NASA/CR–2009-215373

Initial Investigation of Operational Concept Elements for

NASA’s NextGen-Airportal Project Research

Johnathan Lee

U.S. Department of Transportation, John A. Volpe National Transportation Systems Center

Cambridge, Massachusetts

Gary Lohr

NASA Langley Research Center, Hampton, Virginia

James L. Poage

JLP Performance Consulting, Lexington, Massachusetts

Leonard Tobias

University of California, Santa Cruz, California

July 2009
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NASA/CR–2009-215373

Initial Investigation of Operational Concept Elements for

NASA’s NextGen-Airportal Project Research

Johnathan Lee

U.S. Department of Transportation, John A. Volpe National Transportation Systems Center

Cambridge, Massachusetts

Gary Lohr

NASA Langley Research Center, Hampton, Virginia

James L. Poage

JLP Performance Consulting, Lexington, Massachusetts

Leonard Tobias

University of California, Santa Cruz, California

July 2009

National Aeronautics and

Space Administration

Ames Research Center

Moffett Field, California 94035-1000
Available from:

NASA Center for AeroSpace Information National Technical Information Service

7115 Standard Drive 5285 Port Royal Road

Hanover, MD 21076-1320 Springfield, VA 22161

(301) 621-0390 (703) 487-4650

Acknowledgments

The Airportal Concepts Team would like to thank Douglas Lee of the Volpe National Transportation

Systems Center for his contribution to Section 2.1, Air Traffic Demand Attributes for Airport Services. He

generously provided the descriptions of attributes of the future demand environment in which the concepts

might operate.

The Airportal Concepts Team would also like to thank everyone who has reviewed this document and

provided feedback to improve its usefulness, content, and clarity. In particular, we would like to acknowledge David Hinton, Michael Madson, John Koelling, Yoon Jung, Harry Paul Stough, Steven Green, Sandra

Lozito, and Savita Verma for their review and guidance.

Prepared for NextGen-Airportal Project Deliverable
iii

TABLE OF CONTENTS

List of Tables ................................................................................................................................. vi

Glossary/Acronyms/Abbreviations............................................................................................... vii

Executive Summary..................................................................................................................... viii

1 Introduction................................................................................................................................1

1.1 Purpose of the Airportal Concept ..................................................................................2

1.2 Scope of the Airportal Concepts....................................................................................2

1.3 Approach to Develop Airportal Concept .......................................................................3

1.4 Organization of This Document.....................................................................................3

2 Future Setting for Airport Capacity Improvements...................................................................4

2.1 Air Traffic Demand Attributes for Airport Services......................................................4

2.2 Airport Capacity Attributes............................................................................................5

2.3 Sources of Airport Capacity...........................................................................................6

3 Surface Concept Elements.........................................................................................................6

3.1 Runway Management ....................................................................................................7

3.1.1 Constraint/problem for runway management ..........................................................7

3.1.2 Description of runway management ........................................................................7

3.1.3 Benefits from runway management.........................................................................8

3.1.4 Required technology and infrastructure for runway management...........................8

3.1.5 Potential research topics for runway management ..................................................9

3.2 Taxi Route Planning ......................................................................................................9

3.2.1 Constraints and problems for taxi route planning....................................................9

3.2.2 Description of taxi route planning ...........................................................................9

3.2.3 Benefits from taxi route planning ..........................................................................10

3.2.4 Required technology and infrastructure for taxi route planning............................11

3.2.5 Potential research topics for taxi route planning....................................................11

3.3 Surface Super Density Operations (SDO) ...................................................................12

3.3.1 Constraints and problems for surface SDO ...........................................................12

3.3.2 Description of surface SDO...................................................................................12

3.3.3 Benefits from surface SDO....................................................................................13

3.3.4 Required technology and infrastructure for surface SDO......................................14

3.3.5 Potential research topics for surface SDO .............................................................14

3.4 Surface Weather and Environmental Planning............................................................15

3.4.1 Constraints and problems for surface weather and environmental planning.........15

3.4.2 Description of surface weather and environmental planning ................................15

3.4.3 Benefits for surface weather and environmental planning ....................................16

3.4.4 Required technology and infrastructure of surface weather and environmental 

planning..................................................................................................................16

3.4.5 Potential research topics of surface weather and environmental planning ............16

4 Terminal Concept Elements.....................................................................................................17

4.1 Precise Spacing and Separation Assurance..................................................................17

4.1.1 Constraints and problems for precise spacing and separation assurance...............17

4.1.2 Description of precise spacing and separation assurance ......................................17

4.1.3 Benefits from precise spacing and separation assurance .......................................18

4.1.4 Required technology and infrastructure for precise spacing and separation 

assurance ................................................................................................................19

4.1.5 Potential research topics for precise spacing and separation assurance ................19
iv

TABLE OF CONTENTS (cont.)

4.2 Dynamic Airspace Management..................................................................................20

4.2.1 Constraints and problems for dynamic airspace management...............................20

4.2.2 Description of dynamic airspace management ......................................................20

4.2.3 Benefits from dynamic airspace management .......................................................21

4.2.4 Required technology and infrastructure for dynamic airspace management.........21

4.2.5 Potential research topics ford airspace management .............................................21

4.3 Adapting Operations to Conditions .............................................................................22

4.3.1 Constraints and problems for adapting operations to conditions...........................22

4.3.2 Description of adapting operations to conditions ..................................................22

4.3.3 Benefits from adapting operations to conditions...................................................23

4.3.4 Required technology and infrastructure for adapting operations to conditions.....23

4.3.5 Potential research topics for adapting operations to conditions.............................23

4.4 Metroplex Operations ..................................................................................................24

4.4.1 Constraints and problems for metroplex operations..............................................24

4.4.2 Description of metroplex operations......................................................................24

4.4.3 Benefits from metroplex operations.......................................................................25

4.4.4 Required technology and infrastructure for metroplex operations........................25

4.4.5 Potential research topics for metroplex operations................................................26

5 Coordination and Integration of Concept Elements.................................................................26

5.1 Coordination and Integration among Airport Surface Operations...............................27

5.1.1 Constraints and problems for coordination and integration among airport surface 

operations...............................................................................................................27

5.1.2 Description of coordination and integration among airport surface operations ....27

5.1.3 Benefits from coordination and integration among airport surface operations .....28

5.1.4 Required technology and infrastructure for coordination and integration 

among airport surface operations...........................................................................28

5.1.5 Potential research topics for coordination and integration among airport surface 

operations...............................................................................................................29

5.2 Coordination and Integration among Terminal Airspace Operations..........................29

5.2.1 Constraints and problems for coordination and integration among terminal 

airspace operations.................................................................................................29

5.2.2 Description of coordination and integration among terminal airspace operations 29

5.2.3 Benefits from coordination and integration among terminal airspace operations.30

5.2.4 Required technology and infrastructure for coordination and integration among 

terminal airspace operations ..................................................................................31

5.2.5 Potential research topics for coordination and integration among terminal 

airspace operations.............................................................................................................31

5.3 Coordination and Integration among Airport Surface and Terminal Airspace 

Operations....................................................................................................................31

5.3.1 Constraints and problems for coordination and integration among airport 

surface and terminal airspace operations...............................................................32

5.3.2 Description of coordination and integration among airport surface and

terminal airspace operations ..................................................................................32

5.3.3 Benefits from coordination and integration among airport surface and 

terminal airspace operations ..................................................................................33
v

TABLE OF CONTENTS (cont.)

5.3.4 Required technology and infrastructure for coordination and integration 

among airport surface and terminal airspace operations........................................33

5.3.5 Potential research topics for coordination and integration among airport 

surface and terminal airspace operations...............................................................33

5.4 Coordination and Integration among Metroplex Operations.......................................34

5.4.1 Constraints and problems for coordination and integration among metroplex .........

operations...............................................................................................................34

5.4.2 Description of coordination and integration among metroplex operations ...........34

5.4.3 Benefits from coordination and integration among metroplex operations ............35

5.4.4 Required technology and infrastructure for coordination and integration 

among metroplex operations..................................................................................35

5.4.5 Potential research topics for coordination and integration among metroplex 

operations...............................................................................................................36

5.5 Overarching Research Topics for Integration and Coordination.................................36

6 Small Airports ........................................................................................................................38

6.1 Constraints and Problems for Small Airports..............................................................38

6.2 Description of Small Airports......................................................................................38

6.3 Benefits from Small Airports.......................................................................................39

6.4 Required Technology and Infrastructure for Small Airports.......................................39

6.5 Potential Research Topics for Small Airports .............................................................40

7 Advanced Concept Elements...................................................................................................40

7.1 Adaptive Metroplex Operations...................................................................................40

7.1.1 Constraints and problems for adaptive metroplex operations................................41

7.1.2 Description of adaptive metroplex operations.......................................................41

7.1.3 Benefits from adaptive metroplex operations........................................................42

7.1.4 Required technology and infrastructure for adaptive metroplex operations..........43

7.1.5 Potential research topics for adaptive metroplex operations .................................43

7.2 Advanced Airport Design Tools..................................................................................43

7.2.1 Constraints and problems of advanced airport design tools ..................................44

7.2.2 Description of advanced airport design tools.........................................................44

7.2.3 Benefits of advanced airport design tools..............................................................44

7.2.4 Required technology and infrastructure for advanced airport design tools...........44

7.2.5 Potential research topics for advanced airport design tools...................................45

8 Crosscutting Attributes of Concept Elements..........................................................................45

8.1 Human Factors.............................................................................................................45

8.1.1 Description of human factors.................................................................................45

8.1.2 Potential research topics for human factors...........................................................46

8.2 Safety ...........................................................................................................................47

8.2.1 Description of safety..............................................................................................47

8.2.2 Potential research topics for safety ........................................................................47

8.3 Environment.................................................................................................................48

8.3.1 Description of environment ...................................................................................48

8.3.2 Potential research topics for environment..............................................................48
vi

TABLE OF CONTENTS (cont.)

8.4 System Failure .............................................................................................................49

8.4.1 Description of system failure .................................................................................49

8.4.2 Potential research topics for system failure ...........................................................49

9 Further Development and Evolution of the Airportal Concept ...............................................50

Appendix A – Mapping of Airportal Concept Elements...............................................................51

Appendix B – Summary of Concept Elements and Sub-Elements................................................53

Bibliography ..................................................................................................................................67

LIST OF TABLES

Table B-1. Summary of Concept Elements and Sub-Elements ...................................................53
vii

GLOSSARY/ACRONYMS/ABBREVIATIONS

4D Fourth Dimension

AAR Airport Arrival Rate

ADR Airport Departure Rate

ADS-B Automatic Dependent Surveillance-Broadcast

AOC Airline Operations Center

ATC Air Traffic Control

ATIM Airportal Transition and Integration Management

ATM Air Traffic Management

ATM/ATC Air Traffic Management/Air Traffic Control

ATSP Air Traffic Service Provider

CADOM Coordinated Arrival/Departure Operations Management

CD&R Conflict Detection and Resolution

CDM Collaborative Decision-Making

ConOps Concept of Operations

CSPR Closely-Spaced Parallel Runways

DAC Dynamic Airspace Configuration

ETA Expected Time of Arrival

EVO Equivalent Visual Operations

JPDO Joint Planning and Development Office

NAS National Airspace System

NextGen Next Generation

PBS Performance-Based Services

PRT Personal Rapid Transit

RFA Research Focus area

RNAV Area Navigation

RNP Required Navigation Performance

SA Separation Assurance

SATS Small Aircraft Transportation Systems

SDO Super Density Operations

SESO Safe and Efficient Surface Operations

SLDAST System-Level Design, Analysis and Simulation Tools

SUA Special Use Airspace

SWIM System-wide Information Management

TFM Traffic Flow Management

TPSU Trajectory Prediction, Synthesis, and Uncertainty

TRACON Terminal Radar Approach Control
viii

EXECUTIVE SUMMARY

These concepts have been developed for NASA’s Next Generation Air Transportation System 

(NextGen)-Airportal Project under the Airspace Systems Program. The NextGen-Airportal 

Project supports NextGen by providing key research results to enable integrated solutions for 

safe, efficient, and high-capacity airports.

The NextGen-Airportal Project is organized into three research focus areas: Safe and Efficient 

Surface Operations (SESO), Coordinated Arrival/Departure Operations Management (CADOM), 

and Airportal Transition and Integration Management (ATIM). The content in this document was 

derived from an examination of constraints and problems at airports for accommodating future 

increases in air traffic, and from an examination of capabilities envisioned for NextGen. The 

concepts are organized around categories of constraints and problems and therefore do not 

precisely match the research focus areas. However, the categories generally reflect the research 

focus areas.

The concepts provide a framework for defining and coordinating research activities that are and 

will be conducted by the NextGen-Airportal Project. The concepts will help the research 

activities function as an integrated set focused on future needs for airport operations and will aid 

in aligning the research activities with NextGen key capabilities. The concepts are presented as 

concept elements with more detailed sub-elements under each concept element. The concept 

elements and cross-cutting attributes of the concept elements are:

Surface

Runway Management

Taxi Route Planning

Surface Super Density 

Operations 

Surface Weather and 

Environmental Planning 

Terminal Airspace

Precise Spacing and 

Separation Assurance

Dynamic Airspace 

Management 

Adapting Operations to 

Conditions

Metroplex Operations

Coordination and Integration 

of Concept Elements

Coordination and Integration 

among Airport Surface 

Operations

Coordination and Integration 

among Terminal Airspace 

Operations

Coordination and Integration 

among Airport Surface and 

Terminal Airspace 

Operations

Coordination and Integration 

among Metroplex Operations 

Small Airports

Advanced Concepts Elements

Adaptive Metroplex 

Operations

Advanced Airport Design 

Tools

Crosscutting Attributes of 

Concept Elements

Human Factors

Safety

Environment

System Failure

For each concept element, the following topics are discussed: constraints and problems being 

addressed, benefit descriptions, required technology and infrastructure, and an initial list of 

potential research topics. Concept content will be updated and more detail added as the research 

progresses. The concepts are focused on enhancing airportal capacity and efficiency in a 

timeframe 20 to 25 years in the future, which is similar to NextGen’s timeframe.
1

INITIAL INVESTIGATION OF OPERATIONAL CONCEPT ELEMENTS FOR 

NASA’S NEXTGEN-AIRPORTAL PROJECT RESEARCH 

Jonathan Lee,1 Gary Lohr,2 James L. Poage,3 and Leonard Tobias4

Ames Research Center 

1 INTRODUCTION 

These concepts have been developed for NASA’s Next Generation Air Transportation System 

(NextGen) - Airportal Project under the Airspace Systems Program. The program conducts Air 

Traffic Management (ATM) research in support of the NextGen being developed by the Joint 

Planning and Development Office (JPDO). The NextGen-Airportal Project supports NextGen by 

providing key research results to enable integrated solutions for safe, efficient, and high-capacity 

airports. 

The major goal of the NextGen-Airportal Project is to enable capacity improvements in the terminal 

and airport domains to achieve the NextGen target of a two- to three-fold capacity increase for the 

National Airspace System (NAS). This goal will be pursued with consideration for safety 

implications, mitigation of environmental impacts, system efficiency and flexibility, and user 

preferences (i.e., preferences of the aircraft operator). Since every airport is a unique environment 

and demand is not expected to increase equally at each airport, the project will develop and evaluate 

a suite of capacity-increasing concepts and the system analysis capability to aid tailoring solutions to 

specific needs. 

The NextGen-Airportal Project is organized into three research focus areas: Safe and Efficient 

Surface Operations (SESO), Coordinated Arrival/Departure Operations Management (CADOM), 

and Airportal Transition and Integration Management (ATIM). The content in these concepts was 

derived from an examination of constraints and problems at airports for accommodating future 

increases in air traffic and from an examination of capabilities in NextGen. The concepts are 

organized around categories of constraints and problems and therefore do not precisely match the 

research focus areas. However, the categories generally reflect the research focus areas. 

 

1

 U.S. Department of Transportation, John A. Volpe National Transportation Systems Center, 55 Broadway, Cambridge, 

MA, 02142. 

2

 NASA Langley Research Center, 100 Nasa Road, Hampton, VA 23681. 3

 JLP Performance Consulting, 17 Westwood Road, Lexington, MA 02420. 

4

 University of California, Santa Cruz, CA 95064; retired Ames Research Center, Moffett Field, CA 94035-1000. 
2 

1.1 Purpose of the Airportal Concept 

The concepts provide a framework for defining and coordinating research activities that are and will 

be conducted by the NextGen-Airportal Project. The concepts will help the research activities 

function as an integrated set focused on future needs for airport operations and will aid in aligning 

the research activities with NextGen key capabilities. This content will aid the project in identifying 

research issues, determining specific research activities for the issues, and forming the “right mix” of 

research activities. The concepts will also support analysis of benefits, examining human-automation 

interactions and other human factor issues, safety impacts, and environmental implications. In fact, 

analyses of these topics are the subject of companion documents currently being prepared. 

The concepts are also intended to provide a basis for exchanging ideas and coordinating research 

with the Airspace Project and the JPDO. Both the Airportal and Airspace Projects involve the 

terminal airspace, and thus there is overlap between the projects. Roles for the two projects 

regarding the terminal airspace will be coordinated as the two projects plan their research activities. 

This document discusses Airportal operational concept elements. It is not a “Concept of 

Operations,” which typically describes such topics as roles and responsibilities of participants in 

operations, how Air Traffic Management/Air Traffic Control (ATM/ATC) services will be provided, 

and how aircraft will fly gate-to-gate. Since the Airportal concepts are intended to provide a 

framework for defining and coordinating the project’s research activities, they do not present a 

detailed statement of specifics about how future concept elements for airport operations will be 

performed. 

The Airportal concepts might be viewed as performance-level concepts in that they present elements 

of airport operations, but not the details on how this performance will be realized. The concepts 

describe constraints and problems for meeting future airport demand, concept elements for 

operations to overcome these problems, high-level benefits of these operational improvements, and 

research topics to develop the operational improvements. The research topics are presented as 

suggestions; the actual research activities to be conducted are planned by the SESO, CADOM, and 

ATIM research focus areas. While roles and responsibilities of humans and automaton are not 

described in the concept, there is a discussion of potential research issues for human-automation 

interactions. 

