**Expedite Departure Path (EDP)**

# General Description {#general-description .unnumbered}

# January 31, 2002 {#january-31-2002 .unnumbered}

# NAS2-98005 {#nas2-98005 .unnumbered}

# Technical Research in Advanced Air Transportation Technologies {#technical-research-in-advanced-air-transportation-technologies .unnumbered}

Final

General Description

Expedite Departure Path (EDP)

CDRL Item 5e

# Prepared under {#prepared-under .unnumbered}

# RTO - 62 {#rto---62 .unnumbered}

# AATT Operational Concept for ATM -- Year 2002 Update {#aatt-operational-concept-for-atm-year-2002-update .unnumbered}

#### January 31, 2002 {#january-31-2002-1 .unnumbered}

#### Prepared For: NASA Ames Research Center {#prepared-for-nasa-ames-research-center .unnumbered}

#### Moffett Field, CA 94035-1000 {#moffett-field-ca-94035-1000 .unnumbered}

#### Prepared By: Titan Systems Corporation -- SRC Division {#prepared-by-titan-systems-corporation-src-division .unnumbered}

#### Billerica, MA 01821-4134 {#billerica-ma-01821-4134 .unnumbered}

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

**ACKNOWLEDGEMENT**

The majority of the descriptions presented in this document have been
taken directly from:

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

-   National Aeronautics and Space Administration, Ames Research Center,
    *Center TRACON Automation System -- Expedite Departure Path*; July
    2000 <http://ctas.arc.nasa.gov/project_description/edp.html>; and,

-   Expedite Departure Path (EDP) Operational Concept; Johnson (MIT/LL),
    Isaacson and Lee (NASA ARC); Report #: NASA/A-3; August 1999

Minor modifications have been made to the text to provide readability.
The Expedite Departure Path Functional 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 EDP Tool Developers and the associated NASA AATT
contractors.

**Table of Contents**

1.  **Description 1**

2.  **Operational Concept 2**

3.  **Functional Flow 6**

# List of Figures {#list-of-figures .unnumbered}

1.  **EDP System Overview 3**

2.  **EDP Functional Flow 7**

3.  **EDP Software Architecture 7**

# Appendices {#appendices .unnumbered}

### Bibliography

## EXPEDITE DEPARTURE PATH (EDP) {#expedite-departure-path-edp .unnumbered}

## GENERAL DESCRIPTION {#general-description-1 .unnumbered}

**1. DESCRIPTION**

**Purpose:**

The purpose of the Expedite Departure Path (EDP) Tool is to assist
terminal area controllers in efficiently directing airborne departure
traffic by providing speed, direct climb, and where appropriate, heading
advisories. This set of tools makes use of the aircraft
performance-model-based trajectory planning capabilities of the Center
TRACON Automation System (CTAS) to provide an advisory decision support
capability to assist Air Traffic Controllers (ATCs).

The intent of this tool is to:

-   assist controllers in load management for departing aircraft.

-   assist in the sequencing, spacing, and merging of departing aircraft
    into the en route traffic stream.

-   provide aircraft sequencing and departure gate balancing information
    to TRACON Traffic Management Coordinators.

-   meter and/or provide clearance advisories for departing aircraft
    that merge over a given fix.

-   provide conflict-free, fuel-efficient speed and turn advisories to
    improve utilization of terminal airspace.

-   Utilize conflict probe functionality to expedite departures that
    cross arrival routes by determining when unrestricted climbs can be
    given to specified aircraft (in en route airspace).

**Users:**

EDP will aid traffic management specialists in the Traffic Management
Unit (TMU) as well as sector controllers in terminal, en route, tower,
and/or airline operational control facilities. Local facility procedures
will be incorporated into EDP. Initial functionality will provide
departure management assistance to TRACON controllers with en route
functionality to be provided in the future.

**Field Sites:**

None

## Expected Benefits: {#expected-benefits .unnumbered}

Benefits are dependent on:

-   Traffic loading of airport(s)

-   The dependencies of arrivals and departures at an airport

-   Traffic flow between multiple airports within a TRACON and in the
    extended terminal area.

Airspace User Benefits:

-   Reduced aircraft fuel burn and block times due to improved departure
    trajectories and improved coordination of aircraft from satellite
    airports. (Note: This could have significant benefits for General
    Aviation aircraft.)

