September 2013

NASA/TM2013-218040

Air Traffic Management Technology 

Demonstration-1 Concept of Operations 

(ATD-1 ConOps), Version 2.0

Brian T. Baxley and William C. Johnson

Langley Research Center, Hampton, Virginia

Harry N. Swenson, John E. Robinson, and Tom Prevot

Ames Research Center, Moffett Field, California

Todd J. Callantine

San Jose State University

Ames Research Center, Moffett Field, California

John Scardina and Michael Greene

Crown Counsulting, Arlington, Virginia
NASA STI Program . . . in Profile

Since its founding, NASA has been dedicated to the 

advancement of aeronautics and space science. The 

NASA scientific and technical information (STI) 

program plays a key part in helping NASA maintain 

this important role. 

The NASA STI program operates under the 

auspices of the Agency Chief Information Officer. 

It collects, organizes, provides for archiving, and 

disseminates NASA’s STI. The NASA STI 

program provides access to the NASA Aeronautics 

and Space Database and its public interface, the 

NASA Technical Report Server, thus providing one 

of the largest collections of aeronautical and space 

science STI in the world. Results are published in 

both non-NASA channels and by NASA in the 

NASA STI Report Series, which includes the 

following report types: 

 TECHNICAL PUBLICATION. Reports of 

completed research or a major significant phase 

of research that present the results of NASA 

Programs and include extensive data or 

theoretical analysis. Includes compilations of 

significant scientific and technical data and 

information deemed to be of continuing 

reference value. NASA counterpart of peerreviewed formal professional papers, but 

having less stringent limitations on manuscript 

length and extent of graphic presentations. 

 TECHNICAL MEMORANDUM. Scientific 

and technical findings that are preliminary or of 

specialized interest, e.g., quick release reports, 

working papers, and bibliographies that contain 

minimal annotation. Does not contain extensive 

analysis. 

 CONTRACTOR REPORT. Scientific and 

technical findings by NASA-sponsored 

contractors and grantees. 

 CONFERENCE PUBLICATION. 

Collected papers from scientific and 

technical conferences, symposia, seminars, 

or other meetings sponsored or cosponsored by NASA. 

 SPECIAL PUBLICATION. Scientific, 

technical, or historical information from 

NASA programs, projects, and missions, 

often concerned with subjects having 

substantial public interest. 

 TECHNICAL TRANSLATION. 

English-language translations of foreign 

scientific and technical material pertinent to 

NASA’s mission. 

Specialized services also include organizing 

and publishing research results, distributing 

specialized research announcements and feeds, 

providing information desk and personal search 

support, and enabling data exchange services. 

For more information about the NASA STI 

program, see the following: 

 Access the NASA STI program home page 

at http://www.sti.nasa.gov

 E-mail your question to help@sti.nasa.gov

 Fax your question to the NASA STI 

Information Desk at 443-757-5803 

 Phone the NASA STI Information Desk at 

443-757-5802 

 Write to: 

 STI Information Desk 

 NASA Center for AeroSpace Information 

 7115 Standard Drive 

 Hanover, MD 21076-1320 
National Aeronautics and 

Space Administration

Langley Research Center 

Hampton, Virginia 23681-2199

September 2013

NASA/TM2013-218040

Air Traffic Management Technology 

Demonstration-1 Concept of Operations 

(ATD-1 ConOps), Version 2.0

Brian T. Baxley and William C. Johnson

Langley Research Center, Hampton, Virginia

Harry N. Swenson, John E. Robinson, and Tom Prevot

Ames Research Center, Moffett Field, California

Todd J. Callantine

San Jose State University

Ames Research Center, Moffett Field, California

John Scardina and Michael Greene

Crown Counsulting, Arlington, Virginia
Available from:

NASA Center for AeroSpace Information

7115 Standard Drive

Hanover, MD 21076-1320

443-757-5802
 i 

Table of Contents 

1.0 INTRODUCTION/SCOPE .................................................................................................... 1

1.1 BACKGROUND .................................................................................................................................. 2

1.2 PROBLEM STATEMENT .................................................................................................................... 3

1.3 IDENTIFICATION ............................................................................................................................... 3

1.4 OPERATIONAL NEED ........................................................................................................................ 4

1.5 ATD-1 CONOPS OVERVIEW ............................................................................................................ 5

1.6 INTEGRATION WITH ANSP GROUND SYSTEMS AND AIRCRAFT SYSTEMS ................................... 6

2.0 OPERATIONS AND CAPABILITIES ................................................................................. 7

2.1 DESCRIPTION OF USERS IN CURRENT OPERATION ....................................................................... 7

2.2 SUPPORTING CAPABILITIES ............................................................................................................ 9

3.0 DESCRIPTION AND JUSTIFICATION OF CHANGES ............................................... 12

4.0 ATD-1 CONCEPT OF OPERATIONS .............................................................................. 13

4.1 CONCEPT GOAL ............................................................................................................................. 13

4.2 CONCEPT DESCRIPTION ................................................................................................................ 13

4.3 ASSUMPTIONS AND REQUIREMENTS ............................................................................................. 16

4.4 OPERATIONAL ENVIRONMENT ...................................................................................................... 17

4.5 OPERATIONS BY ATD-1 TECHNOLOGY ........................................................................................ 18

4.5.1 TMA with Terminal Metering (TMA-TM) ............................................................................... 18

4.5.2 Controller-Managed Spacing (CMS) ......................................................................................... 20

4.5.3 Flight Deck Interval Management (FIM) .................................................................................. 23

4.6 BENEFITS TO BE REALIZED ........................................................................................................... 27

4.6.1 Overall Benefits ......................................................................................................................... 27

4.6.2 Benefits to ANSP ....................................................................................................................... 28

4.6.3 Benefits to Flight Crew .............................................................................................................. 28

4.6.4 Benefits to Airline ...................................................................................................................... 28

4.6.5 Benefits to Airport ..................................................................................................................... 29

5.0 OPERATIONAL SCENARIOS .......................................................................................... 30

5.1 ATD-1 SCENARIO BY PHASE ......................................................................................................... 30

5.2 EVENTS AND PROCEDURES DURING ATD-1 OPERATIONS .......................................................... 38

5.2.1 ATC changes arrival sequence .................................................................................................. 38

5.2.2 ATC Display of CMS or FIM Information ................................................................................ 38

5.2.3 ATC Amends a FIM Clearance ................................................................................................. 38

5.2.4 ATC Suspends or Resumes a FIM Operation ............................................................................ 38

5.2.5 ATC Terminates a FIM Operation ............................................................................................. 39

5.2.6 ATC issues an infeasible FIM clearance ................................................................................... 39

5.2.7 Flight Crew Terminates a FIM Operation ................................................................................. 39

5.3 CONTINGENCY ATD-1 OPERATIONS ............................................................................................ 40

5.3.1 User terminates the use of the ATD-1 technology ..................................................................... 41

5.3.2 Significant weather event........................................................................................................... 41

5.3.3 Airport configuration change or runway closure ....................................................................... 42

5.3.4 Aircraft emergency or priority handling .................................................................................... 42

5.3.5 Different levels of aircraft avionic equipage ............................................................................. 42
ii 

6.0 SUMMARY OF IMPACTS ................................................................................................. 43

7.0 REFERENCES ...................................................................................................................... 44

APPENDICES ............................................................................................................................. 47

APPENDIX A: GLOSSARY AND DEFINITIONS ...................................................................................... 47

APPENDIX B: CHANGES TO ATD-1 CONOPS ..................................................................................... 52

APPENDIX C: RELATED ATM CONCEPTS AND RESEARCH ............................................................... 53

APPENDIX D: LIMITATIONS TO THE CONOPS DURING THE ATD-1 DEMONSTRATION .................. 57

APPENDIX E: ASSUMPTIONS AND REQUIREMENTS FOR ATD-1 ....................................................... 59

APPENDIX F: DESCRIPTION OF ALGORITHMS ................................................................................... 63

APPENDIX G: CONTROLLER-PILOT PHRASEOLOGY ......................................................................... 65

G.1 Route and runway assignment by en route controller .................................................................. 66

G.2 FIM Clearance Issued by ATC .................................................................................................... 67

G.3 Flight crew FIM status notification to ATC................................................................................. 68

G.4 FIM Clearance Amended by ATC ............................................................................................... 69

G.5 Suspending and Resuming FIM Operation .................................................................................. 70

G.6 Termination of FIM Operation .................................................................................................... 70

G.7 ATC Requests FIM Operation Report ......................................................................................... 71

APPENDIX H: EXAMPLE OF ATD-1 ARRIVAL AND APPROACH PROCEDURES ................................. 72

List of Figures 

Figure 1. Position of ATD-1 within FAA operational concept hierarchy. .................................... 3

Figure 2. Integrated NASA technologies in the ATD-1 ConOps. ................................................. 6

Figure 3. Notional GIM-S displays and aircraft full data block. ................................................. 10

Figure 4. Nominal ATD-1 operation. .......................................................................................... 14

Figure 5. Block diagram of ATD-1 ConOps users. ..................................................................... 18

Figure 6. TMA-TM meter list. ..................................................................................................... 20

Figure 7. CMS tools and displays. ............................................................................................... 22

Figure 8. FIM status indications. ................................................................................................. 23

Figure 9. ADS-B Guidance Display (AGD) with FIM speed. ..................................................... 26

Figure 10. Auxiliary display with FIM clearance and traffic. ..................................................... 26

Figure 11. Operational procedure flowchart. ............................................................................... 31

Figure 12. ATD-1 operation: Schedule Phase. ........................................................................... 33

Figure 13. ATD-1 operation: Precondition Phase. ...................................................................... 34

Figure 14. ATD-1 operation: Initiation Phase. ........................................................................... 35

Figure 15. ATD-1 operation: Operation Phase. .......................................................................... 36

Figure 16. ATD-1 operation: Termination Phase. ...................................................................... 37

Figure 17. Arrival does not connect to the Approach. ................................................................. 72

Figure 18. Arrival does connect to the Approach. ....................................................................... 74

Figure 19. Approach procedure. .................................................................................................. 76

List of Tables 

Table 1. Contingency Operations Matrix ..................................................................................... 40

Table 2. Summary of Impacts ...................................................................................................... 43

Table 3. Glossary and Definitions ............................................................................................... 47
 1 

1.0 Introduction/Scope 

This document updates the Concept of Operations (ConOps) for the Air Traffic Management 

(ATM) Technology Demonstration #1 (ATD-1) [ref 1]. It describes the goals, benefits, 

technologies, and procedures for ATD-1 operations, and is an update to the original version 

(Version 1.0) published in 2012. Significant changes between versions are highlighted in 

Appendix B. 

ATD-1 is sponsored by the National Aeronautics and Space Administration (NASA) System 

Analysis, Integration, and Evaluation (SAIE) Project, part of NASA’s NextGen Airspace System 

Program (ASP). The ATD-1 goal is to operationally demonstrate the capability of three 

integrated NASA research technologies, along with Automatic Dependent Surveillance – 

Broadcast (ADS-B) In technology, to achieve Trajectory-Based Operations from cruise to the 

runway threshold while maintaining high throughput in busy terminal airspace. The expected 

benefits of reduced fuel consumption and improved schedule integrity are intended to address the 

forecasted increase in aircraft operations and flight delay, as well as stimulate equipage with 

ADS-B In to achieve these benefits [ref 2, ref 3]. 

The technologies are: 

 TMA-TM: “Traffic Management Advisor with Terminal Metering” (TMA-TM) for 

precise time-based schedules to the runway and meter points within terminal airspace 

 CMS: “Controller-Managed Spacing” (CMS) decision support tools for terminal airspace 

controllers to better manage aircraft delay using speed control 

 FIM: “Flight-deck Interval Management” (FIM) aircraft avionics and flight crew 

procedures to conduct airborne spacing operations 

In the near future, NASA, the FAA, and industry partners will define the scope, location, and 

schedule of these demonstration activities. Results from the research into these technologies and 

the demonstration activities will be used for technology transfer to the operational systems 

employed by the FAA and industry partners. These technologies and their transfer are currently 

in the FAA roadmap and decision making documents for operational deployment. 

The ATD-1 ConOps is an integrated system that could be deployed in the 2015-2020 

timeframe, and aligns with the Federal Aviation Administration’s (FAA) NextGen Mid-Term 

ConOps [ref 4], the Terminal Sequencing and Spacing (TSS) Concept of Operations [ref 5], the 

Time-Based Flow Management (TBFM) ConOps [ref 6], and is consistent with the FAA’s 

expected National Airspace System Enterprise Architecture Operational Improvements (OI) in 

the 2015-2018 timeframe. In its NextGen Mid-Term Implementation Plan (NGIP) [ref 7], the 

FAA has accepted the Air Traffic Control Association (ATCA) NextGen Mid-term Task Force’s 

Tier 1 recommendations, which included specific guidance that the FAA and the aviation 

industry should agree on the set of capabilities that warrant equipage incentives. The FAA has 

stated that it will establish priorities for incentivizing operator equipage for Performance-Based 

Navigation (PBN), Automatic Dependent Surveillance–Broadcast (ADS-B) and 

Data Communications (DataComm). 
2 

The ATD-1 ConOps also closely aligns with the FAA Surveillance Broadcast Services (SBS) 

Program’s Interval Management – Spacing (IM-S) ConOps [ref 8]. In addition to these ConOps, 

the ATD-1 ConOps also supports NASA’s Integrated Arrival, Departure, and Surface (IADS) 

concept for the Mid-Term [ref 9], and takes advantage of PBN specifications and requirements 

[ref 10]. Related ATM research and concepts are described in Appendix C. 

This document is consistent with FAA guidance for ConOps development [ref 11], and 

provides concept-level requirements for supporting services, systems, technologies, tools, 

procedures, and airspace changes. This document focuses on the arrival scenarios and 

procedures to be used during the ATD-1 operational evaluation of TMA-TM and CMS (planned 

for 2015-2016), and flight test of FIM avionics with TMA-TM and CMS (planned for 2016). 

Aircraft data transmitted via ADS-B will be used by air traffic ground tools and by aircraft 

equipped to receive that data. The end-state operational concept of these capabilities include 

other flight phases (e.g., departure operations), incorporate other technologies (e.g., 

DataComm.), and incorporate more sophisticated controller decision support tools; however only 

the ATD-1 operations and procedures that are enabled by technology expected to be fielded by 

the demonstration timeframe are discussed in this document. 

1.1 Background 

To prepare the National Airspace System (NAS) for the traffic volume increases predicted by 

2025 and to improve the efficiency of the air transportation system, Congress enacted the Vision 

100 – Century of Aviation Reauthorization Act and created the Joint Planning and Development 

Office (JPDO) in 2003. The JPDO – composed of representatives from the FAA, NASA, the 

aviation industry, the Departments of Transportation, Defense, Homeland Security, and 

Commerce, and the White House Office of Science and Technology Policy – was tasked to 

develop a vision of the NAS in the year 2025 that promotes scalability of air traffic operations. 

The JPDO published a Concept of Operations for NextGen that describes a high-level vision for 

the air transportation system for the year 2025 and includes a description of the roles for the 

various operating elements within the air transportation system [ref 12]. The ATD-1 ConOps is 

thematically consistent with this JPDO NextGen ConOps. 

Increasing the capacity and efficiency of the NAS are primary goals of the JPDO NextGen 

ConOps and ATD-1 ConOps. Achieving these goals requires that the throughput to the highdensity airports and the efficiency of arrival operations be simultaneously optimized. The FAA’s 

NextGen Operational Improvements (grouped by Solution Set) associated with ATD-1 and the 

capabilities that enable them are: 

 Initiate Trajectory Based Operations (TBO) 

 102137 Automation Support for Separation Management (2014-2018) 

 104120 Point-in-Space Metering (2014-2018) 

 108209 Increase Capacity and Efficiency Using Area Navigation (RNAV) and 

Required Navigation Performance (RNP) (2010-2014) 

 Increase Arrival/Departure at High Density Airports (HD) 

 104123 Time-Based Metering Using RNAV/RNP Route Assignments (2012-2016) 

 104128 Time-Based Metering in the Terminal Environment (2015-2018) 

 Increase Flexibility in the Terminal Environment (FLEX) 

 104124 Use of Optimized Profile Descents (2010-2017) 
 3 

 Increase Safety, Security, and Environmental Performance (SSE) 

 109319 Environmentally and Energy Favorable ATM Concepts, Phase I (2011-2015) 

1.2 Problem Statement 

The 2013-2033 FAA Aerospace Forecast predicts U.S. commercial aviation revenue 

passenger miles will grow on average 2.9% annually throughout these twenty years. By 2033, 

U.S. commercial air carriers are projected to fly 1.74 trillion available seat-miles – 

approximately 175% the seat-miles flown in 2012 [ref 13]. Arrivals into high-density airports, 

especially during peak traffic periods and inclement weather, experience significant 

inefficiencies due to the use of miles-in-trail procedures and step-down descents. These 

procedures contribute to not achieving the airport’s maximum capacity, increase controller 

workload, increase arrival delay, and increase aircraft fuel burn, emissions and noise. While 

advanced PBN procedures exist at a limited number of sites (e.g., RNAV arrivals and optimized 

profile descents), they are not well utilized due to the lack of supporting scheduling and spacing 

tools and the lack of ATC awareness of aircraft capability (flight crew training and aircraft 

equipage) early in the arrival sequencing process. 

1.3 Identification 

Figure 1 shows the position of the ATD-1 ConOps within the FAA’s structure of Concept 

Levels (Level 1: Enterprise; Level 2: Service; Level 3: Sub-service; Level 4: Solution). While 

the ATD-1 ConOps was developed to directly support the Mid-Term Concept of Operations for 

the NAS [ref 4], the Level 2 and Level 3 ConOps are examples closely related to ATD-1, but not 

formally guiding the development of the ATD-1 ConOps. 

Figure 1. Position of ATD-1 within FAA operational concept hierarchy. 
4 

1.4 Operational Need 

The operational need for the capabilities represented in the ATD-1 ConOps is driven by 

present day shortfalls in the air traffic management areas of capacity, flexibility, efficiency, 

safety, and environment [ref 4]. 

1.4.1 Capacity 

For domestic flights in 2008, there was a total of approximately 3.2 million hours of delay 

according to the FAA’s Aviation System Performance Metrics (ASPM) system [ref 4]. 

Approximately 20% of these hours were airborne delays (much more costly to airlines than 

ground delays), and these delays are expected to more than double in the next ten years without 

NextGen improvements [ref 14]. Throughput in high-density airspace, particularly around major 

metropolitan airports, is reaching its limit using current technology and procedures, in part due to 

ground automation lacking the means to identify areas of unused capacity in busy overhead and 

arrival/departure streams. Current automation lacks the means to not only identify areas of 

unused capacity, but to also forecast these areas.

1.4.2 Flexibility 

Constraints in the infrastructure of today’s NAS impart a limited flexibility on the Air 

Navigation Service Provider (ANSP) workforce. From the perspective of the ANSP, facilities 

offer limited flexibility in their ATM operations, in particular, their ability to respond to changes 

in traffic demand, weather, Special Activity Airspace, and other events. Challenges also exist for 

delegating tasks to flight crews, and for supporting operations other than first-come/first-served 

schedules (e.g., best-equipped/best-served). 

1.4.3 Efficiency 

Minimizing the cost of flight operations and the disruptions to the flying public require more 

efficient and predictable operations. The cost to operators is exacerbated by limitations on 

operating practices and routing options, while the flying public contends with an increase in 

flight delays and cancellations. This is especially true during inclement weather. Rather than 

allowing more efficient and direct routing to destination airports, flight plans are constrained by 

airspace design limitations, fixed airways, and inefficient arrival and departure procedures. 

Ground and airborne operations, particularly those in high-density airspace, are not integrated to 

maximize operational efficiency and capacity during peak demand. Aircraft navigation 

performance capabilities are not fully considered when providing separation management 

services or solving traffic flow management problems. Altitude, heading, and speed changes 

issued verbally by ATC are not entered into controller automation, which reduce the accuracy of 

conflict predictions generated by this automation, and reduce the fuel-efficiency of the aircraft‘s 

flight path. Furthermore, efficiencies gained in the en route airspace through advanced 

scheduling automation are often lost in terminal airspace due to that information not being shared 

with terminal airspace controllers. Finally, the inability of controller automation and cockpit 

automation to directly communicate with each other causes a loss of throughput during all phases 

of flight and across all operational conditions. 

1.4.4 Safety 

A primary goal of aviation is to continue to improve safety in all phases of flight, and 

secondarily to accommodate increased traffic growth and new types of aircraft in the years to 
 5 

come. The need to improve safety is particularly important for those areas in which accidents and 

incidents have historically been more likely to occur, such as taxi operations, during convective 

weather events or periods of low visibility, and in operations in areas without surveillance 

services. The approach to aviation safety must evolve into one in which safety information and 

lessons learned are shared more freely, and combined with a cultural transformation for users 

and service providers from a reactive to a proactive approach to safety improvements. 