1.2 Scope of the Airportal Concepts 

The concepts are focused on enhancing airport capacity and efficiency in a timeframe 20 to 25 years 

in the future, which is similar to NextGen’s timeframe. While the NextGen Concept of Operations 

(ConOps) has considerable detail on airspace operations, it has few details on airport operations. 

Thus, this document goes beyond the information presented about airport operations in the ConOps. 

The content of these concepts are not limited by current research activities of the NextGen-Airportal 

Project. 

Several topics related to airport operations are beyond the scope of this concept and are therefore not 

addressed. These include changing the size of aircraft to handle future passenger demand, changing 
3

schedules to spread out demand, other changes in business models of aircraft operators, and 

transition planning and mixed equipage of aircraft during transition. Aircraft are assumed to have the 

equipage needed to operate under the future concept elements described. Security is also not 

addressed, since this is not a NASA role. 

1.3 Approach to Develop Airportal Concept 

The concept elements presented in these concepts were identified by discussions with managers of 

the NextGen-Airportal Project, by reviewing NextGen concept documents and briefings (e.g., 

Concept of Operations for the Next Generation Air Transportation System, 2007), by reviewing 

journal papers on surface and terminal airspace (listed in the Bibliography), by reviewing concepts 

developed by others (e.g., Virtual Airspace Modeling and Simulation System-Wide Concept, 2006 

and RTCA Free Flight Steering Committee, 2002), and by drawing upon the experience of the four 

concept authors.5

The writing of these concept elements involved interactions with the NextGen-Airportal Project’s 

Principal Investigator, Project Scientist, Project Manager, and Associate Principal Investigators. 

There was also coordination with the Airspace Project to ensure that the directions of the Airportal 

and Airspace Projects are compatible. 

1.4 Organization of This Document 

Before presenting the concept elements to improve airport capacity, Section 2.0 discusses the future 

setting in which the improvements will operate. This examination is presented to help ensure that the 

concept elements are robust enough to meet future airport needs. 

Sections 3.0, 4.0, and 5.0 present concept elements for surface, terminal airspace, and coordination 

and integration areas. In addition to describing concept elements, the sections discuss the constraints 

and problems being addressed, benefit descriptions, required technology and infrastructure, and an 

initial list of potential research topics. Section 6.0 discusses concept elements for small city and rural 

airports since these airports are likely to have more air traffic with an increase in point-to-point 

flights. 

Section 7.0 describes advanced concepts elements that are likely to apply farther in the future. One is 

adaptive metroplex operations, where an aircraft’s arrival airport (within a metroplex) can be 

changed dynamically prior to, or during, a flight. Another is planning tools to design airport layouts 

 

5

 The range of experience of the authors includes: development of ATM and ATC decision aids (e.g., NASA projects of 

Center-TRACON Automation System (CTAS), Virtual Airspace Modeling and Simulation (VAMS), and Advanced Air 

Transportation Technologies(AATT)); experience as an air traffic controller; experience working on Federal Aviation 

Administration (FAA) projects (e.g., Safe Flight 21 and FAA R&D program); and experience in optimization methods. 
4 

that take advantage of the elements to be developed by the NextGen-Airportal Project. Section 8.0 

discusses topics that cut across the various concept elements presented in Sections 3.0 through 7.0, 

such as human factors, safety, and environmental issues. Section 9.0 discusses further development 

of the Airportal concepts. 

Appendix A maps the Airportal concept elements into the Airportal and Airspace Project research 

focus areas. Appendix B summarizes the Airportal concepts in one multipage table. The table has 

three columns presenting the concept elements and summaries of the constraints or problems 

addressed by each element, the sub-elements of each element, and potential research topics for each 

element. This table assembles the concept elements and sub-elements in one easy-to-use display. 

A bibliography of documents examined to identify airport capacity enhancing ideas is included. The 

papers include documentation of other air transportation concepts, studies of airport operations, and 

descriptions of techniques developed by various authors for enhancing particular aspects of airport 

operations. 

2 FUTURE SETTING FOR AIRPORT CAPACITY IMPROVEMENTS 

The future air traffic demand that will require increased capacity at the nation’s airports is more than 

just an increase in total aircraft. There are many attributes of future air traffic that will affect how 

successfully the NextGen-Airportal Project will provide increased capacity. Such attributes include 

aircraft fleet mix (i.e., mix of jumbo jets, large jets, medium jets, regional jets, business jets, very 

light jets, and general aviation aircraft); scheduling of aircraft using particular airports (e.g., extent 

of peak period traffic); origin-destination traffic patterns; extent of hub operations; extent of pointto-point services; and extent of service to small airports. No set of future capacity-improving 

concept elements will provide the capacity to meet unlimited future air traffic demand. The ability of 

the future air transportation system to satisfy the needs for passenger and cargo transit will depend 

on both the attributes of capacity provided and the attributes of demand. 

Attributes of air traffic demand for airport services in 20 to 25 years are unknown. To overcome this 

lack of future knowledge and to help ensure that the NextGen-Airportal Project research activities 

will be effective regardless of the attributes of future demand, it would be helpful for the capacity 

improvements to be robust enough to work in a variety of future demand scenarios. This section 

provides a brief discussion of the attributes of future demand and the concept elements presented in 

this document to deal with a range of demand scenarios. 

2.1 Air Traffic Demand Attributes for Airport Services 

Many designs and analyses of air transportation concepts assume that the distribution of persons to 

aircraft sizes, the distribution of aircraft sizes to airports, and the scheduling of aircraft to airports 

will remain fixed. Under these assumptions, the future demand is determined by increasing the total 

number of flights while keeping unchanged the distribution of aircraft size, distribution of aircraft to 

particular airports, and proportion of aircraft using airports by time of day. However, these 

distributions of demand attributes will change in the future due to changes in aircraft operator’s 
5

business models or to responses to future airport services. Noted below are some attributes in 

demand that may change in the future and will be considered in designing airport capacity 

enhancements. 

Possible attributes of future airport demand include: 

• Aircraft size mix – The future is expected to bring more heavy jets and very light jets, as well 

as changes in the use of other aircraft types. Changes in aircraft size mix affect the ability of 

overall airport capacity to meet demand because of the number of aircraft that may want to 

use a specific airport at peak times, sequencing landing aircraft to account for wake, and 

distribution of flights among major and small airports. 

• Scheduling aircraft at peak periods – Aircraft operators may shift flights away from peak 

periods to gain efficiency in their operations. Future congestion pricing, in whatever form, 

may also shift flights. 

• Hub and Point-to-Point operations – Changes in the number of future flights operated in a 

hubbing mode or in point-to-point will change the demand at particular airports and may 

shift flights from major hub airports to smaller airports. Such changes will influence the 

potential for metroplex operations and the need to provide more services at smaller airports. 

• Changes in the number of air carriers – There may be continued consolidation in the number 

of air carriers that could decrease the number of flights, or there may be additional carriers 

with new business models (e.g., low-cost carriers, carriers focused on providing first class or 

business class service, or on-demand air taxi service with very light jets) that will increase 

the number of flights as well as change the demand for service at particular airports. 

• Air carrier demand changes in poor weather – Collaborative Decision-Making (CDM) is 

changing the demand for airport services in poor weather by air carriers notifying ATC of 

cancelled flights or changes in flight plans. There may be other future changes in demand 

scheduling during poor weather that may affect airport demand. 

2.2 Airport Capacity Attributes 

The possible attributes of future demand for airport service, which are listed in Section 2.1, and the 

extent to which they are uncertain, need be addressed in the formulation of the Airportal concepts. 

This document deals with these demand attributes in a variety of ways, for example: concept 

elements to increase capacity at major airports (although it needs to be noted that there are limits in 

the ability to increase capacity at existing major airports to handle future demand); runway balancing 

and sequence improvements to tackle changes in fleet mix; provision for Closely-Spaced Parallel 

Runways (CSPR) to increase airport capacity; virtual and automated towers to enable small airports 

to handle more demand for point-to-point flights; equivalent visual operations (EVO) to maintain 

system capacity in poor weather; and metroplexes to handle increased demand at metropolitan areas. 
6 

2.3 Sources of Airport Capacity 

Future capacity to provide for aircraft arrivals and departures will arise from the utilization of more 

airports, and from increased operations at existing hub airports, which can be expressed as 

Total Capacity = [Utilize more airports] + [Better utilize existing hub airports]. 

Better utilization of existing hub airports is provided by increasing their base capacity and by 

mitigating weather impacts on capacity, thus 

Total Capacity = [Utilize more airports] + [(Increased base capacity at existing hub airports) 

+ (Mitigate weather impact on capacity)]. 

In addition to identifying constraints and problems for meeting future demand for airport services, 

these views of sources of increased airport capacity were also examined in identifying airport 

capacity concept elements. Examples of capacity enhancements resulting from utilizing more 

airports include the use of virtual or automated towers at small airports to increase the level of traffic 

they can support, and metroplexes of multiple airports that make better use of nonhub airports in a 

metropolitan area. Examples of increasing base capacity at existing hub airports include runway 

balancing and scheduling, CSPR operations, reducing runway occupancy time, improving taxi 

routing, and reducing wake constraints. Finally, examples of mitigating weather impacts on capacity 

include EVO, runway and taxi configuration management, and adjustment of surface operations for 

wet or snowy runway conditions. 

Section 3.0 begins the presentation of concept elements and more detailed sub-elements for 

increasing airport capacity. The term “concept element” is used to indicate a specific means for 

improving airport capacity, and the term “concept sub-element” is used for a more detailed 

breakdown of how airport capacity can be improved under a particular concept element. An example 

is the four concept elements for improving surface capacity: runway management, taxi route 

planning, surface Super Density Operations (SDO), and surface weather and environmental 

planning. Several concept sub-elements are presented for the runway management concept element: 

optimized runway and taxiway configuration change, dynamic allocation of runways, and more 

efficient departure sequences and schedules. 

3 SURFACE CONCEPT ELEMENTS 

Surface concept elements are presented for runway management, taxi route planning, surface SDO, 

and surface weather and environmental planning. Increasing runway capacity is a goal of NextGen 

as indicated by the statement, “The movement of aircraft ... on the airport surface requires new 

logistics, management, and technology in order to enable the efficiencies required with NextGen.” 

from the Concept of Operations for the Next Generation Air Transportation System, Version 2.0, 

June 2007. 
7

3.1 Runway Management 

Runway management addresses which runways are used for arrivals, departures, and mixed 

operations, and which runway will be used by a particular aircraft. It also addresses changing 

runway and taxiway configurations to meet wind and demand conditions. 

3.1.1 Constraint/problem for runway management 

The airport ground infrastructure is fixed since the runways and taxiways are constructed of concrete 

and cannot be changed in any short timeframe. Thus, the Air Traffic Management (ATM) aspect of 

runways and taxiways is to determine which ones to use given wind, traffic demand, and 

environmental considerations. A particular runway configuration is usually selected to maximize 

capacity for given wind conditions. Environmentally friendly configurations (i.e., configurations that 

reduce noise) are selected when possible. Taxiway configurations are selected to fit the runways 

being used and gate locations. Any change in runway configuration includes changing the taxi routes 

of departing aircraft and the arrival routes in terminal airspace of arriving aircraft. Redirecting 

aircraft arriving and departing at the runways being changed may result in a long transition period 

with accompanying delays depending on the amount and location of surface traffic, the preparation 

time available prior to the change, and the surface taxiway layout. Currently, controllers have few 

tools to support configuration management and must react as conditions change. 

3.1.2 Description of runway management 

Airport runway management is a complex issue. Runway configuration needs to be changed based 

on wind, demand, and noise considerations; departures and arrivals on specific runways need to be 

handled based on their relative demand and terminal airspace route availability. Future airport 

operations will have advanced tools to manage runway operations more effectively. There are 

human factor issues for new runway management operations as was stated in Section 1.4. Human 

factor issues cut across most all of the concept elements to be presented and are discussed in Section 

8.0 on crosscutting issues. 

The concept elements for runway management will include: 

• Optimized runway and taxiway configuration change 

Runway and taxiway configurations will be optimized for capacity based on weather 

(primarily wind), arrival and departure demands, dynamic wake separation criteria, 

environmental constraints, and other Traffic Flow Management (TFM) considerations. 

Transition of arrival and departure operations to a changed runway and taxiway 

configuration will be planned to minimize disruptions to capacity. The precise factors that 

influence optimizing runway configurations will be determined and incorporated into 

configuration planning tools. 

• Dynamic allocation of runways (for a given configuration) 

The allocation of arrival and departure slots to runways, often called runway balancing, will 

be based dynamically on predicted demand to maximize overall airport capacity. Other 

factors will be considered, such as weather (wind direction in particular), airline preference, 

noise restrictions, and controller workload. Runway assignments will be accomplished in an 
8 

effective manner compared with today’s operation where there are considerable 

inefficiencies associated with such assignments. 

• More efficient departure sequences and schedules 

Departure sequences and schedules will be generated based on current predictions of 

available time of a departure slot at the runway and with more accurate wake data. The 

departure queues at multiple runways will be balanced to maximize capacity and minimize 

delay. Arrival sequences and schedules will be generated by the Terminal Radar Approach 

Control (TRACON) facility, but will be tightly coordinated with the surface to maximize 

runway usage based on arrival/departure demand. Reordering sequences of aircraft will be 

conducted to respond to user preferences when possible without harming capacity. 

3.1.3 Benefits from runway management 

Benefits of the above concept elements are to: 

• Maximize airport surface capacity 

− Benefit arises from identifying and using the most efficient runway configuration to gain 

the maximum arrival and departure capacity 

− Benefit arises from assigning runways to arriving and departing aircraft in an integrated 

manner that maximizes the capacity of the runways 

− Benefit arises from sequencing aircraft to minimize the impacts of wake on separation 

and, hence, capacity 

• Minimize transient delays during runway configuration change 

− Benefit arises from generating an optimum plan for changing the runway configuration 

and shifting aircraft to the new runway configuration 

• Increase runway throughput by optimal allocation of departure slots 

− Benefit arises from allocating departure slots to take advantage of any windows in arrival 

streams. 

3.1.4 Required technology and infrastructure for runway management 

The technology listed in these sub-sections on required technology is what is assumed to be needed 

for each concept element. As the research progresses and results become available, the technology 

requirements may be modified. 

The following technology and infrastructure items are assumed to be provided for the concept 

elements. Benefits include: 

• Information sharing between airport facilities and airspace facilities controlling operations of 

terminal/en route/System Command Center (e.g., demand information) 

• Information sharing between airport, pilot, and airline operations center (AOC) on time 

aircraft available for pushback 

• Enhanced weather prediction information 
9

3.1.5 Potential research topics for runway management 

Some potential research topics for the sub-elements listed in this subsection are suggested below. 

The list is not definitive; it is included to aid in identifying research needs. Crosscutting research 

issues for human factors, safety, and environment are described in Section 8.0. 

• Develop algorithm(s) to determine optimum runway configuration and provide efficient 

transition to change configuration 

• Develop algorithms to allocate runways to departures and arrivals and to schedule time for 

departing aircraft to arrive at departure runways. Parameters on which to base this 

optimization include predicted arrival/departure demand, weather forecast, and fleet mix. 

• Develop algorithms to sequence and schedule aircraft to use runways, including responding 

to user preferences 

• Study how to include fairness in tradeoff with capacity maximization in managing runway 

allocation and changes. 

3.2 Taxi Route Planning 

Taxi route planning addresses planning the 4D taxi route for departing and arriving aircraft (the term 

4D refers to the three spatial dimensions in airspace plus the time dimension). On the surface, there 

are only two spatial dimensions. It has become common usage to use the term 4D on the surface as 

well as in the air. This permits only one term to be used to indicate a precise trajectory specified in 

both spatial and time dimensions. 

3.2.1 Constraints and problems for taxi route planning 

As airport traffic increases, taxiing aircraft are subject to increased delays, and this adds to overall 

gate-to-gate time. There are several aspects of taxi movements that constrain surface capacity, 

including: taxi routes that take longer than if taxi routes are planned together; aircraft waiting for 

clearances for taxi route segments; queuing to cross active runways; departure queues; getting 

arriving aircraft off the runway quickly; and aircraft pushing back from the gate that block other 

aircraft. 

3.2.2 Description of taxi route planning 

There is a need to develop more effective algorithms for taxi route planning. This is analogous to 

airborne path planning, but there are striking differences. For instance, surface path variations are 

limited by the airport taxiway structure, and by greater uncertainties in key parameters (e.g., 

pushback time, time to cross an active runway, and stopping for taxi segment clearances). 

• Plan efficient taxi routes under specific airport constraints 

The primary purpose of taxi route planning is to generate the route that will deliver aircraft to 

their assigned runways or gates at specified times, with minimum time spent taxiing. 

However, each airport has unique physical layouts and constraints that often severely limit 

the control actions that can be taken. For example, at Logan Airport in Boston, some gates 

are next to taxiways, and pushing back from the gate can effectively block the movement of 

other aircraft. Techniques are needed to coordinate pushback and other operations in the gate 

vicinity for more efficient management. 
10 

• Increase density of surface operations 

Precision taxi route planning, combined with precision surveillance and navigation aids, will 

support increasing the density of taxiing aircraft, and will increase the surface capacity of 

airports. It is noted that increased density of surface operations requires analysis to compare 

its benefits to those of other options, such as holding aircraft at gates and surface 

infrastructure design. 

• Minimize queuing and provide clearances for longer taxiing segments 

Taxi route planning will minimize queuing at runway crossing points and at the departure 

runway, which shortens taxi time and, in turn, reduces fuel consumption and emissions. 

Crossing active runways with little or no queuing is a particularly difficult surface challenge, 

given the interaction between taxiing aircraft needing to cross the runway and aircraft 

arriving or departing on the runway being crossed. In addition to queue minimization, 

automated handoffs will eliminate stopping time of taxiing aircraft to accommodate handoffs 

between controllers. Clearances for longer taxi segments will reduce or eliminate stopping of 

taxiing aircraft to await a clearance for the next part of a taxi segment. 

• Provide for equipage differences, user preferences, and fairness 

Differences in equipage may impact a departure runway (e.g., due to runway length, or noise 

concerns) and therefore also selection of the taxi route. Taxi planning algorithms will 

maximize airport capacity while, to the extent possible, responding to user preferences and 

maintaining fairness to all users. As such, negotiation between users and air traffic service 

provider regarding 4D taxi routes will be part of taxi route planning. 