-   Reduced taxi delay

Airspace Traffic Service Benefits:

-   TRACON capacity improvements through more effective balancing and
    sequencing of arrival and departure traffic (for airports either
    having dependent arrival and departure runways or runways that
    simultaneously handle arrival and departure operations).

-   Improved runway systems utilization

-   Reduced tower-to-tower verbal communication, especially in dependent
    departure situations (e.g., OAK-SFO; Northeast Corridor)

**Future:**

The EDP is in the concept exploration phase. Some initial concept
development work and preliminary potential benefits studies are
underway.

**Overview**

As shown in Figure 1, the EDP network uses aircraft flight plans and
position data from FAA computers, inputs from TRACON departure
controllers, and current weather predictions, to produce advisories to
assist controllers in managing departure traffic. TRACON departure
controllers interact with EDP, both receiving advisories and providing
inputs, through standard FAA hardware. Center and TRACON TMCs interact
with EDP through a dedicated EDP display, although the center TMU
provides no inputs to EDP.

**2. OPERATIONAL CONCEPT**

In the current operational environment, there is only a minimal set of
automation to assist air traffic controllers. The most advanced
automation for controllers includes PlanView Displays (PVDs) in the
ARTCCs and Full Digital ARTS Displays (FDADs) in the TRACONs (though the
majority of TRACONs have even earlier generation displays). These
displays are monochrome, and have very limited capabilities. As a
result, controllers are forced to rely primarily on their mental skills
to solve the complex problems presented to them. While controllers have
always done an excellent job with these complexities, some situations
are beyond the scope of their informational awareness. Incomplete
information creates a setting where controllers tend to be conservative.
This conservatism includes restricting aircraft from airspace boundaries
and perceived traffic, even where there is no actual conflicting
traffic. The lack of information creates situations where controllers do
not know what is happening in adjacent facilities. In these cases, lack
of information leads to inefficiencies.

Once an aircraft is airborne, a radar tracking system acquires the
target and a transponder is interrogated. This information is processed
by the ARTS computer system, and information associated with the
aircraft (aircraft identification, aircraft type, position, altitude,
speed, etc.) is displayed to the controller in the form of a Full Data
Block (FDB) on an FDAD or PVD. This information is the basis for the
controller's decisions. When a controller sees a departure aircraft's
FDB, decisions are made based on current procedures. The decisions are
also based

![](media/image2.wmf){width="5.99375in" height="4.836805555555555in"}

**Figure 1: EDP System Overview**

upon any FDBs associated with potentially conflicting traffic. If, for
example, the procedural route of a departure will intersect the
procedural route of arrival aircraft, the controller will scan the
arrival route backward from the intersection point to assess potential
conflicts. In this manner, the controller mentally calculates when
attention will need to be devoted to resolve this potential conflict. As
the departure aircraft progresses toward the intersection point, the
controller attention becomes more focused on the potential conflict.
Generally, these aircraft are procedurally separated by altitude,
restricting departures below arrivals until there is no risk of
conflict.

Another operational situation involves merging departures. This occurs
most frequently in the form of merging over a fix, but occasionally
takes the form of sequencing through a gate. When aircraft are sequenced
in this manner there is often a lack of shared information between
controllers. For example, when aircraft are merging over a fix, there
may be several controllers working numerous departures, all bound for
the same fix. In this case, there is little or no information shared
between the controllers. The aircraft are procedurally separated by
altitude and must eventually be merged into a single stream at the same
altitude by the controller who works the airspace beyond the departure
fix. To help achieve this goal, while reducing controller workload, a
miles-in-trail constraint for aircraft bound for the departure fix is
often levied on the departure controllers. In the case of sequencing
departures through a gate, miles-in-trail restrictions are also the
norm.

EDP is designed to provide advisory information to minimize the
inefficiencies as aircraft transition into the en route system.
Controllers are presented with advisories based upon a more complete
picture of the air traffic control system. These advisories will likely
be presented in the FDB.