1.4.5 Environment 

Environmental concerns have become a global issue to which the aviation community must 

respond. The current airspace design and route structure typically requires aircraft to plan and to 

fly to waypoints that create inefficient horizontal routes and altitude profiles, in turn consuming 

additional fuel and time while contributing to greenhouse gas emissions. Current arrival and 

departure procedures often include incremental climbs and descents that are undesirable both 

from a fuel consumption and flight time perspective, and generate an undesirable noise footprint 

around airports. The more frequent use of complete PBN procedures increases the aircraft 

arrival time accuracy, which in turn reduces delay and increases throughput efficiency, which in 

turn reduces engine emissions, noise, and fuel consumption. 

1.5 ATD-1 ConOps Overview 

The ATD-1 ConOps combines advanced arrival scheduling, controller decision support tools, 

and aircraft avionics to enable de-conflicted and multiple efficient arrival streams in high-density 

terminal airspace (Figure 2). To achieve increased fuel efficiency during periods of high traffic 

demand, aircraft will use PBN procedures that include a transition from the arrival procedure to 

the instrument approach procedure of the assigned runway. 

When the aircraft crosses the Freeze Horizon (see section 4.4.1), the TMA-TM tool assigns 

the most suitable runway and freezes the Scheduled Time of Arrival (STA) for the Meter Fix, 

terminal Meter Points, and runway threshold. The relevant schedule information is shown to en 

route and terminal controllers. The same route and schedule information is used by the software 

that calculates the data displayed to controllers (CMS) and flight crew (FIM). 

En route controllers will issue the arrival procedure and expected runway to all aircraft, and 

use their current displays and GIM-S software to achieve the time calculated at the Meter Fix by 

TMA-TM. When the required delay is predicted to exceed the capability of speed-only 

operations, the en route controller will use path stretching (vectors) or step down the aircraft to 

lower altitudes to absorb the delay, and then revert to speed-only control when feasible. At that 

point, the controller will issue the flight crew the clearance to descend via the arrival procedure, 

and for equipped aircraft, issue a FIM clearance. If the delay isn’t absorbed as expected, the 

controller interrupts the descend-via arrival procedure (and suspends the FIM operation if 

appropriate), then reverts to traditional separation strategies such as speed control, vectoring, and 

altitude assignments (step-downs) until the delay has been reduced. 

Terminal controllers receive aircraft data and STA information, graphical information 

(spacing circles), as well as CMS advisories on their controller display to correct the remaining 

spacing error. Terminal controllers will use this information and the CMS advisories when 

speed control is sufficient to absorb the remaining delay. 
6 

All flight crew fly the appropriate speed (in prioritized order: controller assigned, FIM [if so 

equipped], published, company assigned) during the arrival and approach. Flight crews of FIM 

equipped aircraft will be issued a FIM clearance after the Freeze Horizon and after vectors (to 

absorb required delay) are no longer expected. The FIM clearance consists of the Target (or 

lead) aircraft, the Target’s route of flight, and the Assigned Spacing Goal (ASG) between the 

two aircraft. FIM operations may use Target aircraft on the same or different arrival procedure 

as the FIM aircraft. Controllers will “suspend” FIM operations if the need exists to momentarily 

vector either the FIM aircraft or Target aircraft, and any controller issued vector or speed 

instruction takes priority of published procedures or FIM guidance. 

Figure 2. Integrated NASA technologies in the ATD-1 ConOps. 

1.6 Integration with ANSP Ground Systems and Aircraft Systems 

The ATD-1 ConOps and operations require the ATD-1 ground side technologies to be 

integrated with the Time-Based Flow Management system (TBFM), the En Route Automation 

Modernization system (ERAM), and the Standard Terminal Automation Replacement System 

(STARS). Interoperability with the FAA’s soon-to-be-fielded Ground-based Interval 

Management – Spacing (GIM-S) capabilities is also required. 

On the flight deck, the FIM technology required for aircraft systems may be installed either 

“forward-fit” for advanced aircraft (in particular, integrated with the autoflight system), or 

“retro-fit” for aircraft currently in operational use (such as one or more auxiliary displays, to 

include one in the primary field of view). The “retro-fit” option is considered the most likely 

airborne integration option to meet the planned ATD-1 demonstration time frame. 
 7 

2.0 Operations and Capabilities 

This section provides a description of the present-day operational elements supporting 

arrivals into high-density airports, with emphasis on aspects that the ATD-1 ConOps proposes to 

change. 

2.1 Description of Users in Current Operation 

 An aircraft landing at a high-density airport traditionally executes a series of step-down 

descents starting at its cruise altitude, flies along a published airway, transitions to a Standard 

Terminal Arrival Route (STAR), and enters terminal airspace at a metering fix or corner-post. 

The aircraft is then handed off by the Air Route Traffic Control Center (ARTCC) to the Terminal 

Radar Approach Control (TRACON). The STAR simplifies issuing the arrival procedure but 

frequently does not connect to the instrument approach procedure, particularly when the aircraft 

is approaching the runway from opposite the direction of landing traffic (i.e., downwind routes). 

When the STAR and instrument approach procedure do not connect, those aircraft must be given 

radar vectors to the final approach course by the terminal controllers. 

During current arrival operations, aircraft may conduct an Optimized Profile Descent (OPD), 

or fuel-efficient profile descent from cruise to the runway in light to moderate traffic. The 

vertical profile of the OPD trajectory can vary based on several factors (aircraft type and weight, 

terminal area winds, etc.), and can be unpredictable for controllers. This variability and 

unpredictability make it difficult for the ANSP to maintain aircraft separation without controller 

intervention, particularly at merge points, making it difficult to maintain the OPDs during 

periods of high throughput. Recently, some newly certified RNAV STARs have been designed 

to achieve OPD benefits by reducing or eliminating level segments on the procedure. They 

include vertical and speed constraints to make the procedures more predictable; however, 

challenges still exist that require controller intervention, especially when managing the 

separation of aircraft at merge points within TRACON airspace. 

The stakeholders supporting arrival operations into high-density airports include: 

2.1.1 Traffic Flow Management (TFM) Traffic Management Coordinators (TMCs) 

 For airports with sufficient levels of traffic demand to necessitate arrival metering 

operations, Traffic Flow Management TMCs use TMA to perform metering by assigning arrival 

metering point time (MPT) constraints. TMA uses these arrival MPT constraints to determine 

the time for each aircraft to cross into TRACON airspace, and uses en route MPT constraints for 

aircraft upstream from the arrival sector. By assigning arrival MPT constraints, TMCs plan 

aircraft sequences and spacing (in time) across each arrival meter point to help ensure that the 

airport will receive arrival demand that matches its prescribed arrival capacity. TMCs also 

maintain the airport configuration and decide when a reschedule of a single aircraft or a global 

reschedule of all aircraft is needed. 

2.1.2 En Route (ARTCC) Sector Controllers 

En route controllers monitor flight progress and maintain separation in en route airspace, 

issue descent clearances, merge arrival steams prior to the TRACON boundary, and ensure that 

Traffic Management Initiatives (TMIs), including specifications for sequencing and spacing, are 
8 

maintained. When an aircraft has been assigned an MPT by TMA, the en route controller 

manages the aircraft, as necessary, to ensure that the aircraft meets its assigned MPT and 

maintains separation with other aircraft. Maneuvers used to meet the MPT constraints could 

include a lateral maneuver (vector to a heading and then back direct to a fix on the route), an 

altitude adjustment (such as a step descent), or a speed adjustment. Current practice is to adjust 

speed first to achieve the required meter time, and then if needed, step the aircraft down in 

altitude to lower the ground speed, or issue a vector to path-stretch the route. Controllers also 

have the option of altering the TMA-calculated sequence of arriving aircraft (known as 

“swapping”) when they find it operationally advantageous. 

2.1.3 Terminal (TRACON) Controllers 

Terminal controllers monitor flight progress, separate departure and arrival flows using 

altitude limits for departure and arrival aircraft, maintain separation among aircraft within each 

specific flow, merge arrival streams in TRACON airspace, and make runway assignments. After 

aircraft enter TRACON airspace, arrival controllers monitor their descent, maneuvering them as 

necessary to maintain required separation. When the STAR connects to the approach procedure, 

controllers are frequently able to use primarily speed control to maintain the required separation. 

When the STAR does not connect to the approach procedure, TRACON controllers assign a 

number of heading, speed, and altitude changes to establish the aircraft onto the final approach 

course of its assigned runway. The terminal controllers have no information from the TMA 

system to aid in these tasks. The controllers use their experience and standard operating 

procedures to select a landing runway and to guide the aircraft from the entrance of the 

TRACON to the runway threshold. 

2.1.4 Flight Crews 

The flight crew is able to plan and execute a vertical profile (altitude and speed) along a 

lateral path that is optimized for their specific aircraft make and model, using its Flight 

Management System (FMS) and autoflight system. The FMS has data on the detailed 

performance specifications of the aircraft (desired performance requirements, engine model, fuel 

onboard, cargo weight, etc.), state information (present location, altitude, current winds, forecast 

winds, etc.), and other data (altitude constraints, noise abatement procedures, etc.) to optimize 

the vertical profile within the constraints of the assigned arrival procedure. Since the vertical 

profile is based on the aircraft’s energy state, the trajectory generated by the Flight Management 

System, and airframe-specific data, each aircraft will have a different vertical profile. The 

vertical profile differences between aircraft, particularly between different airframe types, can be 

significant. Most current generation FMSs only calculate the vertical profile prior to the aircraft 

reaching its top-of-descent point, and do not recalculate the vertical profile after the aircraft has 

started its descent. If the planned vertical profile is interrupted (i.e., the aircraft is temporarily 

held at an intermediate altitude or vectored off the expected lateral path), the vertical profile is 

not automatically recalculated. 

Throughout the flight, crews adhere to ATC instructions such as altitude changes, vectors, 

and speed adjustments to achieve the appropriate sequence and required spacing interval. Since 

most arrivals into busy terminal areas are interrupted by controller instructions, flight crews are 

seldom able to fly the FMS-calculated lateral and vertical path all the way to final approach. The 

non-FMS guidance modes routinely used by flight crews and the additional distance in both 
 9 

lateral and vertical flight path in busy terminal areas result in increased fuel consumption, 

aircraft noise, and engine emissions. 

Flight crews of aircraft equipped with cockpit display of traffic information may monitor the 

position of other aircraft. Regardless of aircraft equipage, en route and terminal controllers have 

the responsibility of maintaining separation between aircraft. This is particularly challenging, 

especially during periods of high traffic demand, which results in nearly all OPDs being 

interrupted to maintain the desired separation between aircraft. 

2.1.5 Airline Operations Center (AOC) 

During the mid-term ATD-1 demonstration, connectivity between the ATD-1 technologies 

and the AOC will not exist. However, in the long-term vision of the ATD-1 ConOps, the Airline 

Operations Center (AOC) will have all current-day operational capabilities and responsibilities, 

as well as those presently being developed outside of the ATD-1 effort. It is postulated that the 

better arrival predictability could improve ground-handling functions conducted by the AOC, 

and potentially allow for the reduction in block times at the airport. 

2.2 Supporting Capabilities 

2.2.1 Current FAA Automation 

During periods of congestion, arrival operations are characterized by significant interactions 

between the controller and pilots for the issuance of heading vectors, descent clearances, and 

speed changes to moderate the demand during the arrival process. The identification of 

congested periods is often accomplished using controller experience-based judgment, augmented 

by a number of tools (Flight Schedule Monitor, Flow Evaluation Area, Monitor Alert, etc.), as 

well as interactions between the TRACON and ARTCC. Whether it is the ad hoc experience or 

the TMA automation, decisions are made to apply delay such that the demand is safely 

moderated to the arrival capacity. Using ad hoc experience, the identification of congestion is 

done by observing how the final approach courses to the runways are being extended from the 

nominal (i.e., uncongested) procedures as well as utilizing the tools mentioned earlier. Upon 

observation that controllers need to continually extend the final approach segment to maintain 

aircraft separation minima (frequently referred to as “tromboning”), the TRACON Traffic 

Management Unit (TMU) may issue a miles-in-trail restriction to the ARTCC to moderate the 

controller workload and traffic flow. These restrictions are again ad hoc and experience-based, 

and they often cause excessive delay in the ARTCC. Miles-in-trail restrictions between the 

ARTCC and the TRACON may be generated by either the TRACON or ARTCC or in 

collaboration to meet an airport acceptance rate. 

Proactive use of the TMA automation identifies periods of traffic congestion, and distributes 

delay between the ARTCC and TRACON using meter fix crossing times, known as scheduled 

time-of-arrivals (STAs). Though the TMA predicts congestion at the runway and moderates the 

flow at the meter fixes of the ARTCC/TRACON boundary, the TRACON does not have the 

ability to follow the TMA runway schedules due to a lack of controller interfaces and limited 

TMA modeling of merging procedures within the TRACON. To maintain the integrity of the 

schedule, TMA currently adds a buffer to the required separation to allow the TRACON to safely 
10 

moderate the congestion. This means the maximum runway capacity (based on the minimum 

separation requirements) is not realized. Even with this limitation, the TMA’s proactive 

congestion identification and the arrival metering at the meter fixes has been shown to efficiently 

distribute arrival delay and controller workload between the ARTCC and TRACON while 

maintaining the runway throughput at the desired airport arrival rate. During periods of 

congestion, enroute controllers manage aircraft to the TMA generated meter times by issuing 

speed instructions, and if additional delay is required, they may descend the aircraft early or 

vector it off its route. Within the TRACON, terminal controllers manage the separation of 

aircraft by speed instructions and vectoring, as well as tromboning the turn to final. 

2.2.2 FAA Automation to be Fielded for ATD-1 

Ground Based Interval Management for Spacing (GIM-S) is part of the FAA’s work to 

support Extended Metering. GIM-S adds additional meter points, called constraint satisfaction 

points (CSP), upstream from the arrival airport, and speed advisories to these points should 

mitigate or eliminate the dependency on miles-in-trail constraints. By conditioning the arrival 

flow, GIM-S is intended to reduce the number of interventions required by the controller, thereby 

reducing controller workload in busy arrival sectors. An aircraft’s arrival time at the runway 

during the ATD-1 demonstration will be calculated by TMA-TM (see section 4.1.1), then 

coordinated with the FAA’s GIM-S software to provide ARTCC controllers speed advisories for 

aircraft not conducting FIM operations. The GIM-S display and speed information will be used 

during the ATD-1 demonstration in ARTCC airspace by center controllers, since their software 

update cycle will not include CMS displays by the 2015-2020 timeframe. Center controllers will 

use the GIM-S speed for any aircraft not conducting a FIM operation. 

Notional depictions of the GIM-S tool and aircraft full data block are shown in Figure 3. 

From left to right in the left panel, the columns represent the aircraft identification, STA at the 

respective waypoint, minutes early or late, and the GIM-S speed advisory (in Mach or Calibrated 

Airspeed). In the right panel, the full data block adds a fourth (bottom) row to show the 

controller assigned heading and Mach or calibrated airspeed. 

 Figure 3. Notional GIM-S displays and aircraft full data block. 
 11 

2.2.3 Aircraft Avionics 

The aircraft’s avionics systems have limited information on surrounding traffic. The use of 

the Traffic Alert and Collision Avoidance System (TCAS) gives the flight crew an approximate 

picture of the immediate surrounding traffic, but it does not provide enough information to allow 

maneuvering in a manner integrated with ground control to achieve the overall air traffic 

management goals. 

This limitation applies to the typical current minimum equipage for air transport aircraft. 

Certain aircraft are also equipped with Cockpit Display of Traffic Information (CDTI) devices, 

for example, some aircraft flying oceanic routes and participating in the In-Trail Procedures 

evaluation. These aircraft receive additional traffic information from Traffic Information Service 

- Broadcast (TIS-B). This additional equipage allows crews to conduct certain procedures, or 

make more informed requests, which enables more efficient operation of the aircraft. 
12 

3.0 Description and Justification of Changes 

The ATD-1 ConOps addresses essential elements of NextGen by integrating several 

important ground-based and flight deck technologies to achieve efficient trajectory-based 

operations into a high-density airport during peak traffic periods. This section outlines changes 

to the current air traffic system in the NextGen mid-term (described in Section 2) and the 

justification for them. The benefits for NAS stakeholders that are expected from these changes 

are discussed in Section 4.5. 

The following capabilities will be used during the ATD-1 operational evaluation and flight 

test activities: 

 The use of a comprehensive, accurate, time-deconflicted schedule for all aircraft, to 

include runway assignment and adjustment for the forecasted terminal area winds 

- Enables the required delay to be distributed more efficiently 

- Allows schedule integrity to be maintained between en route and terminal 

airspace, creating fewer sequence swaps or changes to the assigned runway. 

 Controller automation support to provide the schedule, assigned runway, waypoint meter 

times, and speed advisories to meet them, in both en route and terminal airspace 

- Reduces controller workload since using GIM-S or CMS speed advisories which 

should result in fewer events that require a vector from the controller 

- Reduces size of additional spacing buffer to aircraft separation requirements, in 

turn reducing total delay or increasing throughput. 

 Extensive use of PBN procedures from the en route cruise altitude to the runway during 

periods of high-density traffic 

- Reduces controller workload due to fewer instructions required to issue the arrival 

procedure 

- Reduces flight crew workload due to less data entry into the FMS 

- Increases use of the aircraft auto-flight system to fly the PBN procedure, in 

particular using the FMS-calculated trajectory and TOD, will improve aircraft 

fuel efficiency, as well as reduce engine noise and emissions 

- Reduces the amount of airspace used for arrivals and increase the amount of 

airspace available for other procedures, such as arrivals to secondary airports. 

 Increased use of advanced flight deck capabilities, to include ADS-B In and FIM 

technologies, displays, and procedures 

- Provides additional improvements in aircraft fuel efficiency, and reduction in 

noise and emissions 

- Enables the flight crew to predictably and accurately achieve the assigned spacing 

interval established by the schedule 

- Reduces controller workload due to fewer vectors and speed instructions required. 
 13 

4.0 ATD-1 Concept of Operations 

4.1 Concept Goal 

The operational goal of the ATD-1 ConOps is to enable aircraft, using their onboard autoflight systems, to plan for and fly PBN procedures to the maximum extent possible, from cruise 

to the runway at a high-density airport, during peak traffic demand, using primarily speed control 

to maintain in-trail spacing and the arrival schedule. The three technologies in the ATD-1 

ConOps achieve this by calculating a precise arrival schedule, using decision support tools to 

provide terminal controllers with speeds for aircraft to fly to meet times at particular meter 

points, and using onboard software providing flight crews with speeds for the aircraft to fly to 

achieve a particular spacing behind the preceding aircraft. Small increases or decreases in the 

speed flown by the aircraft during the arrival procedure (to retain aircraft fuel efficiency) will be 

calculated by the CMS or FIM software to achieve the schedule and thus the desired throughput. 

By integrating time-deconflicted arrival scheduling with CMS tools and FIM capabilities in 

the terminal environment of high-density airports, the ATD-1 ConOps enables several important 

capabilities in the mid-term: 

 Mixed Equipage Operations – A combination of ground-based and flight-deck-based 

Interval Management tools can help achieve sustained fuel-efficient operations during 

periods of high throughput while an aircraft fleet mix containing both less capable 

avionics and more advanced avionics. 

 Terminal Metering – Advanced arrival scheduling enables flow conditioning throughout 

the entire arrival phase of flight to ensure efficiency gains achieved by advanced 

automation in en route airspace are not lost in terminal airspace. 

 Trajectory-Based Operations – Integration of the arrival scheduling and Interval 

Management capabilities enables trajectory-based operations to be continued in terminal 

airspace during periods of high throughput when these fuel-efficient operations would 

otherwise be interrupted to maintain aircraft separation. 

4.2 Concept Description 

The ATD-1 ConOps provides de-conflicted and efficient operations of multiple arrival 

streams of aircraft, passing through multiple merge points, from top-of-descent to touchdown 

(see Figure 4). PBN arrival procedures, such as RNAV OPDs, are combined with advanced 

arrival scheduling through TMA-TM, CMS speed advisories and displays, and FIM capabilities 

(for those aircraft equipped) in the terminal environment of a high-density airport. These RNAV 

OPDs provide a lateral path from the en route jet route structure to the runway threshold 

(including transitions that connect the STAR to the instrument approach procedure), and specify 

vertical constraints, as required, and a speed for most segments of the arrival procedure. This 

enables the TMA-TM software to create a more accurate schedule, and allows flight crews to use 

their onboard autoflight systems to fly from en route cruise altitude to landing while requiring 

fewer controller interventions and fly fewer level flight segments [ref 15]. (RNAV OPDs are 

developed by the FAA and are independent from the ATD-1 project; however, the ATD-1 

ConOps intends to enable aircraft to remain on PBN procedures more often, thus improving 

aircraft efficiency and airspace throughput.) 
14 

Figure 4. Nominal ATD-1 operation. 

Where continuous RNAV OPD procedures do not exist from the enroute environment to the 

runway, TMA-TM uses supplemental information from the facilities standard operating 

procedures to calculate the arrival schedule. The same route and supplemental information is 

used by the CMS and FIM software to calculate the data provided by those displays, however, 

the CMS and FIM operation itself is terminated if the terminal controller must issue the flight 

crew a vector to intercept the final approach course (occurs when the STAR and instrument 

approach are not connected). 

