+-----------------------------------+----------------------------------+
| #                                 |                                  |
|   {#section .Front-Matter-Header} |                                  |
+-----------------------------------+----------------------------------+
|                                   | #  {                             |
|                                   | #section-1 .Front-Matter-Header} |
+-----------------------------------+----------------------------------+

+-----------+----------------------+---+---+----------+-----------+---------+
| #  {#sect |                      |   |   |          |           |         |
| ion-2 .Fr |                      |   |   |          |           |         |
| ont-Matte |                      |   |   |          |           |         |
| r-Header} |                      |   |   |          |           |         |
+-----------+----------------------+---+---+----------+-----------+---------+
| #  {#sect |                      |   |   |          |           |         |
| ion-3 .Fr |                      |   |   |          |           |         |
| ont-Matte |                      |   |   |          |           |         |
| r-Header} |                      |   |   |          |           |         |
+-----------+----------------------+---+---+----------+-----------+---------+
| **Coo     |                      |   |   |          |           |         |
| rdination |                      |   |   |          |           |         |
| Draft 12  |                      |   |   |          |           |         |
| August    |                      |   |   |          |           |         |
| 1999**    |                      |   |   |          |           |         |
|           |                      |   |   |          |           |         |
| **For     |                      |   |   |          |           |         |
| Free      |                      |   |   |          |           |         |
| Flight    |                      |   |   |          |           |         |
| Select    |                      |   |   |          |           |         |
| Committee |                      |   |   |          |           |         |
| Sur       |                      |   |   |          |           |         |
| veillance |                      |   |   |          |           |         |
| Working   |                      |   |   |          |           |         |
| Group     |                      |   |   |          |           |         |
| Use**     |                      |   |   |          |           |         |
+-----------+----------------------+---+---+----------+-----------+---------+
|           |                      | # |   |          |           |         |
|           |                      |   |   |          |           |         |
|           |                      |   |   |          |           |         |
|           |                      | { |   |          |           |         |
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|           |                      | e |   |          |           |         |
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|           |                      | n |   |          |           |         |
|           |                      | - |   |          |           |         |
|           |                      | 4 |   |          |           |         |
|           |                      |   |   |          |           |         |
|           |                      | . |   |          |           |         |
|           |                      | F |   |          |           |         |
|           |                      | r |   |          |           |         |
|           |                      | o |   |          |           |         |
|           |                      | n |   |          |           |         |
|           |                      | t |   |          |           |         |
|           |                      | - |   |          |           |         |
|           |                      | M |   |          |           |         |
|           |                      | a |   |          |           |         |
|           |                      | t |   |          |           |         |
|           |                      | t |   |          |           |         |
|           |                      | e |   |          |           |         |
|           |                      | r |   |          |           |         |
|           |                      | - |   |          |           |         |
|           |                      | H |   |          |           |         |
|           |                      | e |   |          |           |         |
|           |                      | a |   |          |           |         |
|           |                      | d |   |          |           |         |
|           |                      | e |   |          |           |         |
|           |                      | r |   |          |           |         |
|           |                      | } |   |          |           |         |
+-----------+----------------------+---+---+----------+-----------+---------+
|           |                      | # |   |          |           |         |
|           |                      |   |   |          |           |         |
|           |                      |   |   |          |           |         |
|           |                      | { |   |          |           |         |
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|           |                      | s |   |          |           |         |
|           |                      | e |   |          |           |         |
|           |                      | c |   |          |           |         |
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|           |                      | i |   |          |           |         |
|           |                      | o |   |          |           |         |
|           |                      | n |   |          |           |         |
|           |                      | - |   |          |           |         |
|           |                      | 5 |   |          |           |         |
|           |                      |   |   |          |           |         |
|           |                      | . |   |          |           |         |
|           |                      | F |   |          |           |         |
|           |                      | r |   |          |           |         |
|           |                      | o |   |          |           |         |
|           |                      | n |   |          |           |         |
|           |                      | t |   |          |           |         |
|           |                      | - |   |          |           |         |
|           |                      | M |   |          |           |         |
|           |                      | a |   |          |           |         |
|           |                      | t |   |          |           |         |
|           |                      | t |   |          |           |         |
|           |                      | e |   |          |           |         |
|           |                      | r |   |          |           |         |
|           |                      | - |   |          |           |         |
|           |                      | H |   |          |           |         |
|           |                      | e |   |          |           |         |
|           |                      | a |   |          |           |         |
|           |                      | d |   |          |           |         |
|           |                      | e |   |          |           |         |
|           |                      | r |   |          |           |         |
|           |                      | } |   |          |           |         |
+-----------+----------------------+---+---+----------+-----------+---------+
|           |                      | # |   |          |           |         |
|           |                      |   |   |          |           |         |
|           |                      |   |   |          |           |         |
|           |                      | { |   |          |           |         |
|           |                      | # |   |          |           |         |
|           |                      | s |   |          |           |         |