Once an aircraft is airborne, EDP advisories will be generated and
displayed to controllers. Altitude advisories will indicate the highest
useable altitude for each departure, based upon procedural constraints
and conflicting traffic. The calculation of traffic conflicts will be
based upon EDP trajectory predictions for the departures and potentially
conflicting arrivals. Speed and heading advisories will indicate the
optimal path and speed for sequencing departures over a fix or through a
gate. The calculations will be based upon trajectory predictions for
each of the departures relevant to the sequence. EDP information will
also be displayed in the TRACON and ARTCC TMUs. In addition to advisory
information displayed on the PGUIs, TMCs can view timelines indicating
when the departures will cross various fixes.

There are three categories of operational uses for EDP. The first
category is Climb Advisories. Climb advisories are presented to
controllers only when altitude restrictions are required. The second
category is Merging Over a Fix. Advisories are presented to controllers
in order to optimize en route spacing over a fix. The third category is
Merging Into the En Route Stream. The primary difference between the
second and third category is that these advisories are associated with
vectoring aircraft through a gate, instead of over a fix.

There are numerous cases where EDP climb advisories can provide benefits
in the operational environment. Many major TRACONs have operational
procedures where departures are restricted below arrivals. Often this
occurs because there is an intersection between an arrival route and a
departure route close to the airport. In these cases, the departure is
often restricted below the arrival path until there is an assurance that
no conflict exists. Scenarios describing situations where EDP climb
advisories will improve efficiency include:

-   [Restricted Climbs Due to Traffic]{.underline}: In today's
    environment, controllers generally choose to restrict the departure
    below the arrival. This is primarily due to a lack of information
    regarding the ascent trajectory associated with the specific
    departure aircraft. Even if the controller thinks that the departure
    might out climb the arrival, there is a tendency to be conservative
    and restrict the departure in order to ensure separation. This is
    even more pronounced when the arrival is descending from a higher
    altitude to level off at the restricted altitude.

-   [Unrestricted Climbs]{.underline}: EDP can expedite the climb of
    departure aircraft. When EDP computes that a departure can safely
    climb, it displays an advisory to the air traffic controller,
    eliminating unnecessary altitude restrictions.

EDP can also reduce controller workload while optimizing the flow of
aircraft into the en route stream. EDP generates speed, vector, and
altitude advisories to sequence

aircraft into the en route stream. These advisories allow aircraft to be
spaced efficiently, while minimizing aircraft maneuvers and controller
clearances. Both uses will improve overall system efficiency. Scenarios
describing situations where EDP advisories will improve efficiency
include:

-   [Merging Over a Fix]{.underline}: It is common in the existing
    operational environment for numerous controllers to be working
    different aircraft bound for the same fix. Today, these aircraft are
    restricted by altitude, to ensure separation at the airspace
    boundary. Moreover, departure controllers are often required to
    space their departures using miles-in-trail constraints. This is
    done to provide gaps in the stream, allowing for potential merges.
    For example, if there are two departure routes being merged into one
    en route stream, 20 miles in trail from the two departure routes
    should allow for 10 miles in trail along the en route stream. No
    attempt is made to sequence or space the traffic on an aircraft by
    aircraft basis. This creates situations where one departure route
    may be empty, while the other is unnecessarily constrained. Even
    with these potential inefficiencies there are still cases where
    aircraft from multiple departure controllers arrive over the en
    route at the same time. For example, two aircraft may arrive from
    the departure routes (separated by altitude) followed by a 20 mile
    gap and then two more aircraft. This causes additional workload on
    the controller trying to sequence and space the aircraft beyond the
    fix, which often leads to additional miles-in-trail constraints.

> EDP advisories are designed to reduce these inefficiencies. Speed and
> vector advisories allow for departure aircraft to be sequenced and
> spaced laterally allowing for a smooth transition into the en route
> system. EDP calculates and compares the trajectories for each
> departure aircraft bound for the fix. The EDP algorithm then generates
> a solution whereby speed and vector changes enacted prior to crossing
> the fix sequences and spaces the traffic as close to the desired
> result as feasible. Speed and vector commands are generally sufficient
> degrees of control to ensure minimum separation. Where additional
> controllability is required, EDP also generates an altitude advisory
> to ensure safety.
>
> There are operational instances in which (due to airspace constraints,
> traffic conflicts, and aircraft performance characteristics) speed and
> heading controls are not sufficient to safely space aircraft over a
> fix. In these instances, EDP will improve system performance by
> reducing controller workload and enhancing departure efficiency
> through the use of speed, heading, and altitude advisories. Altitude
> controls are generally considered to be a short-term solution, since
> the aircraft will ultimately need to be spaced in-trail along the
> route.