During ATD-1 operations, it is expected upstream flow conditioning will, in most situations, 

allow speed control alone to be sufficient to achieve the arrival schedule. The TMA-TM 

scheduling software continuously calculates ETAs and STAs for aircraft to all eligible active 

runways. The trajectories associated with these ETAs incorporate the aircraft’s route-of-flight, 

top of descent, its intended speed profile, and the forecasted winds. When the aircraft crosses the 

Freeze Horizon (the goal is for this to occur prior to the aircraft’s TOD), the TMA-TM tool 

assigns the most suitable runway and freezes the STAs for the runway threshold, Final Approach 

Fix, terminal meter points, and meter fix. The schedule information at each meter point is 

presented to the appropriate en route and terminal controllers (display of the information is 

contingent on the FAA’s plan to implement updated software). (Note: the En Route Flow Meter 
 15 

Point (ERFMP) shown in Figure 4 illustrates the potential interaction between ATD-1 and other 

concepts in the future, however an ERFMP will not be used by the ground scheduler or 

controllers during the ATD-1 demonstration.) 

En route controllers will issue the arrival procedure and expected runway to all aircraft. 

They will also use their current DSR displays and GIM-S software to achieve the time calculated 

at en route meter points by TMA-TM when speed control is sufficient to absorb the remaining 

meter fix or en route meter point delays. When the delay is predicted to exceed the capability of 

speed-only operations, the en route controller will use path stretching (vectors) or lower altitudes 

to incur the required delay, and then revert to speed-only control when feasible. At that point, the 

controller will issue the flight crew a clearance to descend via the arrival procedure, then a FIM 

clearance to the flight crew of FIM-equipped aircraft. 

Traffic permitting, flight crews will normally be given discretion to initiate descent from 

cruise altitude in order to utilize the FMS calculated trajectory and their onboard autoflight 

system to fly the RNAV OPD. If the delay isn’t absorbed as expected, the controller will 

interrupt the descend-via arrival procedure, suspend FIM operations, and revert to traditional 

separation strategies such as speed control, vectoring, and altitude assignments (step-downs) 

until the delay has been reduced. At that time, the controller instructs the crew to resume the 

arrival procedure and FIM operation. 

Terminal controllers receive aircraft data and STA information, graphical information 

(spacing circles), as well as CMS advisories on their STARS display to correct the remaining 

spacing error. Terminal controllers will use CMS advisories when speed control is sufficient to 

absorb the remaining runway or terminal meter point delays. However, the CMS spacing circles 

can still be displayed to facilitate the aircraft being returned to the PBN procedure after vectoring 

to achieve more delay than speed control affords. If the situation permits, terminal controllers 

can use CMS once the aircraft is able to resume its PBN procedure and speed control is 

sufficient. 

FIM clearances will be issued as soon as possible after the schedule freeze and once 

vectoring is no longer expected; however, they may be issued after TOD to reduce the number of 

required voice instructions. FIM clearances may use Target aircraft on the same arrival as the 

FIM aircraft, or on a different arrival and crossing a different meter point to enter the TRACON. 

FIM clearances may be amended by ATC issuing a change to the ASG; however, controllers will 

“suspend” FIM operations if the need exists to momentarily vector either the FIM aircraft or 

Target aircraft. Changes to the arrival sequence, route of flight, or assigned runway require the 

FIM operation be terminated and a new FIM clearance issued if desired. 

FIM operations normally terminate at the Achieve By Point (the Final Approach Fix for 

ATD-1). When ATC terminates a FIM operation prior to that point, the flight crew maintains the 

current or assigned speed, removes all FIM indications from cockpit displays, and deletes FIM 

clearance information from the avionics. When the STAR and instrument approach procedure 

do not connect, the FIM operation is also terminated when the controller issues the flight crew a 

vector to intercept the final approach course. 
16 

4.3 Assumptions and Requirements 

Programmatic assumptions and requirements to accomplish ATD-1 include: 

 NASA develops and the FAA implements TMA-TM at the ATD-1 demonstration site to 

support integrated scheduling and spacing within the TRACON (i.e., terminal metering). 

 FAA implements ERAM changes to support display of the TMA-TM runway assignment 

for every aircraft, and to support use of GIM-S speed advisories by en route controllers. 

 Controller procedures and ERAM automation changes needed for FIM initiation and 

monitoring may not be available by the ATD-1 demonstration timeframe, and 

remains an area of on-going discussion with the FAA. 

 NASA develops and the FAA implements CMS automation and displays within STARS 

at the ATD-1 demonstration site. 

 Controller procedures and STARS automation changes needed for CMS may not be 

available by the ATD-1 demonstration timeframe, and remains an area of on-going 

discussion with the FAA. 

 The FAA develops and implements PBN procedures from the en route environment to 

the runway at the ATD-1 demonstration site. 

 Where PBN procedures are not available, ATD-1 technologies and operations will 

use adapted standard operating procedures (for example, a Letter of Agreement). 

 Most aircraft scheduled to land at the high-density airport during peak traffic periods are 

equipped for RNAV operations. 

 Some aircraft scheduled to land at the high-density airport during peak traffic periods are 

equipped for FIM operations (ADS-B In plus FIM displays and software). 

 Controller-pilot communications will be by voice during the ATD-1 demonstration. 

Technical assumptions and requirements are presented in Appendix E. Highlights include: 

 ANSP retains responsibility for maintaining separation between all aircraft, and meeting 

the schedule for aircraft not conducting FIM operations. 

 The TMA-TM schedule establishes the time-deconflicted arrival sequence of aircraft, and 

is available to all controllers. 

 All controllers will actively manage to the schedule to the maximum extent possible, 

using published procedures and GIM-S or CMS advisories (when available). 

 En route controllers will attempt to issue “Descend Via” clearances to flight crews, which 

authorizes them to meet fly the arrival procedure and meet the published altitude and 

speed constraints. The FMS may be utilized to maximize the aircraft’s efficiency while 

conforming to these constraints, thereby maximizing fuel efficiency as well as reducing 

noise and emissions. 

 Flight crews retain responsibility for operating the aircraft in accordance with procedures 

and instructions (ATC instructions, FIM software speed guidance, etc.). 

 The FIM clearance may be issued to any suitably equipped aircraft. The Target aircraft 

must be transmitting ADS-B and be assigned to the same runway as the FIM aircraft. 

However, it is not required that the Target aircraft to be in the same sector or to be on the 

same arrival procedure as the FIM aircraft, and it is not required that the FIM clearance 

be issued only after the Target aircraft is within ADS-B range of the FIM aircraft. 
 17 

4.4 Operational Environment 

The operational environment targeted for the ATD-1 ConOps is the latter part of NextGen 

Mid-Term (2015-2020). The ConOps will optimize the efficiency of arrival operations into 

high-density airports as well as the throughput of the airport. This ConOps will work with 

current and future ATC programs, and will subscribe to FAA, Aeronautical Information 

Conceptual Model (AICM), Aeronautical Information Exchange Model (AIXM) 5.0, the Flight 

Information Exchange Model (FIXM), the Weather Information Exchange Model (WXXM), and 

International Civil Aviation Organization (ICAO) data standards. Key related programs include 

TBFM, Terminal Automation Modernization and Replacement (TAMR) and its Standard 

Terminal Automation Replacement System (STARS) equipment, and developments in PBN such 

as RNAV STARs and RNP approach procedures. The controller procedure and automation 

changes needed for FIM initiation and monitoring may not be available by the ATD-1 

demonstration timeframe on the En Route Automation Modernization (ERAM) platform for 

ARTCC, and this remains an area of on-going discussion with the FAA. The ATD-1 ConOps 

also relies on the FAA requirements for GIM-S capabilities to be added to ERAM. All of the 

required capabilities outlined in the requirements and operational environment are elements of 

the NextGen mid-term plan, and are expected to be available for the ATD-1 operational 

evaluation and flight test activities. 

Within this operational environment, the three NASA technologies required to implement the 

NextGen mid-term ATD-1 ConOps are: 

 An advanced version of TMA incorporating Terminal Metering (TMA-TM) [ref 16-19] 

 Controller Managed Spacing (CMS) decision support software and displays [ref 20-21] 

 Flight-deck Interval Management (FIM) spacing software and displays [ref 22-24] 

A high-level description of each technology is provided in Appendix F. 

The ATD-1 ConOps users and their notional relationship to each other during the mid-term 

are shown below in Figure 5. The final location of the NASA technologies will be determined 

by the FAA, and may vary based on the specific site. Not shown are other expected users and 

their interactions in the long-term version of ATD-1 operations, such as the AOC and Tower. 
18 

Figure 5. Block diagram of ATD-1 ConOps users. 

4.5 Operations by ATD-1 Technology 

4.5.1 TMA with Terminal Metering (TMA-TM) 

A key element of the ATD-1 project is an advanced ground tool for ATM that determines an 

appropriate arrival schedule and the landing time intervals between aircraft, and then computes 

the appropriate speed required to space aircraft close to the minimum time or distance allowed 

for the runway conditions and meter points. TMA as presently deployed by the FAA in ARTCCs 

and some TRACONS, assists controllers and traffic managers in meeting STAs to closely match 

the desired separations, Airport Arrival Rate, as well as other constraints. The FAA also has 

systems and procedures being developed for extended metering and coupled scheduling (an 

enhancement to TBFM that allows for meter points and times to be defined well prior to the 

TRACON boundary) to precondition traffic flows further upstream. 

While TMA and other decision support tools provide ancillary environmental benefits, their 

primary objective has been to reduce delay and increase throughput. Recent NASA research has 

focused on enhancing TMA and controller advisory tools to enable OPDs for the specific 

purpose of reducing fuel burn, emissions and noise impact. The TMA-TM system is a 

trajectory-based strategic planning and tactical control tool that consists of trajectory prediction, 

constraint scheduling and runway balancing, controller advisories, and flow visualization. The 

trajectory prediction, constraint scheduling, and runway balancing functions are built on the 

existing TMA. The controller spacing and metering advisories are built upon the research of the 

Controller Managed Spacing (CMS) and Efficient Descent Advisor (EDA) technologies. NASA 

simulations have shown that TMA-TM is beneficial in the development of a fully integrated 

trajectory-based automation that enables both more efficient utilization of the airport’s capacity, 

and more fuel and emission-efficient operations from cruise to touchdown for NextGen. 
 19 

TMA-TM extends the basic TBFM scheduling capability by including merge fixes inside 

TRACON airspace, and optimizes the flow of multiple arrival stream merges into an airport. The 

terminal delay model is enhanced to be more compatible with PBN procedures, and to enforce 

separation constraints at merges within the terminal area. The TMA-TM constraint scheduling, 

runway balancing logic, and algorithms necessary for the diverse operational requirements of 

ATC are beyond the scope of this paper, however the basic functional logic is a first-come-firstserved algorithm that is then modified for separation requirements (radar and wake vortex). This 

logic is also coupled with a runway balancing algorithm that uses available runway capacity and 

a delay distribution in the terminal and en route airspace to create the aircraft specific STA. This 

creates conflict-free schedules simultaneously at the Center meter-fixes, terminal meter points, 

and the runway threshold. Additional details include: 

 Freeze Horizon: a prescribed point at which (1) the aircraft’s landing runway is 

calculated, (2) deconflicted STAs to the Meter Fix (TRACON boundary), terminal 

Meter Points, and runway are calculated, and (3) the runway STA is “frozen” (no 

longer updated automatically). 

 Meter Fix Constraints: multi-step schedule process based on earliest ETA to the 

Meter Fix, with the first aircraft in the sequence STA equal to its earliest ETA, and 

subsequent aircraft STA set to ensure in-trail separation constraints are met. 

 Runway Constraints: ensure required runway threshold separation is met (wakevortex standards based on aircraft weight class, runway dependencies, etc.). 

Controllers may increase these values due to weather or other significant events. 

 Delay Distribution Function: the delay distribution function sets the amount of delay 

that can be absorbed within the TRACON airspace when runway demand exceeds 

capacity, using only speed control. 

 Meter Point Constraints: the STAs at TRACON meter points are evaluated 

simultaneously with the evaluation of STAs for the Meter Fix and runway to ensure 

that separation constraints are not violated. This is repeated until all aircraft have 

been scheduled without violating separation constraints at any merge-point. 

 Runway Allocation: an event-driven algorithm that occurs periodically up until the 

aircraft crosses the freeze horizon, at which point the runway allocated to that aircraft 

is fixed. The algorithm considers the active flight plan, aircraft position, and total 

system time delay for all aircraft. Flight time for each aircraft is evaluated for the 

scheduled and alternate runways, and the runway allocated to the aircraft is based on 

the least total system time delay. Future versions of the runway allocation algorithm 

could include other factors, such as preferential scheduling of FIM-equipped aircraft. 

Though TMA-TM creates an aircraft arrival sequence, it does not consider controller 

technique or workload. To reduce workload, controllers may re-sequence from one to five 

aircraft in one entry. Some events require a complete recalculation of the schedule (sequence, 

deconflicted STAs) for all aircraft inside the freeze horizon (airport configuration change, 

acceptance rate change, etc). This procedure is done by the controlling TMU. Controller displays 

(meter lists, speed advisors, and slot markers) are updated for both events. 

The TMA-TM schedule and meter list has also been expanded to support en route controllers 

issuing GIM-S speed advisories and FIM clearances. Figure 6 displays the aircraft identification 

for NASA1 and NASA2, two aircraft proceeding to the waypoint SQUEZ. From left to right, the 
20 

asterisk indicates the aircraft’s runway and STA is frozen, followed by the STA at SQUEZ and 

the amount of delay required to achieve it. Directly below the “T” is the GIM-S speed advisory 

(in Mach and Airspeed) calculated to achieve the STA at SQUEZ. SCADE is the Achieve By 

Point for the FIM aircraft, 124 the Assigned Spacing Goal in seconds, and the data on the right is 

the Target aircraft identification and the Target aircraft’s route. (Note: to mitigate the expected 

lack of datalink communications in the ATD-1 Demo timeframe, the Achieve By Point has been 

removed from the FIM clearance to reduce controller and flight crew workload and voice 

transmissions, and will be removed from the meter list shown below.) 

Figure 6. TMA-TM meter list. 

The TMA-TM schedule itself does not identify which aircraft are FIM capable, rather the 

“problem resolver” function within ERAM will identify those aircraft to enable generation of the 

FIM clearance. This function will also update the FIM status indicator when events occur that 

changes the FIM clearance. (Not updating or terminating a FIM clearance when these events 

occur could result in the FIM aircraft attempting to achieve the assigned spacing interval behind 

an aircraft no longer its lead.) TBFM is expected to calculate the GIM-S speeds, and ERAM will 

manage the display and advisory information. 

4.5.2 Controller-Managed Spacing (CMS) 

Controller-Managed Spacing (CMS) tools assist terminal controllers in achieving their goal 

of maximizing throughput on capacity-constrained runways. They ensure that the terminal 

controllers have knowledge of, and follow, the same arrival schedule that en route controllers use 

to manage the flows of traffic into the terminal airspace. The CMS tools provide the information 

necessary to more accurately achieve arrival schedule conformance using speed commands. This 

information is expected to allow terminal controllers to reduce the use of tactical vectoring, 

thereby minimizing interruptions to fuel-efficient PBN arrival procedures [ref 20-21]. 

The CMS tools consist of schedule timelines, slot markers (or ‘slot marker circles’), 

early/late indicators, and speed advisories shown in Figure 7. These tools function as follows: 

 Schedule Timeline (left panel): 

The schedule timeline displays the TMA-TM-computed schedule at the scheduling 

point relevant for a particular controller position. Entries for each aircraft show the 

aircraft identification code and a symbol that identifies the aircraft’s weight class. 

Estimated time-of-arrival (ETA) entries appear on the left side of the timeline (always 

shown in white); scheduled time-of-arrival (STA) entries appear on the right side. The 

STA is colored green for aircraft that have not initiated hand-off to the sector, bright 

white when the upstream controller initiates hand-off, and the same white as the ETA 

when the receiving controller accepts the hand-off. 
 21 

 Slot markers (top right and bottom right panels) 

Slot markers translate the temporal schedule information into a spatial target on a 

controller’s display. The slot marker circles indicate where an aircraft should be at a 

given time if it were to fly the arrival and approach procedures, meeting all published 

speed and altitude restrictions, and arrive on schedule. The instantaneous indicated 

airspeed of the slot marker is also displayed adjacent to the slot marker circle. In the 

figure, the aircraft shown are travelling right to left. In the top right panel, an aircraft 

that is close to on-time appears inside the circle, while in the bottom right panel an 

aircraft that is slightly early appears ahead of the circle. Note that the slot markers are 

always positioned along the RNAV OPD used to schedule the aircraft, even if the 

associated aircraft has been temporarily vectored off the procedure. 

 Early/Late Indicators (top right panel) 

Early/late indicators in an aircraft’s Full Data Block (FDB) enable controllers to 

quickly assess the schedule conformance of that aircraft, in a manner similar to the 

delay countdown timer (DCT) presently available to ARTCC controllers. An early/late 

indicator is displayed using three characters in the third line of the FDB. Early/late 

indicators display the required delay with one-second precision when the absolute delay 

is less than 100 seconds (e.g., -15 indicates an aircraft is fifteen seconds late); larger 

delay values are shown with one-minute precision (e.g., +2M indicates an aircraft is 

approximately two minutes early). Thus, SWA353 is currently estimated to be three 

seconds early. 

 Speed advisories (bottom right panel) 

Speed advisories display airspeeds computed to put the aircraft back on schedule. The 

advised airspeed is computed using information about the nominal speed profile along 

the assigned RNAV OPD, and are displayed in ten-knot increments. If an aircraft is 

late, a speed increase may be advised. The speed advisories appear in the same threecharacter field on the third line of the FDB that is used to display the early/late 

indicator. Thus, the speed advisory for SWA1184 is 190 knots, which is slower than 

the nominal speed of 210 knots for that segment, causing the aircraft to move towards 

the slot marker. If TMA-TM cannot compute a speed advisory different than the 

nominal speed, or the required speed is outside the available speed control margin, the 

early/late indicator is displayed instead. The CMS speed advisories are completely 

independent of the GIM-S speed advisories. 
22 

Figure 7. CMS tools and displays. 

Controllers may configure which CMS tools are displayed, as well as specific CMS-tool 

properties. Three ‘overall’ modes are available: 

1. No CMS displays shown 

2. Early/late indicators and speed advisories shown in FDBs, and slot markers shown when 

the cursor dwells on the FDB 

3. Early/late indicators and speed advisories shown in FDBs, and slot marker always shown 

for all tracks 

In addition, when the slot marker is displayed, the size of the slot marker is configurable to 

represent a specified time in seconds (referenced to the aircraft’s instantaneous ground speed), a 

distance in tenths of nautical miles, or raw pixels. When the early/late indicators (absolute delay 

must exceed the specified value) and speed advisories (the aircraft’s instantaneous airspeed must 

differ from the computed advisory speed by at least the specified value) are displayed is also 

configurable, and can be set to met the requirements of a particular operation. 

Additional display functionality beyond the basic CMS tools has also been developed to help 

controllers monitor the status of FIM operations, using either Display System Replacement 

(DSR) in ARTCCs (top row of Figure 8), or STARS in the TRACON (bottom row of Figure 8). 
 23 

Figure 8. FIM status indications. 

The top panel in Figure 8a illustrates how a FIM-equipped aircraft’s FDB appears to a Center 

controller before the FIM clearance is issued. The DSR FDB includes a yellow “@” symbol that 

indicates the aircraft is FIM-equipped and can therefore accept a FIM clearance (no comparable 

equipage symbol is provided for TRACON controllers since they do not have FIM clearance 

information available). (Note: recent development work indicates it may be desirable to have the 

“@” symbol indicate FIM-available; that is, FIM-equipped and a FIM clearance is available.) 

The top panel in Figure 8b shows a magenta “@” symbol, which occurs when the ARTCC 

controller issues a FIM clearance. The top panel in Figure 8c shows the FDB has been updated 

to reflect that the flight crew reported commencing the FIM operation, and the controller updated 

the symbol to a magenta “S”. 

FIM status information entered in the ARTCC is transferred to the TRACON, and the bottom 

row of Figure 8 corresponds to the same sequence of FIM status as the top row. TRACON 

controllers also make entries to change the FIM status indications to match aircraft reports. 

Suspending a FIM operation requires the controller to return the indicator to the ‘FIM issued’ 

status (Figure 8b), and terminating a FIM operation requires updating the FDB to a FIM 

equipped status (Figure 8a). 

4.5.3 Flight Deck Interval Management (FIM) 

FIM enables the flight crew to actively assist both en route and terminal controllers in 

maximizing throughput while operating the aircraft in a fuel-efficient profile. It also enables the 

en route controller to issue a single strategic clearance to the flight crew to achieve the ASG 

behind a Target aircraft. This is accomplished by using the Target aircraft state data received via 

ADS-B In technology to calculate the necessary airspeed onboard the FIM aircraft that will meet 

the controller issued FIM clearance by the Achieve-By Point. For the ATD-1 demonstration, the 

Achieve-By Point will always be the Final Approach Fix (FAF). 