• Integrate ground vehicle movement into surface traffic flow 

Ground support vehicles will be considered in taxi route planning. As the density of aircraft 

on taxiways increases, these support vehicles still need to be accommodated. 

• Execute and adhere to precise taxi routes 

Executing and monitoring adherence to a 4D taxi route plan, by both the flight deck and air 

traffic service provider, will be increasingly important due to the tighter separation between 

taxiing aircraft and the coordination with other parts of the ATM system. Executing 4D taxi 

routes can be aided by developing onboard displays that will assist with pilot compliance, or 

even by onboard automation controlling the aircraft to follow the 4D taxi route. Automation 

will support controllers and pilots in monitoring adherence to taxi routes and in responding to 

deviations from assigned taxi routes. 

3.2.3 Benefits from taxi route planning 

Benefits of the above concept elements are: 

• To increase surface capacity via planning of more efficient taxi routes and precise execution 

of these 4D taxi routes 
11

− Benefit arises from planning taxi routes for aircraft as an integrated whole to take the 

least time; from planning taxi routes to accommodate constraints of the airport layout; 

and from aircraft precisely executing the planned taxi routes. 

• Reduced queuing when crossing runways and at departure runways 

− Benefit arises from an aircraft arriving at a runway to be crossed at the precise time such 

that it does not need to stop and wait in a queue. 

− Benefit arises from an aircraft arriving at the departure runway at the precise time such 

that it does not need to stop and wait in a queue but can roll onto the runway and depart. 

• To increase surface capacity via increased density of taxiing aircraft 

− Benefit arises from planning and aircraft executing 4D taxi routes and from more precise 

surface surveillance of aircraft position. Such precise routes allow for more aircraft 

moving on the aircraft surface at any time. 

• Safe surface operations via enhanced planning and collision avoidance algorithms 

• Reduced fuel consumption and emissions by minimizing delays in surface movements 

• More user preferences honored 

− Benefit arises from automated taxi route planning being able to handle more information 

about taxi routes and more complex taxi route planning. Thus, more “use requested 

preferences for taxi routes” can be honored, which provides a benefit to the aircraft 

operators. 

3.2.4 Required technology and infrastructure for taxi route planning 

The following technology and infrastructure items are assumed to be provided for the concept 

elements. Benefits include: 

• Information sharing between airport, terminal, and en route airspaces 

• Information sharing between airport and pilot/AOC 

• Data link to communicate 4D taxi route to aircraft and for negotiation 

• Aircraft automation hardware to provide automation for aiding, or actually executing, 4D 

taxi routes. 

3.2.5 Potential research topics for taxi route planning 

Some potential research topics for the sub-elements listed in this subsection are presented below. 

The list is not definitive; it is included to aid in identifying research needs. 

• Determine the most effective means of 4D control: tight conformance to a 4D schedule or 

control at selected points along the planned route 

• Reduce uncertainties in pushback time 

• Determine the controllability provided by taxiways/holding areas 

• Cross active runways with little or no queuing 

• Automation of clearances/handoffs on the surface to reduce need for stopping while taxiing 
12 

• Incorporate user preferences and negotiating for taxi routes 

• Onboard automation and display to aid pilot in following a 4D taxi route or to control the 

aircraft to follow a 4D taxi route 

• Procedures for negotiating 4D taxi routes 

• Efficient taxi route operations in the presence of large uncertainties 

• Understand tradeoffs in optimal vs. robust operations 

• Fairness issues in managing taxiway operations 

• Roles and responsibilities of the pilot and controllers and their automation tools to plan, 

coordinate, negotiate, and monitor surface operations in an integrated manner 

• Investigate the relationship of surface layout changes (e.g., new/extended runway, new 

taxiway/holding area) to increase surface capacity and flexibility. 

3.3 Surface Super Density Operations (SDO) 

Surface SDO will accommodate arrivals and departures during periods of peak demand through such 

sub-elements as reduced arrival and departure separation, EVO, and operations on CSPR. Many of 

these concept elements are a combination of surface and terminal airspace operations. 

3.3.1 Constraints and problems for surface SDO 

During peak periods, airport capacity is often not sufficient to support the demand. The increased 

density of traffic using runways and taxiways increases controller workload. It becomes more 

complex to handle operations such as intersecting or converging runways, taxiing aircraft crossing 

active runways, and aircraft landing on CSPR. The noise impact of dense operations and of closelyspaced arrivals may be unacceptable to local communities. Runway incursions become a bigger 

concern as the number of aircraft using an airport increases. A paper by Barnett et. al. suggests that 

the potential for runway incursion accidents increases with the square of the number of aircraft using 

an airport. 

3.3.2 Description of surface SDO 

There is a need for a greater capacity increase on the airport surface during periods of peak demand. 

• Reduced runway incursions and taxiway conflicts 

As today’s traffic increases at hub and other airports, runway incursions are a significant 

concern. Part of the problem will be ameliorated in the future by the use of sensor systems to 

enhance and monitor surface situations. However, the impact of SDO on the surface will be 

increased runway and taxiway operations. Enhanced planning and conflict detection 

algorithms will help enable these operations without negatively impacting safety. 

• Precision runway/taxi operations 

Surface operations will be conducted with increased density without creating gridlock. 

Surface operations will accommodate more arrivals and departures on runways due to 

reduced separation in the terminal airspace and other enhancements. Multiple aircraft will 
13

simultaneously occupy a runway with an aircraft crossing an active runway as soon as 

possible after the arriving or departing aircraft using the runway has passed the crossing 

point. 

• Reduced runway occupancy time 

SDO will depend upon a new generation of surface operations including reduced runway 

occupancy time and high-speed runway exits. Airport SDO related to the surface will get 

arriving aircraft off the runway quickly after landing and will handle multiple aircraft after 

touchdown on CSPR. It is noted that the implications of this sub-element for increasing 

surface capacity needs further analysis and understanding. 

• Equivalent visual operations (EVO) 

Aircraft will operate on the surface in the same capacity as in visual conditions to the extent 

possible. Precision surveillance and navigation aids will permit maintaining capacity during 

poor visibility. Automation will be developed that enables the execution of 4D taxi routes in 

poor visibility. 

• Reduction of wake vortex impacts 

Improved detection, prediction, and integration into terminal airspace and surface 4D 

trajectory planning will reduce the impact of wake vortex hazards on airport capacity. 

• Intersecting and converging runways 

Improved planning for arrival and departure operations on intersecting and converging 

runways, along with precise 4D trajectories, will increase departure and arrival rates in a 

manner that ensures proper separation between aircraft and avoids runway incursions. 

Intersecting and converging runway operations will be coordinated with terminal airspace 

operations and with taxi operations. 

• Weather and environment 

Automation will plan 4D taxi routes with adjustments as needed to maintain capacity during 

poor weather. For example, rain or snow on the runway may decrease available capacity, but 

the planning automation will minimize this capacity reduction. Better weather prediction and 

increased precision in surveillance and navigation will permit less disruption to airport 

operations during convective weather. This increased traffic activity will be within the 

bounds of acceptable noise and emissions levels. 

3.3.3 Benefits from surface SDO 

Benefits of the above concept elements include: 

• Increased surface capacity allowing for increased arrival rates, increased traffic density on 

taxiways, reduced queues, reduced runway occupancy times, CSPR operations, and increased 

flexibility in planning surface operations 

− Benefit arises in a variety of ways: 
14 

 More precise taxi planning and conformance monitoring tools lead to more efficient 

operations 

 Appropriately sized gaps in runway use are created for efficient use by aircraft 

needing to cross the runways 

 Aircraft coordinate and plan for exiting runways as soon as possible, which allows for 

additional operations on the runway 

 Reducing wake vortex separation requirements 

 Increased precision planning for operations on crossing and converging runways. 

• Increased capacity in poor visibility provides EVO 

− Benefit arises because limits to operations in poor visibility are removed and most 

operations can be conducted in the more efficient Visual Flight Rules (VFR) mode. 

• Safe surface operations, including prevention of runway incursions, via enhanced planning 

and collision avoidance procedures 

− Benefit arises from precisely coordinated air/ground planning and more accurate conflict 

prediction and detection. 

3.3.4 Required technology and infrastructure for surface SDO 

The following technology and infrastructure items are assumed to be provided for the concept 

elements. Benefits include: 

• High-speed turnoffs from runways 

• Coordination between airport and terminal/en route on arrival time at the runway 

• Precision surveillance, navigation, and other sensors to support CSPR operations 

• New CSPR 

• Automated aircraft braking systems (to safely reach precoordinated runway exit) 

• Technology to provide location information for aircraft, runways, taxiways, and other objects 

during poor visibility 

• Limiting or restricting access to airport operations for aircraft not suitably equipped for the 

needed operations 

• Surface surveillance to allow less separation between taxiing aircraft, and collision avoidance 

techniques. 

3.3.5 Potential research topics for surface SDO 

Some potential research topics for the sub-elements listed in this subsection are presented below. 

The list is not definitive; it is included to aid in identifying research needs. 

• Conflict detection and resolution (CD&R) and other safety aspects in the closely-spaced 

environment of SDO, including during EVO 

• Low altitude, runway, and taxiway collision avoidance 

• Procedures, algorithms, automation, and equipage requirements for CSPR operations 
15

• Procedures, algorithms, automation, and equipage requirements for precise taxi operations 

• Procedures, algorithms, automation, and equipage requirements for planning and executing 

4D taxi routes 

• Reduction of impact of wake vortex 

• Airborne and ground roles and responsibilities (conformance monitoring, conflict detection 

and resolution) 

• Determine ground arrival capacity for major airports under SDO. 

3.4 Surface Weather and Environmental Planning 

A key objective of the NextGen-Airportal Project is to increase airport capacity. This objective must 

be achieved by mitigating the impact of weather and by understanding environmental constraints. 

3.4.1 Constraints and problems for surface weather and environmental planning 

Winds can cause arrivals and departures to be assigned to a less efficient set of runways. If changes 

in wind direction are poorly predicted, configuration changes may be required which can result in 

inefficient and lengthy transition periods. Surface movement can be slowed considerably by reduced 

visibility, or by wet or snowy surface conditions. As for the environment, if current operations are at 

or near environmental limits, increased capacity may not be possible without technological advances 

to reduce airframe and power plant noise and emissions output. 

3.4.2 Description of surface weather and environmental planning 

Weather can dramatically degrade the capacity of surface operations. If such capacity degradation 

occurs too frequently and with a great impact, aircraft operators will not be able to plan schedules to 

take advantage of capacity increases that occur only in good weather. Also, the public generally will 

not accept negative environmental impacts from increased airport capacity. 

• Weather 

Automation to plan 4D taxi routes and airport surface configuration will account for weatherrelated phenomena, such as moving weather cells, low visibility operations, and wet or 

snowy runways. Surface operations will efficiently account for deicing operations when 

needed, either at the gate or at separate deicing stations. Scheduling of arrivals and 

departures will be adapted for the weather conditions. The NextGen-Airportal Project will 

not develop sensor technologies or predictors for weather; it will utilize these “enablers” to 

improve the efficiency of operations impacted by weather-related phenomena. 

• Environment 

Airport planning will address the environmental issues of noise and emissions while planning 

capacity-increasing operations. Tools will be developed to monitor environmental impacts 

during surface operations and provide inputs to planning surface routes to mitigate negative 

impacts. Precision Required Navigation Performance (RNP) allows for more precise 

maneuvering to reduce noise/emissions. 
16 

3.4.3 Benefits for surface weather and environmental planning 

Benefits of the above concept elements include: 

• Reduced disruption in capacity during adverse weather conditions 

− Benefit arises because reduced visibility does not limit capacity. If changes in wind 

direction are predicted more reliably, runway and taxiway configuration modifications 

may be planned in a more effective manner. 

• Reduced negative impacts on capacity operations during deicing 

− Benefit arises because deicing can be accomplished in a timely manner prior to departure 

so that the deicing process does not need to be repeated. 

• Reduced negative impacts on noise and emissions from increased surface operations 

− Benefit arises by reducing the aircraft’s “engine-on” time on the surface, applying noise 

sensitivity to runway usage and taxi route planning, and segregating noisier aircraft to 

less noise sensitive areas. 

3.4.4 Required technology and infrastructure of surface weather and environmental 

planning 

The following technology and infrastructure items are assumed to be provided for the concept 

elements. Benefits include: 

• More accurate prediction of weather phenomena 

• New quieter aircraft 

• New reduced-emission power plants 

• Data sharing/exchange for coordinated planning of nonvisual operations 

• Environmental impact sensors for noise and emissions 

• Better RNP technology for ground and flight deck. 

3.4.5 Potential research topics of surface weather and environmental planning 

Some potential research topics for the sub-elements listed in this subsection are presented below. 

The list is not definitive; it is included to aid in identifying research needs. 

• Develop procedures to utilize improved weather predictions 

• Incorporate environmental impacts into surface operation planning 

• Develop human and automation roles for operations involving weather and environmental 

impacts. 
17

4 TERMINAL CONCEPT ELEMENTS 

Terminal concept elements are aimed at increasing capacity in the terminal airspace. Elements are 

presented for precise spacing and separation assurance, dynamic airspace management, adapting 

operations to conditions, and metroplex operations. The Airspace Management portion of the 

Airportal concepts supports several of the key capabilities under NextGen: Performance-Based 

Services, Trajectory-Based Operations, EVO, and SDO. 

As was explained at the end of Section 2.0, the term “concept element” is used to indicate a specific 

means for improving airport capacity, and the term “concept sub-element” is used for a more 

detailed breakdown of how airport capacity can be improved under a concept element. 

4.1 Precise Spacing and Separation Assurance 

More precise surveillance data, adherence to 4D trajectories, and enhanced conflict detection and 

resolution will allow more precise spacing in the terminal airspace, which will, in turn, enable 

reduced separation standards and CSPR operations. Enhanced separation assurance will also support 

EVO. 

4.1.1 Constraints and problems for precise spacing and separation assurance 

The ability to reduce spacing and separation between traffic is currently limited. Surveillance 

capabilities are limited by accuracy and update rate. Likewise, flying accurate 4D trajectories is 

needed to permit improved spacing precision. Finally, improvement in conflict detection is needed 

for closer spacing between aircraft. 

4.1.2 Description of precise spacing and separation assurance 

The primary role of the ATC system is to separate aircraft. This is substantiated by the provision in 

the Air Traffic Control Handbook (FAA Order 7110.65), which establishes the priorities as the 

“safe, orderly, and expeditious” flow of air traffic. Reductions in separation standards are central to 

capacity gains. Improved surveillance capabilities, navigational accuracy, and improved 

communications capabilities can all serve to reduce basic separation standards. These standards 

could potentially be dynamic depending on conditions. The concept elements for separation 

assurance will include: 

• Precise spacing 

The application of precise spacing, whether flight deck or ground based, will provide 

increased capacity. In many cases, precise spacing will enable reduced separation. Onboard 

displays and algorithms permit aircrews to achieve either time-based or distance-based 

separation and/or spacing to higher degrees of precision. Ground-based solutions to achieve 

precise spacing can also show benefits. Time-based separations can be particularly beneficial 

as they can allow for speed profiles typically flown in the terminal areas resulting in target 

spacing at the runway threshold. 
18 

• Reduced wake vortex separation criteria 

Detection and planning to reduce the separation which is currently required behind aircraft to 

avoid hazardous encounters with wake vortices will be part of a future system. Reduced 

wake vortex separation standards will help enable efficient CSPR operations. It will also be a 

significant step in moving towards EVO during weather conditions that currently require the 

use of instrument approaches. Finally, a better understanding of the wake vortex 

phenomenon will enable separation standards to better reflect the hazard. 

• Closely Spaced Parallel Runway (CSPR) operations 

Separations for CSPR and converging runway operations can be reduced if navigation and 

separation assurance are provided with a greater degree of precision. The use of 4D 

trajectories can permit precise spacing of aircraft relative to adjacent parallel-runway traffic. 

This can position an aircraft aft of a collision risk and at the same time forward of a location 

where wake is a hazard. As aircraft operate in closer proximity with CSPRs, ground-based or 

flight-deck–based conformance monitoring and conflict detection needs to be explored. 

Algorithms and procedures for alerting and for avoidance maneuvers will also have to be 

developed to support these operations. 

• Scheduling and sequencing interactions with surface and en route 

4D trajectories in the terminal airspace will be coordinated with the en route and surface 

domains. This will enable landing aircraft to reach arrival fixes and the runway threshold at 

desired times and departing aircraft to take-off and be integrated into the en route airspace at 

desired times. 

• Intersecting trajectories in airspace 

Precise spacing and improved conflict detection and avoidance will allow new, and in some 

cases more complex, arrival and departure paths (4D trajectories) that can increase capacity 

when there are intersecting departure and/or arrival paths. There will also be the ability to 

dynamically change intersecting 4D trajectories depending on conditions. 

4.1.3 Benefits from precise spacing and separation assurance 

Benefits of the above concept elements include: 

• Increased capacity for both arrival and departures due to reductions in spacing and wake 

separation criteria. 

− Benefit arises from more precise positional information, automation to provide guidance 

or spacing cues, and an improved wake detection and prediction capability. 

• Increased runway capacity due to added flexibility for runway usage at airports with CSPR 

by accurately determining when wake vortices are not an issue; greater latitude in runway 

selection by more accurately determining when a wake separation penalty will not be 

incurred. 

− Benefit arises from the application of wake detection and prediction capabilities to reflect 

the true wake hazard, and to optimize runway configuration and assignments. 
19

• Less fuel burn due to more efficient speed management with minimum throttle adjustment 

from time-based clearances issued at the terminal boundary. 

− Benefit arises from the use of automation in generating speed cues for aircraft, based on 

required spacing at the runway threshold. 

• Possible decrease in controller workload due to flight-deck managed spacing or automationassisted ground-based separation resulting in precision spacing. 

− Benefit arises from the generation of speed cues to the pilot from an onboard algorithm 

that reduces communications and controller conflict-detection tasks; ground based 

algorithms offer similar benefits. 

4.1.4 Required technology and infrastructure for precise spacing and separation 

assurance 

The following technology and infrastructure items are assumed to be provided for the concept 

elements. Benefits include: 

• Automatic Dependent Surveillance – Broadcast (ADS-B) capability 

• Area Navigation (RNAV) capability 

• 4D Trajectory capability 

• Advanced aircraft surveillance technology 

• Data-link communications 

4.1.5 Potential research topics for precise spacing and separation assurance 

Some potential research questions to provide the sub-elements listed in this subsection are presented 

below. The list is not definitive; it is included to aid in identifying research needs. Crosscutting 

research issues for human factors, safety, and environment are described in Section 8.0. 