-   [Merging Into an En Route Stream]{.underline}: In the existing
    operational environment, there are situations where controllers
    vector departures through a departure gate. Since the departure gate
    is generally a 10-mile arc, controllers have more flexibility than
    routing aircraft over a departure fix. However, the aircraft must
    still be sequenced in-trail of one another, and the additional
    flexibility may actually create inefficiencies. When controllers are
    attempting to space aircraft out a departure gate, they typically
    provide miles-in-trail spacing based upon the arc that defines the
    gate. This creates situations where, for example, even though the
    second aircraft is spaced 10 miles away from the arc when the first
    aircraft passes it, the second aircraft may actually be more than 10
    miles-in-trail of the first aircraft based on the angular distance.
    This distance is based upon the Cosine of the angle of displacement.
    Thus, the farther away from the en route stream, the greater the
    distance.

> EDP advisories are designed to reduce this inefficiency. Speed and
> vector advisories allow for departure aircraft to be sequenced and
> spaced in trail of the aircraft that they will be following after
> merging, instead of the arc that defines the gate***.*** Moreover, if
> the controller needs to issue numerous speeds and headings to achieve
> the prescribed spacing, EDP can also provide benefit by reducing
> controller workload. The precise calculations of the EDP advisories
> can reduce the number of clearances required to achieve the desired
> spacing or sequencing.
>
> Another example of how EDP can enhance the current operational
> environment is when a departure must cross a fix at or above a
> specified altitude. The Loop Departure procedure at LAX and San Jose,
> for example, require aircraft to depart in one direction (westbound)
> and then turn back toward the airport and cross the VOR at the airport
> at or above a specified altitude. Although controllers have a general
> idea of the climb characteristics of each aircraft type, they can not
> accurately know the climb performance of individual aircraft.
> Consequently, controllers often turn the aircraft later than
> necessary, to be sure the aircraft can achieve the proper crossing
> altitude. This creates inefficiencies.

**3. FUNCTIONAL FLOW**

Figure 2 illustrates the detailed functional flow of EDP 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 EDP are:

-   Data Acquisition and Processing

-   Data Formatting and Distribution

-   Trajectory Generation

-   Departure Planning

-   Advisory Generation

-   Conflict Detection

-   Display Message Processing

The narrative contained in the following section provides adequate
description for the EDP functional flow (see Figure 2) and for the
proposed EDP Software architecture (see Figure 3) which is based on
report #1 in the bibliography. The EDP system will be divided into nine
software modules: Communications Manager (CM) , Weather Data Acquisition
Daemon (WDAD), and Weather Data Processing Daemon (WDPD), Route Analyzer
(RA), Trajectory Synthesizer (TS), EDP Scheduling Process (ESP), Input
Source Manager (ISM), Planview Graphical User Interface (PGUI), Timeline
Graphical User Interface (TGUI). The CM controls the flow of information
between the modules and manages system start-up and shutdown procedures.
The WDAD and WDPD retrieve and process weather predictions for both
ARTCC and TRACON airspace.

![](media/image3.wmf){width="7.125in"
height="4.113888888888889in"}**Figure 2: EDP Functional Flow**

**Figure 3: EDP Software Architecture**

The RA generates and analyzes predicted possible routes for each
aircraft. The TS computes predicted 4D trajectories given the aircraft
routes, weather conditions, and aircraft performance models. The RA, in
conjunction with the TS, produces 4D trajectories and Estimated Times of
Arrival (ETAs) spanning the range of possible paths for each aircraft.
Given the set of likely flight paths for all aircraft in the system,
produced by the RA/TS combination, ESP generates an efficient
conflict-free schedule and the corresponding advisories required to meet
this schedule. The ESP accomplishes this task in coordination with the
arrival scheduler, insuring the departure schedule is not in conflict
with the arrival schedule. This architecture allows all aircraft
trajectories to be updated within the radar update cycle.