ARTCC:

TRACON:

(a) (b) (c)
24 

 Prior to issuing the FIM clearance, the en route controller issues the arrival procedure and 

expected runway to the flight crew. In addition to entering this data into the aircraft’s FMS, the 

flight crew ensures that the current forecasted terminal area winds are entered into both the FMS 

and FIM equipment. The controller is expected to issue the FIM clearance shortly after the 

TMA-TM Freeze Horizon and prior to Top-of-Descent (TOD) if the difference between the 

aircraft’s ETA and STA at the Meter Fix is manageable by speed control only, typically one to 

two minutes. When the difference between the ETA and STA at the Meter Fix is greater than 

that, controllers will first pre-condition the aircraft (vectors to path stretch or altitude step-down 

to reduce ground speed) until that difference is minimized, and then issue the FIM clearance. 

The FIM clearance includes the Target aircraft’s identifier, the Target aircraft’s arrival 

procedure, and the ASG. However, the use of voice communication between controllers and 

pilots during the ATD-1 demonstration may make issuing the FIM clearance after TOD more 

appropriate and procedurally simpler (see note in Appendix G). 

The Target aircraft may not be in the same airspace sector as the FIM aircraft, and may be on 

a different arrival procedure as the FIM aircraft (and therefore cross the TRACON boundary at a 

different meter fix). To accommodate the limitations of voice communication, partial integration 

of the ATD-1 technologies into the ground air traffic software, and range of Target and FIM 

aircraft geometries that will occur during the ATD-1 demonstration, two different phraseologies 

are available for the controller to issue a FIM clearance (see Appendix G). The “WHEN ABLE” 

clearance is used to initiate FIM operations as soon as feasible, and would be used primarily 

when the Target and FIM aircraft are on the same arrival procedure, and the controller does not 

expect either aircraft to require vectors off their arrival procedures to absorb required delay. The 

“AFTER (waypoint name)” clearance is used allow the flight crew to enter the clearance as soon 

as feasible, but to not initiate FIM operations until the specified waypoint. This is expected to 

typically occur when the Target and FIM aircraft are on different arrival procedures or in 

different sectors, or if the controller anticipates the need for vectors for either the Target or FIM 

aircraft to absorb required delay. 

During the ATD-1 demonstration, the FIM speed will be calculated and available to the flight 

crew after both the Target and FIM aircraft have passed the first waypoint on their respective 

arrival procedure that contains a speed constraint. Published arrival procedures that do not 

connect to an approach procedure to the assigned runway will be augmented by the standard 

operating procedures for that TRACON to define the FIM route to connect the arrival procedure 

to approach procedure. No changes to published procedures will occur for ATD-1, nor will the 

crew enter additional waypoints or constraints in the FMS unless instructed to do so by the 

controller. 

The FIM airspeed calculated by the spacing tool is the airspeed required to achieve the ASG 

by the Achieve-By Point. The spacing tool does this by calculating the ETA at the Achieve-By 

Point of both the Target and FIM aircraft along their respective routes, then comparing the 

difference between those ETAs to the ASG. This difference between the ETAs and the ASG is 

the time error that must resolved by minor speed adjustments around the published or expected 

airspeed profile. Once the flight crew determines this FIM speed is feasible, they notify ATC 
 25 

that the Interval Spacing operation is commencing, then set the speed value in the Mode Control 

Panel speed window to match the FIM speed advisory. 

The flight crew manages the aircraft speed using the FIM software to achieve the inter-arrival 

spacing by the Achieve-By Point, while flying the FMS lateral and vertical path defined by the 

arrival and approach procedures. To provide predictability to controllers and flight crew, as well 

as stability to subsequent aircraft, the FIM speed calculated by the FIM equipment is limited to 

15% faster or slower than the published or standard speed for that segment of the arrival or 

approach procedure. However, the FIM speed will always comply with operational speed 

restrictions (250 KIAS or less when at or below 10,000 feet Mean Sea Level, etc.). 

After commencing the FIM operation, the flight crew will operate the aircraft in accordance 

with normal flight deck procedures, with the exception that the FIM speed supersedes any 

published speed (similar to a controller issued speed instruction). If the flight crew is not able to 

follow the FIM speed command or experiences a system error, they will notify the controller that 

they are unable to continue the FIM operation, and traditional air traffic control methods will be 

used (for example, published speed or instructions from the controller). The FIM operation is 

complete when the FIM aircraft crosses the Achieve-By Point, at which point all FIM displays 

are automatically cleared. If the arrival procedure does not connect with the approach procedure, 

the FIM operation is terminated when the controller issues a vector to intercept the final 

approach course, at which point the flight crew manually clears the FIM displays. When the 

FIM operation is terminated in this case, whether the controller states “Cancel Interval Spacing” 

or not, and the flight crew will depress the FIM “terminate” button to remove all FIM displays 

and fly the last assigned or standard operating airspeed. 

Controllers always have sole responsibility for aircraft separation, and flight crews have 

responsibility for spacing; that is, to fly the FIM speed. At any time, the controller can intervene 

with a speed instruction or a vector, which takes precedence over a FIM generated speed and 

suspends the FIM operation. If the controller anticipates the speed instruction or vector will 

resolve the issue and the aircraft will return to the arrival procedure in a timely manner, the 

controller will suspend the FIM operation as part of the speed instruction or vector, and may 

resume the FIM operation after returning the aircraft to the arrival procedure. If the controller 

does not anticipate a timely return to the arrival procedure, or if the assigned runway for either 

the Target or FIM aircraft has changed, the controller will terminate the FIM operation. If 

desired, a new FIM clearance can be issued with the updated information (new Target aircraft, 

change to the Target route, or change to the assigned runway). 

Cockpit displays for the flight crew to conduct FIM operations will be developed by the 

airline and avionic partners participating in the ATD-1 demonstration. Options investigated in 

previous research include displaying the FIM speed on an ADS-B Guidance Display (AGD) and 

auxiliary displays, or displaying the FIM speed on the Primary Flight Display (PFD). Figure 9 is 

an example of an AGD from previous development work, and Figure 10 depicts a possible 

auxiliary display for use during FIM operations. 
26 

Figure 9. ADS-B Guidance Display (AGD) with FIM speed. 

Figure 10. Auxiliary display with FIM clearance and traffic. 
 27 

4.6 Benefits to be Realized 

4.6.1 Overall Benefits 

PBN arrival procedures generally provide less flexibility for the controller to maintain 

aircraft separation using traditional tactical control techniques (i.e., moderate amounts of 

vectoring and step-down descents in terminal airspace), but they enable reduced track miles 

(benefit for the airline) and improved track predictability (a safety and capacity benefit). The 

integration of scheduling and spacing is needed to achieve the required arrival time accuracy and 

its associated inter-arrival spacing precision. 

While TMA-TM, CMS, and FIM technologies each exhibit benefits individually, their 

impact when integrated will realize significantly more benefits, especially at high-density 

airports during peak traffic periods. Advanced scheduling allows better planning of arrival 

operations by considering separation at key terminal meter points. CMS tools help controllers 

achieve the arrival time accuracy required of non-FIM aircraft. FIM equipment and operations 

further increase the precision of inter-arrival spacing precision, and are intended to reduce 

controller workload as well. The benefits of the three technologies and their associated 

procedures when integrated can be realized at any airport during any traffic density, and the 

greatest benefits are provided for complex arrivals during peak traffic periods. 

A summary overview of key features during ATD-1 operations and their intended benefits is 

listed below, with subsequent sections providing additional details of ATD-1 benefits that have 

been grouped by users of the ConOps. 

 Consistent schedule-driven trajectory-based operations throughout entire arrival phase 

 Enables more frequent assignment of advanced arrival procedures 

 OPDs enable more fuel-efficient and reduced emissions vertical profiles 

 Enables required delay to be absorbed more efficiently 

 Absorbing required delay using speed control results in fewer vectors and less 

level distance flown in terminal area, thereby reducing fuel consumption 

 Better flow conditioning to the same schedule throughout the arrival phase of 

flight is expected to result in the aircraft requiring smaller deviations from the 

FMS optimized speed and vertical profile. 

 Improvement of arrival time accuracy and in-trail spacing precision 

 Allows advanced arrival procedures to be maintained more often 

 Mitigates typical reduction in aircraft fuel-efficiency as traffic demand increases 

 Reduces excess spacing buffers needed to account for uncertainty 

 Fewer tactical interventions will reduce workload for controllers and flight crews 

 Increases effective airport throughput (at same delay per aircraft) or deceases system 

and aircraft delay (at same traffic throughput). 

 Flight crew understands the entire arrival procedure earlier in the operation 

 Arrival plan (including expected runway assignment) communicated earlier, and 

flight crew enters information into FMS to calculate entire trajectory 

 Improve situational awareness for controller and flight crew 

 Typically reduces workload for controller and flight crew in en route environment. 
28 

 Use of FIM capability by ADS-B In equipped users 

 Situational awareness further improved, voice communication further reduced 

 Increased inter-arrival spacing precision enables improved throughput 

 Predictable behavior of aircraft while meeting overall air traffic goal results in less 

vectoring, thereby reducing fuel-consumption, noise and emissions in addition to 

those generated by the integrated schedule. 

4.6.2 Benefits to ANSP 

Increased arrival time accuracy allows arrival schedules to be planned earlier and followed 

throughout the entire arrival phase of flight. These schedules enable the use of strategic speed 

control to achieve and maintain the desired aircraft separation. Strategic use of speed control 

allows less delay to be taken in the form of path stretching in terminal airspace. Use of CMS 

tools increases the arrival time accuracy as compared to today’s manual operations. Increased 

arrival time accuracy can reduce the size of the spacing buffer added to aircraft separation 

criteria, and reduces the frequency of controller intervention to maintain separation. Smaller 

spacing buffers also increase the achievable runway throughput at high-density airports. Use of a 

single and accurate schedule, coupled with displays and tools for the controllers and flight crew 

to achieve it, minimizes the need for radar vectoring of each and every flight by controllers. 

Radar vectoring is used less frequently and only when speed control is insufficient to maintain 

aircraft separation. Using ATD-1 technologies and procedures to conform to the same arrival 

schedule in terminal airspace that was used in en route airspace will reduce the frequency of 

aircraft being re-sequenced or rescheduled. 

4.6.3 Benefits to Flight Crew 

Use of advanced arrival procedures minimizes the need for radar vectoring of each flight by 

controllers. Instead, flight crews are able to use their onboard FMS and autoflight systems to 

efficiently navigate from cruise to landing. Radar vectoring is used less frequently and only 

when speed control is insufficient to maintain aircraft separation. The increased predictability of 

the arrival operation and reduction in required voice communications are expected to enhance 

the flight crew’s situation awareness and reduce their workload. 

 Use of FIM capabilities allows the delegation of routine spacing to the flight deck. Spacing 

will be achieved and maintained using small speed corrections to the arrival procedure’s nominal 

speed profile. These speed adjustments will be provided by onboard automation instead of by 

voice clearances from the controller. Use of ADS-B In and the corresponding FIM capabilities 

allows the flight crews to take a more active role in arrival spacing than is possible using current 

procedures and technology. Reduced voice communication and vectoring is expected to reduce 

the flight crew’s workload. 

4.6.4 Benefits to Airline 

The synergy of precision scheduling (TMA-TM) and tools to achieve that schedule (CMS 

and FIM) can be used to not only increase throughput by reducing delay, but also reduce the cost 

of the delay taken. The ATD-1 procedures allow for much of the delay to be incurred more 

efficiently at higher altitudes or by small deviations from the aircraft’s optimum descent speed, 

instead of within TRACON airspace by using vectors or path stretches. Operationally, this 
 29 

means shorter and fewer fuel-inefficient level segments at lower altitudes, reducing fuel 

consumption as well as reducing noise and greenhouse gas emissions from aircraft. 

Fuel economy will also be improved by PBN procedure clearances being issued more 

frequently, which includes the aircraft’s FMS calculating the most efficient TOD for that arrival. 

The increased frequency is primarily enabled by the integrated schedule and pre-conditioning of 

the arrival flow prior to TOD. The use of the aircraft FMS calculated trajectory and TOD point 

is enabled by issuing a “Descend Via” clearance when traffic permits, which is expected to also 

occur more frequently due to the schedule and pre-conditioning. 

Airline benefits from FIM equipage include increased flight crew awareness, reduction in 

controller – flight crew voice communication needed to maintain desired spacing, and increased 

probability of remaining on fuel-efficient PBN procedures (or decreased probability of being 

issued vectors). The long-term implementation of ATD-1 functionality could allow for the 

reduction in size of the buffers added to the separation criteria (not part of this demonstration), 

thereby further improving throughput or reducing delay. 

4.6.5 Benefits to Airport 

Use of CMS and FIM tools increases the arrival time accuracy as compared to today’s 

operations. Increased arrival time accuracy should enable the reduction of additional spacing 

buffers above aircraft separation requirements, creating an effective increase in the achievable 

runway throughput at high-density airports. 

The ATD-1 ConOps and procedures are expected to produce longer periods of sustained 

high-throughput at the airport runways, or be used to reduce delay at the same traffic density 

levels. Increasing the use of PBN procedures (such as environmentally efficient OPDs) during 

periods of high-density traffic will reduce noise and greenhouse gas emissions from aircraft, in 

turn reducing the number of noise complaints received by the airport. Furthermore, the precision 

of these PBN procedures results in less airspace required for arrival operations, in turn making 

more airspace available for other procedures (departures, arrivals to satellite airports, etc.). 
30 

5.0 Operational Scenarios 

The procedures for a “nominal” (expected or typical) ATD-1 operation are described in 

section 5.1, with section 5.2 providing details for each phase of the operation. Section 5.3 

describes events that may occur during an ATD-1 operation, and section 5.4 describes 

contingency ATD-1 operations. Limitations to the fully-implemented ATD-1 ConOps required 

during the 2015-2020 timeframe are outlined in Appendix D. 

Most controller-pilot phraseology remains unchanged from what is used today (sector 

frequency check-in, initiation of descent, etc.), and phraseology to be used during ATD-1 

operations is documented in Appendix G. This phraseology aligns to the maximum extent 

possible with the international standard for Interval Management procedures [ref 25], the 

proposed FIM Data Link messages [ref 26], and the FAA’s Air Traffic Control documentation 

[ref 27]. Modifications have been made to accommodate the mid-term voice communication 

environment expected during the ATD-1 demonstration, and feedback from research 

experiments conducted at NASA Ames and Langley Research Centers for ATD-1. 

5.1 ATD-1 Scenario by Phase 

A flowchart of controller-pilot procedures to be used during ATD-1 operations is shown in 

Figure 11. A numbering system is provided in the upper left of each box to assist in grouping 

and establishing relationships between various events. The schema is the first digit indicates the 

phase of the operation (0-schedule, 1-precondition, 2-initiation, 3-operation, 4-termination), the 

second digit indicates the user (0-schedule, 1-controller, 2-flight crew not equipped with FIM, 3-

flight crew equipped with FIM), and the third digit is a sequential index for that user during that 

phase. 

Figure 12 through Figure 16 present the ATD-1 ConOps described in Section 4.2 by phase, 

with each phase linked to the respective procedure shown in the procedure flowchart (Figure 11). 

 
 31 

Figure 11. Operational procedure flowchart. 

2.3.2 FC-FIM 

Acknowledge; enter FIM 

clearance into avionics 

Ye No 

TMA-TM ARTCC

Schedule Phase Precondition Phase Initiation Phase 

0.0.1 TMA-TM 

Calculate schedule; fix STA 

after Freeze Horizon, provide 

FIM clearance if appropriate

1.1.1 ATC 

Issue vector, altitude step down, or speed if 

required delay at Meter Fix exceeds speed 

only control (ERAM and GIM-S) 1.3.1 FC-FIM 

Acknowledge 

and comply 

2.3.3 Avionics 

Calculate FIM airspeed

2.3.4 FC-FIM 

Speed feasible? 

2.3.5 FC-FIM 

Notify ATC 

commencing 

FIM operation 

0.0.2 TMA-TM 

Schedule to ARTCC

Phase / Location ATC non-FIM operation FIM operation

1.2.1 FC 

Acknowledge 

and comply 

2.1.1 ATC 

Issue arrival procedure and assigned or 

expected runway to all aircraft 

2.2.1 FC 

Acknowledge; enter 

data and wind into 

FMS 

2.3.1 FC-FIM 

Acknowledge; enter data 

and forecast wind into FMS 

and FIM equipment 

2.1.2 ATC 

Issue FIM clearance to 

appropriately equipped aircraft 

2.3.6 FC-FIM 

Notify ATC 

unable FIM 
32 

Figure 11. Operational procedure flowchart (concluded). 

ARTCC

3.3.1 FC-FIM 

Fly FIM speed; 

notify ATC during 

initial check-in 

conducting FIM 

3.1.1 ATC 

Monitor separation of all 

aircraft; meet Meter Fix STA 

(ERAM and GIM-S)

3.1.3 ATC 

Amend, suspend, or terminate 

FIM clearance if required 

4.3.1 FC-FIM 

FIM complete at 

Achieve By Point 

3.1.2 ATC 

Correct spacing error 

3.1.4 ATC 

Transfer aircraft to TRACON 

3.2.1 FC 

Acknowledge 

and comply 

3.3.3 FC-FIM 

Fly FIM speed; 

notify ATC during 

initial check-in 

conducting FIM 

3.1.5 ATC 

Monitor separation 

of all aircraft 

(STARS and CMS) 

3.1.8 ATC 

Transfer aircraft to Tower 

3.2.2 FC 

Acknowledge 

and comply 

TRACON Tower 

Operati

on Phase

T

erminati

on 

3.1.7 ATC 

Amend, suspend, or terminate 

FIM clearance if required 

3.1.6 ATC 

Correct spacing error 

3.3.2 FC-FIM 

Acknowledge and 

comply 

3.3.4 FC-FIM 

Acknowledge 

and comply 

Phase / Location ATC non-FIM operation FIM operation

4.2.1 FC 

CMS complete 

when transferred 

to Tower control 

0.0.3 TMA-TM 

Schedule to
 33 

Figure 12. ATD-1 operation: Schedule Phase. 

The blue area shown in Figure 12 highlights the airspace and subset of aircraft in the 

schedule phase of ATD-1 operations (that is, prior to the Freeze Horizon), and an overview of 

activities that occur during this phase are listed on the right. The numbers in the left column of 

the table below correspond to the operational procedures in Figure 11. 

0.1 Prior to the aircraft crossing the Freeze Horizon, TMA-TM continuously calculates the ETA 

for that aircraft to all suitable runways, and updates the STA to all runways as well. At the 

Freeze Horizon, the TMA-TM software assigns the aircraft to a runway, and freezes the 

STA for that aircraft and runway. The TMA-TM ETA for each aircraft is used to update 

delay advisories, GIM-S speed advisories, and CMS advisories. 

0.2 The TMA-TM information and GIM-S speed advisories are available to en route controllers on 

the DSR as part of the meter list and aircraft’s full data block, and include arrival metering 

information, expected runway assignment for all aircraft, and FIM clearance information 

for those aircraft so equipped. 

0.3 The TMA-TM information and CMS indications are available to terminal controllers on the 

STARS display, include arrival metering information and speed advisors for all aircraft. 

 
34 

Figure 13. ATD-1 operation: Precondition Phase. 

Figure 13 illustrates the aircraft and activities that occur during the precondition phase of 

ATD-1 operations, that is, what occurs when speed control alone is not sufficient to absorb the 

required delay assigned by TMA-TM. Based on demand and the effectiveness of up-stream flow 

control, aircraft may or may not require this phase. When aircraft cross the Freeze Horizon and 

do not require vectors or step-down in altitude to meet the Meter Fix (AFMP) time assigned by 

TMA-TM, the Initiation phase commences immediately after the Schedule phase. The numbers 

in the left column of the table below correspond to the operational procedures in Figure 11. 

1.1.1 If required, en route controller issues vectors, altitude step-downs, or speed instructions to 

achieve desired time delay (TMA-TM schedule to interface with GIM-S, which provides 

display) to any aircraft not conducting FIM operations. 

 

 
 35 

Figure 14. ATD-1 operation: Initiation Phase. 

Figure 14 illustrates the aircraft and activities that occur during the initiation phase of ATD-1 

operations, that is, when controllers issue a FIM clearance to suitably equipped aircraft, and the 

flight crews respond. During this phase, speed control alone is typically sufficient, however 

vectors may be required if the schedule changes or other operational considerations require 

controller intervention. The numbers in the left column of the table below correspond to the 

operational procedures in Figure 11. 

2.1.1 The en route controller issues the arrival route and expected runway to all aircraft, the FIM 

clearance to those aircraft so equipped, and clears all aircraft for the arrival procedure. 

2.2.1 The flight crew enters the arrival procedure, expected runway, and current terminal area 

forecasted winds into the aircraft’s FMS and FIM equipment (if so equipped). 

2.1.2 The en route controller issues a FIM clearance to the flight crew of FIM-equipped aircraft. 

2.3.2 The FIM crew acknowledges ATC, and enters the FIM clearance into the aircraft avionics. 

2.3.3 The FIM aircraft software calculates the Mach number or airspeed needed to achieve the 

Assigned Spacing Goal behind the Target aircraft by the Achieve-By Point. 