• What separations can be achieved for CSPR operations with greater aircraft navigation and 

surveillance precision? 

• What is the best solution for precision spacing: flight-deck managed, ground-based managed, 

or some combination of both? 

• Regarding separation responsibility, what role is appropriate for the flight deck and for ATC? 

• What alerting is needed to detect separation violations in an environment where standards are 

closer? 

• What are the information requirements for groundside if airborne-managed separation is 

used? 

• What are the information requirements for the flight deck if groundside separation is used? 

• How precisely can wake information be provided? What levels of reduced separation, CSPR 

operation, and EVO can be attained by using the wake information that will be available? 

• How to respond to off-nominal situations? 
20 

4.2 Dynamic Airspace Management 

Dynamic airspace re-allocation will allocate airspace among preplanned alternative airspace 

structures. The re-allocation of airspace sectors to accommodate demand, weather, and runway 

constraints can enable the terminal airspace to provide more capacity for the particular constraints 

being experienced. 

Airspace sector structures are currently redesigned infrequently, consequently the structures are slow 

to respond to changes in schedule or origin-destination air traffic that may result over a year or 

several years. More frequent updating of the alternative airspace structures available for reallocation 

would better accommodate long-term changes in traffic that uses an airport. 

Both the dynamic re-allocation of terminal airspace structure among alternative structures and the 

occasional redesign of the underlying alternative structures are covered in this section. 

4.2.1 Constraints and problems for dynamic airspace management 

Inefficiencies in the flow of traffic occur as a result of generally static and inflexible airspace 

allocation. The current system does not provide, with few exceptions, the re-allocation of airspace to 

meet ever-changing demand. Hence, traffic is delayed while parcels of airspace go unutilized. 

Controllers, lacking tools or procedures that would facilitate quickly adapting to realigned or 

resectorized airspace, are not equipped to quickly reorient to adjustments of airspace boundaries. 

A common complaint from pilots is that in some cases they are being separated from airspace. For 

example, an airport located in the middle of the country gets a heavy arrival push from the east 

coast, with few departures during one period, so a portion of the airspace is heavily utilized, while 

another is underutilized. Many of these aircraft depart for both east and west coast destinations with 

few arrivals during another period. Inflexible airspace limits the efficiency of these operations. 

At many locations, segments of airspace are defined in letters of agreement that permit coordination 

among ATC facilities for use of that airspace on an ad hoc basis. An example where this type of 

airspace use might be required is during operations when an unusual direction of arrivals or departs 

is needed. Rather than coordinate use of adjacent airspace for each individual flight, use of a 

predefined area may be requested for a given period of time. This level of flexibility today must be 

predefined for a particular situation. 

4.2.2 Description of dynamic airspace management 

The Airportal concepts will accommodate flexible allocation of terminal airspace. 

• Dynamic terminal airspace sector allocation 

Re-allocating airspace will maximize the airspace available for arrivals and departures 

depending on demand, weather, and other factors. This re-allocation can be in a consistent 

manner (e.g., daily basis, specific hours) where traffic flows are predictable, or on an “ad 

hoc” basis to respond to changes that are not periodic, such as weather. 
21

• Airspace sector redesign 

The alterative airspace structures to be re-allocated in the above bullet will likely have been 

previously designed. More frequent redesign of the alternative airspace sectors to be 

dynamically reallocated will provide a more timely adjustment to changes in demand that 

occur over the course of a year or more. 

4.2.3 Benefits from dynamic airspace management 

Benefits of the above concept elements include: 

• More efficient use of airspace and, hence, more airspace capacity resulting in delay 

reductions 

− Benefit arises from re-allocation of airspace to meet dynamic needs of traffic demand 

under weather and other constraints. 

• Fuel savings for users 

− Benefit arises from shorter flight paths based on availability of airspace that might 

otherwise not be used due to coordination or other issues. 

4.2.4 Required technology and infrastructure for dynamic airspace management 

The following items are required technology and infrastructure that are assumed to be provided: 

• Automation tools that predict sector loading 

• Mechanisms for alerting affected entities to new airspace boundaries 

4.2.5 Potential research topics ford airspace management 

Some potential research questions are listed below. The list is not definitive; it is included to aid in 

identifying research needs. 

• How can airspace be reallocated to meet demand and be done in a way that increases 

efficiency of operators? 

• What time horizon is required for all affected entities to adjust to new boundaries? 

• How to dynamically implement transitions to new airspace configurations so that the 

transitions are efficiently achieved without confusion or uncertainty for air traffic service 

providers or pilots? 

• Is there additional workload from more aircraft in sectors, and is it manageable? 

• How to design the new airspace structures to be dynamically allocated? Is new modeling 

capability required? 

• What are the interactions of terminal airspace with en route airspace to maximize the benefit 

of changes made in terminal airspace? 
22 

4.3 Adapting Operations to Conditions 

The Airportal concepts will contain automation to manage a variety of changes to operations. Some 

adjustments will be for changing conditions, such as runway configurations, weather, and demand. 

Others will be for off-nominal conditions, such as missed approaches and emergency operations. 

4.3.1 Constraints and problems for adapting operations to conditions 

There are a myriad of situations that can be categorized as changes in the flow of air traffic 

operations, either among alternative operational modes (e.g., change between automated groundbased separation assurance and self-separation) or to react to off-nominal conditions. These 

situations require strategies and procedures that minimize impact on the overall operation while 

achieving specific objectives. There are many challenges in dealing with these situations based on 

competing interests: e.g. airline: economics; air traffic service provider: localized and systemic flow 

efficiency; public; noise; and others. Landing aircraft that have missed approaches will have more 

impacts on future capacity due to denser traffic utilizing airports. 

4.3.2 Description of adapting operations to conditions 

Concept elements for adapting to conditions, whether to changes among alternative operation modes 

or reacting to off-nominal condition, are provided below. 

• Respond to runway changes 

In the case of a runway change, the goal is to reroute arrival traffic through airspace to 

accommodate the new configuration in the least disruptive manner. 

• Reduction of wake vortex impacts 

Improved detection and prediction of the wake hazard, complemented by enhanced 4D 

trajectory planning, will reduce the impact of wake vortex hazards on airport capacity. 

• React to weather deviations/reroutes 

More precise 4D trajectories, utilizing improved weather forecasts, will be available to fly 

around weather. The EVO sub-element explained in Section 3.3.2 for surface operations will 

extend into the terminal airspace as necessary. The dynamic allocation of terminal airspace 

described in Section 4.2 also supports the terminal airspace in maintaining capacity during 

adverse weather. 

• Environment 

Further precision in flying 4D trajectories will allow flying more curved arrival and 

departure paths to avoid noise sensitive areas and to fly routes that reduce emissions. The 

ability to change routes often will allow modification to routes in response to changing 

conditions (e.g., weather and demand) that affect noise profiles and emissions dispersions. 

Improved sensors to monitor environmental impacts during operations will provide input to 

route planning to reduce negative impacts. 
23

• Recovery from missed approaches 

The degree to which missed approaches disrupt the system are a function of several factors: 

current traffic demand, available runways (can a departure runway be used?), current traffic 

loading in the terminal airspace, etc. As separation becomes more precise, strategies for 

landing missed approaches or reabsorbing them in an efficient manner into traffic streams 

will be able to mitigate impacts on capacity. 

4.3.3 Benefits from adapting operations to conditions 

Benefits of the above concept elements are: 

• Reduce flight time and fuel usage while changing aircraft trajectories in reacting to changes 

in conditions 

− Benefit arises from increase in throughput and efficiency resulting from more effective 

responses to off-nominal conditions 

4.3.4 Required technology and infrastructure for adapting operations to conditions 

The following technology and infrastructure items are assumed to be provided for the concept 

elements. Benefits include: 

• Aircraft-based or ground-based separation tools 

• Improved weather predictions and information on current weather 

• Sensors to monitor noise and air quality levels 

• Automation to predict the delay required for a runway change, opening of a runway after a 

closure, etc. 

4.3.5 Potential research topics for adapting operations to conditions 

Some potential research topics are listed below. The list is not definitive; it is included to aid in 

identifying research needs. 

• Algorithms to adjust terminal airspace routes for changes in runway configurations 

• Adjusting to changing wake separation requirements in the terminal airspace 

• Dynamic changes in terminal airspace routes to adjust to weather information provided by 

improved weather forecasts 

• Planning precise and more varied (e.g., curved arrival and departure paths approaches) 4-D 

trajectories to avoid noise sensitive areas and to fly routes that reduce emissions. Use the data 

from environment sensors for planning trajectories 

• What are the off-nominal situations, in addition to missed approaches, that should be 

addressed in developing automation aids for terminal operations? How should these offnominal conditions be addressed? How should recovery transition from off-nominal 

conditions be addressed? 
24 

4.4 Metroplex Operations 

Metroplexes utilize multiple airports in a metropolitan area to handle future increases in air traffic to 

that area, and have the potential to be a major factor in increasing capacity in the nation’s air 

transportation system. 

4.4.1 Constraints and problems for metroplex operations 

At virtually all airports, there are constraining factors that limit capacity. Often there are nearby 

airports that might be used to increase overall capacity for a metropolitan area. Many airports are 

also constrained by operations arriving at, or departing from, surrounding airports. This can occur 

for several reasons, such as conflicting arrival/departure paths and shared arrival/departure fixes. 

Traffic increases at airports that currently experience high demand, as well as increases at airports 

with light traffic loading, will further exacerbate the aforementioned constraints and form new 

interdependencies. With these issues in mind, traffic flow management strategies that reflect these 

interdependencies and provide for operations at multiple airports in a metropolitan area will be 

required. 

4.4.2 Description of metroplex operations 

A metroplex, as defined in the Airportal concepts, is a network or group of airports with one or more 

interacting constraining characteristics. These constraining characteristics may be in the form of 

operational interdependencies or the inability of a particular airport(s) to meet traffic demand such 

that significant delays are incurred. As the issues with respect to “inter” and “intra” metroplex 

operations are numerous and varied, the approach to solutions will have to be multifaceted. 

• Precisely flown paths 

The greater and more complex density of traffic traveling to and from the airports within a 

metroplex will be accommodated with the precisely flown flight paths. The precisely flown 

flight paths will permit traffic flows to handle a high density of traffic to multiple airports in 

a metroplex. It follows that these flight paths will be deconflicted through procedural or 

tactical means. 

• Flexible flight paths 

Flexible flight paths, including curved paths, for approaches will increase the capacity of 

metroplex airspace. The current requirement for long straight-in segments for instrument 

approaches is inherently restrictive and poses constraints on airspace design. Flexible, curved 

paths allow for turns onto the final approach course closer to runway, permitting greater 

flexibility for use of the airspace. In dense metroplex operations, competition for airspace 

restricts many operations, including the implementation of instrument approaches. The use of 

curved approaches, which require less of a straight-in segment, could permit the 

implementation of approaches where they are currently not operationally feasible. 

• Increased TFM planning horizon 

Optimized plan-ahead (i.e., surface rerouting) tools for the surface, coupled with advanced 

air traffic flow management between terminal and en route airspace, will ensure that delays 

for aircraft departing from, or arriving at, airports within the metroplex are absorbed on the 
25

ground or outside the airspace-constrained metroplex area. This will enhance the capacity of 

the metroplex airspace, and will not increase workload for controllers and pilots involved 

with the metroplex airspace. 

• Route planning and execution under adverse weather 

To the extent feasible, metroplex operations under adverse weather will be conducted as 

EVO. Such operations will account for different airports being impacted by weather to 

different degrees at different times. There will be tools for the planning of routes under 

adverse weather and for aircraft to execute the routes under adverse weather. 

• Increased capacity at uncontrolled airports 

Uncontrolled airports (no control tower) within a metroplex, many of which are currently 

underutilized, will experience increased traffic activity as larger airports become capacity 

constrained. Absent the ability to provide on-site ATC services, alternative solutions will be 

required that will increase capacity. Potential solutions for this problem include selfseparation (e.g., small aircraft transportation systems (SATS) environment) or the 

implementation of virtual or automated towers. This topic of increasing capacity at 

uncontrolled airports is addressed in Section 6.0, and will not be covered further in 

Section 4.0. 

4.4.3 Benefits from metroplex operations 

Benefits of the above concept elements are: 

• Overall improvement in throughput for airports within the metroplex 

− Benefit arises from coordinated operations reflecting a systemic strategy; better overall 

management of airport configurations and traffic flows. 

• More efficient trajectories for aircraft within metroplex result in saved time and reduced fuel 

burn 

− Benefit arises from design of airspace and traffic flows that accommodate efficient flight 

paths. 

• Greater capacity, time savings, and less fuel use due to efficiency for aircraft operations 

through improved scheduling and planning 

− Benefit arises from a systemic approach to using Metroplex resources that considers 

overall NAS efficiency. 

• Greater capacity, time savings, and less fuel use through improved flexibility in airspace 

usage 

− Benefit arises from more flexibility to adjust airspace to meet demand, weather, and other 

conditions. 

4.4.4 Required technology and infrastructure for metroplex operations 

The following technology and infrastructure items are assumed to be provided for the concept 

elements. Benefits include: 

• Improved navigational and surveillance capabilities 
26 

• Improved communication capabilities 

• Navigation aids, surveillance equipment, and virtual tower capabilities at currently 

uncontrolled airports to enable increased capacity with ATC automation tools 

• Airports in the metroplex with adequate infrastructure, such as runway length and pavement 

condition, passenger and baggage processing facilities, and aircraft servicing facilities. 

4.4.5 Potential research topics for metroplex operations 

Some potential research questions for the sub-elements listed in this subsection are presented below. 

The list is not definitive; it is included to aid in identifying research needs. 

• How to plan arrival and departure routes for multiple airports in a metroplex? 

• How close can arrival and departure paths be located for separation purposes? 

• How can arrival and departure paths in a metroplex be dynamically changed to account for 

changes in weather and in constraints at particular airports? 

• How can airspace be designed and dynamically changed to account for changes in weather 

and in constraints at particular airports? 

• How can metroplex operations be planned and executed under adverse weather? 

• What information should be shared among air traffic service providers at airports, terminal 

airspace, and en route airspace? 

5 COORDINATION AND INTEGRATION OF CONCEPT ELEMENTS 

Section 3 addressed Airportal concept elements on the surface and Section 4 addressed terminal 

airspace. This section presents concept elements for integrating among the surface concept elements, 

among the terminal concept elements, and across the surface and terminal concept elements. 

Coordinated operations within and among these concept elements is expected to yield additional 

airport capacity benefits by minimizing unused arrival and departure slots and increasing the overall 

density of traffic possible in airports. 

The concept elements addressed in this section relate to several NextGen key capabilities: 

Performance-based Services, Weather Assimilated into Decision-making, Broad-area Precision 

Navigation, Aircraft Trajectory-based Operations, EVO, and SDO. 

Integrated operations among surface concept elements will be presented first in Section 5.1. 

Integrated operations among terminal concept elements will be addressed in Section 5.2, followed 

by integration among surface and terminal operations in Section 5.3, and coordination and 

integration among metroplex operations in Section 5.4. 

Many of the research topics identified in Section 5 cut across the various concept elements for 

coordination and integration. To accommodate this and not be redundant, research topics specific to 

a particular coordination and integration concept element are presented in that section while research 

topics that apply to multiple concept elements are presented in Subsection 5.5. 
27

5.1 Coordination and Integration among Airport Surface Operations 

Integrated operations within the airport surface are addressed in this section. 

5.1.1 Constraints and problems for coordination and integration among airport 

surface operations 

Many potential constraints and conflicts can arise on the airport surface from the different surface 

concept elements and sub-elements interacting with each other, such as runway assignments 

interacting with scheduling and sequencing on each runway, taxi route planning interacting with 

runway availability, and gate/runway assignments for multiple aircraft causing interactions among 

surface operations for these aircraft. These constraints and conflicts, if not managed, can cause 

inefficiency and delay. 

5.1.2 Description of coordination and integration among airport surface operations 

The airport surface coordination and integration concept element addresses interactions among the 

different planning processes from the surface concept elements and provides the optimal 4D taxi 

trajectory for each arrival and departure flight. There are four primary airport surface elements to be 

integrated, which were described in Section 3: (1) runway management, (2) taxi route planning, 

(3) surface SDO, and (4) weather and environmental planning. 

The airport surface coordination and integration concept element will consider inputs from terminal 

airspace and AOC, although planning functions do not fully integrate these domains until the subelements described in Section 5.3 are developed. The inputs include the flight plan, runway 

preference, gate assignment, aircraft position, type, equipage, and other ground traffic. These inputs 

will be used as constraints during the planning process. The concept elements for surface integration 

include: 

• Surface Flow Constraint 

Based on the current weather, weather forecast, and time of day, the surface flow constraint 

sub-element will calculate the separation requirements while satisfying the safety and 

environmental constraints. These constraints will feed into the surface SDO concept element 

and the runway management concept element. The surface SDO concept element, based on 

the separation requirement, aircraft type, aircraft weight, and equipage, will calculate the 

minimal runway occupancy time as well as the maximum taxi speed for each aircraft. These 

flow constraints will be inputs to the following Surface Flow Management sub-element. It is 

noted that the impacts of runway occupancy time and taxi speed on surface capacity need 

further analysis and understanding. 

• Surface Flow Management 

The surface flow management sub-element will integrate runway configuration planning and 

runway allocation based on taxi route capacities, runway capacities, runway preference, 

separation requirement, minimal runway occupancy time, gate assignment, flight plan, 

current aircraft positions, and capacity limitations. 
28 

• Surface Trajectory Planning 

The surface trajectory-planning sub-element will calculate the optimal taxi route based on the 

assigned runway, minimal runway occupancy time, maximal taxi speed, assigned gate, and 

other ground traffic. The airport surface coordination and integration element will iterate 

between the runway configuration management and the taxi route planning sub-elements to 

obtain the optimal 4D trajectory for each aircraft arriving or departing the airport, as well as 

the trajectories of ground vehicles. 