Although much of the CHI requirement discovery has yet to take place,
the notion is that the EDP advisories will be displayed in the full data
blocks with associated symbology to indicate where the advisory should
either be issued or implemented. It is likely that color will be used
either for the advisory, for an indicator of when to issue the advisory,
or both. During the CTAS Build 2 requirement definition process, the
TGUI CHI requirements were extensively documented. The Build 2 CHI
Requirements Document (1) provides an excellent starting point for the
display of EDP advisories in the TMU. CHI issues surrounding the display
of controller advisories in the STARS and DSR environment still need to
be explored.

The evaluation of EDP functionality will be affected by the usability of
EDP advisories. Consequently, the basic CHI requirements of the proposed
EDP advisories must be defined first. A series of simulations involving
air traffic controllers will be used to determine these requirements.
The simulations are designed to evaluate aspects of the EDP advisories
in an incremental manner. Three phases of simulations will study
advisory characteristics, advisory implementation, and advisory
presentation.

The first phase will focus on the physical characteristics of the
advisories. The preliminary color and advisory formats will be presented
to air traffic controllers, assessed and modified, until they meet
controller acceptance. This phase will be conducted using static
presentations and Visual Basic mock-ups of simple moving data tags.

The second phase will focus on the implementation of the advisories. The
placement of the advisory, the timing of the display, the timesharing
features, and the priority of the advisories will be varied, assessed,
and modified until they meet controller acceptance. This phase will
consist of scripted scenarios in a \"shadowing\" mode. The scripted
scenarios will be generated from live traffic or PAS (Pseudo Aircraft
Systems) generated simulations, so that the traffic will appear
realistic. Actual data will be used to script the degree of turn, speed,
or altitude clearance for the advisories. These advisories will then be
displayed to controllers on the Planview Graphical User Interface
(PGUI), a given distance/time prior to the point at which the aircraft
changes speed, heading, or altitude. Therefore, the controller will not
be actively controlling aircraft, but will perform handoffs for aircraft
entering and exiting the sector. The controller will be asked to
acknowledge the onset of an advisory, and specify the point at which the
advisory would be issued to the aircraft. Reaction-time will be measured
for both of these events. This will allow data collection and feedback
on the format and timing of advisories under varying traffic conditions,
as well as to determine initial limits on traffic complexity and
clutter. The color and format of the advisories will also be re-visited
in this phase, evaluating these issues under traffic control conditions.

The third phase will incorporate the EDP algorithms to investigate the
simultaneous presentation of multiple advisories, to evaluate limits on
the number and types of advisories that can be presented. Issues of
advisory adherence, the effects of early, late, or missed advisories, as
well as acceptance of the system as defined in the first two phases will
be investigated.

Once the physical characteristics of the EDP advisories are determined,
the procedural implications must be addressed. Since the advisories may
be displayed to controllers in several facilities, communication and
coordination issues are significant. Controllers, traffic managers, and
human factors engineers must work together to solve these issues. The
EDP information displayed on a TGUI to TMCs may also be evaluated at
this stage.

**APPENDIX A: BIBLIOGRAPHY**

1.  "Center-TRACON Automation System (CTAS) Operational Concept Document
    for Build 1," MIT Lincoln Laboratory. 28 May, 1996.

2.  "CENTER TRACON AUTOMATION SYSTEM BUILD 2 OPERATIONAL DESCRIPTION
    DOCUMENT," MIT Lincoln Laboratory. 16 July, 1997

3.  "Active FAST Shadow Simulation Test Plan Draft," Lee, Kathy and
    Quinn, Cheryl 27 April, 1998.

4.  "CTAS TMA Reference Manual, Release 5.3.1," NASA Ames Research
    Center. 5 June, 1998

5.  "Center-TRACON Automation System (CTAS) Build 2 Computer-Human
    Interface (CHI) Requirements Specification," MIT Lincoln Laboratory.
    Final Revision, 28 August, 1998.

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

7.  National Aeronautics and Space Administration, Ames Research Center,
    *Center TRACON Automation System -- Expedite Departure Path*; July
    2000 <http://ctas.arc.nasa.gov/project_description/edp.html>

8.  Expedite Departure Path (EDP) Operational Concept; Johnson (MIT/LL),
    Isaacson and Lee (NASA ARC); Report #: NASA/A-3; August 1999

9.  Volpe Center; A Safety Hazard Assessment Process For AATT Decision
    Support Tools With An Assessment Of Expedite Departure Path (EDP);
    July 2000