2.3.4 The FIM flight crew determines if the speed is operationally feasible. 

2.3.5 If the FIM speed is feasible, the flight crew notifies ATC they are commencing FIM operation. 

2.3.6 If the FIM speed is not feasible, the FIM flight crew notifies ATC that they are unable to 

conduct the FIM operation. 
36 

 

Figure 15. ATD-1 operation: Operation Phase. 

Figure 15 illustrates the aircraft and activities that occur during the operation phase of ATD-1 

operations, that is, controllers use primarily speed control to achieve TMA-TM scheduled times 

and crews fly FIM speed to achieve the assigned spacing interval. The numbers in the left 

column of the table below correspond to the operational procedures in Figure 11. 

3.1.1 En route controllers retain safe separation responsibility for all aircraft within their sector. 

3.1.2 En route controllers use GIM-S information to assign speeds to all aircraft not conducting FIM 

operations (non-FIM equipped, or FIM equipped aircraft prior to issuing FIM clearance). 

3.3.1 Flight crews conducting FIM will notify ATC when commencing the operation, and fly the 

FIM calculated speed during the arrival and approach. 

3.1.3 If needed, en route controllers may amend, suspend, or terminate FIM operations. Controller 

instructions always take precedence over the FIM speed calculated onboard the aircraft. 

3.3.2 Flight crews will acknowledge ATC when the FIM clearance has been amended, suspended, or 

terminated. 

3.1.5 Terminal controllers retain safe separation responsibility for all aircraft within their sector. 

3.1.6 Terminal controllers use CMS information to assign speeds to crews of non-FIM aircraft. 

CMS speeds may also be used for FIM aircraft if necessary. 

3.3.3 Crews conducting FIM operations will state so during initial check-in with each controller. 

3.1.7 If needed, terminal controllers may amend, suspend, or terminate FIM operations. Controller 

instructions always take precedence over the FIM speed calculated onboard the aircraft. 
 37 

Figure 16. ATD-1 operation: Termination Phase. 

Figure 16 shows the aircraft and activities that occur during the termination phase of ATD-1 

operations. CMS operations cease when the flight crew changes to the Tower frequency, and 

FIM operations terminate at the Achieve-By Point or when the controller issues a vector to 

intercept the final approach. Operations may also be suspended or terminated if vectors or 

altitude step-downs are needed to absorb the required time delay. Crews may terminate FIM 

operations (no Target data, FIM equipment failure, etc.) by notifying the controller, who then 

issues a new FIM clearance or reverts to normal control procedures. The numbers in the left 

column of the table below correspond to the operational procedures in Figure 11. 

4.2.1 CMS operations are complete when the flight crew switches from the Final controller to Tower 

frequency. No specific communication is required. 

4.3.1 FIM operations are complete when the aircraft crosses the Achieve-By Point. No 

communication is required if FIM terminates at the Achieve-By Point. When the arrival 

and instrument procedure do not connect, the FIM operation is terminated when the 

controller issues a vector to the crew to intercept the final approach course. 
38 

5.2 Events and Procedures During ATD-1 Operations 

This section addresses events and procedures that occur in response to common but 

unanticipated events during ATD-1 operations. These events may require a TMA-TM sequence 

swap, a TMA-TM reschedule, discontinue use the GIM-S or CMS speed advisory, or suspend or 

terminate FIM operations. 

When events occur that affect the controllers’ or flight crews’ ability to conduct ATD-1 

operations, the contingency plan is to revert to current day procedures. Examples of events that 

may trigger contingency procedures includes incorrect or undesirable information on controller 

decision support tools, incorrect or infeasible information on cockpit displays, failure of 

hardware or software, or changes to the goal of the air traffic plan. Use of current day operations 

as the contingency plan for when ATD-1 operations must be terminated has proven viable in 

NASA’s concept development and testing phase since aircraft separation criteria, as well as the 

roles and responsibilities assigned to controllers and flight crew, are the same in both operations. 

5.2.1 ATC changes arrival sequence 

Controller may need to change arrival sequence. When this occurs, the CMS displays are 

automatically updated to reflect the new TMA-TM schedule. If the sequence swap affects either 

the Target or FIM aircraft of a FIM operation, the existing FIM clearance must be terminated by 

the controller, and a new one issued if desired. (The long-term vision for the ATD-1 ConOps 

has the ground automation providing the controller a message that the FIM clearance must be 

cancelled, and offer a new clearance. However, this functionality will not be available by the 

demonstration time-frame.) 

5.2.2 ATC Display of CMS or FIM Information 

Each controller will have the ability to individually turn off and back on CMS information 

(slot markers, speed advisors) and FIM information (aircraft status, FIM clearance). This is an 

optional technique available to the controller to mitigate an unexpected and rapidly occurring 

event that momentarily causes deviation from the TMA-TM generated schedule, resulting in 

outdated or incorrect CMS or FIM information. Once the schedule has been updated, the 

controller has the ability to turn back on the CMS or FIM information. 

5.2.3 ATC Amends a FIM Clearance 

A controller may amend the FIM clearance by changing the ASG to allow space for 

departing aircraft, etc. (Changing the Target aircraft, Target aircraft route, or FIM aircraft route 

require ATC to terminate the FIM clearance, then issue a new one if desired). Compared to 

terminating the current FIM clearance and entering a new one, amending a FIM clearance 

requires less workload for the flight crew. 

5.2.4 ATC Suspends or Resumes a FIM Operation 

When ATC temporarily suspends a FIM operation (expected to resume at a later time), the 

flight crew remove the FIM speed from cockpit displays with a single button push, but retain the 

FIM clearance information in the application. FIM operations are suspended whenever a 

controller issues a vector or speed instruction to the FIM aircraft, even if not explicitly stated so 

by the controller. Altitude change instructions to the FIM aircraft do not suspend FIM 

operations. Vectors or speed instructions to the Target aircraft should also cause the FIM 
 39 

operation to be suspended, however the controller for the FIM aircraft may not be aware of those 

instructions to the Target aircraft. Therefore the logic in the FIM software will cause the FIM 

application to automatically switch to a suspend mode whenever it determines the Target aircraft 

is greater than 2.5 nmi off the arrival or approach procedure, or has a greater than 10% deviation 

from the expected airspeed. Altitude changes by the Target aircraft do not cause the FIM 

software to switch to a suspend mode. The resume procedure allows the crew to return the FIM 

speed for the previously issued FIM clearance to the cockpit displays with a single button push. 

5.2.5 ATC Terminates a FIM Operation 

FIM operations normally terminate at the Achieve By Point (the Final Approach Fix for 

ATD-1), and no controller or pilot communication is required. When ATC terminates a FIM 

operation prior to that point, the flight crew maintain the current or assigned airspeed, remove all 

FIM indications from cockpit displays, and delete the FIM clearance information from the 

avionics. Several operational events that may require ATC to terminate a FIM operation early 

include a change to the route or runway of either the Target or FIM aircraft, or a schedule resequence that impacts either the Target or FIM aircraft. The FIM operation is also terminated 

prior to the Achieve By Point when the STAR and instrument approach procedure do not 

connect, and the controller issues the flight crew a vector to intercept the final approach course. 

If ATC does not terminate the FIM operation for the FIM aircraft when one of the events 

above occurs, the FIM flight crew will continue to fly speeds designed to achieve the Assigned 

Spacing Goal behind the Target aircraft. This may result in undesirable performance by the FIM 

aircraft. (The long-term ATD-1 ConOps envisions a change to either the Target or FIM 

aircraft’s route results in an automatic update to the schedule and FIM clearances. The updated 

schedule will exist by the ATD-1 demonstration timeframe, however the capability to update the 

FIM clearance will not exist by then.) 

5.2.6 ATC issues an infeasible FIM clearance 

The FIM clearance issued by ATC may not be feasible for the flight crew. Examples of 

causes for this event include turbulence may require the flight crew to fly a slower speed than the 

commanded FIM speed, or the FIM clearance includes a Target route not known to the FIM 

aircraft. The flight crew procedure is to notify ATC that they are unable to conduct FIM. 

5.2.7 Flight Crew Terminates a FIM Operation 

Flight crews conducting FIM operations may need to terminate FIM operations for a variety 

of reasons. Examples include: the FIM speed becomes infeasible (for example, too fast or too 

slow), the ADS-B data from the Target aircraft is lost or no longer has sufficient quality, the 

ADS-B data from the Target is not received, or the FIM spacing tool has failed. The flight crew 

will state ‘UNABLE INTERVAL SPACING’, and if possible, include the reason for termination 

(considered likely only in low traffic density conditions). Controllers may use the provided 

GIM-S or CMS tools to complete the arrival operation. 
40 

5.3 Contingency ATD-1 Operations 

Contingency ATD-1 operations typically require controllers and flight crews to revert to 

current day procedures. Examples of events that may trigger contingency procedures include 

incorrect or undesirable displays on controller decision support tools, incorrect or infeasible 

displays for flight crew, failure of hardware or software, or changes to the goal of the air traffic 

plan. Reversion to current day operations as the contingency plan when ATD-1 operations must 

be terminated has proven viable in NASA’s concept development and testing phase since aircraft 

separation criteria, as well as the roles and responsibilities assigned to controllers and flight 

crew, are the same in both operations. An overview of some of these events and their impact by 

ATD-1 technology is provided in the Table below, with more detail in subsequent paragraphs. 

Table 1. Contingency Operations Matrix 

Event TMA-TM CMS FIM 

User terminates the 

use of the ATD-1 

technology 

Revert to current day 

operations. ATC may 

use ground delay or 

miles-in-trail to reduce 

throughput. 

Revert to current day 

operations. CMS 

displays turned off, 

controllers issue 

instructions. 

Revert to current day 

operations. FIM 

operation cancelled, 

controllers issue vectors 

or speed instructions. 

Significant 

weather event 

Revert to current day 

operations. ATC may 

use ground delay or 

miles-in-trail to reduce 

throughput. 

Revert to current day 

operations. ATC turns 

off CMS displays until 

TMA-TM reschedules, 

then resume ATD-1 

operations. 

Revert to current day 

operations. ATC issues 

vectors or speeds until 

TMA-TM reschedules, 

then resume ATD-1 

operations. 

Airport 

configuration 

change or runway 

not available 

Revert to current day 

operations. ATC may 

use ground delay or 

miles-in-trail to reduce 

throughput. 

Revert to current day 

operations. ATC turns 

off CMS displays until 

TMA-TM reschedules, 

then resume ATD-1 

operations. 

Revert to current day 

operations. ATC issues 

vectors or speeds until 

TMA-TM reschedules, 

then resume ATD-1 

operations. 

Aircraft 

emergency or 

priority handling 

Current day 

procedures remain 

unchanged for priority 

aircraft; others use 

ATD-1 procedures. 

Current day procedures 

remain unchanged for 

priority aircraft; all 

others operate using 

ATD-1 procedures. 

Current day procedures 

remain unchanged for 

priority aircraft; all 

others operate using 

ATD-1 procedures. 

Different levels of 

aircraft avionic 

equipage 

ATD-1 operations not 

affected, if the 

technology has 

awareness of the 

aircraft’s equipage and 

can assign the 

optimum procedure. 

ATD-1 operations 

should not be affected. 

ATD-1 operations 

should not be affected, 

unless the FIM 

aircraft’s spacing 

software does not have 

the Target aircraft’s 

procedure. 
 41 

5.3.1 User terminates the use of the ATD-1 technology 

The three ATD-1 technologies are designed to be configurable by the user, and to be turned 

off or re-initialized if appropriate. Examples are given below. 

 TMA-TM: TMA is currently operationally deployed in today’s NAS, and no change 

is envisioned to controller procedures during schedule contingencies when TMA-TM 

is deployed. Two of many possible events and their outcome include: 

o The required delay reaches a level that controllers cannot achieve (due to 

runway closure, significant weather event, etc). In this case the use of 

metering is frequently, but not always, terminated. 

o The arrival sequence in the schedule becomes out of sequence or is not 

desired by the controller. In this case the TMC may recalculate the or ripple 

the list. 

 CMS: CMS displays and information are calculated based on the TMA-TM 

schedule. Terminal controllers may turn off the CMS displays and information if the 

schedule is infeasible or undesirable, reverting the controller scope to current day 

standards. 

 FIM: FIM speeds are calculated to achieve the spacing between aircraft set by the 

TMA-TM schedule. If the FIM speed becomes infeasible or undesirable (spacing 

error too great, environmental or airframe conditions require a different airspeed, 

etc.), the flight crew may suspend or terminate the FIM operation. Current day 

operations are used by the flight crew when this occurs. 

The ATD-1 ConOps technologies have a one-way interaction with each other, in that changes 

to the TMA-TM schedule cause the CMS information to update, and a new FIM clearance must 

be issued (if appropriate). Although the CMS and FIM displays and information can be turned 

off, the CMS or FIM information itself cannot be modified by the user, and there is no feedback 

mechanism to the schedule. 

 

5.3.2 Significant weather event 

Weather events will have a range of impacts on ATD-1 operations based on condition type 

and location of the event. Generally, conditions such as fog, rain, low ceiling or visibility, and 

convective weather that prevent aircraft from flying through it, will reduce the airport’s arrival 

throughput. However, low ceiling or low visibility weather typically causes a stable condition 

that can be managed with TMA-TM over long periods of time. Convective weather on the other 

hand, is more dynamic and makes strategic tools like TMA-TM more difficult to manage 

especially in cases where the growth, decay, and movement of weather is not easy to predict. 

The location of the weather is another major factor in determining the magnitude of the impact to 

ATD-1 operations. Weather requiring a re-routing of traffic in the enroute environment may 

have little impact on ATD-1 operations or airport throughput, while weather overhead the airport 

may require suspending all arrival and departure operations. This will require a varied response 

that allows some aircraft to deviate and rejoin their routes, possibly changing the arrival 

sequence or rippling the list, and some areas will be impacted to such a degree that ATD-1 

operations and tools would not be usable. 
42 

5.3.3 Airport configuration change or runway closure 

When the runway configuration changes (change in wind direction, noise abatement, etc.) or 

a runway is no longer available (aircraft disabled on the runway, etc.), some aircraft must be 

rerouted and a new arrival schedule calculated. Based on the timing and type of event, the 

impact to the arrival schedule may be minor or significant while TMA-TM is updated. Similar 

to the procedures for a significant weather event, controllers and flight crew have the ability to 

selectively turn off ATD-1 displays until the information presented has been updated to reflect 

the new runway status and condition. 

5.3.4 Aircraft emergency or priority handling 

An aircraft may unexpectedly require priority for landing (medical emergency, system 

malfunction, etc.), or unexpectedly require a slot in the arrival stream (go-around, tower arrival, 

etc.). These events may require some other aircraft to absorb delay to create the slot for the 

priority aircraft. When this occurs, vectors are normally required for the aircraft that must 

absorb delay, resulting in potentially incorrect controller and flight crew displays related to 

schedule information. Similar to the significant weather event, controllers and flight crew 

selectively turn off displays with incorrect information, and use current day non-Trajectory 

Based Operations and procedures. 

5.3.5 Different levels of aircraft avionic equipage 

Aircraft are equipped with a wide range of avionics that creates a broad spectrum of aircraft 

navigation capability. Mixed operations, or aircraft of widely varying navigation capability 

intermingled in the same arrival stream, can lead to certain inefficiencies or challenges. By the 

ATD-1 demonstration timeframe, it is possible that TMA-TM will not have access to complete 

and current information for all aircraft, such as RNP versus non-RNP equipped, or FIM versus 

non-FIM equipped. Should that occur, some of the benefits offered through ATD-1 operations 

will not be realized, or the aircraft will be manually updated outside of the normal data process. 

CMS operations should not be impacted by mixed operations, unless the aircraft is flying an 

arrival or approach procedure not assigned by TMA-TM (for example, a visual turn to final 

instead of the ground track anticipated by TMA-TM). FIM operations in a mixed equipage 

operation should not be impacted, unless the spacing software does not contain in its database the 

arrival or approach procedure of the Target aircraft. 
 43 

 6.0 Summary of Impacts 

The anticipated impacts of the proposed ATD-1 ConOps on current operations are 

summarized in Table 2 below: 

Table 2. Summary of Impacts 

User Current Operational Use Enhanced Use with ATD-1 ConOps 

Traffic 

Management 

Coordinators 

Use the Traffic Flow Management 

System automation and TMA to 

establish the sequence and schedule 

for aircraft arriving at the highdensity airport. 

Use the Traffic Flow Management System 

automation and TMA-TM to establish a 

higher fidelity sequence and more precise 

schedule for aircraft arriving at the highdensity airport. 

En route 

Controller 

(ARTCC) 

Comply with facility procedures for 

delivering aircraft to meet the TMA 

schedule. This includes issuing route 

clearances (such as “Descend Via”) 

and expected runway assignments 

using standard operating procedures. 

Comply with facility procedures for 

delivering aircraft to meet the TMA-TM 

schedule. This includes issuing route 

clearances and the expected runway 

assignments using TMA-TM information. 

Controllers will also issue FIM clearances to 

those aircraft suitably equipped, issue speed 

instructions (based on GIM-S) to aircraft not 

conducting FIM operations, and monitor safe 

separation of all aircraft. 

Terminal 

Controller 

(TRACON) 

Comply with facility procedures for 

delivering aircraft to meet the posted 

airport acceptance rate. Maintain 

aircraft separation and deliver them to 

the runway. There is no access to the 

TMA runway assignments or 

schedule. 

Comply with facility procedures for 

delivering aircraft to meet TMA-TM 

scheduled metering plans to the assigned 

runway. Use CMS automation to improve 

the delivery accuracy to the runway of 

aircraft not conducting FIM. Update or 

terminate FIM operations if required. 

Monitor safe separation of all aircraft. 

Flight crew Comply with all established 

procedures and controller 

instructions. 

Comply with all established procedures and 

controller instructions. Crews conducting 

FIM operations will also enter FIM clearance 

and forecast winds into the spacing avionics, 

monitor the FIM status, notify ATC when 

that status changes, and fly the speed 

calculated by the FIM software. 

 
44 

7.0 References 

The References section credits published and unpublished works used throughout the 

document, and includes higher level and adjacent concepts on which this document depends. 

1. Baxley, B., Johnson, W., Swenson, H., Robinson, J., Prevot, T., Callantine, T., Scardina, J., Greene, 

M., “Air Traffic Management Technology Demonstration-1 Concept of Operations (ATD-1 

ConOps)”, NASA/TM—2012-217585, July 2012 

2. Robinson III, J.., “ADS-B Enabled Green Operations Using Integrated Scheduling and Spacing 

(AEGIS),” Demonstration Description and Plan, Version 2.3, Aug. 5, 2011 

3. Prevot, T., Baxley, B., Callantine, T., Johnson, W., Quon, L., Robinson, J., Swenson, H., “NASA’s 

ATM Technology Demonstration-1: Transitioning Fuel Efficient, High Throughput Arrival 

Operations from Simulation to Reality”, HCI Aero 2012, Brussels, Belgium, Sept 2012 

4. Federal Aviation Administration, “NextGen Mid-Term Concept of Operations for the National 

Airspace System”, FAA ATO, Version 2.0, April 30, 2010 

5. MITRE, “Terminal Sequencing and Spacing (TSS) Concept of Operations”, MITRE CAASD, 

MP130330, July 2013 

6. Federal Aviation Administration, “Concept of Operations for Time-Based Flow Management 

(TBFM) -- DRAFT”, FAA ATO, Dec 27, 2012 

7. Federal Aviation Administration, “NextGen Implementation Plan,” ATO, NextGen Integration and 

Implementation Office, March 2012 

8. Federal Aviation Administration, “Arrival Interval Management – Spacing (IM-S) Concept of 

Operations for the Mid-Term Timeframe”, FAA ATO-E, Surveillance and Broadcast Services (SBS) 

Program Office, PMO-010, Revision 01, Jan 8, 2013 

9. Federal Aviation Administration, “Integrated Arrival, Departure, and Surface (IADS) Concept for the 

Mid-Term”, working draft, Aug 23, 2010 

10. “Performance-based Navigation (PBN) Manual”, ICAO Doc 9613, 3rd Edition, 2008 (Block Upgrade 0) 

11. Federal Aviation Administration, “Concept of Operations Guidance and Template”, FAA ATO, 

Version 1.0, May 2011 

12. Joint Planning and Development Office, “Concept of Operations for the Next Generation Air 

Transportation System, Version 3.2”, Sept., 2010 

13. Federal Aviation Administration, “FAA Aerospace Forecast, Fiscal Years 2013-2033” 

14. “Your Flight Has Been Delayed Again; Flight Delays Cost Passengers, Airlines, and the U.S. 