• Surface Tactical Control 

The airport surface tactical control sub-element will actively monitor conformance of each 

aircraft to its planned taxi route as well as for off-nominal operations. If an aircraft is out of 

conformance during taxiing or has passed its pushback time, alternative plans would be 

generated to cope with the discrepancy between planned and actual trajectories in a manner 

that minimizes impacts on other taxiing aircraft. Surface tactical control will also detect and 

initiate action for runway incursions and taxi conflicts. 

5.1.3 Benefits from coordination and integration among airport surface operations 

Benefits of the above concept elements include: 

• Increase system throughput and reduce delay on airport surface 

− Benefit arises from better coordination of various airport surface planning processes that 

may otherwise impose conflicting constraints and result in reduced throughput and 

increased delay. This includes better coordination of minimizing delays in crossing 

runways while taxiing, better aircraft surface routing, better aircraft control (e.g., less 

difference between planned and actual trajectory), and better planning (runway 

balancing). 

• Maintain airport throughput in reduced visual conditions 

− Benefit arises from the use of better surveillance and navigation technologies (not 

constrained by weather on runway or taxiways) and better flow management. 

• Increase controller productivity 

− Benefit arises from the use of automation tools. 

• Reduce aircraft fuel burn on the surface 

− Benefit arises from more efficient taxi routing and runway crossing resulting from better 

planning (runway assignment), prediction, and aircraft trajectory execution on airport 

surface (e.g., less difference between planned and actual trajectory). 

5.1.4 Required technology and infrastructure for coordination and integration 

among airport surface operations 

The following technology and infrastructure items are assumed to be provided for the concept 

elements. Benefits include: 

• Better communication tools, including digital data link 

• Better surveillance and navigation technologies 
29

• Improved weather prediction 

• 4D trajectory technology on ground and on aircraft 

• Better information sharing (i.e., system-wide information management (SWIM)). 

5.1.5 Potential research topics for coordination and integration among airport 

surface operations 

The beginning of Section 5.0 mentioned that many issues related to integrating surface and terminal 

airspace concept elements are similar and will be presented in Section 5.5. Also issues related to 

human factors, safety, and environment will be discussed in Section 8.0. 

One research question specific to coordination among the surface concept elements is: 

• How to obtain better prediction of pushback time? In the context of probabilistic information, 

how to better characterize the pushback time for coordination and integration purpose? 

5.2 Coordination and Integration among Terminal Airspace Operations 

Integrated operations within terminal airspace are addressed in this section. 

5.2.1 Constraints and problems for coordination and integration among terminal 

airspace operations 

In the future, more aircraft will transition through terminal airspace, there will be CSPR operations, 

and wake vortex separation will be more critical. Separation assurance, terminal airspace 

management, arrival and departure path planning, and handling non-normal operations will all 

interact in the terminal airspace to affect capacity. Optimizing each of these concept elements will 

help increase capacity, but also coordinating and integrating these concept elements will provide 

further capacity enhancements. 

5.2.2 Description of coordination and integration among terminal airspace 

operations 

The terminal airspace coordination and integration element manages the different planning processes 

from the concept elements within the terminal airspace to provide the optimal 4D trajectory for each 

arrival and departure flight. There are four primary terminal airspace elements, described in Section 

4.0, to be integrated: (1) separation assurance, (2) airspace management, (3) off-nominal operations, 

and (4) metroplex operations. The first three are addressed in this subsection, and metroplex 

operations are addressed in Section 5.4. 

The terminal airspace coordination and integration element will consider inputs and constraints from 

user preferences, en route airspace, and airport surface, although planning functions do not fully 

integrate these domains until the sub-elements described in Section 5.3 are developed. The inputs 

include the flight plan, runway preference, aircraft position, type, equipage, current aircraft weight, 

airport arrival rate (AAR), and airport departure rate (ADR). These inputs will be used as constraints 

during the planning process. 
30 

• Terminal Airspace Flow Constraint. 

Based on the current weather, weather forecast, and time of day, separation requirements will 

be calculated while satisfying the safety and environmental constraints. These separation 

requirements will feed into the SDO sub-element and the terminal airspace management subelement. Separation requirements will be also determined for CSPR operations. These 

separations requirements will be inputs to the following Terminal Airspace Flow 

Management sub-element. 

• Terminal Airspace Flow Management. 

This terminal airspace flow management sub-element will coordinate terminal airspace 

configuration management with other elements of terminal airspace operations to insure the 

airspace structure will accommodate the traffic demand with minimal delay. Furthermore, 

any changes in airspace configuration will be coordinated with overall airspace operations to 

provide a smooth transition. 

• Terminal Airspace Trajectory Planning. 

This concept sub-element will calculate the optimal 4D airspace arrival route for single or 

multiple runways, or CSPR. This trajectory calculation will include the arrival aircraft 

converging into the arrival stream prior to landing. This concept sub-element will factor in 

weather, environmental, equipage, runway configuration, and other constraints. In addition, 

the optimal point for each arrival aircraft to efficiently merge into the arrival stream will be 

calculated. For departure aircraft, this sub-element will determine the optimal 4D airspace 

departure route, and optimal turn-off point to merge with en route traffic. The terminal 

trajectory planning sub-element will calculate the optimal arrival or departure sequence for 

aircraft to minimize separation and hence maximize capacity, based on the current separation 

standard, current aircraft position, aircraft type, weight, equipage, and weather condition, as 

well as satisfying environmental constraints and en route sector capacity limits. 

• Terminal Airspace Tactical Control 

The terminal airspace tactical control sub-element will monitor conformance of each aircraft 

to its planned 4D trajectory. If an aircraft is out of conformance, actions will be generated to 

cope with the discrepancy between planned and actual trajectories in a manner that 

minimizes impacts on other aircraft. This sub-element will also resolve off-nominal 

situations and coordinate to obtain the terminal resources needed to resolve such situations. If 

there is a conflict among any processes within the terminal airspace, the terminal airspace 

tactical control sub-element will formulate a resolution for the conflict. 

5.2.3 Benefits from coordination and integration among terminal airspace 

operations 

Benefits of the above concept elements are: 

• Increase throughput and reduce delay in terminal airspace 

− Benefit arises from better coordination of various terminal airspace planning processes 

that may otherwise impose conflicting constraints and result in reduced throughput and 

increased delay. Examples of coordinated terminal planning processes are precise 4D 
31

trajectories using reduced separation standards, better aircraft sequencing (e.g., a small 

before a heavy vs. a heavy in front of a small), and better aircraft control (e.g., less 

difference between planned and actual trajectory) in the terminal airspace. 

• Maintain terminal throughput in reduced visual condition 

− Benefit arises from the use of better surveillance and navigation technologies (not 

constrained by weather over corner posts) and better flow management (e.g., dynamic 

corner posts and terminal airspace routes that are not impacted by weather). 

• Increase controller productivity 

− Benefit arises from the use of advanced automation tools. 

• Reduce aircraft fuel burn 

− Benefit arises from more efficient terminal routing and less path stretching resulting from 

better planning, prediction, and better aircraft trajectory execution during the transition 

between en route and terminal airspaces. 

5.2.4 Required technology and infrastructure for coordination and integration 

among terminal airspace operations 

The following technology and infrastructure items are assumed to be provided for the concept 

elements to give benefits: 

• Better communication tools, including digital data link 

• Better surveillance and navigation technologies 

• Improved weather prediction 

• 4-D trajectory technology on ground and on aircraft 

• Better information sharing (i.e., SWIM). 

5.2.5 Potential research topics for coordination and integration among terminal 

airspace operations 

A potential research question for the sub-elements listed in this subsection is presented below. 

• How to obtain better-than-expected time of arrival (ETA) at arrival fixes for the planning 

purposes? In the context of probabilistic information, how to better characterize the ETA at 

the arrival fixes for coordination and integration purposes? 

5.3 Coordination and Integration among Airport Surface and Terminal Airspace 

Operations 

After discussing integrated operations within the surface domain and within the terminal airspace 

domain in Sections 5.1 and 5.2 respectively, this section addresses integration between surface and 

terminal airspace domains. 
32 

5.3.1 Constraints and problems for coordination and integration among airport 

surface and terminal airspace operations 

Airport surface and terminal airspace have different operational characteristics and limitations. An 

aircraft flying through the two domains encounters different constraints and requirements. 

Optimizing traffic capacity in each domain separately does not imply that overall capacity is 

maximized. 

5.3.2 Description of coordination and integration among airport surface and 

terminal airspace operations 

The airport surface and terminal integration and coordination concept element integrates the 

planning for airport and terminal operations. It also incorporates constraints from en route airspace 

and the System Command Center into joint surface and terminal airspace planning. The result of the 

integrated planning is an optimal 4D trajectory through terminal airspace and surface taxiing for 

each arrival and departure flight. 

The integrated airport and terminal coordination and integration concept element will consider user 

preferences and inputs from en route airspace and the AOC. Inputs include the flight plan, runway 

preference, gate assignment, aircraft position, type, equipage, current aircraft weight, other ground 

traffic, en route sector capacity, and the Airspace Flow Program imposed by the System Command 

Center. Collaborative decision-making procedures will enable effective use of this data. These inputs 

will be used as limitations during the planning process. 

• Integrated Flow Constraint 

The integrated flow constraint sub-element will coordinate constraints, particularly 

separation requirements, from terminal airspace and surface taxi with surface and terminal 

airspace weather and environmental planning, SDO, and terminal separation assurance. The 

constraints will be inputs to the following Integrated Flow Management. 

• Integrated Flow Management 

Based on the separation standards, the integrated flow management sub-element will iterate 

between runway management and airspace management sub-elements so that overall traffic 

flow in and out of the airports maximizes capacity. 

• Integrated Trajectory Planning 

A 4D trajectory through terminal airspace and surface taxi for each aircraft will be derived 

by iterating between the taxi route planning function and terminal airspace route planning 

function. The trajectories will maximize capacity for the overall airport and will provide 

maximum efficiency for an aircraft in and out of the airport. 

• Integrated Tactical Control 

The integrated tactical control sub-element will actively monitor conformance of each 

aircraft through both terminal airspace and airport surface. If an aircraft is out of 

conformance, this sub-element will coordinate response to the discrepancy between planned 

and actual trajectories. 
33

5.3.3 Benefits from coordination and integration among airport surface and terminal 

airspace operations 

Benefits of the above concept elements are: 

• Increase system throughput and reduce delay in airport operations 

− Benefit arises from better coordination of terminal and airport planning processes that 

may otherwise impose conflicting constraints and result in reduced throughput and 

increased delay. Examples of processes coordinated are terminal airspace and airport 

surface route planning, better utilization of resources, minimizing delays in crossing 

runways, and better aircraft trajectory execution. 

• Maintain airport system throughput in reduced visual conditions 

− Benefit arises from the use of better surveillance and navigation technologies (not 

constrained by weather on runway, taxiways, or terminal) and better flow management. 

• Increase controller productivity 

− Benefit arises from the use of automation tools. 

• Reduce aircraft fuel burn 

− Benefit arises from more efficient routing and coordination in terminal airspace and 

airport surface resulting from better planning, prediction, and aircraft control integrated 

for terminal airspace and surface. 

5.3.4 Required technology and infrastructure for coordination and integration 

among airport surface and terminal airspace operations 

The following technology and infrastructure items are assumed to be provided for the concept 

elements. Benefits include: 

• Better communication tools, including digital data link 

• Better surveillance and navigation technologies 

• Improved weather prediction 

• 4D trajectory technology on ground and on aircraft 

• Better information sharing (i.e., SWIM). 

5.3.5 Potential research topics for coordination and integration among airport 

surface and terminal airspace operations 

A potential research question for the sub-elements listed in this subsection is presented below. 

• How to obtain better prediction of pushback time and ETA at arrival fix? In the context of 

probabilistic information, how to better characterize the pushback time and ETA at arrival 

fixes for coordination and integration purpose? 
34 

5.4 Coordination and Integration among Metroplex Operations 

Sections 5.1, 5.2, and 5.3 discussed integrated operations within and among the surface and terminal 

airspace concept elements. This section presents integration and coordination activities for 

metroplex operations. Metroplex operations are more complicated than those for a single airport 

since all the issues discussed in Sections 5.1 through 5.3 are involved, plus the integration and 

coordination required among multiple airports. 

5.4.1 Constraints and problems for coordination and integration among metroplex 

operations 

Metroplex operations include the same constraints as the integrated airport and terminal operations. 

In addition, there are aircraft flying into and out of the metroplex airports instead of just the single 

airport, and there are overlapping operations among the airports in the metroplex to utilize the shared 

terminal airspace. Coordinating all the terminal airspace arrivals and departures with the availability 

of capacity at the individual airports will be complex. 

5.4.2 Description of coordination and integration among metroplex operations 

The metroplex coordination and integration element directs the different planning processes among a 

network of airports and with their combined terminal airspace, while incorporating constraints from 

en route airspace and the System Command Center. The metroplex coordination and integration 

element provides the optimal 4D trajectory for each arrival and departure flight based on the 

constraints imposed by each airport and its terminal planning elements. 

The metroplex coordination and integration element will consider user preferences, and inputs from 

en route airspace and AOC. Inputs include the flight plan, runway preference, gate assignment, 

aircraft position, type, equipage, current aircraft weight, other ground traffic, en route sector 

capacity, and the Airspace Flow Program imposed by System Command Center. These inputs will 

be used as limitations during the planning process. 

The metroplex coordination and integration element is similar to the integrated airport and terminal 

coordination and integration element. The major enhancement is inclusion of the interactions 

between streams of flights into and out of several airports instead of a single airport, as well as 

coordination of runway management among the airports in the metroplex accounting for demand 

and weather conditions at the individual airports. 

y Metroplex Flow Constraint

The metroplex flow constraint sub-element will coordinate the flow constraints associated 

with overall metroplex airspace and the runways at the metroplex airports, and align them as 

an aircraft flies through shared terminal airspace. 

• Metroplex Flow Management 

The metroplex flow management sub-element will coordinate the metroplex airspace 

configuration management and runway configuration management at the metroplex’s 

airports to coordinate the overall flow of the metroplex. 
35

• Metroplex Trajectory Planning 

The metroplex trajectory planning sub-element plans terminal airspace arrival and departure 

4D trajectories that account for demand at each airport, each airport’s runway capacities, 

weather in the metroplex terminal airspace and at each airport, and other constraints. It also 

plans, to the extent practical, the taxi routes at each airport so that they are coordinated with 

that airport’s arrivals and departures. The terminal airspace trajectories may be in close 

proximity to each other. The trajectories will be implemented in a manner that will ensure 

safe separation in normal and off-nominal operations, and will accommodate recovery from 

off-nominal operations. 

• Metroplex Tactical Control 

The metroplex tactical control sub-element will actively monitor conformance of each 

aircraft in the metroplex to its planned trajectory. If an aircraft is out of conformance, this 

sub-element will coordinate an action to cope with the discrepancy between planned and 

actual trajectories while accounting for the existing traffic in the metroplex. 

5.4.3 Benefits from coordination and integration among metroplex operations 

Benefits of the above concept elements are: 

• Increase system throughput and reduced delay 

− Benefit arises from better coordination of terminal and airport planning processes among 

airports in the metroplex that may otherwise impose conflicting constraints and result in 

reduced throughput and increased delay. Examples of coordinated processes are planning 

terminal and airport routes, better utilization of resources (e.g., decreased runway 

occupancy time), minimizing delays in runway crossing, minimize interactions between 

flights to or from different airports in close proximity, and better aircraft trajectory 

execution. 

• Maintain metroplex system throughput in reduced visual condition 

− Benefit arises from the use of better surveillance technologies (not constrained by 

weather on runway, taxiways, or terminal) and better flow management. 

• Increase controller productivity 

− Benefit arises from the use of automation tools. 

• Reduce aircraft fuel burn 

− Benefit arises from more efficient routing and coordination in terminal and airports 

resulting from better planning, prediction, and aircraft trajectory execution. 

5.4.4 Required technology and infrastructure for coordination and integration 

among metroplex operations 

The following technology and infrastructure items are assumed to be provided for the concept 

elements. Benefits include: 

• Better communication tools, including digital data link 

• Better surveillance and navigation technologies 
36 

• Improved weather prediction 

• 4D trajectory technology on ground and on aircraft 

• Better information sharing (i.e., SWIM). 

5.4.5 Potential research topics for coordination and integration among metroplex 

operations 

Some potential research questions to provide the sub-elements listed in this subsection are presented 

below. The list is not definitive; it is included to aid in identifying research needs. 

• How to efficiently and safely recover from off-nominal situations in the NextGen metroplex 

airspace? 

• How do system operators effectively monitor the conformance of multiple aircraft for 

multiple airports? 

5.5 Overarching Research Topics for Integration and Coordination 

As was mentioned previously, many issues related to integrating automation within and among 

surface and terminal airspace operations are similar. Therefore many research questions on 

coordination and integration are listed once in this subsection. The list is not definitive; it is included 

to aid in identifying research needs. 

• Understand the dynamics of the interactions among surface, terminal airspace, en route 

airspace, and metroplex operations. 

− What is the impact of a new trajectory due to the renegotiation of the 4D trajectory? 

− How, and how often, can 4D trajectories be negotiated and renegotiated? 

• Many objectives are possible for coordinating and integrating airport operations. For 

example, is the objective to maximize the throughput of the system, to be equitable to all 

users in the system, or to maximize the throughput while subject to some equity constraints? 

The objective will give direction on how the coordination and integration will be done. Some 

issues regarding objectives are: 

− How would a particular objective impact aircraft with different equipage levels? 

− What is the trade-off for using different objectives? 

− What type of user preference requests can be accommodated by the coordination and 

integration function and how? 

− What is the optimal time horizon of each planning function? 

− What are the different ways to coordinate competing objectives (e.g., between the local 

and national level)? 

• Even with a well-defined objective, there could be several possible actions to achieve the 

desired result. Which ones should be considered feasible in the coordination and planning 

process? For example, can a coordination and integration automation aid suggest the 

slowdown of an aircraft by ten minutes from its predicted arrival time so as to optimize the 
37

surface traffic? Should the actions be bounded to ensure system stability? What is the set of 

feasible actions? 

− There are multiple parties operating in, or interfacing with, the airport (e.g., en route 

centers, TRACON, airports, and AOC). Each party may have different goals and 

objectives. Since there may be several actions to achieve the same desired results, what is 

the process to enable negotiation among the different parties to arrive at the optimal 

action? 

