIAA Guidance, Navigation,
    and Control Conference, Boston, MA; August 1998

8.  **Robinson III, J. E., T. J. Davis, and D. R. Isaacson**; *[Fuzzy
    Reasoning-Based Sequencing of Arrival Aircraft in the Terminal
    Area](../CTAS/robinson_08_97.pdf);* AIAA Guidance, Navigation and
    Control Conference, New Orleans, LA; August 1997

9.  **Lee, K. K. and T. J. Davis**; [*The Development of the Final
    Approach Spacing Tool(FAST): A Cooperative Controller-Engineer
    Design Approach*](../CTAS/lee_08_96.pdf); Journal of Control
    Engineering Practice, Vol. 4, No. 8, pp. 1161-1168; August 1996

10. **Lee, K. K., and T. J. Davis**; *[The Development of the Final
    Approach Spacing Tool (FAST): A Cooperative Controller-Engineer
    Design Approach](../NASA/950081_lee.pdf),* NASA TM 110359; August
    1995 and *Proceedings the Fifth IFAC Symposium on Automated Systems
    Based on Human Skill*; September 1995

11. **Krzeczowski, K. J., T. J. Davis, H. Erzberger, I. Lev-Ram,
    and C. P. Bergh**; *Knowledge-Based Scheduling of Arrival Aircraft
    in the Terminal Area*; Proceedings of the AIAA Guidance, Navigation,
    and Control Conference, Paper No. AIAA-95-3366, Baltimore, MD;
    August 1995

12. **Slattery, R. A.**; *Terminal Area Trajectory Synthesis for Air
    Traffic Control Automation*; submitted to the American Control
    Conference; June 1995

13. **Bergh, C. P., K. J. Krzeczowski, and T. J. Davis**; *TRACON
    Aircraft Arrival Planning and Optimization through Spatial
    Constraint Satisfaction*; Air Traffic Control Quarterly, Vol. 3, No.
    2; 1995

14. **Davis, T. J., K. J. Krzeczowski, and C. Bergh**; [*The Final
    Approach Spacing Tool*](../CTAS/davis_09_94.pdf); IFAC Thirteenth
    Symposium on Automatic Control in Aerospace, Palo Alto, CA;
    September 1994

15. **Credeur, L., W. R. Capron, G.W. Lohr, D. J. Crawford, D. A. Tang,
    and W. G. Rodgers, Jr.**; *A Comparison of Final Approach Spacing
    Aids for Terminal ATC Automation*; Air Traffic Control Quarterly,
    Vol. 1(2) 135-178; 1993

16. **Davis, T. J., H. Erzberger, S. M. Green, and W. Nedell**; *Design
    and Evaluation of an Air Traffic Control Final Approach Spacing
    Tool*; Journal of Guidance, Control and Dynamics, Vol. 14, No. 4;
    July/August 1991

17. [*NASA: Beyond Free Flight Phase 1
    Tools*](http://www.aero-space.nasa.gov/library/nasao/nbffp1t.htm);
    NASA Office of Aero-Space Technology

18. **Smith, Colin,** National Air Traffic Services Ltd, England;
    ***FINAL APPROACH SPACING TOOL***; December 1998

19. **Credeur, L., W.R. Capron, G.W. Lohr, D. J. Crawford, D. A. Tang,
    and W. G. Rodgers, Jr.**; *Final-Approach Spacing Aids (FASA)
    Evaluation for Terminal-Area, Time-Based Air Traffic Control*; NASA
    Technical Paper 3399; December 1993

20. **Davis, T. J., H. Erzberger, and S. M. Green**; *Simulator
    Evaluation of the Final Approach Spacing Tool*; American Control
    Conference; San Diego, CA; May 1990; NASA Technical Memorandum
    102807; 1990

21. **Davis, T. J., H. Erzberger, and H. Bergeron**; *Design of a Final
    Approach Spacing Tool for TRACON Air Traffic Control*; NASA
    Technical Memorandum 102229; Ames Research Center, 1989

22. **Erzberger, H., and Nedell, W**., "Design of Automated System for
    Management of Arrival Traffic," NASA TM-102201, June 1989.

23. "Center TRACON Automation System Build 2 Operational Description
    Document," MIT Lincoln Laboratory, July 1997.

24. **Swenson, H. N., Hoang, T., Engelland, S., Vincent, D., Sanders,
    T., Sanford, B., Heere, K.,** "Design and Operational Evaluation of
    the Traffic Management Advisor at the Fort Worth Air Route Traffic
    Control Center", 1^st^ USA/Europe Air Traffic Management Research &
    Development Seminar, Saclay, France, June 1997

25. **Davis, T. J., Erzberger, H., Green, S. M., Nedell, W.,** "Design
    and Evaluation of an Air Traffic Control Final Approach Spacing
    Tool", Journal of Guidance, Control, and Dynamics, Vol. 14, No. 4,
    pp. 848-854.

26. "Center-TRACON Automation System (CTAS) Build 2 Computer-Human
    Interface (CHI) Requirements Specification," MIT Lincoln Laboratory,
    August 1998.

27. **Quinn, C., Zelenka, R. E**., "ATC/Air Carrier Collaborative
    Arrival Planning", 2^nd^ USA/Europe Air Traffic Management Research
    & Development Seminar, Orlando, FL, December 1998.

28. **Davis, T. J., Isaacson, D. R., Robinson, J. E. III, den Braven,
    W., Lee, K. K., Sanford, B**., "Operational Field Test Results of
    the Final Approach Spacing Tool", Proceedings of the IFAC 8^th^
    Symposium on Transportation Systems, Chania, Greece, June 1997.

29. **Isaacson, D. R., Davis, T. J., Robinson J. E. III,**
    "Knowledge-based Runway Assignment for Arrival Aircraft in the
    Terminal Area", AIAA Guidance, Navigation, and Control Conference,
    New Orleans, LA, August 1997.

30. **Zelenka, R. E., Beatty, R., Engelland, S.,** "Preliminary Results
    of the Impact of CTAS Information on Airline Operational Control",
    AIAA-98-4481.

31. **Slattery, R.,** "Examination of Possible Future Terminal Area
    Procedures", AIAA Guidance, Navigation, and Control Conference, San
    Diego, CA, July 1996.

32. **Lee, K. K., Sanford, B., Slattery, R.,** "The Human Factors of FMS
    Usage in the Terminal Area", AIAA Modeling and Simulation
    Technologies Conference, New Orleans, LA, August 1997.

33. **Hinton, D. A.,** "Aircraft Vortex Spacing System (AVOSS)
    Conceptual Design", NASA TM 110184, August 1995.

34. **Clarke, J. B., Hansman, R. J.,** \"Systems Analysis of Noise
    Abatement Procedures Enabled by Advanced Flight Guidance
    Technology,\" AIAA-97-0490, Presented at the 35th Aerospace Sciences
    Meeting, Reno, Nevada, January 6-9, 1997.

35. **Welsch, Jerry D., Andrews, John W.,** \"An Examination of Prior
    aFAST Benefits Analysis Studies - Interim Report; MIT/LL
    92PM-AATT-0002, December 1, 1999

36. 

37. **Welsch, Jerry D., Andrews, John W.,** \"Final Approach Spacing
    Tool Benefits Final Report\", MIT/LL 92PM-AATT-0009, September 15,
    2000