Economy Billions,” A Report by the Joint Economic Committee Majority Staff, Senator Schumer, 

(www.jec.senate.gov), May 2008 
 45 

15. Thipphavong, J., et al., “Evaluation of the Controller-Managed Spacing Tools, Flight-deck Interval 

Management and Terminal Area Metering Capabilities for the ATM Technology Demonstration #1”, 

10th USA/Europe Air Traffic Management Research and Development Seminar (ATM2013), 

Chicago, IL, June 2013 

16. Isaacson, D., Swenson, H., Robinson III, J., “A Concept for Robust, High Density Terminal Air 

Traffic Operations,” 10th AIAA Aviation Technology, Integration, and Operations Conference 

(ATIO), Fort Worth, TX, Sept. 13-15, 2010 

17. Robinson III, J. , Kamgarpour, M., “Benefits of Continuous Descent Operations in High-Density 

Terminal Airspace Under Scheduling Constraints,” 10th AIAA Aviation Technology, Integration, and 

Operations Conference (ATIO), Fort Worth, TX, Sept. 13-15, 2010 

18. Thipphavong, J., Mulfinger, D., “Design Considerations for a New Terminal Area Arrival 

Scheduler,” 10th AIAA Aviation Technology, Integration, and Operations Conference (ATIO), Fort 

Worth, TX, Sept. 13-15, 2010 

19. Swenson, H., Thipphavong, J., Sadovsky, A., Chen, L., Sullivan, C., Martin, L., “Design and 

Evaluation of the Terminal Area Precision Scheduling and Spacing System,” 9th USA/Europe Air 

Traffic Management Research and Development Seminar (ATM2011), Berlin, Germany, June 13-16, 

2011 

20. Callantine, T., Palmer, E., Kupfer, M., “Human-In-The-Loop Simulation Of Trajectory-Based 

Terminal-Area Operations,” ICAS2010, 27th International Congress of the Aeronautical Sciences, 

Nice, France, Sept. 19-24, 2010 

21. Kupfer, M., Callantine, T., Martin, L., Mercer, J., and Palmer, E., “Controller Support Tools for 

Schedule-Based Terminal Operations,” 9th USA/Europe Air Traffic Management Research and 

Development Seminar (ATM2011), Berlin, Germany, June 13-16, 2011 

22. Barmore, B.., Abbott, T., Capron, W., Baxley, B., “Simulation Results for Airborne Precision 

Spacing along Continuous Descent Arrivals,” 8th AIAA Aviation Technology, Integration, and 

Operations Conference (ATIO), Anchorage, AK, Sept. 14-19, 2008 

23. Murdoch, J., Barmore, B., Baxley, B., Abbott, T., Capron, W., “Evaluation of an Airborne Spacing 

Concept to Support Continuous Descent Arrival Operations,” 8th USA/Europe Air Traffic 

Management Research and Development Seminar (ATM2009), Napa, CA, June 29 – July 2, 2009 

24. Wilson, S., Murdoch, J., Hubbs, C., Swieringa, K., “Evaluation of Flight Deck-Based Interval 

Management Crew Procedure Feasibility“, AIAA Modeling and Simulation Technologies 

Conference, Boston, MA, August 2013 

25. “Safety, Performance and Interoperability Requirements Document for Airborne Spacing-Flight Deck 

Interval Management (ASPA-FIM),” RTCA DO-328, RTCA, Washington, DC, June 22, 2011 

26. “Airborne Spacing – Flight Deck Interval Management (ASPA-FIM / FIM-S) Controller Pilot Data 

Link Communications (CPDLC) Messages”, RTCA SC-214/EUROCAE WG-78 and RTCA SC186/EUROCAE WG-51 Tiger Team, Draft 2.0, 7 Nov 2011 
46 

27. “Air Traffic Control Procedures and Phraseology”, FAA Order JO 7110.65U, Feb 9, 2012 

28. Abbott, T., “A Revised Trajectory Algorithm to Support En Route and Terminal Area Self-Spacing 

Concepts,” NASA/CR-2010-216204, NASA Langley, Hampton, VA, Feb. 2010 
 47 

Appendices 

Appendix A: Glossary and Definitions 

Table 3. Glossary and Definitions 

Acronym Term Definition 

-- Four-dimensional trajectory The centerline of a path formed by segments that link consecutive 

trajectory change points; each point defined by a longitude, latitude, 

altitude, however not every point will have a time. NOTE: some 

waypoints may have time, altitude, and/or speed constraints, and can 

be equality or inequality constraints. 

 -- Closed trajectory The ANSP automation, the controller, and the aircraft automation 

have the same view of what the aircraft is doing. There is agreement 

between automation on the ground and in the air, and actions are 

synchronized. (FAA APNT) 

 -- Open trajectory The aircraft is no longer flying to an agreement with the automation. 

The aircraft and the ground are not in synchrony and the aircraft is 

flying off the agreed-upon trajectory for operational reasons like 

weather avoidance, a vector for sequencing or spacing, and/or a speed 

adjustment that will impact timing. (FAA APNT) 

-- Airborne Metering A form of time-based metering in which air traffic controllers issue 

clearances to active flights in their sectors that cause the flights to 

absorb arrival delays. 

-- Achieve-By Point The point on the FIM Aircraft’s flight path where the Assigned 

Spacing Goal behind the Target Aircraft is expected to be achieved. 

For ATD-1, this point is the Final Approach Fix. 

ADS-B Automatic Dependent 

Surveillance – Broadcast 

ADS-B is a technology where aircraft avionics (or ground equipment) 

autonomously broadcasts the aircraft’s (or ground vehicle’s) position, 

altitude, velocity, and other parameters. “ADS-B Out” refers to the 

broadcast of ADS-B transmissions from an aircraft or vehicle, and 

“ADS-B In” refers to reception of ADS-B transmissions from other 

aircraft or vehicles. 

AGD ADS-B Guidance Display A flight deck display that presents the airspeed calculated by the 

onboard spacing software to achieve the Assigned Spacing Goal 

behind the Target aircraft (based on the FIM clearance given by ATC 

and entered by the flight crew into the software). 

AIXM Aeronautical Information 

Exchange Model 

An XML-based aeronautical data format developed jointly by the 

FAA and Eurocontrol. 

ANSP Air Navigation Service 

Provider 

Government or private organizations that manage flight traffic on 

behalf of a company, region, or country. 

AOC Airline Operations Center Responsible for decision-making and operational control of an 

airline's daily schedules and facilitating disruption recovery. 

ARTCC Air Route Traffic Control 

Center 

A facility providing air traffic control service to aircraft operating on 

IFR flight plans within controlled airspace, principally during the en 

route phase of flight. 

ASG Assigned Spacing Goal The inter-arrival time in seconds (may also be given as a distance) 

between the Target and the FIM Aircraft assigned by the controller as 

part of the FIM clearance. 
48 

Table 2. Glossary and Definitions (continued) 

Acronym Term Definition 

ASTAR Airborne Spacing for Terminal 

Arrival Routes 

Advanced flight deck-based automation that constantly calculates the 

airspeed required to position an aircraft at the Achieve By Point at the 

Assigned Spacing Goal behind the Target aircraft. 

ATCA Air Traffic Control 

Association 

Independent, non-profit organization for promoting the air traffic 

control profession and the aviation community. 

ATD-1 Air Traffic Management 

Technology Demonstration #1 

The first of a planned series of NASA NextGen Airspace Systems 

Program technology demonstrations. This demonstration integrates 

three research efforts to achieve high throughput fuel-efficient arrival 

operations using precision time-based schedules, aircraft speed 

control, and controller display technologies. 

CMS Controller-Managed Spacing Controller decision support tools and display symbology to assess an 

aircraft’s conformance to the arrival schedule and desired in-trail 

spacing, and to provide speeds to resolve any errors. 

ConOps Concept of Operations Document describing a proposed operation that utilizes new 

technologies or procedures. 

CSP Constraint Satisfaction Point Meter points used by GIM-S in en route airspace. 

DSR Display System Replacement Displays and equipment used by en route air traffic controllers. Flat 

screen displays replaced older en route equiment suite in 2000. 

EDA Efficient Descent Advisor Decision-support tool for air-trafficcontrollers managing arrival 

airspace in enroute facilities. 

ERAM En Route Automation 

Modernization 

FAA program that provides the platform for NextGen improvements, 

including System Wide Information Management, Data 

Communications, and Automatic Dependent Surveillance-Broadcast. 

ERFMP En Route Flow Management 

Point 

Flow management point prior to Top-Of-Descent. Time assigned by 

TBFM. 

ETA Estimated Time-of-Arrival The current estimate of the aircraft’s time-of-arrival at a point along 

its flight path based on forecasted winds, aircraft performance and 

defined arrival procedures, but not adjusted to compensate for traffic 

separation or metering delays. The ETA is re-calculated on events 

and radar updates. 

FAF Final Approach Fix The fix from which the final approach to an airport is executed and 

which identifies the beginning of the final approach segment. 

FAS Final Approach Speed The speed flown by the aircraft from the Final Approach Fix to 

touchdown on the runway. There are flight crew and airline 

variances for when this speed is achieved. 

FDB Full Data Block Lines of information next to aircraft icon containing pertinent data for 

the air traffic controller. 

FIM Flight deck Interval 

Management 

Flight crew makes use of specialized avionics that provides speed 

commands for interval management. 

-- FIM aircraft The aircraft receiving speed commands from the onboard FIM 

equipment to achieve the assigned spacing behind the Target aircraft. 

This aircraft must have ADS-B In equipment, and be equipped for 

FIM operations. 

-- FIM clearanance The FIM clearance during ATD-1 operations are the Target aircraft’s 

identification (Target ID), Target’s route of flight, and the Assigned 

Spacing Goal (ASG). The remaining data fields identified in 

Reference 25 are not included (accomodation for use of voice 

communication). 

 
 49 

Table 2. Glossary and Definitions (continued) 

Acronym Term Definition 

-- FIM operations Refers to one or more FIM aircraft actively spacing to achieve the 

ASG behind their Target aircraft. Responsibility for spacing 

(accomplished by flying the FIM speed) resides with the flight crew, 

aircraft separation responsibility remains with ATC. 

-- FIM speed The speed calculated and provided by the aircraft FIM equipment 

during a FIM operation to achieve the Assigned Spacing Goal behind 

the Target by the Achieve-By Point. 

FIXM Flight Information Exchange 

Model 

A data interchange format to share flight information. 

FMS Flight Management System An FMS is a computerized avionics component found on most 

commercial and business aircraft to assist pilots in navigation, flight 

planning, and aircraft control functions. It is composed of: FMC 

(Flight Management Computer), AFS (Auto Flight System), 

Navigation System including IRS (Inertial Reference System) and 

GPS, and EFIS (Electronic Flight Instrument System). 

-- Freeze Horizon After an aircraft crosses the Freeze Horizon for an En Route Flow 

Management Point (ERFMP) or Arrival Flow Management Point 

(AFMP), the Scheduled Time-of-Arrival (STA) for that aircraft to that 

waypoint is “frozen” (no longer updated). 

GIM-S Ground-based Interval 

Management - Spacing 

Ground-based functions intended to support aircraft crossing the 

TRACON boundary along the route of flight at specific metered times 

or STAs, as well as stand-alone CSPs. Part of ERAM v4.1.

-- GIM operations Refers to one or more aircraft not conducting FIM operations that are 

spaced by ATC. This spacing can be aided by tools (GIM, 3D-PAM, 

CMS, etc) or unaided (manual operations). 

ICAO International Civil Aviation 

Organization 

United Nations agency that codifies international air navigation 

standards and practices. 

ID Identification code The alphanumeric code used to identify an aircraft. The aircraft ID is 

shown on controller and cockpit displays, and used to define the 

Target aircraft within a FIM clearance when using voice 

communication. The aircraft code is not always the same as the 

aircraft callsign. 

MPT Metering Point Time Time calculated for an aircraft’s arrival at a given Meter Point. The 

Meter Point STA is an example of a Metering Point Time. 

MF Meter Fix A Constraint Satisfaction Point (CSP) used for managing arriving 

aircraft; one of several points referred to as Arrival Flow Meter Points 

(ARFMP). This ATD-1 document uses Meter Fix as the transition 

from en route to terminal airspace. 

MP Meter Point A Constraint Satisfaction Point (CSP) used for managing en route 

aircraft; one of several points referred to as En Route Flow 

Management Points (ERFMP). Examples include Airspace Meter 

Point (AMP), Extended Metering Point (XMP), and Coupled 

Metering Point (CMP). Meter Points in Terminal airspace (Terminal 

Meter Points) are a new functionality for ATD-1. 

-- Non-FIM aircraft Aircraft receiving heading, speed, and altitude commands from ATC 

to manage the spacing behind the preceding aircraft. This aircraft 

may also be a Target aircraft for the subsequent aircraft. 

 
50 

Table 2. Glossary and Definitions (continued) 

Acronym Term Definition 

OPD Optimized Profile Descent OPDs are designed to reduce fuel consumption, emissions, and noise 

during descent by allowing aircraft to fly an optimized descent during 

an arrival procedure (such as a STAR) with engines near idle. Ideally 

the OPD extneds to the runway threshold, however, it may not include 

the instrument approach portion. OPD procedures specify the lateral 

path and vertical boundaries of the procedure, and some segments 

include a speed. Vertical boundaries are established to accommodate a 

wide range of descent profiles, and speeds are defined to enable the 

use of speed control only by controllers and flight crews. 

PBN Performance-Based 

Navigation 

Area navigation based on performance requirements for aircraft on a 

route, approach procedure, or designated airspace. Navigation 

performance requirements are expressed in terms of accuracy, 

integrity, continuity, availability, and functionality needed for the 

proposed operation. [ref 10] 

RNAV Area Navigation A method of navigation which permits aircraft operation on any 

desired flight path within the coverage of ground or space-based 

navigation aids, or within the limits of the capability of self-contained 

aids, or a combination of these two. 

RNP Required Navigation 

Performance 

The navigation performance necessary for operation within defined 

airspace. (May be used but not a ATD-1 requirement.) 

-- Separation The spacing of aircraft to achieve their safe and orderly movement in 

flight and while landing and taking off. (FAA Pilot/Controller 

Glossary) 

1) Applicable separation minima remain unchanged by any ATD-1 

operation. 

2) During ATD-1 operations, the controller remains responsible for 

providing separation between aircraft. 

3) Flight crew conducting FIM operations are responsible for 

achieving the assigned spacing from a designated (Target) 

aircraft as stipulated by the controller. 

SI Spacing Interval The true horizontal along-path spacing (expressed in time) between 

the FIM and Target Aircraft. The SI should equal the ASG by the 

Achieve-By Point (the FAF in ATD-1). 

STA Scheduled Time-of-Arrival Calculated by the ground scheduling software to meet all of the 

scheduling and sequence constraints, set at ‘Freeze Horizon’, and 

normally not changed. Changing a frozen STA is a ‘reschedule’, and 

is triggered manually by the Traffic Manager in response to a 

significant event (weather, runway change, etc.). 

STAR Standard Terminal Arrival 

Route 

A pre-planned instrument arrival procedure published for pilot use in 

graphic and/or textual form. Provides transition from the en route 

structure to an instrument approach fix in the terminal area. 

STARS Standard Terminal Area 

Replacement System 

Displays and equipment used by controllers in terminal radar 

approach control facilities and towers. 

-- Target Aircraft The lead aircraft specified by ATC for the FIM aircraft. Must be 

equipped with ADS-B Out (transmit), but is not required to be ADS-B 

In (receive) equipped or capable of FIM operations. 

TAMR Terminal Automation 

Modernization and 

Replacement 

FAA program designed to modernize the air traffic control system at 

all the major US airports. 

 
 51 

Table 2. Glossary and Definitions (concluded) 

TBFM Time-Based Flow 

Management 

An operational concept using time to more efficienty utilize available 

airport capacity without decreasing safety or increasing workload. 

TCP Trajectory Change Point A full 4-D trajectory is defined by a series of trajectory change points 

(TCPs). Every point along the track where an altitude, heading, or 

speed transition occurs. 

TMA Traffic Management Advisor A traffic flow management tool that calculates Estimated Times-ofArrival (ETA) and corresponding Scheduled Times-of-Arrival (STA) 

at various points along the aircraft flight path to an airport to optimize 

the flow of aircraft into capacity-constrained areas. TMA also 

provides the STA and delay times to the respective En Route 

controller to maintain the optimum flow rates to runways from the 

ARTCC to the TRACON. 

TMA-TM Traffic Management Advisor 

with Terminal Metering 

An enhancement to TMA that calculates precise time-based, conflictfree schedules to the runway and all meter points. This information is 

available to TRACON controllers. 

TMU Traffic Management Unit Non-control, coordination positions in the ARTCC and the TRACON, 

connected to the central flow control function and responsible for 

dissemination of flow control information at the local level.

TOD Top-Of-Descent The computed transition from the cruise phase of flight to the descent 

phase, the point at which the descent to final approach altitude is 

initiated. 

TRACON Terminal Radar Approach 

Control Facility 

Radar control facility associated with an airport. 

WXXM Weather Information 

Exchange Model 

International standard weather model currently under development. 
52 

Appendix B: Changes to ATD-1 ConOps 

The initial ATD-1 ConOps document published in 2012 [ref 1] benefited greatly from 

an in-depth review by the FAA and industry partners that generated over 350 individual 

comments and numerous pages of feedback. Also contributing to the update were several 

experiments conducted at NASA Ames and Langley Research Centers specifically 

designed to test the ATD-1 ConOps. A partial list of changes made to the ATD-1 

ConOps in Version 2 includes: 

 Clarified ATD-1 demonstration goal and objectives 

 Regrouped and clarified changes to the current air traffic system needed for 

ATD-1 operations, and the expected benefits for stakeholders 

 Expanded explanation of three NASA technologies 

 Added text and a graphic of CMS displays and FIM data block displays 

 Provided updates to FIM operations, including: 

o the removal of Scheduled Time of Arrival (STA) functionality, 

o clarification of when FIM speed is first calculated, 

o ability to commence operations when not on a published route, 

o when FIM operations commence and terminate, 

o added detail to contingency operations 

 Corrected errors and added detail to graphics and text that describe the phases 

of ATD-1 operations 

 Clarified that flight crews are not expected to manually enter additional 

waypoints and constraints in the FMS to enable FIM operations 

 Added text that flight crews conducting FIM operations will ensure the most 

current terminal area wind forecast is in both the FMS and FIM equipment 

 Added Appendices to document changes from previous version of ConOps, 

and to highlight related concepts and work B 

 Assumptions and requirements in body of text and Appendix E updated 

 Added detail on TMA-TM algorithm and calculations in Appendix F 

 Simplified phraseology, clarified some terminology, removed and added 

terminology in Appendix G 
 53 

Appendix C: Related ATM Concepts and Research 

This Appendix briefly describes related ATM concepts and research efforts, and how 

the ATD-1 ConOps compares to, supports, or benefits from them. 

C.1 TBFM and TSS 

Several planned TBFM enhancements have relevance to or can be supported by the 

long-term ATD-1 ConOps, in particular Terminal Sequencing and Spacing (TSS). The 

TBFM enhancements are not expected to occur in time to impact the mid-term ATD-1 

demonstration; however the TSS enhancements are directly tied to NASA’s TMA-TM 

development. The FAA TBFM and TSS documentation is paraphrased below. 

C.1.1 Time-Based Flow Management (TBFM) 

Path Stretch Controller Advisories. Provides controllers with tools to assist in 

absorbing delays during time-based metering operations. The enhancement is based on 

the mature TBFM trajectory modeler, which is used to compute the additional distance 

needed to absorb a flight’s metering delay at an assigned airspeed. From the additional 

distance, it computes a closed-form lateral path stretch maneuver that is conflict free. It 

computes a change to the flight’s trajectory that increases the distance flown and hence 

the flight time, but does not involve an altitude change. 

Metering During Reroute Operations (MDRO). Four new capabilities that allow 

time-based metering to be continued during severe weather conditions in which today 

metering would be suspended. 

 

 Predefined Meter Points (PDMP). When convective areas become 

sufficiently large and severe, normal traffic routes are closed, and one or more 

PDMPs will be activated where the merging of rerouted and normal traffic 

flow creates high traffic volumes. Metering to the PDMPs regulates traffic 

volume into the affected points and assists in merging the flows. 

 Weather Avoidance Fields (WAF). These allow metering to continue when 

localized convective weather causes flights to deviate, but normal routes 

remain open and the deviations stay within the affected sectors. 

 Data integration to improve metering. Data integration with other systems 

improves TBFM system capabilities to facilitate the continuation of metering 

in severe weather conditions. 

 Cumulative metering delays. Tracking the cumulative delay flights have 

already received at upstream meter points will allow downstream meter points 

to schedule flights more equitably. 
54 

C.1.2 Terminal Sequencing and Spacing (TSS) 

Terminal Sequencing and Spacing introduces three new TRACON Time-Based 

Metering capabilities. Much of the development comes directly from the NASA research 

and testing done to develop TMA-TM. These capabilities are: 

 Terminal Runway Assignment (TRA). TRA will consider real-time 

operational air traffic conditions within terminal airspace along with 

operational objectives to determine appropriate runway assignments for 

aircraft arriving at airports within the terminal airspace. 

 Terminal Arrival Runway Sequencing Assignment (TARSA). TARSA will 

consider real-time operational air traffic conditions within terminal airspace 

along with operational objectives to determine appropriate terminal arrival 

runway sequencing assignments for aircraft arriving at airports within the 

terminal. 

 Terminal Merge Points (TMP). TMP will provide the TRACON controllers 

the ability to meet a metering constraint inside terminal airspace to support 

mixed equipage operations and also to allow continuous metering in 

TRACONs with expanded airspace. 

C.2 Interval Management 

The NASA FIM procedures used in ATD-1 are a subset of the Arrival Interval 

Management – Spacing (IM-S) concept and procedures developed by the FAA. The 

NASA research has been closely linked with the FAA’s development, and the ATD-1 

demonstration is intended to support the FAA’s decision making process regarding 

NextGen decisions. The FAA IM-S ConOps documentation is paraphrased below. 