• Many control actions are likely to be feasible, and the reality of how to construct or identify 

the best action set, with limited computational power and limited time, is a research area. 

Each aircraft goes through several different operations and each operation has several 

possible control actions. The total number of possible control action sets grows exponentially 

as a function of the number of aircraft. How can the best combination of control actions be 

constructed for each aircraft? 

• Off-nominal events will always occur and not everything will happen as anticipated. In a 

coordinated and integrated system, many operations are coupled together. If an off-nominal 

event forces an operation to deviate from the plan and schedule, the event may also force 

other operations to deviate from their plans and schedules. A research issue is how to 

coordinate and integrate airport operations when an off-nominal event occurs so that there 

will be minimal impact to other operations 

• The coordination and planning process is likely to be dynamic when dealing with offnominal events. During off-nominal events, it is necessary to consider the different possible 

control action sets in real-time. A fast and accurate model is necessary to evaluate the control 

action. Currently, such a model for the airport surface and terminal airspace is lacking, and 

thus could be a research issue for the NextGen-Airportal Project. 

• Current operations are planned based on deterministic input information (e.g., aircraft 

pushback time at 9:36 a.m.). The information often turns out to be inaccurate and highly 

dynamic. In the future, input information may be presented as a probability distribution. 

Future operations can then be planned based on probability distributions of input data (e.g., 

using a probability density function that describes the likelihood of when an aircraft may 

pushback over a period of time). Research is needed on how to effectively present and utilize 

the probabilistic input information. This research topic can be generalized to decisionmaking under uncertainty. 

• There is a need to optimize the parts that make up surface operations to provide maximum 

capacity practical while addressing safety and environment considerations. There is a similar 

need to optimize across the components of terminal airspace operations and across surface 

and terminal operations. An investigation of possible optimization techniques for different 

parts of surface and terminal airspace operations, how to combine these different surface and 

airspace local optimizations into integrated, global optimized operations, and how to deal 

with uncertainty in these optimizations are subjects for research. 

• There could be multiple stakeholders in the coordination and integration process with 

different, or even competing, interests. Procedures and rules may be necessary to establish 

effective and equitable collaborative-decision processes for different types of negotiations. 
38 

Research is needed on the proper decision-making and negotiation procedures and their 

impacts. 

− What are the most effective ways to negotiate or renegotiate 4D trajectories? 

• Airport operations are integrated and coordinated. Failures in either avionics or systems used 

by the Air Traffic Service Provider (ATSP) are possible. Graceful failure of the future 

system is a desired characteristic. What is considered graceful failure? What are the different 

ways to achieve a graceful failure? What are the tradeoffs of the different ways to achieve a 

graceful failure? 

6 SMALL AIRPORTS 

Sections 3.0 through 5.0 have dealt primarily with large airports and metroplexes. Some of the 

airports in the metroplexes may be smaller airports. Future air transportation is also likely to bring 

more point-to-point service to airports in small cities removed from major metropolitan areas or 

airports in rural areas. These small airports may not have towers to ensure safe operations as usage 

increases, or to provide service during poor visibility. Commercial aircraft serving these small 

airports may include commercial jets, regional jets, commuter piston-driven aircraft, and very light 

jets (air taxi service). In addition, general aviation and business aircraft will likely be users of 

smaller airports, as may cargo aircraft of various sizes. There also needs to be the means to ensure 

safety and service in poor weather. 

It is noted that the concept elements discussed in this section on smaller airports are applicable to 

regional and small airports that are part of a metroplex and to such airports removed from 

metroplexes. 

For lower-demand airports, staffed or automated virtual towers may be implemented, enabling 

services equivalent to those provided by traditional towers at more airports than is affordable today 

and/or for extended hours of service. 

6.1 Constraints and Problems for Small Airports 

Small airports without towers will have trouble handling an increase in traffic or traffic in poor 

visibility. This will inhibit an increase in direct point-to-point routes to such small airports and the 

use of such small airports in metroplexes. 

6.2 Description of Small Airports 

Aircraft will be able to arrive and depart from small airports safely and in weather conditions that 

will replicate the types of weather for which major airports will have EVO. There are a variety of 

ways in which services can be provided at small airports to provide safe operations in adverse 

weather conditions. Some possible examples are listed below. These need to be investigated to 

determine those that are best suited to various types of small airports. 
39

• Airports that serve a large enough air traffic base will have tower-provided ATC services 

with some sub-elements listed in Sections 2.0 through 5.0, as appropriate. 

• ATC services for arriving and departing aircraft can be provided by a staffed virtual tower, 

whereby tower-type services are supplied by remotely-located human controllers supported 

with advanced airport sensors and supporting airport automation at the small airport. 

• Automated ATC services, in what might be called an automated virtual tower, could be 

provided to a nontowered airport and its surrounding airspace for traffic flying into and out 

of the airport. Aircraft utilizing such an automated virtual tower airport would likely need a 

minimum equipage level, such as 2-way digital radio and a Mode C transponder. It is 

possible for automated ground-based separation assurance to be used for properly equipped 

aircraft. 

• Another option for nontowered airports is for aircraft to operate in a self-separating mode. It 

may be possible to develop equipment for such self-separation operations to help ensure safe 

operations under many weather conditions. 

6.3 Benefits from Small Airports 

Benefits of the above possible concept elements for improving capacity at small airports are: 

• Provide safe operations at small city and rural airports 

− Benefit arises from alternative ways to provide services to ensure separation between 

arriving and departing aircraft as usage of the small airport increases. 

• Provide operations in many adverse weather conditions at small city and rural airports 

− Benefit arises from alternative ways to provide services during poor visibility to ensure 

separation between arriving and departing aircraft and to ensure aircraft land on and take 

off at safe locations on the runway. 

6.4 Required Technology and Infrastructure for Small Airports 

The following technology and infrastructure items are assumed to be provided for the concept 

elements. Benefits include: 

• Equipment (e.g., sensors, communications, hardware, etc.) to provide virtual towers, whether 

staffed or automated. 

• Aircraft-based equipage for operations with staffed virtual towers, automated virtual towers, 

or self-separation at nontowered airports. 

• Ground transportation and terminal facilities to serve passengers at small city and rural 

airports. 
40 

6.5 Potential Research Topics for Small Airports 

Some potential research topics for the sub-elements listed in this subsection are presented below. 

The list is not definitive; it is included to aid in identifying research needs. Crosscutting research 

issues for human factors, safety, and environment are described in Section 8.0. 

• Identification and development of any algorithms and procedures for operations at airports in 

small cities and rural areas, whether staffed virtual tower, automated virtual tower, or selfseparation airports. 

• Controller interface issues for managing operations remotely for multiple airports 

• Impact of traffic growth at small city and rural airports on hub airport traffic demand and 

operations. Will there be a change in city-pair service that affects hub airports? 

7 ADVANCED CONCEPT ELEMENTS 

Section 7.0 describes concept elements that are likely to apply further in the future than those 

described in Sections 2.0 through 6.0. One is adaptive metroplex operations where an aircraft’s 

arrival airport within a metroplex can be changed dynamically prior to, or during, the flight. Another 

is a set of planning tools to design airport layouts that take advantage of the technology discussed in 

this document. Adaptive metroplex operations will not likely occur until options for improving 

operations at traditional metroplexes are exhausted. The airport design tools would be useful for new 

airports and for major reconfigurations or additions to existing airports. 

7.1 Adaptive Metroplex Operations 

Metroplexes comprised of multiple airports are described in Section 5.4. In this case, scheduled 

flights used the same airports within the metroplex for each flight. Section 7.1 describes a metroplex 

as a set of integrated airports that operate in some sense as a very large airport. The biggest 

difference with the adaptive metroplex is that aircraft arriving at the adaptive metroplex are not 

prescheduled to arrive at a specific airport. Rather, aircraft are dynamically assigned, either before 

take-off from the originating airport, or during flight, to an arrival airport within the metroplex. This 

flexibility maximizes the capacity of the metroplex as a whole. If one airport has restricted capacity 

due to weather (e.g., a passing thunderstorm), aircraft can be assigned dynamically to land at another 

airport in the metroplex. 

There are numerous hurdles for such an adaptive metroplex to be acceptable to aircraft operators, 

pilots and passengers. One hurdle to overcome is local transportation of passengers to and from 

whichever airport within the metroplex their flight might depart from or arrive at. Such a local 

transportation network might include a central gathering terminal from which passengers are 

dispersed to, or gathered from, their departing and arriving airports, and rapid transportation between 

airports for passengers transferring between aircraft. Airlines would need aircraft turnaround and 

maintenance services. Baggage and gate services for passengers would be needed. These and other 
41

aspects are discussed further below as concept elements for the adaptive metroplex. The concept of 

adaptive metroplex goes beyond what is currently being considered by NextGen. 

7.1.1 Constraints and problems for adaptive metroplex operations 

The use of metroplexes with flights assigned to specific airports, as discussed in Section 4.4, is 

likely to provide sufficient airport capacity for some time to come. However, given the difficulty in 

building new airports, and in adding runways to existing airports, even metroplexes using existing 

airports may reach capacity as air travel demand reaches three times that of today. Also, when the 

demand at a metroplex nears the available capacity, the metroplex becomes susceptible to 

congestion and delays when weather or demand patterns cause a perturbation in the available 

capacity. Thus, some way of handling the large demand and weather perturbations would be useful. 

The concept described in this section, adaptive metroplex, can provide flexible metroplex operations 

to support a higher capacity and to handle perturbations of weather and demand. 

7.1.2 Description of adaptive metroplex operations 

Section 5.4.2 describes several concept elements related to flight operations for a metroplex. The 

flight-operation elements that also apply to the adaptive metroplex are precisely flown paths, flexible 

flight paths, increased TFM planning horizon, increased capacity at uncontrolled airports, route 

planning and execution under adverse weather, and airport clustering strategies. 

The additional concept sub-elements that apply to the adaptive metroplex are described in this 

subsection. 

• Scheduling aircraft to airports 

Aircraft will be assigned dynamically to the airport within an adaptive metroplex at which 

they will land, either before takeoff or during the flight. This decision will be made based on 

the availability of airports within the adaptive metroplex, and the preference of the aircraft 

operator. The preference of the aircraft operator might be to always land at the same airport. 

However, for adaptive metroplex to be feasible, there needs to be flexibility to land at 

another airport if the desired airport is not available. The aircraft operators’ preferences in 

the adaptive metroplex concept are assumed to be for a particular airport given circumstances 

unique to the moment. There will be automation aids to do the scheduling of aircraft to 

airports. There will be a minimum time before landing after which there cannot be a change 

in the arrival airport within the adaptive metroplex. 

• Ground transportation network 

A local ground metroplex transportation network will transport passengers to and from their 

arrival/departure airport as needed. Part of this concept sub-element might include one or 

more central gathering stations where passengers can park, check their baggage, and wait 

until their departure airport is announced. Then they will use the local ground metroplex 

transportation network to travel to their departure airport. Arriving passengers will pick up 

any luggage and leave their arriving airport or will travel to a central gathering station to pick 

up their luggage, meet relatives or friends, retrieve their car from parking, or take other 

means of transportation to their final local destination. These central gathering stations could 

be colocated at airports, city centers, or other locations as appropriate. A metropolitan area 

could contain more than one central gathering station. 
42 

The local ground metroplex transportation network might be a rapid rail system, a network of 

rapid, dedicated buses, an airborne-based system, such as helicopters or vertical take-off 

aircraft, a new technology such as Personal Rapid Transit (PRT), or a combination of any or 

all of these systems. 

• Aircraft servicing 

Currently airlines service their own aircraft. Since the number and type of an airline’s aircraft 

at any particular airport in the adaptive metroplex may vary from day-to-day, other concepts 

for servicing aircraft will likely be needed from those used today. Aircraft servicing might be 

provided by a common company for all aircraft using a particular airport. 

• Baggage and terminal passenger services 

As with aircraft, baggage and passenger services within the terminal at any airport would 

likely be provided by a common company. Concepts for transferring baggage to a central 

gathering station, to a connecting flight at the same or different airport, or arranging for pickup by passengers at that airport, would be needed. Similarly, means to plan passenger 

transfers, and to communicate to each passenger what they are expected to do, would be 

needed. 

• Very advanced concepts for adaptive metroplexes 

The above concept elements, while a departure from today’s airline operations, can be 

viewed as an extension of current practices. These may be concept sub-elements that are very 

different from today that bear investigation. One example is that the airline dynamically 

assigns an aircraft to a particular origin/destination flight based on the airport within the 

metroplex where the aircraft will land before its next flight. Thus, it would be known only 

shortly before a flight what aircraft, and possibly what crew, would be assigned to a 

particular flight. Another example is that an airline might use an aircraft owned by another 

airline for one of its flights. This is a variation of the run-through of railroad locomotives 

used by today’s railroads. The locomotive supplied by a particular railroad at the origin of a 

train’s journey will stay with the train and be operated by a crew of another railroad when the 

train enters that railroad’s tracks. Such an operation would be more complicated for airlines 

since airlines have different cockpit setups and flight procedures. There would need to be 

more standardization of cockpits and airline operations than today. These aspects are 

illustrations of ideas to explore. 

7.1.3 Benefits from adaptive metroplex operations 

Benefits of the above concept elements are: 

• Maximize capacity provided by airports in a metropolitan area by reacting to weather and 

demand variations 

− Benefit arises from flexibility of directing an arriving aircraft to an airport that can handle 

the flight when another airport originally planned as the destination is unavailable. 
43

• Maximize flexibility in airspace usage depending on weather and demand 

− Benefit arises from flexibility of directing an arriving aircraft to use available airspace, 

when some airspace might be restricted due to weather, since the aircraft can land at an 

airport that has airspace available to it. 

7.1.4 Required technology and infrastructure for adaptive metroplex operations 

The following technology and infrastructure items are assumed to be provided for the concept 

elements. Benefits include: 

• Local ground metroplex transportation network to transport passengers among airports and 

central gathering stations 

• Central gathering stations for passengers to enter and exit the adaptive metroplex to begin or 

end air journeys 

• Common aircraft servicing facilities at airports in the adaptive metroplex 

• Baggage handling and transfer facilities. 

7.1.5 Potential research topics for adaptive metroplex operations 

Some potential research questions for the sub-elements listed in this subsection are presented below. 

The list is not definitive; it is included to aid in identifying research needs. Crosscutting research 

issues for human factors, safety, and environment are described in Section 8.0. 

• What are incentives and requirements for a successful adaptive metroplex operation? This 

includes examining incentives from the viewpoint of all stakeholders, such as air carrier 

operators, passengers, airport operators, local government agencies, etc. 

• How will final airport destinations be decided and how will negotiations be conducted? 

• How will changes in airport destinations be implemented and flight routes changed? 

• How will arrival routes and departures for multiple airports in a metroplex be planned? 

• How close can arrival and departure paths be located for separation purposes? 

• How can arrival and departure paths in a metroplex be dynamically changed to account for 

changes in weather and in constraints at particular airports? 

• How can metroplex operations be planned and executed under adverse weather? 

• What information should be shared among AOCs, flight deck, and air traffic service 

providers at airports, terminal airspace, en route airspace, and flow control facilities? 

7.2 Advanced Airport Design Tools 

For many of the proposed concept elements to succeed, a greater flexibility and maneuvering 

capability is needed than currently exists at major hub airports. Taxi planning, in particular, benefits 

from establishing 4D paths based on a set of optimization criteria, and is not merely first-come, firstserved scheduling. Implicit in these advanced operations is the ability to manipulate the order of 

departures and arrivals at the gate. This, in turn, requires a level of controllability that may not exist 
44 

at all airports. Does the airport have the needed taxiways to resequence the traffic? Does it have 

holding/staging areas where aircraft can be held awaiting their gate area departure, rather than 

occupying a gate needed for an arriving aircraft? Are there alternative taxi routes available, like 

perimeter taxiways, to avoid delays and congestion at runway crossings? These questions can be 

answered by airport designs that utilize the new concept elements described in this document. 

7.2.1 Constraints and problems of advanced airport design tools 

Airports in 20 to 25 years will operate with technologies derived from many of the concept elements 

in this document. New airports, and existing airports that have changes in their runways, taxiways, 

or other surface infrastructure, will be able to capture more capacity and efficiency benefits if the 

airports are designed to utilize concept elements appropriate to each airport’s particular requirements 

and constraints. 

7.2.2 Description of advanced airport design tools 

The focus is the design of airports that will fully capitalize upon innovative taxi-route planning. The 

ground rules to conceive and develop tools are as follows: (1) a clean-sheet-of-paper design, and 

(2) the surface sensors and automation technologies are in place to enable a radar-like, highly 

automated environment, rather than out-the-window observation and manual control. 

There is primarily one operational aspect to the Advanced Airport Design Tools concept element, 

which is: 

• New airports and existing airport changes designed by Advanced Airport Design Tools 

Airports will be designed to take maximum advantage of new automation for airport 

operations on the surface and in terminal airspace. Examples of airport infrastructure that 

will be designed by such a tool include staging areas, perimeter taxiways, new taxiways, 

high-speed exits from runways, deicing facilities, runway layout, CSPR, noise and emissions, 

and even some innovative mechanisms for manipulation and control of surface traffic. The 

design tools will also account for human performance compatibility, and the appropriate 

roles of humans and automation in the operation of the resulting airport. 

7.2.3 Benefits of advanced airport design tools 

Benefits of the above concept elements are: 

• Increased surface capacity through better design of airport surface layouts 

− Benefit arises from more surface capacity and more efficient taxi routing and movements 

that are due to improved design of taxiway, ramp areas, and runways to take advantage of 

the concept elements. 

7.2.4 Required technology and infrastructure for advanced airport design tools 

The following technology and infrastructure items are assumed to be provided for the concept 

elements. Benefits include: 

• Technology to provide location information for aircraft on runways, taxiways, and for other 

objects during poor visibility 

• Surface and terminal airspace surveillance to allow less separation between taxiing aircraft 
45

• Improved weather predictions and information on current weather 

• Better communication tools, including digital data link 

• Sensors to monitor noise and air quality levels. 

7.2.5 Potential research topics for advanced airport design tools 

Some potential research questions for the sub-element listed in this subsection are presented below. 

The list is not definitive; it is included to aid in identifying research needs. Crosscutting research 

issues for human factors, safety, and environment are described in Section 8.0. 

• What attributes of airports should be addressed in the design functions of the tool? 

• What concept elements of future operations should be addressed in the design tool? 

• How should the design tool operate and what form should the user interface take? 

8 CROSSCUTTING ATTRIBUTES OF CONCEPT ELEMENTS 

There are several research topics related to the operation of future concepts for airport operations 

that cut across the concept elements presented in Sections 2.0 through 7.0. These include human 

factors, safety, and environment. These aspects are discussed in Section 8.0. 

8.1 Human Factors 

The human-automation roles and interfaces under future airport operations raise several key human 

factors issues. This section gives a summary overview of the drivers of change for humanautomation interactions and potential human factor issues. 

8.1.1 Description of human factors 

A study of the following attributes, and their implications, will support the allocation of roles in 

conducting airport tasks among humans and automation, and will support the design of the humans’ 

tasks. 

• More Precision – This refers to tighter tolerances for aviation operations, including the use 

of time-based metering to achieve assigned 4D trajectories (i.e., position in both space and 

time), reduced separation, and EVO. The precision would be enabled by new surveillance 

technology with increased accuracy, improved weather predictions, improved traffic 

displays, and other technological advances. Reducing separation and other tolerances will 

result in the ability of more aircraft to pass through a given airspace in a given time period 

and in more aircraft landing at an airport in a given time period. 

Human factors implications under more precision will arise from precise actions that need to 

be taken at precise times (both for safety and to achieve capacity benefits) and from there 

being less time to react to off-nominal situations. 
46 

• More Information and Information Sharing – This refers to the increased information to be 

available in the NAS, as well as the sharing of information among all users. More 

information would enable the more efficient operation of the NAS. 

Human factors implications under more information and information sharing will arise from 

more information to access, interpret, and judge whether to use. 

• More Automation – This refers to the computer-based technology for planning and execution 

of ATM/ATC. More automation enables taking advantage of the greater precision, and of the 

availability of more information. 

Human factors implications under more automation will arise from extensive use of decision 

support tools and from automation roles ranging from automation that aids the human 

execution of tasks, to the automation of entire tasks. 

• Extended Horizon for Planning and Operations – This refers to the planning of ATM/ATC 

operations over a larger geographic region, and longer time horizon, than today. The 

extended planning horizon would permit increased optimization, and hence greater efficiency 

and capacity. 

Human factors implications for the allocation of flight deck tasks to human and automation, 

under an extended horizon for planning and operations, will arise from humans and 

automation needing to be aware of conditions (e.g., weather, traffic levels, special use 

airspace (SUA)) over a larger geographic region and longer time horizon than today, and 

needing to remember to conduct actions farther into the future than today. 

• Collaborative Decision-Making (CDM) – This refers to decisions made through negotiations 

among users and ATSPs. CDM will give users a greater role in ATM and provide more 

efficiency. More CDM implies more user requests, and negotiation between flight deck and 

ATSP about how to honor these requests. 

Human factors implications under CDM will arise from more user requests and more 

negotiations. 

• Flexibility – This refers to dynamically changing ATM/ATC airspace configuration and 

operations in response to changing conditions, such as weather, demand, and security needs. 

Flexibility enables more efficient handling of changing conditions in the NAS, thus enabling 

greater capacity. 

Human factors implications for more airspace flexibility will arise from the flight deck 

operating in more, and in changing, modes of operation. 

8.1.2 Potential research topics for human factors 

Research topics for human factors that arise from the above discussion include: 

• Workload for different operations to be conducted during airport operations, during transition 

between modes of operation, and the ability to carry out actions at precise times 

• Understandability and clarity of tasks in any mode of operation 
47

• Suitability and stability of tasks under different modes of operation and for emergency 

response actions under different modes of operation 

• Robustness of human performance to contingencies 

• Prospective memory issues, including remembering what to do in a particular mode of 

operation; remembering roles of automation, what the automation is doing now, and what it 

will probably do next; knowing who is responsible for overall safety; and remembering a 

response to an anomalous situation while in a different mode of operation 

• Alertness to respond to new information and indicators 

• Completeness and clarity of steps for transition between modes of operations 

• Conveying of information, including the information display and what information to push 

and to pull 

• What tasks to allocate, and how to allocate tasks between humans and automation in future 

airport operations when automation will have more functionality than today, and modes of 

operation will change more frequently than today 

• When should task allocations between humans and automation change and how should the 

transition should be designed 

• Transition from automation to humans to handle anomalies 

• How to conduct training for new roles and responsibilities of humans. 

8.2 Safety 

It will be necessary to reduce the accident rate in the future as air traffic levels grow. Runway 

incursion accidents, in particular, have been a continual focus of the FAA. 

8.2.1 Description of safety 

While NASA’s Aviation Safety Program is aimed directly at improvements to aviation safety, the 

NextGen-Airportal Project (within the Airspace Systems Program) shares a complimentary 

consideration to at least understand the safety implications of its research. This includes safety 

considerations of human-automation roles, resultant procedures from new concept elements, and 

technology performance including possible failures. 

8.2.2 Potential research topics for safety 

Safety implications of the concept sub-elements being developed by individual research activities 

may include: 

• Impacts of new operations and procedures on safety 

• Impacts of new automated planning and operations on performance of controllers and pilots 

related to safety 

• Failure mode impacts on safety. 
48 

8.3 Environment 

As the number of flight operations continues to increase, noise and emissions will become 

increasingly problematic. Unless environmental issues are addressed, higher-capacity operations 

may result in increased noise and emissions levels, which in turn may limit any potential capacity 

gains. The next generation of aircraft will be more environmentally friendly, but 20 years from now, 

the aircraft fleet at major hubs will still include a substantial number of today’s aircraft. Hence, 

environmental concerns must be considered as a component of research activities. 

8.3.1 Description of environment 

Strategies must be developed to keep environmental impact at least within today’s bounds (i.e., 

based on current traffic levels) even as the capacity increases. This means an average reduction in 

noise and emissions, keeping noise contained within the airport boundary, or the routing of traffic 

over areas away from populated areas. While increased capacity at airports is likely to bring 

increased noise and emission impacts, concept elements in this document have the potential to help 

mitigate these adverse environmental impacts. These concepts enable more flexibility for executing 

more noise-sensitive routes, such as funneling traffic over areas with low population density, routing 

older aircraft via less sensitive noise areas, using runway configurations with lower noise impact, 

and modifying routing based on changes in wind direction. Enabling aircraft to fly fuel-efficient 

routes will help to reduce emissions. Environmental constraints for noise and emissions can be 

integrated into the airport planning and operational processes through environmental advisory tools. 

There are broader issues related to the environment that need to be addressed, and are identified by 

NextGen, including water quality, energy intensity, and global climate change. There are emerging 

topics of discussion at the international level concerning emissions trading schemes whereby 

operators can buy or sell emissions allowances. However, these issues are beyond the scope of this 

document. 

8.3.2 Potential research topics for environment 

Research topics for environment that arise from the above discussion include: 

• Relationship of concept elements in this document to environmental impacts of noise and 

emissions. 

• Understand the environmental impacts resulting from the amount of time aircraft operate on 

the surface under different 4D taxi trajectories, including taxi speed and acceleration, and 

from aircraft operating in the terminal airspace under different 4D terminal airspace 

trajectories, including engine acceleration for departure and power needs for descent. These 

include examining the types of trajectories that can reduce population exposure to noise and 

emissions, as well as reducing the noise and emissions generated from aircraft. 

• Examine how to incorporate impacts on environment into the design of individual concept 

elements for airport capacity increases. 

• Software tools that analyze environment impacts of airport operations under alternative 

concept elements. 

• Understand how real-time noise and emissions information from sensors could be used by 

surface and terminal airspace trajectory planning tools to reduce environmental impacts. 
49

8.4 System Failure 

The previous presentations of concept elements have included responding to off-nominal situations, 

such as a missed approach, deviation from a flight trajectory, or deviation from a taxi route. More 

serious events that affect airport operations more extensively, and for a longer time period, might be 

considered to be system failures. System failure is defined as a significant difference between 

planned and realized operations. A system failure can be caused by human error, hardware/software 

failure, accident, disaster, or severe weather (significant weather disruptions are included as system 

failures since the system is unable to provide its intended services). As operations in the NAS 

become more precise and interdependent in the future, system failure can have a significant impact 

on the operations of the NAS. Ways to minimize the occurrence of a system failure, to mitigate the 

consequences of a failure, or to recover from a failure, is an important area of research. 

8.4.1 Description of system failure 

When a system failure occurs, there may be a significant impact on the NAS. With closer separation 

between aircraft in the future, there is less time to react to a failure in equipment, whether ground 

ATC service equipment or equipment on the aircraft. Major delays can arise in the NAS, disrupting 

many passengers, when a snowstorm moves unexpectedly slow across a major hub over a holiday 

weekend. With two or three times the aircraft flying in the future as today, and with the precision 

and interactions required in the future air transportation system, research is needed to minimize the 

occurrence and potential impact of a system failure. 

Examples of general topics related to system failure include degradation failure to allow time for 

recovery; new equipment, software-based aids, and procedures robust enough to operate in a variety 

of conditions; and consideration of human-automation roles and interactions to prevent system 

failures and aid recovery should a system failure occur. There is a need to study where system 

failures might occur in future operations and what the consequences might be. This requires better 

understanding of the increasing complex NAS dynamics and interdependences between different 

components in the NAS. 

8.4.2 Potential research topics for system failure 

Research topics for system failure that arise from the above discussion include: 

• Causes of system failures. In particular, examine interdependencies between different 

planning processes and NAS components. 

• What does graceful failure mean in the future air transportation system? Are there any 

tradeoffs between the different ways to achieve graceful failure? What are the metrics that 

can measure a graceful failure? What are the implications of the use of different metrics? 

• Design within new automation to detect conditions that are precursors to system failure 

• Design within new automation to minimize the likelihood of system failures from human 

errors, such as verifying with the human user if they want to perform an action that the 

automation senses is questionable, or automation reminding the user of the current mode of 

operation and what tasks are to be performed 

• Contingency planning 

• Recovery from a system failure 
50 

• How would CDM work during a system failure? How can CDM minimize the impact of 

system failure? 

• Equity among users during system failure. 

9 FURTHER DEVELOPMENT AND EVOLUTION OF THE AIRPORTAL CONCEPT 

Concept elements have been presented for the surface, terminal airspace, integrating and 

coordinating operations between the surface and terminal airspace and with the en route airspace, 

small airports, and advanced concepts. Changes, additions, and/or deletions to this initial set of 

concept elements are expected as research activities within and beyond the project yield results over 

time. The set of concept elements may evolve with both changes in the “integration” of research 

activities across Airportal and Airspace Project research focus areas and collaboration with the 

JPDO and community partners. 

Moreover, as research progresses and knowledge is gained, the concept document is expected to 

evolve into more of a concept of operations including such topics as roles and responsibilities of 

participants and supporting automation/technologies, how services will be provided, and how 

aircraft would operate in the future system. In the meantime, this initial version provides a common 

framework and context for defining and coordinating research activities that are and will be 

conducted by the NextGen-Airportal Project. 
51

APPENDIX A – MAPPING OF AIRPORTAL CONCEPT ELEMENTS 

Mapping of Airportal Concept Elements to the Airportal and Airspace Project Research Focus Areas 

where Primary Contributions Reside (or would reside if funded) 

NextGen-Airportal Research Focus 

Areas: 

SESO: Safe and Efficient Surface 

Operations 

CADOM: Coordinated Arrival and 

Departure Operations 

Management 

ATIM: Airportal Transition and 

Integration Management 

NextGen-Airspace Research Focus Areas:

TPSU: Trajectory Prediction, Synthesis, 

and uncertainty 

PBS: Performance-Based Services 

DAC: Dynamic Airspace Configuration 

TFM: Traffic Flow Management 

SA: Separation Assurance 

SDO: Super Density Operations 

SLDAST: System-Level Design, Analysis, 

and Simulation Tools 

Airportal Concept Elements Related Airportal and Airspace 

Research Focus Areas 

3.0 

Surface Concept 

Elements 

3.1 Runway Management SESO, CADOM, TFM 

3.2 Taxi Route Planning SESO 

3.3 Surface Super Density Operations SESO 

3.4 Surface Weather and 

Environmental Planning 

SESO 

4.0 Terminal 

Concept Elements 

4.1 Precise Spacing and Separation 

Assurance 

CADOM, SDO 

4.2 Dynamic Airspace Management DAC, SDO 

4.3 Adapting Operations to Conditions CADOM, SDO 

4.4 Metroplex Operations ATIM, SDO 

5.0 Coordination 

and Integration of 

Concept Elements 

5.1 Coordination and Integration among 

Airport Surface Operations 

SESO 

5.2 Coordination and Integration among 

Terminal Airspace Operations 

CADOM, SDO 

5.3 Coordination and Integration among 

Airport Surface and Terminal 

Airspace Operations 

ATIM, SESO, CADOM, SDO 

5.4 Coordination and Integration among 

Metroplex Operations 

ATIM, SDO, TFM 

6.0 

Small Airports 

6.0 Small Airports None6

 (SESO, CADOM, ATIM) 

7.0 Advanced 

Concept Elements 

7.1 Adaptive Metroplex Operations ATIM 

7.2 Advanced Airport Design Tools None (ATIM, SESO) 

 

6

 Currently, there is no Airportal or Airspace Research Focus Area (RFA) on this Airportal Concept Element. If this 

concept element is funded, the RFAs where the primary contribution would reside are listed in the parenthesis. 
52 
APPENDIX B – SUMMARY OF CONCEPT ELEMENTS AND SUB-ELEME

Appendix B summarizes the concepts in one multipage table. The table has three columns. The first column lists and summarizes the constraint or problem addressed by the concept element. The second column lists the sub-ele

element. The third column summarizes the potential research topics for the concept elements. 

TABLE B-1. SUMMARY OF CONCEPT ELEMENTS AND SUB-ELEMENTS 

Concept Elements Concept Sub-Elements Potential Resea

3.0 Surface 3.1 Runway Management

Adjusting runway and taxiway configuration for winds, traffic demand, and environmental considerations is slow, infrequent, and inefficient for enhancing capacity. 

3.2 Taxi Route Planning

As airport traffic increases, taxiing is subject to increased delays, and this adds to overall gate-to-gate time. There are several aspects of taxi movements that constrain surface capacity, including taxi routes that are of longer time than if taxi routes are planned as a whole; 

• Optimized runway and taxiway 

configuration change 

• Dynamic allocation of runways (for a given 

configuration) 

• More efficient departure sequences and 

schedules 

• Plan efficient taxi routes under specific 

airport constraints 

• Increase density of surface operations • Minimize queuing and provide clearances 

for longer taxi segments 

• Provide for equipage differences, user 

preferences, and fairness 

• Develop algorithms to determin

configuration and provide efficiconfiguration 

• Develop algorithms to allocate 

and arrivals and to schedule timto arrive at departure runways 

• Develop algorithms to sequenc

to use runways, including respopreferences 

• Study how to include fairness i

maximization in managing runwchanges. 

• Determine the most effective m• Reduce uncertainties in pushba• Determine the controllability pr

taxiways/holding areas 

• Cross active runways with little • Automation of clearances/hand

reduce need for stopping while 

 53 
54 

Concept Elements Concept Sub-Elements Potential Resea

aircraft waiting for clearances for taxi route segments; queuing to cross active runways and for departure runways; getting arriving aircraft off the runway quickly; and aircraft pushing back from gate blocking other aircraft. 3.3 Surface SDO 

During peak periods, airport capacity is often not sufficient to support the demand. Increased density of traffic using runways and taxiways increases workload. It becomes more complex to handle such operations as intersecting or converging runways, taxiing aircraft crossing active runways, and aircraft landing on CSPR. The noise impact of dense operations and of closely-spaced arrivals may be unacceptable to local communities. Runway incursions become a bigger concern as the number of aircraft using an airport increases. 

• Integrate ground vehicle movement into 

surface traffic flow 

• Execute and adhere to precision taxi 

routes 

• Reduced runway incursions and taxiway 

conflicts 

• Precision runway/taxi operations • Reduced runway occupancy time • EVO • Intersecting and converging runways • Weather and environment 

• Incorporate user preferences a

routes 

• Onboard automation and displa

a 4D taxi route or to control the taxi route 

• Procedures for negotiating 4D • Efficient taxi route operations in 

uncertainties 

• Understand tradeoffs in optima• Fairness issues in managing ta• Roles and responsibilities of th

and their automation tools to pnegotiate, and monitor surface integrated manner 

• Investigate the relationship of s

(e.g., new/extended runway, neto increase surface capacity an

• Safety CD&R in the closely-spa

SDO, including during EVO 

• Low altitude, runway, and taxiw• Procedures, algorithms, autom

requirements for CSPR operat

• Procedures, algorithms, autom

requirements for precise taxi o

• Procedures, algorithms, autom

requirements for planning and 

• Reduction of impact of wake vo• Airborne and ground roles and 

(conformance monitoring, CD&

• Determine ground arrival capac

under super density operations 

54 
Concept Elements Concept Sub-Elements Potential Resea

3.4 Surface Weather and Environmental Planning 

Winds can result in changing arrivals and departures to a less efficient set of runways. If changes in wind direction are poorly predicted, configuration changes may be required which can result in inefficient, lengthy transition periods. Surface movement can be slowed considerably by reduced visibility or wet/snowy surface conditions. As for the environment, if current operations are at or near environmental limits, increased capacity may not be possible. 4.0 Terminal Concept Elements 4.1 Precise Spacing & Separation 

Assurance

Spacing and separation between traffic is currently a function of limitations in a number of areas. Surveillance capabilities are limited by accuracy and update rate; improvements in these areas will permit improvements to spacing precision. Likewise, improvement in flying more accurate 4D trajectories will also permit improved spacing precision. Finally, improvements in the ability to detect conflicts will allow consideration of closer spacing between aircraft. 

• Weather • Environment • Precise spacing • Reduced wake vortex separation criteria • CSPR operations • Scheduling and sequencing interactions 

with surface and en route 

• Intersecting trajectories in airspace

• Develop procedures to utilize im

predictions 

• Incorporate environmental imp

operation planning: 

- Directly as goals for increas

reduced taxi times during a

- Indirectly as constraints, su

limitations 

• Develop roles of human and au

involving weather and environm

• What separations can be achie

operations with greater aircraft surveillance precision? 