The arrival IM-S concept employs a ground-based flow component to support the 

management of arrival streams for the setup and conduct of Optimized Profile Descents 

(OPDs) in en route airspace through the use of time-based flow management (TBFM) 

and speed advisory functionality. The IM ground-based flow component is intended to 

increase the opportunity to conduct OPD operations for medium levels of traffic. This 

concept also employs a flight deck-based component to support the conduct of OPDs. 

This component is expected to further increase the opportunities to conduct OPD 

operations during higher throughput rates. 

The arrival IM-S concept utilizes Automatic Dependent Surveillance – Broadcast 

(ADS-B). The deployment of ADS-B will support increased accuracy in trajectory 

prediction for the ground-based flow component, and will also be a critical enabler for 

the flight deck-based spacing component. FIM-S is identified as the flight deck-based 
 55 

spacing component for this concept. For the FIM-S descriptions in this document, the 

FIM-S aircraft is the “trailing” aircraft performing FIM-S operations and receiving speed 

guidance from onboard avionics to achieve the assigned spacing goal behind its “target” 

(or “leading”) aircraft, with this aircraft providing ADS-B Out surveillance information. 

C.3 RNAV and RNP 

The development of arrival and approach procedures to leverage new technologies 

and capabilities, such as RNAV/OPD STARs and RNAV/RNP approaches, directly 

impact the ATD-1 effort. ATD-1 depends on these base FAA programs, and these 

programs stand to benefit from ATD-1. Early trials and implementations of RNAV/OPD 

STARs have seen the need for ground and/or airborne tools to allow use of the 

procedures under high traffic density conditions. Trials of RNAV/RNP procedures that 

connect merging traffic streams to common or parallel approaches require new controller 

procedures and possibly tools like those designed for ATD-1. Coordination of FAA and 

industry efforts at RNAV/OPD and RNP procedure development with ATD-1 is critical 

to the success of both efforts. 

One example of this coordination is the “Greener Skies” work at Seattle by the FAA, 

which is an effort to use RNP in lieu of the ILS for closely spaced runways. Airports 

throughout the United States are deploying Area Navigation/ Required Navigation 

Performance (RNAV/RNP) routing capabilities, yet full use of these capabilities is being 

inhibited by the lack of approved procedures and rule changes that incorporate the unique 

abilities of PBN-equipped aircraft. Research is needed to explore the operational limits 

associated with this technology and explore the potential changes to the relevant 

operational criteria and procedures to fully use the PBN technologies. The FAA, in 

partnership with the Port of Seattle, industry, and other local and state governments, is 

seeking to improve efficiency and minimize the environmental impact on the ground and 

in the air by reducing aircraft noise and emissions at Seattle-Tacoma International Airport 

through expanded use of RNP, RNAV, and OPDs. 

A second example of this type of work is the RNP approaches in Atlanta being 

developed by Delta Airlines and the FAA. “Peachy Skies” is an effort to use the 

“Greener Skies” capabilities in visual meteorological conditions in lieu of changes to the 

FAA air traffic regulation. The current spacing requirements [ref 27, Chapter 5, Section 

9] create large inefficiencies in the NAS when an airport conducts simultaneous 

operations. This work used RNAV and RNP to provide a means to reduce these 

inefficiencies through path keeping capability, monitoring, and alerting. 

C.4 Tailored Arrivals 

The development of Tailored Arrivals (TAs) has benefited the ATD-1 ConOps 

conceptually and by assisting in developing phraseology and procedures. The FAA 

Tailored Arrival ConOps is paraphrased below. 
56 

Tailored Arrival (TA) operations are a central component of the joint US and Europe 

Atlantic Interoperability Initiative to Reduce Emissions (AIRE) project and the Asian 

Pacific Initiative to Reduce Emissions (ASPIRE). Early development of this concept 

provides an arrival route that is “tailored” to account for individual aircraft performance, 

environmental factors, and other air traffic. The desired end state is a dynamic 

optimized trajectory that may be data-linked to the aircraft. Until then, the TA is 

composed of playbooks from which the controller will select the optimal arrival route. 

The uplinked clearance contains speed and altitude constraints for points in the 

profile. These constraints can be assigned to either named points or specified by latitude 

and longitude. Using non-named points for clearance construction provides greater 

flexibility for controller manipulation and reduces the demands for navigational database 

storage by the FMS. The instrument approach and runway assignment are provided to 

allow a full 4D trajectory computation and control by the FMS. Clearance to fly the 

approach and actual runway assignment are provided by the TRACON or Tower as 

appropriate. 

C.5 Time-Based Procedures 

One of the Single European Sky ATM Research (SESAR) efforts was the 

Environmentally Responsible Air Transport (ERAT) project, which explored enhanced 

departure and arrival services into major airports. The concept of time-based continuous 

descent operations was developed and applied to the Stockholm Arlanda Airport and the 

surrounding airspace environment. The concept used Controlled Times-of-Arrival (CTA) 

as a constraint for inbound aircraft to achieve a more orderly and predictable arrival 

sequence. This CTA time constraint was applied to dedicated waypoints on the different 

arrival routes to the airport. Experience from previous projects indicated the most optimal 

CTA waypoint was located at a distance of 30NM to the runway with the present state of 

technology and procedures. This distance allowed good probability to execute successful 

CDA approaches, and still provide sufficient airspace after the CTA point for final 

corrections by the approach controllers, as necessary. 

 

 
 57 

Appendix D: Limitations to the ConOps During the ATD-1 Demonstration 

This Appendix contains a partial list of operational limitations that are expected to 

exist during the demonstration that precludes full implementation of the long-term ATD1 ConOps and operations, and results in the mid-term ATD-1 ConOps and operations as 

described in the body of this document. Although these limitations to varying degrees 

are expected to impact the ATD-1 demonstration results, improvements in efficiency and 

workload should still be realized. 

1. Only ATD-1 arrival operations to a single airport with independent runway 

operations will be demonstrated. 

 Some ATD-1 technologies are envisioned during departure, en route, and 

oceanic environments. ATD-1 concept and technology development could 

eventually support closely spaced parallel runway operations. 

 Impact when resolved: as ATD-1 procedures become prevalent in all 

operational environments and phases of flight, 

- ATD-1 operations provide greater benefit for the cost required to upgrade 

software and equipment, and 

- increased familiarity with procedures should reduce controller and flight 

crew workload. 

2. Trajectory from aircraft’s position to runway not known by all users and automation. 

 Some information required by the ground (ERAM, STARS, etc) and airborne 

(FMS, FIM, etc) systems to implement the long-term ATD-1 ConOps is not 

expected by the demonstration timeframe. Some of the data elements not 

universally available include: 

- aircraft’s cruise airspeed and descent profile, 

- scheduler’s plan for the aircraft’s cruise speed and descent profile, 

- aircraft ETA at waypoints and the runway, 

- scheduler’s STA at waypoints and the runway, 

- aircraft’s intended trajectory, and 

- scheduler’s intended trajectory for that aircraft. 

 Impact when resolved: 

- flight crew increase frequency using FMS calculated Top-Of-Descent, 

- fewer controller interventions (vectors, altitude step down) required, 

- CMS and FIM operations continue to Achieve By Point (the Final 

Approach Fix) instead of terminating early when the Final controller 

issues a vector to intercept final course (when the arrival procedure does 

not connect to the approach procedure), and 

- more correct and desirable FIM operations since Target aircraft’s actual 

trajectory will be used to calculate FIM speed. 

3. Ground automation systems (TMA-TM, ERAM, STARS) do not have capability to 

exchange all data between each other, and not all controller displays for that data will 

have been developed. 

 Impact when resolved: 
58 

- complete schedule, including FIM clearance, is known to all controllers 

(may be accomplished during the ATD-1 demonstration via direct 

coordination between the TMU and controller), 

- phraseology by flight crew stating FIM operation in effect may not be 

required during initial check-in, and 

- sequence swaps and reschedules trigger notification to the controller to 

terminate a FIM clearance if required. 

4. Coupled scheduling between ARTCCs not in use (still in development). 

 Impact when resolved: 

- TMA-TM will be able to expand on coupled scheduling increased ETA 

accuracies, and 

- enhanced Arrival System scheduling accuracy. 

5. ATD-1 technologies not yet integrated with other emerging technologies, such as 

Efficient Descent Advisor. 

 Impact when resolved: 

- arrival accuracy of ATD-1 operations will be enhanced. 

6. Ground and airborne automation do not have Data Comm to send complete route, 

complex routes, or dynamically tailored routes. 

 Impact when resolved: 

- air traffic ground tools cognizant of aircraft’s planned trajectory in 

sufficient detail to calculate and predict aircraft separation, 

- aircraft FIM software no longer limited to using published procedures for 

Target aircraft’s route, and 

- FIM operation may not be terminated when the Final controller issues a 

vector to intercept the final approach course. 

7. FIM operations not fully implemented by the ATD-1 demonstration timeframe. 

 Impact when resolved: 

- any waypoint may be issued as the Achieve By Point and Terminate Point, 

and those two points may be different, 

- FIM Turn functionality available (as defined in reference 25), 

- FIM to Closely Spaced Parallel Runways functionality available, and 

- FIM operations continue unless specifically suspended or terminated by 

controller (for example, step down altitudes or vectors to final). 

8. The Airline Operations Center (AOC) is not expected to be part of the demonstration. 

 Impact when resolved: 

- AOC to have connectivity to TMA-TM as well as the flight crew, and 

- aircraft operations will be tailored inflight (for example, change of the cost 

index) to assist in achieving scheduled time of arrivals at particular points. 
 59 

Appendix E: Assumptions and Requirements for ATD-1 

This Appendix outlines the technical assumptions and requirements of the operating 

environment to successfully accomplish the ATD-1 demonstration. 

E.1 Schedule Phase 

 The arrival and approach procedures used by ATD-1 will support PBN from the 

current aircraft position to the assigned runway. These procedures will define a 

speed for each segment of the PBN procedure, and when required, altitude or 

speed constraints at some waypoints, if required. Examples are CROSS AT 

(altitude), CROSS AT OR ABOVE (altitude), and NO SLOWER THAN (speed).

- Where PBN procedures are not published all the way to the runway (that 

is, the arrival does not connect to the approach or airspeed is not defined 

on a segment), the TMA-TM, CMS and GIM-S functions will use adapted 

standard operating procedures which describe the operation from cruise to 

touchdown.

- The FIM software requires knowledge of the fully defined trajectory of 

both the Target and FIM aircraft. Therefore the software cannot produce a 

valid FIM airspeed until both aircraft are on a speed-constrained portion of 

their respective procedures. Prior to both aircraft being on a speed 

constrained portion of the arrival, the FIM software will indicate either the 

clearance has been loaded, or the clearance is loaded and valid ADS-B 

data from the Target is available but a speed cannot yet be calculated.

 The ground scheduler will determine a STA at the runway threshold and all 

upstream meter points for each aircraft within the scheduler’s Freeze Horizon. 

These times create the intended aircraft arrival sequence. The associated spacing 

intervals between aircraft meet or exceed all air traffic separation requirements, 

including wake separation standards, safe separation practices, runway occupancy 

requirements, etc.

 The TMA-TM schedule will use the most detailed aircraft data available. This 

includes: aircraft identification code, state information (latitude, longitude, 

altitude, velocity), intent information (route of flight, runway assignment, etc.), 

and aircraft specific data (aircraft type, navigation equipment identifier, etc.).

 The TMA-TM schedule will only use aircraft transmitting ADS-B data as a valid 

Target aircraft for a FIM operation.

 The ground scheduler will derive FIM clearances for the controller to issue to 

FIM-equipped aircraft based on the arrival sequence, and the difference in runway 

STA for that pair of aircraft.

 The TMA-TM arrival schedule will be available to ARTCC controllers on the 

DSR displays. The types of information presented to the ARTCC controller will 

include metering information (aircraft identification code, time to the appropriate 

meter point, assigned runway) for all aircraft, and the FIM clearance information 

(Target identification code, Target route, and spacing interval) for suitably 

equipped aircraft. 

 The TMA-TM arrival schedule will be available to TRACON controllers. The 

types of information presented to the TRACON controller include sequence and 
60 

meter point information for all aircraft, and FIM status via the data tag block for 

suitably equipped aircraft. 

 Unique RNAV and RNP navigation capabilities are not required for ATD-1 

operations, other than those required for the air traffic facility’s arrival and 

approach procedures.

- Although non-RNAV procedures and non-RNAV equipped aircraft can be 

utilized by ATD-1 technologies and procedures, the intended 

improvements in airport throughput and aircraft efficiency would not be 

fully realized without the use of RNAV or RNP.

E.2 Precondition Phase 

 When significant metering delay must be absorbed, ARTCC controllers may use 

controller derived speed instructions, GIM-S speed advisories, vectors, or step 

down the aircraft's altitude to achieve the needed delay.

 When significant delay does not need to be absorbed, ATD-1 operations proceed 

from the Schedule Phase directly to the Initiation Phase. 

E.3 Initiation Phase 

 The en route controller will retain positive control over all aircraft in the sector, 

and retain responsibility for separation of all aircraft.

 All aircraft will have at least standard separation between aircraft for any ATD-1 

operation.

 The en route controller will have the necessary information and displays to 

include Meter Fix ETA and STA for all aircraft, issue speed commands (using 

GIM-S displays), and issue FIM clearances.

 En route controllers will issue the arrival procedure and expected runway to all 

aircraft as soon as feasible after the Freeze Horizon. This is to enable the FMS to 

calculate the TOD and a fuel-efficient trajectory for that arrival based on aircraft 

weight and forecasted winds.

 En route controllers will attempt to issue “Descend Via” clearances to flight 

crews, enabling the flight crew to fly the arrival procedure and meet the published 

altitude and speed constraints. The FMS may be utilized to maximize the 

aircraft’s efficiency while conforming to these constraints, thereby maximizing 

fuel efficiency as well as reducing noise and emissions.

 The FIM clearance will be issued as soon as feasible after the schedule is frozen. 

It is desired to be issued prior to the FIM aircraft’s TOD, however should be 

issued after the Descend Via instruction. 

 FIM clearances will be issued via voice from ATC to the flight crew.

 The flight crew will acknowledge the FIM clearance or amendment as 

expeditiously as possible, as other cockpit tasks allow.

 The Target aircraft and FIM aircraft may be in the same or different airspace 

sectors, and may be on the same or different arrival procedure (therefore cross the 

same or different TRACON Meter Fix).
 61 

 The Target aircraft and FIM aircraft of a FIM pair will be assigned to the same 

runway.

 The FIM aircraft must receive ADS-B data from the Target aircraft, but is not 

required to receive ADS-B data from any other aircraft.

E.4 Operation Phase 

 The integrated ATD-1 technologies, procedures, and operations are designed to be 

used in any situation the current TMA is used.

 Controllers will attempt to avoid vectoring aircraft unless safety concerns or other 

operational considerations require they do. Vectoring reduces the accuracy of the 

CMS speed advisory and suspends the FIM operation.

 “Sequence swaps” or “rippling of the list” events that impact either the Target or 

FIM aircraft require the controller to terminate the existing FIM operation, and 

issue a new FIM clearance if still desired.

 Flight crew conducting FIM operations will update the terminal airspace wind 

forecast prior to TOD in both the FMS and FIM equipment. 

 CMS tools and FIM operations can be used simultaneously, that is, aircraft 

receiving controller speed instructions can be on the same arrival procedure as 

aircraft conducting FIM. 

 ATC speed instructions take precedence over published speeds and the FIM 

speed. ATC will suspend or terminate FIM operations prior to issuing vectors or 

speed instructions to the flight crew conducting FIM. If the controller omits the 

term suspend or terminate while issuing the instruction, the FIM operation is 

suspended and the flight crew will adhere to the ATC instruction.

 The terminal airspace controller will have the necessary information and displays 

to issue speed commands (using CMS displays).

 The FIM speed calculated by the spacing software is equivalent to a controller’s 

speed instruction, that is, the FIM speed supersedes the published speed on the 

arrival or approach procedure and must be flown unless the flight crew notifies 

ATC otherwise.

 The flight crew is expected to respond to a FIM speed change as expeditiously as 

possible.

 An aircraft flying a FIM operation will achieve the Assigned Spacing Goal behind 

the Target Aircraft by the Achieve-by Point (the Final Approach Fix).

 The FIM operation is “Suspended” if either the Target or FIM aircraft is vectored. 

If the controller is unaware that the Target aircraft has been vectored off the 

procedure, or the controller’s workload does not permit notifying the flight crew, 

the FIM software will transition to the “suspend” mode when the Target aircraft 

exceeds 2.5 nmi lateral deviation from the assigned Target route.

 The FIM operation is “Suspended” if the FIM aircraft is given a speed instruction. 

If the controller omits the term “suspend” in the instruction, the FIM operation is 

suspended and the flight crew will adhere to the ATC instruction.
62 

E.5 Termination Phase 

 CMS operations cease when the Final controller hands off the aircraft to the 

Tower controller.

 FIM operations cease at the Achieve-By Point when the published arrival and 

approach procedure connect. FIM is terminated by crew interaction.

 FIM operations cease when the Final controller issues the flight crew a vector to 

intercept the final course when the published arrival and approach procedure do 

not connect. FIM is terminated by crew interaction.

 After the Achieve-By Point, the FIM software provides no speed commands to 

correct spacing errors, and crew interaction is not required. The flight crew have 

no FIM related tasks or displays.

 When FIM terminates, the flight crew will maintain the last FIM speed unless the 

controller issues a speed instruction 

 The FIM operation is terminated if either the Target or FIM aircraft is given a 

change to its route.

 If ATC suspends or terminates a FIM operation, the FIM equipment, via flight 

crew interaction, will inhibit the display of FIM speed guidance information.

 The flight crew will notify ATC if they terminate the FIM operation prior to the 

Achieve By Point. 

 
 63 

Appendix F: Description of Algorithms 

This Appendix defines how the algorithms used by the ground scheduling tool and 

airborne spacing tool produce values expected by the other components of the ATD-1 

ConOps. 

F.1 Ground-based Scheduling Algorithm 

 The TMA-TM scheduling algorithm will use the published or standard operation 

arrival procedure to calculate the STA to the runway threshold for each aircraft. 

 The runway STAs are assigned at the runway threshold to as a minimum comply 

with wake vortex separation criteria. The STA is derived from the aircraft’s ETA 

calculated by TMA-TM. 

 The runway STA is used to calculate deconflicted times at the Meter Fix and 

terminal airspace merge points based on the speeds and available time delay for 

each segment. 

F.2 Controller Managed Spacing Algorithm 

Information for early/late indicators comes directly from arrival schedules; thus, it is 

to be communicated to the TRACON controller workstations from TMA-TM. CMS 

advisories are not available to ARTCC controllers. 

Slot marker circles are computed via the following process: 

 Determine the meter point and runway schedules. The meter point and runway 

STAs are generated by TMA-TM. For each Meter Point, TMA-TM calculates the 

STAs and ETAs for all scheduled aircraft. The schedules are updated every six 

seconds and in response to reschedule events. 

 Compute the aircraft’s nominal trajectory. The nominal trajectory is the trajectory 

that the aircraft would fly if it did not receive any speed commands from ATC 

and met all speed and altitude restrictions that are specified in the nominal arrival 

procedure. 

 The Meter Point Times (MPT) are based on adjustments made by the TMA-TM 

schedule to accommodate the required delay for that aircraft. Each trajectory 

point will have a nominal time-of-arrival that represents the time at which an 

aircraft would arrive at that position if it flew the nominal trajectory and arrived at 

the STA at the next meter point. 

 Compute the nominal flight state. Given the trajectory and the adjusted times-ofarrival, use a trajectory-based interpolation algorithm to compute the aircraft’s 

state at the point along the trajectory corresponding to the current time. 

 Store the nominal flight state with the aircraft record. The slot marker circle is the 

graphical representation of the nominal flight state (i.e., spatial representation of 

the schedule). 

Speed advisories are computed via the following process: 

 Determine if speed control can be used to meet the scheduled times-of-arrival at 

each of the meter points. The speed advisory algorithm traverses the meter points 

between the aircraft’s current position and the assigned runway and computes 
64 

whether the desired STA at each meter point lies within the aircraft’s time-ofarrival window. The algorithm uses the fastest and slowest speeds for each 

trajectory segment to make this determination. 

 Construct the speed advisory. For each meter point where a speed advisory is 

possible, iterate over the possible speed values, to change the speed restrictions 

between the current aircraft location and the meter point. For each test speed, 

compute the corresponding trajectory and evaluate the ETA at the meter point. If 

the absolute difference between the STA and the ETA is less than a preset 

threshold (e.g., 2 seconds), indicate success, and quantize (per adaptable 

parameters) the result for display to the controller. 

F.3 Flight-deck Interval Management Algorithm 

The FIM software tool provided by the ATD-1 avionics partner for the demonstration 

should be similar to the ASTAR algorithm [ref 28] used by the NASA research team. 