• What is the best solution for pr

deck managed spacing or grou

• Regarding separation responsi

appropriate for the flight deck a

• What alerting is needed to dete

in an environment where stand

• What are the information requi

airborne-managed separation i

• What are the information requi

deck if groundside separation i

 55 
56 

Concept Elements Concept Sub-Elements Potential Resea

4.2 Dynamic Airspace Management 

Inefficiencies in the flow of traffic occur as a result of airspace allocation, which is generally static and inflexible. The current system does not provide, with few exceptions, the re-allocation of airspace to meet ever-changing demand. Hence, traffic is delayed while parcels of airspace go unutilized. Controllers, absent tools or procedures that would facilitate quickly adapting to realigned or resectorized airspace, are not equipped to quickly reorient to adjustments to airspace boundaries. 4.3 Adapting Operations to Conditions

There are a myriad of situations that can be categorized as changes in the flow of air traffic operations, either changes among alternative operational scenarios or changes to react to off-nominal conditions. These situations require 

• Dynamic terminal airspace sector 

allocation 

• Airspace sector redesign • Respond to runway changes • Reduction of wake vortex impacts • React to weather deviations/reroutes • Environment • Recovery from missed approaches 

• How precise can information be 

a wake is present? What is the applies to required separation, separation, CSPRs, and EVO? 

• How to conduct response to of

• How can airspace be reallocate

be done in a way that increaseoperators? 

• What time horizon is required f

adjust to new boundaries? 

• How to dynamically implement 

airspace configurations so that gracefully achieved, absent of uncertainty for air traffic service 

• Potentially more aircraft in sect

workload: is this manageable aregarding number of aircraft? 

• How will the new airspaces to b

be designed? Is new modeling 

• What are the interactions of ter

route airspace to maximize the made in terminal airspace? 

• Algorithms to adjust terminal a

changes in runway configuratio

• Adjusting to changing wake se

the terminal airspace 

• Dynamic changes in terminal a

to weather information provided 

56 
Concept Elements Concept Sub-Elements Potential Resea

strategies and procedures that minimize impact on the overall operation while achieving specific objectives. There are many challenges in dealing with these situations based on competing interests: e.g. airline: economics; air traffic service provider: localized and systemic flow efficiency; public: noise; and others. Landing aircraft that have missed approaches will have more impacts on future capacity due to denser traffic utilizing airports. Safety, as always, is the first consideration. 4.4 Metroplex Operations

At virtually all airports there are constraining factors that limit capacity to some degree. Often there are nearby airports, which might be used to increase overall capacity for a metropolitan area. Many airports are also constrained by operations arriving at, or departing from, surrounding airports. This can occur for several reasons, such as conflicting arrival/departure paths and shared arrival/departure fixes. Traffic increases at airports that currently experience high demand, as well as increases at airports with light traffic loading, will further exacerbate the aforementioned constraints and form new interdependencies. With these issues in mind, traffic 

• Precisely flown paths • Flexible flight paths • Increased TFM planning horizon • Route planning and execution under 

adverse weather 

• Increased capacity at uncontrolled airports 

forecasts 

• Planning precise and more var

and departure paths approacheavoid noise sensitive areas and reduce emissions 

• What are the off-nominal situat

missed approaches, that shouldeveloping automation aids for How should these off-nominal caddressed? How should recovenominal conditions be address

• How to plan arrival routes and 

airports in a metroplex? 

• How close can arrival and depa

for separation purposes? 

• How can arrival and departure 

dynamically changed to accounand in constraints at particular 

• How can airspace be designed 

changed to account for changeconstraints at particular airports

• How can metroplex operations 

executed under adverse weath

• What information should be sh

service providers at airports, teroute airspace? 

 57 
58 

Concept Elements Concept Sub-Elements Potential Resea

flow management strategies that reflect these interdependencies and provide for operations at multiple airports in a metropolitan area will be required. 5.0 Coordination and Integration of Concept Elements 5.1 Coordination and Integration among Airport Surface Operations

Many potential constraints and conflicts can arise on the airport surface from the different surface concept elements and sub-elements interacting with each other, such as runway assignments interacting with scheduling and sequencing on each runway, taxi route planning interacting with runway availability, and gate/runway assignments for multiple aircraft causing interactions among surface operations for these aircraft. These constraints and conflicts, if not managed, can cause inefficiency and delay. 5.2 Coordination and Integration among 

Terminal Airspace Operations

In the future, more aircraft will transition through terminal airspace, there will be CSPR operations, and wake vortex 

• Surface Flow Constraint • Surface Flow Management • Surface Trajectory Planning • Surface Tactical Control • Terminal Airspace Flow Constraint • Terminal Airspace Flow Management • Terminal Airspace Trajectory Planning • Terminal Airspace Tactical Control 

Note: The issues are similar for 

within and among surface and toperations. Therefore research coordination and integration (i.e5.3, and 5.4) are listed once bel

• How to obtain better predictio

and/or ETA at arrival fix, as apparticular operation? In the coinformation, how to better chatime and/or ETA at arrival fixeintegration purpose? 

• Understand the dynamics of t

surface, terminal airspace, en metroplex operations. 

3⁄4 What is the impact of new 

renegotiation of the 4D tr

3⁄4 How, and how often, can 

negotiated and renegotia

• Many objectives are possible f

integrating airport operations. objective to maximize the throbe equitable to all users in the 

58 
Concept Elements Concept Sub-Elements Potential Resea

separation will be more critical. Separation assurance, terminal airspace management, arrival and departure path planning, and handling nonnormal operations will all interact in the terminal airspace to affect capacity. Optimizing each of these concept elements will help increase capacity, but also coordinating and integrating these concept elements will provide further capacity enhancements. 5.3 Coordination and Integration among Airport Surface and Terminal Airspace Operations

Airport surface and terminal airspace have different operational characteristics and limitations. An aircraft flying through the two domains encounters different constraints and requirements. Optimizing traffic capacity in each domain separately does not imply that overall capacity is maximized. 5.4 Coordination and Integration among 

Metroplex Operations 

Metroplex operations include the same constraints as the integrated airport and terminal operations. In addition, there are more aircraft flying into and out of the 

• Integrated Flow Constraint • Integrated Flow Management • Integrated Trajectory Planning • Integrated Tactical Control • Metroplex Flow Constraint • Metroplex Flow Management • Metroplex Trajectory Planning • Metroplex Tactical Control 

the throughput while subject to constraints? Issues regarding 

3⁄4 How would a particular o

aircraft with different equ

3⁄4 What are the tradeoffs fo

objective functions? 

3⁄4 What type of user prefere

accommodated by the cointegration function and h

3⁄4 What is the optimal time 

function? 

3⁄4 What are the different wa

competing objectives, for local and national level? 

• Which actions, given the objec

considered feasible in the cooprocess? 

3⁄4 There are multiple partie

interfacing with the airpoTRACON, airports, and Ahave different goals and process for negotiation aparties to arrive at an act

• How to construct the best acti

computational power and limitgoes through several different operation has several possible total number of possible contrexponentially as a function of 

• How to coordinate and integra

that when an off-nominal evenminimal impact to various openominal event forces an operaplan and schedule, the event coupled operations to deviate 

 59 
60 

Concept Elements Concept Sub-Elements Potential Resea

metroplex instead of a single airport. Moreover, there are overlapping operations among the airports in the metroplex to utilize the shared terminal airspace. Coordinating all the terminal airspace arrivals and departures with the availability of capacity at the individual airports will be complex. 

schedules. 

• The coordination and planning 

dynamic with a quick solution with off-nominal events. A fasnecessary to evaluate and he

• How to effectively present and 

input information; this researcgeneralized to decision-makin

• Investigate optimization techn

of surface and terminal airspacombine these different surfacoptimizations into integrated, goperations; and how to deal woptimizations. 

• There are likely to be multiple 

coordination and integration awith different, or even competProcedures and rules may be effective and equitable collaboprocesses for different types o

• Failures in either avionics or s

ATSP are possible in airport ointegrated and coordinated. Gfuture system is a desired chaconsidered graceful failure? Wways to achieve a graceful faitradeoffs of the different ways failure? 

60 
Concept Elements Concept Sub-Elements Potential Resea

6.0 Small Airports Small airports without towers will have trouble handling an increase in traffic or traffic in poor visibility. This will inhibit an increase in direct point-to-point routes to such small airports and the use of such small airports in metroplexes. 7.0 Advanced Concepts Elements 7.1 Adaptive Metroplex OperationsThe use of metroplexes with flights assigned to specific airports is likely to provide sufficient airport capacity for some time to come. But, with difficulty in building new airports and adding runways to existing airports, even metroplexes using existing airports may reach capacity as air travel demand reaches three times that of today. With the adaptive metroplex, arriving aircraft are not prescheduled to arrive at the same airport. Rather, the aircraft are dynamically scheduled, either before take off from the originating airport or 

• Airports that serve a large enough air 

traffic base will have tower-provided ATC services with some sub-elements listed in Sections 2.0 through 5.0, as appropriate. 

• ATC services for arriving and departing 

aircraft can be provided by a staffed virtual tower 

• Automated ATC services, in what might 

be called an automated virtual tower 

• Another option for nontowered airports is 

for aircraft to operate in a self-separating mode. 

• Scheduling aircraft to airports • Ground transportation network • Aircraft servicing • Baggage and terminal passenger services • Very advanced concepts for adaptive 

metroplexes 

• Identification and development 

procedures for operations at airural areas, whether staffed virvirtual tower, or self-separation 

• Controller interface issues for m

remotely for multiple airports 

• Impact of growth of traffic smal

on hub airport traffic demand abe a change in city-pair service airports? 

• What are incentives and requir

adaptive metroplex operation? incentives from the viewpoint oas air carrier operators, passenlocal government agencies, etc

• How will final airport destinatio

will negotiations be conducted? 

• How will changes in airport des

implemented and flight routes c

• How to plan arrival routes and 

airports in a metroplex? 

• How close can arrival and depa

for separation purposes? 

• How can arrival and departure 

 61 
62 

Concept Elements Concept Sub-Elements Potential Resea

during flight, as to which airport in the metroplex the aircraft will land. This flexibility maximizes the capacity of the metroplex as a whole. If one airport has restricted capacity due to weather (e.g., a passing thunderstorm), aircraft can be assigned dynamically to land at another airport in the metroplex. 7.2 Advanced Airport Design Tools

Airports in 20 to 25 years will operate with operations derived from many of the concept elements in this Airportal concept. Any new airports constructed, and existing airports that have changes in their runways, taxiways, or other surface infrastructure, will be able to capture more capacity and efficiency benefits of the Airportal concept elements if the airports are designed to operate under the new concept elements. 8.0 Crosscutting Attributes of 

Concept Elements 

There are several research topics that cut across the concept elements presented in Sections 2 through 7. These aspects are listed below. 

• New airports and existing airport changes 

designed by Advanced Airport Design Tools 

Attributes from concept elements that will affect task allocations among humans and automation as well as the design of the humans’ tasks: 

dynamically changed to accounand in constraints at particular 

• How can metroplex operations 

executed under adverse weath

• What information should be sh

deck, and air traffic service proterminal airspace, en route airsfacilities? 

• What attributes of airports shou

design functions of the tool? 

• What concept elements of futu

addressed in the design tool? 

• How should the design tool ope

should the user interface take? 

• Workload for different operatio

during airport operations, durinmodes of operations, and the aat precise times 

62 
Concept Elements Concept Sub-Elements Potential Resea

8.1 Human Factors

The human-automation roles and interfaces under future airport operations raise several human factor issues. 

• More precision • More information and information 

sharing 

• More automation • Extended horizon for planning and 

pperations 

• Collaborative Decision-Making (CDM) • Flexibility 

• Understandability and clarity of 

operation 

• Suitability and stability of tasks 

of operation and for emergency different modes of operation 

• Robustness of human performa• Prospective memory issues, in

what to do in a particular mode remembering roles of automatiis doing now, and what it will pwho is responsible for overall sa response to an anomalous sidifferent mode of operation 

• Alertness to respond to new inf• Completeness and clarity of ste

between modes of operations 

• Conveying of information (with 

available) including display of iinformation to push and to pull 

• What tasks to allocate, and how 

between humans and automatoperations when automation wfunctionality than today, and mchange more frequently than to

• When should task allocations b

automation change and how shshould be designed 

• Transition from automation to h

anomalies 

• How to conduct training for new 

responsibilities of humans. 

 63 
64 

Concept Elements Concept Sub-Elements Potential Resea

8.2 Safety

It will be necessary to reduce the accident rate in the future as air traffic levels grow. While NASA’s Aviation Safety Program is aimed directly at improvements to aviation safety, the NextGen-Airportal Project (within the Airspace Systems Program) shares a complimentary consideration to at least understand the safety implications of its research. 8.3 Environment

As the number of flight operations continues to increase, noise and emissions will become increasingly problematic. Unless environmental issues are addressed, higher-capacity operations may result in increased noise and emissions levels, which in turn may limit any potential capacity gains. 

Potential sources of safety concerns include: 

• Human-automation roles • Procedures resulting from new concept 

elements 

• Technology performance and possible 

failures. 

Major environmental concerns are: 

• Noise • Emissions 

Broader environmental issues are: 

• Water quality • Energy intensity • Global climate change 

• Impacts of new operations and • Impacts of new automated plan

performance of controllers and 

• Failure mode impacts on safety • Relationship of concept elemen

concept to environmental impaemissions 

• Understand the environment im

amount of time aircraft operate different 4D taxi trajectories, inand acceleration, and from aircterminal airspace under differetrajectories, including engine aand power needs for descent. Twhat types of trajectories can rexposure to noise and emissiothe noise and emissions gener

• Examine how to incorporate im

into the design of individual conairport capacity increases 

• Software tools that analyze env

airport operations under alterna

64 
Concept Elements Concept Sub-Elements Potential Resea

8.4 System Failure

The previous presentations of concept elements have included responding to off-nominal situations, such as a missed approach, deviation from a flight trajectory, or deviation from a taxi route. More serious events that affect airport operations more extensively, and for a longer time period, might be considered to be system failures. System failure is defined as a significant difference between planned and realized operations. A system failure can be caused by human error, hardware/ software failure, accident, disaster, or severe weather. As operations in the NAS become more precise and interdependent in the future, system failure can have significant impact on the operations of the NAS. 

Examples of general topics related to system failure include: 

• Graceful failure to allow time for 

recovery 

• New equipment, software-based aids, 

and procedures robust enough to operate in a variety of conditions 

• Consideration of human-automation 

roles and interactions to prevent system failures and aid recovery should a system failure occur 

• Understanding of how real-time 

information from sensors could terminal airspace trajectory plaenvironmental impacts 

• Causes of system failures. In p

interdependencies between difand NAS elements 

• What does graceful failure mea

transportation system? Are thethe different ways to achieve gthe metrics that can measure a are the implications of the use 

• Design within new automation 

are precursors to system failure 

• Design within new automation 

system failures from human erwith the human user if they wathat the automation senses is qautomation reminding the user operations and what tasks are 

• Contingency planning • Recovery from a system failure • How would CDM work during a 

can CDM minimize the impact 

• Equity among users during sys

 65 
66 

66 
67

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Taxi Planning. NLR-TP-2003-475, National Aerospace Laboratory, Amsterdam, the 

Netherlands, Sept. 2003. 

VAMS Project Office, 2006. Virtual Airspace Modeling and Simulation System-Wide Concept 

Report, vols. 1, 2, and 3, NASA Ames Research Center, submitted June 23, 2006. 

VAMS Project Office, Virtual Airspace Modeling and Simulation System-Wide Concept Report, 

Vol. 1 Executive Summary, Vol. 2 Technical, and Vol. 3 Appendices, NASA Ames 

Research Center, submitted June 23, 2006. 
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Venkatakrishnan, C. S.; Barnett, A.; and Odoni, A. R.: Landing at Logan Airport: Describing and 

Increasing Airport Capacity. Transportation Science, vol. 27, no. 3, Aug. 1993, pp. 211–

227. 

Visser, H. G., and Roling, P. C.: Optimal Airport Surface Traffic Planning Using Mixed Integer 

Linear Programming. AIAA 3rd Annual Aviation Technology, Integration, and Operations 

(ATIO) Conf., Denver, Colo., Nov. 17–19, 2003. 

Wanke, Craig; Song, Lixia; Zobell, Stephen; Greenbaum, Daniel; and Mulgund, Sandeep: 

Probabilistic Congestion Management. MITRE Corporation, McLean, Va., 2005. 
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Availability: NASA CASI (301) 621-0390

NASA/CR–2009-215373

21/07/2009

1

U.S. Department of Transportation, John A. Volpe National

 Transportation Systems Center, Cambridge, MA 02142

2

NASA Langley Research Center, Hampton, VA 23681

3

JLP Performance Consulting, Lexington, MA 02420

4

University of California, Santa Cruz, CA 95064

National Aeronautics and Space Administration

Washington, D.C. 20546-0001

Mike D. Madson

Initial Investigation of Operational Concept Elements for NASA's

NextGen-Airportal Project Research

Jonathan Lee,1

 Gary Lohr,2 James L. Poage,3 and Leonard Tobias4

The NextGen-Airportal Project is organized into three research focus areas: Safe and Efficient Surface Operations, Coordinated Arrival/

Departure Operations Management, and Airportal Transition and Integration Management. The content in this document was derived from an

examination of constraints and problems at airports for accommodating future increases in air traffic, and from an examination of capabilities

envisioned for NextGen. The concepts are organized around categories of constraints and problems and therefore do not precisely match, but

generally reflect, the research focus areas. The concepts provide a framework for defining and coordinating research activities that are, and will

be, conducted by the NextGen-Airportal Project. The concepts will help the research activities function as an integrated set focused on future

needs for airport operations and will aid aligning the research activities with NextGen key capabilities. The concepts are presented as concept

elements with more detailed sub-elements under each concept element. For each concept element, the following topics are discussed: constraints and problems being addressed, benefit descriptions, required technology and infrastructure, and an initial list of potential research

topics. Concept content will be updated and more detail added as the research progresses. The concepts are focused on enhancing airportal

capacity and efficiency in a timeframe 20 to 25 years in the future, which is similar to NextGen's timeframe.

NextGen, Airport, Concept

Point of Contact: Mike D. Madson, Ames Research Center, MS 257-1, Moffett Field, CA 94035-1000

(650) 604-3621

Contractor Report

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