Behavior and design goals of the airborne spacing algorithm include: 

 The speed control law is designed to reduce the inter-arrival spacing error 

gradually, but not uniformly, as the operation progresses. The error may 

temporarily increase if the forecasted winds are incorrect. 

 The ASTAR spacing algorithm does not know, nor is it controlling to, the 

adjusted times calculated by TMA-TM for upstream meter points. If these 

adjustments are significant or non-uniform, the speeds flown by aircraft 

conducting FIM may not align with controller CMS displays for that aircraft. 

Therefore, the behavior of the FIM operation will not closely align with the 

behavior indicated by the CMS displays, especially when the Target aircraft is not 

maintaining the airspeed prescribed on a published procedure. 

 FIM speeds greater than 250 KIAS will not be commanded after the aircraft has 

descended below 10,000 feet MSL. 

 FIM speeds will not exceed 15% greater than or 15% less than the published 

speed restriction for any segment of the published route. This value was set to be 

less than observed controller speed instructions, and to provide arrival stream 

stability for subsequent aircraft. 

 The FIM speed commanded by ASTAR is quantized to reduce the number of 

speed changes, and therefore the flight crew workload. 

 The aircraft’s sensed wind, and the forecast wind entered by the crew into the 

FIM application, are used by ASTAR to calculate the aircraft’s trajectory. A gain 

factor is applied to the forecast wind values so that as an aircraft approaches a 

waypoint or altitude, the percentage of forecast wind used in the calculation is 

reduced to zero. The forecast wind values and gain schedule is also applied to the 

Target aircraft’s trajectory calculation. 
 65 

Appendix G: Controller-Pilot Phraseology 

Current controller-pilot phraseology (initial check-in, issuing route instructions, 

‘Descend Via’ clearances, etc.) remains unchanged during ATD-1 operations to the 

maximum extent possible, and no new phraseology has been identified for CMS 

operations. Phraseology in this Appendix unique to FIM operations has been derived 

from the FAA IM Working Group [ref 25-26] and current controller-pilot phraseology 

[ref 27], although several modifications were made to enable shorter transmissions for 

voice communication operations, and some words were changed for increased clarity (for 

example, “Paired” instead of “Interval Spacing” to report FIM engaged). Any FAA 

guidance or direction has precedence over phraseology described in this Appendix. 

The validation of using voice communication to conduct FIM operations in a complex 

and busy terminal airspace is an important supporting objective of the ATD-1 

demonstration. Phraseology in this section has not only been simplified from the 

proposed standards mentioned above (designed with data link capability), but portions of 

the FIM operation have also been procedurally limited and defined (the “Achieve-By 

Point” and “Termination Point” are both the Final Approach Fix, the Assigned Spacing 

Goal is always “precise” and defined in seconds, and the Target and FIM aircraft must 

land on the same runway). Validating this is important so aircraft operators can develop 

business cases for ADS-B In applications. 

The normal procedure is for the en route controller to issue each aircraft their route of 

flight and expected runway assignment prior to Top Of Descent, or as part of the 

“Descent Via” clearance. For those aircraft equipped with FIM equipment, the en route 

controller subsequently issues the FIM clearance. The flight crew read back the FIM 

clearance, notify the controller when the FIM operation commences, and include a FIM 

status as part of the initial check-in on each subsequent frequency. Any controller may 

amend, suspend, or terminate the FIM clearance, and any ATC instruction takes 

precedence over the FIM speed. 

NOTE: the use of voice communications during ATD-1 operations will likely cause 

the FIM clearance to be issued after the flight crew has been given their Descend Via 

arrival instruction. Subsequent air traffic control instructions supersede previous 

instructions, therefore the FIM clearance must be issued after the Descend Via instruction 

to enable the flight crew to fly the FIM speed and not the published arrival speed. 

The terminal feeder controller issues the actual runway assignment to all crews (in 

some cases may be given by an en route controller), and the Final controller normally 

issues the approach clearance to all crews. If the arrival and approach connect via the 

published procedures, controllers are not expected to issue vectors and crews may use the 

auto-pilot system to fly the procedures. If the arrival and approach procedures do not 

connect, controllers issue vectors to place the aircraft on final. 

The elements of a FIM clearance are: 

 Assigned Spacing Goal [in seconds], 

 Target (lead) aircraft identification [phonetic], 
66 

 Target aircraft route [STAR name, and approach if feasible]. 

Phraseology used with the FIM clearance adheres to the following guidance: 

 “WHEN ABLE” is used to instruct the crew to enter the FIM clearance and 

initiate the FIM operation as soon as feasible (dependent on when the Target 

ADS-B data is first received, and the prioritization of other cockpit tasks). 

 “AFTER (waypoint name)” is used to instruct the crew to enter the FIM clearance 

as soon as feasible, but to initiate the FIM operation after the specified waypoint 

(the TRACON Meter Fix during ATD-1). 

 “PAIRED” is used by the flight crew to announce when the FIM operation has 

begun, and to clearly differentiate from the FIM clearance read-back phraseology. 

When referring to the Target aircraft, normally the phonetic alphabet will be used. 

Based on proficiency, frequency congestion, and similarity between the flight 

identification and callsign, controllers may alternatively use letters or the callsign of the 

Target aircraft. In the example below, the aircraft callsign should not be used since it is 

not similar to the flight identification that is visible on controller and flight crew displays. 

 Normal voice phraseology (phonetic) when referring to the Target aircraft 

identification within the FIM clearance: 

- Aircraft Identification Code (phonetically): Romeo Papa Alpha One-Five

 Alternatives: 

- Aircraft Identification Code (letters): R P A One-Five

 Less desirable due to potential lack of clarity 

- Aircraft Callsign: Brickyard One-Five 

 Not desirable when callsign is dissimilar to data tag code 

G.1 Route and runway assignment by en route controller 

During ATD-1 operations, en route controllers will issue the route of flight and the 

expected runway to all aircraft after the Freeze Horizon and prior to Top-Of-Descent. 

The runway may be given as a separate instruction, or by appending it to the STAR or 

Descend Via clearance. Route and runway assignments should also be given prior to 

issuing a FIM clearance to suitably equipped aircraft. Traffic permitting, en route 

controllers will issue a “Descend Via” clearance to authorize the flight crew to descend at 

their discretion Terminal feeder controllers will issue the actual runway and Final 

controllers the approach clearance. 

There are several acceptable variations to this phraseology, and it is influenced by the 

specific facility procedures and Letters Of Agreement with neighboring facilities, 

controller experience and preference, as well as workload and frequency congestion. The 

first example below is intended to represent the situation when the en route controller 

assigns the arrival procedure and the expected runway, and the second example is 

intended to represent the situation when the en route controller clears the aircraft to begin 

the arrival procedure and issues the assigned runway. 
 67 

The first example in this sub-section also depicts a STAR that does not connect to the 

approach procedure, and the second example is when they do connect. Whether or not 

the STAR and approach procedure connect is not linked to whether a route clearance or 

Descend Via instruction is given, nor is it linked to whether the runway is assigned or 

expected. Many combinations and variations are possible, however for brevity only two 

examples are given. 

G.1.1 Route clearance and expected runway (Figure 17 and Figure 19). 

ATC: (Callsign), CLEARED TO PHOENIX VIA BOULDER CITY, THEN THE (MAIER 

Five) ARRIVAL, EXPECT RUNWAY (two-six) TRANSITION. 

Crew: (Callsign), CLEARED TO PHOENIX VIA BOULDER CITY, THEN THE (MAIER 

Five) ARRIVAL, EXPECT RUNWAY (two-six) TRANSITION.

G.1.2 Descend Via and assigned runway (Figure 18 and Figure 19). 

ATC: (Callsign), PROCEED DIRECT (ZUNI), DESCEND VIA THE (EAGUL Five) 

ARRIVAL, RUNWAY (two-six) TRANSITION. 

Crew: (Callsign), PROCEED DIRECT (ZUNI), DESCEND VIA THE (EAGUL Five) 

ARRIVAL, RUNWAY (two-six) TRANSITION. 

G.2 FIM Clearance Issued by ATC 

The FIM clearance will be given after the route and expected runway has been issued. 

This clearance only impacts the speed an aircraft maintains while flying the previously 

assigned arrival and approach. Any subsequent clearance or instruction from ATC, such 

as a speed instruction or Descend Via clearance, terminate the FIM clearance (whether 

the controller states “cancel interval spacing” or not. 

G.2.1 Preparatory call for FIM clearance 

A preparatory voice transmission should be made by ATC prior to issuing a FIM 

clearance similar to issuing any other clearance to flight crew. 

ATC: (Callsign), CLEARANCE AVAILABLE, ADVISE WHEN READY TO COPY. 

Crew: (Callsign) READY TO COPY. 

G.2.2 FIM clearance to commence after a waypoint 

The FIM clearance may be issued to begin FIM operations after a specific waypoint. 

During ATD-1, this point will be the AFMP on the FIM aircraft’s route. This is done if 

any of the following conditions are true: 

 The Target and FIM aircraft are not on the same arrival, 
68 

 The controller is not aware of both aircraft (likely due to the Target on a 

different arrival), 

 The controller believes vectors are still required for either aircraft. 

In this case, after issuing the FIM clearance until the aircraft reaches the AFMP, the 

controller continues to issue speed instructions (if required) using the GIM-S tool to meet 

the assigned time at the AFMP. 

ATC: (Callsign), AFTER (HOMRR), WHEN ABLE SPACE (niner-five) SECONDS 

BEHIND (Alpha Alpha Lima one-three-six) ON THE (KOOLY Four) ARRIVAL. 

REPORT PAIRED. 

Crew: (Callsign), AFTER (HOMRR), WHEN ABLE SPACE (niner-five) SECONDS 

BEHIND (Alpha Alpha Lima one-three-six) ON THE (KOOLY Four) ARRIVAL. 

REPORT PAIRED. 

G.2.3 FIM clearance to commence as soon as feasible 

The FIM clearance may be issued to begin FIM operations as soon as feasible, 

however since the Target aircraft may not be within ADS-B reception range of the FIM 

aircraft, the precise location or time the FIM operation commences is not always known. 

This may be done when all of the following conditions are true: 

 the Target and FIM aircraft are on the same arrival, 

 the controller is aware of both aircraft, and 

 the controller believes no further vectoring is required for either aircraft. 

In this case, the controller should not have to issue further speed instructions after the 

crew reports having begun FIM operations. 

ATC: (Callsign), WHEN ABLE, SPACE (eight-seven) SECONDS BEHIND (Uniform 

Alpha Lima two-five-four) ON THE (KOOLY Four) ARRIVAL. REPORT 

PAIRED. 

Crew: (Callsign), WHEN ABLE, SPACE (eight-seven) SECONDS BEHIND (Uniform 

Alpha Lima two-five-four) ON THE (KOOLY Four) ARRIVAL. REPORT 

PAIRED. 

G.3 Flight crew FIM status notification to ATC 

Flight crews are required to notify ATC when FIM operations commence, and advise 

all subsequent controllers of the status of the FIM operation (during initial check in). The 

term “Interval Spacing” is used by the flight crew to indicate a FIM clearance has been 

received by the operation has not commenced, and “Paired Behind” to indicate the FIM 

operation has commenced (“Paired With” is also acceptable). See Termination section 

(G.6) when the flight crew cannot commence the FIM operation or needs to terminate it 

after it has begun. 
 69 

Normal communication procedures apply during check-in with the receiving 

controller. For example, the flight crew’s initial check-in with any new facility will 

include the altitude the aircraft is currently at or passing through to verify the transponder 

data, and the crew’s initial check-in with the TRACON will include the ATIS code. 

When the crew has been assigned an altitude to descend to, that altitude is included in the 

initial check-in. When the flight crew has been cleared to Descend Via an arrival 

procedure, that procedure name without an altitude is used in the initial check-in. 

For brevity, the communication for only three of many possible combinations is 

given. 

G.3.1 FIM operation commencing, no frequency change 

Crew: (Callsign) PAIRED BEHIND (Romeo Papa Alpha two-two-one). 

ATC: (Callsign), ROGER. 

G.3.2 Intra-facility check-in, FIM operation commenced, initiating descent 

Crew: (Callsign) LEAVING (one-niner thousand), DESCENDING VIA THE (MAIER 

Five) ARRIVAL, PAIRED BEHIND (Delta Alpha Lima one-two-eight). 

ATC: (Callsign), ROGER. 

G.3.3 Initial TRACON check-in, FIM operation pending, in descent 

Crew: (Callsign) PASSING (one-two thousand) DESCENDING VIA THE (MAIER Five) 

ARRIVAL WITH INFORMATION (Tango), WITH SPACING CLEARANCE 

BEHIND (Delta Alpha Lima one-two-eight-niner). 

ATC: (Callsign), ROGER. 

G.4 FIM Clearance Amended by ATC 

The spacing interval of a FIM clearance may be modified by ATC as new information 

becomes available or operational goals change. The intended benefit of amending a FIM 

clearance versus canceling and issuing a new FIM clearance is to reduce both controller 

and pilot workload. Any other change to the FIM clearance (Target aircraft ID, Target 

route) or a change in the FIM aircraft’s route requires the current FIM clearance to be 

terminated and a new FIM clearance issued (if desired). 

Three different scenarios would create minor variations in the phraseology. They are: 

when the FIM operation has already commenced; a FIM clearance to commence after a 

waypoint (G.2.2); and a FIM clearance to commence as soon as feasible (G.2.3). For 

brevity only one example is shown for after the FIM operation has begun. The other two 

scenarios would use phraseology from the appropriate section. 

ATC: (Callsign), AMEND CLEARANCE. WHEN ABLE SPACE (one-three-zero) 

SECONDS BEHIND (Delta Hotel Lima seven-eight-three). 
70 

Crew: (Callsign), AMEND CLEARANCE. WHEN ABLE SPACE (one-three-zero) 

SECONDS BEHIND (Delta Hotel Lima seven-eight-three). 

G.5 Suspending and Resuming FIM Operation 

The FIM operation may be suspended by any controller, and later resumed (by the 

same or a different controller) when needed to achieve other objectives over a short time 

period and FIM is desired to be continued at a later time. The FIM operation must be 

suspended when: ATC issues a speed instruction to the FIM aircraft, a heading change to 

the FIM aircraft, or a heading change to the Target aircraft. 

G.5.1 ATC suspends the FIM operation 

ATC: (Callsign), SUSPEND INTERVAL SPACING, SLOW TO (two-three-zero) 

KNOTS. 

Crew: (Callsign), SUSPEND INTERVAL SPACING, SLOW TO (two-three-zero) 

KNOTS. 

G.5.2 ATC resumes the FIM operation 

The controller may include “WHEN ABLE” if appropriate. This example does not 

include that phraseology. 

ATC: (Callsign), RESUME INTERVAL SPACING BEHIND (Delta six-two-two). 

Crew: (Callsign), RESUME INTERVAL SPACING BEHIND (Delta six-two-two). 

G.6 Termination of FIM Operation 

FIM termination at the Achieve By Point (FAF in ATD-1) does not require 

communication. If ATC terminates the FIM operation prior to that point, the controller 

may use the phrase “cancel interval spacing”, and if not used, the FIM operation is 

implicitly canceled by the subsequent speed instruction, vector, or clearance. If the flight 

crew cannot adhere to the FIM speed or there is no valid FIM speed, the flight crew will 

state “unable interval spacing” and may include the reason and intentions (reason and 

intentions in a low-density traffic environment only). 

Any speed instruction or route clearance issued to the FIM aircraft terminates the 

FIM operation, whether or not the controller states “cancel interval spacing” or not. In a 

low-density traffic environment the controller may state “cancel” or “terminate” prior to 

issuing instructions, however during periods of high-density operations it should be 

expected that the controller will only issue the new instruction. 

For brevity only two examples are given: ATC initiated termination during highdensity operations, and flight crew initiated termination during low-density operations. 
 71 

G.6.1 ATC initiated FIM termination during high-density operations 

An example of ATC terminating FIM operation and instructing the aircraft to fly a 

specific speed, and not stating “cancel interval spacing” due to frequency congestion: 

ATC: (Callsign), MAINTAIN (two one zero) KNOTS. 

Crew: MAINTAIN (two one zero) KNOTS, (Callsign). 

G.6.2 Flight crew initiated termination of FIM operation during low-density 

An example of a FIM speed being operationally undesirable is: 

Crew: (Callsign) UNABLE TO CONTINUE INTERVAL SPACING, (speed too fast). 

ATC: (Callsign), CANCEL INTERVAL SPACING, MAINTAIN (two hundred) KNOTS. 

Crew: (Callsign), CANCEL INTERVAL SPACING, MAINTAIN (two hundred) KNOTS. 

G.7 ATC Requests FIM Operation Report 

ATC may request the flight crew to state their FIM clearance, which may occur when 

the flight crew does not state the information during initial check-in or the original 

transmission was not heard. This request would not be expected when TRACON 

automation fully supports FIM operations. It is not necessary to include the Target route 

since the controller does have that information. 

ATC: (Callsign), VERIFY INTERVAL SPACING CLEARANCE. 

Crew: (Callsign), INTERVAL SPACING CLEARANCE IS (one-zero-five) SECONDS 

BEHIND (Uniform Papa Sierra five-niner-eight).
72 

Appendix H: Example of ATD-1 Arrival and Approach Procedures 

Shown are: 1) the MAIER FIVE arrival procedure with altitude and speed restrictions 

but not connecting to an approach procedure; 2) the EAGUL FIVE arrival procedure with 

altitude and speed restrictions that does connect to an approach procedure; and 3) the ILS 

instrument approach to Runway 26. 

Figure 17. Arrival does not connect to the Approach. 
 73 

Figure 17. Arrival does not connect to the Approach (concluded). 
74 

Figure 18. Arrival does connect to the Approach. 
 75 

Figure 18. Arrival does connect to the Approach (concluded). 
76 

Figure 19. Approach procedure. 
REPORT DOCUMENTATION PAGE Form Approved

OMB No. 0704-0188

2. REPORT TYPE 

Technical Memorandum

 4. TITLE AND SUBTITLE

Air Traffic Management Technology Demonstration-1 Concept of 

Operations (ATD-1 ConOps), Version 2.0 

5a. CONTRACT NUMBER

 6. AUTHOR(S)

Baxley, Brian T.; Johnson, William C.; Swenson, Harry N.; Robinson, 

John E.; Prevot, Thomas; Callantine, Todd J.; Scardina, John; Greene, 

Michael

 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

NASA Langley Research Center

Hampton, VA 23681-2199

 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration

Washington, DC 20546-0001

 8. PERFORMING ORGANIZATION

 REPORT NUMBER

L-20241

10. SPONSOR/MONITOR'S ACRONYM(S)

NASA

13. SUPPLEMENTARY NOTES

12. DISTRIBUTION/AVAILABILITY STATEMENT

Unclassified - Unlimited

Subject Category 03

Availability: NASA CASI (443) 757-5802

19a. NAME OF RESPONSIBLE PERSON

STI Help Desk (email: help@sti.nasa.gov)

14. ABSTRACT

This document is an update to the operations and procedures envisioned for NASA s Air Traffic Management (ATM) Technology Demonstration #1 (ATD-1). 

The ATD-1 Concept of Operations (ConOps) integrates three NASA technologies to achieve high throughput, fuel-efficient arrival operations into busy 

terminal airspace. They are Traffic Management Advisor with Terminal Metering (TMA-TM) for precise time-based schedules to the runway and points within 

the terminal area, Controller-Managed Spacing (CMS) decision support tools for terminal controllers to better manage aircraft delay using speed control, and 

Flight deck Interval Management (FIM) avionics and flight crew procedures to conduct airborne spacing operations. The ATD-1 concept provides 

de-conflicted and efficient operations of multiple arrival streams of aircraft, passing through multiple merge points, from top-of-descent (TOD) to the Final 

Approach Fix. These arrival streams are Optimized Profile Descents (OPDs) from en route altitude to the runway, using primarily speed control to maintain 

separation and schedule. The ATD-1 project is currently addressing the challenges of integrating the three technologies, and their implantation into an 

operational environment. The ATD-1 goals include increasing the throughput of high-density airports, reducing controller workload, increasing efficiency of 

arrival operations and the frequency of trajectory-based operations, and promoting aircraft ADS-B equipage.

15. SUBJECT TERMS

Air Traffic Control; Controller Managed Spacing; Interval Management; Terminal Metering

18. NUMBER

 OF 

 PAGES

83

19b. TELEPHONE NUMBER (Include area code)

(443) 757-5802

a. REPORT

U

c. THIS PAGE

U

b. ABSTRACT

U

17. LIMITATION OF 

 ABSTRACT

UU

Prescribed by ANSI Std. Z39.18

Standard Form 298 (Rev. 8-98)

3. DATES COVERED (From - To)

5b. GRANT NUMBER

5c. PROGRAM ELEMENT NUMBER

5d. PROJECT NUMBER

5e. TASK NUMBER

5f. WORK UNIT NUMBER

 305295.02.31.07.01.03

11. SPONSOR/MONITOR'S REPORT

 NUMBER(S)

NASA/TM-2013-218040

16. SECURITY CLASSIFICATION OF:

The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, 

gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this 

collection of information, including suggestions for reducing this burden, to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and 

Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person 

shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number.

PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS.

1. REPORT DATE (DD-MM-YYYY)

01- 09 - 2013