|           |                      | e |   |          |           |         |
|           |                      | c |   |          |           |         |
|           |                      | t |   |          |           |         |
|           |                      | i |   |          |           |         |
|           |                      | o |   |          |           |         |
|           |                      | n |   |          |           |         |
|           |                      | - |   |          |           |         |
|           |                      | 6 |   |          |           |         |
|           |                      |   |   |          |           |         |
|           |                      | . |   |          |           |         |
|           |                      | F |   |          |           |         |
|           |                      | r |   |          |           |         |
|           |                      | o |   |          |           |         |
|           |                      | n |   |          |           |         |
|           |                      | t |   |          |           |         |
|           |                      | - |   |          |           |         |
|           |                      | M |   |          |           |         |
|           |                      | a |   |          |           |         |
|           |                      | t |   |          |           |         |
|           |                      | t |   |          |           |         |
|           |                      | e |   |          |           |         |
|           |                      | r |   |          |           |         |
|           |                      | - |   |          |           |         |
|           |                      | H |   |          |           |         |
|           |                      | e |   |          |           |         |
|           |                      | a |   |          |           |         |
|           |                      | d |   |          |           |         |
|           |                      | e |   |          |           |         |
|           |                      | r |   |          |           |         |
|           |                      | } |   |          |           |         |
+-----------+----------------------+---+---+----------+-----------+---------+
|           |                      | # |   |          |           |         |
|           |                      |   |   |          |           |         |
|           |                      |   |   |          |           |         |
|           |                      | { |   |          |           |         |
|           |                      | # |   |          |           |         |
|           |                      | s |   |          |           |         |
|           |                      | e |   |          |           |         |
|           |                      | c |   |          |           |         |
|           |                      | t |   |          |           |         |
|           |                      | i |   |          |           |         |
|           |                      | o |   |          |           |         |
|           |                      | n |   |          |           |         |
|           |                      | - |   |          |           |         |
|           |                      | 7 |   |          |           |         |
|           |                      |   |   |          |           |         |
|           |                      | . |   |          |           |         |
|           |                      | F |   |          |           |         |
|           |                      | r |   |          |           |         |
|           |                      | o |   |          |           |         |
|           |                      | n |   |          |           |         |
|           |                      | t |   |          |           |         |
|           |                      | - |   |          |           |         |
|           |                      | M |   |          |           |         |
|           |                      | a |   |          |           |         |
|           |                      | t |   |          |           |         |
|           |                      | t |   |          |           |         |
|           |                      | e |   |          |           |         |
|           |                      | r |   |          |           |         |
|           |                      | - |   |          |           |         |
|           |                      | H |   |          |           |         |
|           |                      | e |   |          |           |         |
|           |                      | a |   |          |           |         |
|           |                      | d |   |          |           |         |
|           |                      | e |   |          |           |         |
|           |                      | r |   |          |           |         |
|           |                      | } |   |          |           |         |
+-----------+----------------------+---+---+----------+-----------+---------+
| Joint     |                      |   |   |          |           |         |
| G         |                      |   |   |          |           |         |
| overnment |                      |   |   |          |           |         |
| /Industry |                      |   |   |          |           |         |
| Sur       |                      |   |   |          |           |         |
| veillance |                      |   |   |          |           |         |
|           |                      |   |   |          |           |         |
| Op        |                      |   |   |          |           |         |
| erational |                      |   |   |          |           |         |
| Concept   |                      |   |   |          |           |         |
| for Free  |                      |   |   |          |           |         |
| Flight    |                      |   |   |          |           |         |
| Enh       |                      |   |   |          |           |         |
| ancements |                      |   |   |          |           |         |
+-----------+----------------------+---+---+----------+-----------+---------+
| 12 August |                      |   |   |          |           |         |
| 1999      |                      |   |   |          |           |         |
+-----------+----------------------+---+---+----------+-----------+---------+
|           |                      |   |   |          |           |         |
+-----------+----------------------+---+---+----------+-----------+---------+
| #  {#sect |                      |   |   |          |           |         |
| ion-8 .Fr |                      |   |   |          |           |         |
| ont-Matte |                      |   |   |          |           |         |
| r-Header} |                      |   |   |          |           |         |
+-----------+----------------------+---+---+----------+-----------+---------+
| #  {#sect |                      |   |   |          |           |         |
| ion-9 .Fr |                      |   |   |          |           |         |
| ont-Matte |                      |   |   |          |           |         |
| r-Header} |                      |   |   |          |           |         |
+-----------+----------------------+---+---+----------+-----------+---------+
|           |                      |   |   |          |           |         |
+-----------+----------------------+---+---+----------+-----------+---------+
|           |                      |   |   |          |           |         |
+-----------+----------------------+---+---+----------+-----------+---------+
|           |                      |   |   |          |           |         |
+-----------+----------------------+---+---+----------+-----------+---------+
|           |                      |   |   |          |           |         |
+-----------+----------------------+---+---+----------+-----------+---------+
|           |                      |   |   |          |           |         |
+-----------+----------------------+---+---+----------+-----------+---------+
|           |                      |   |   |          |           |         |
+-----------+----------------------+---+---+----------+-----------+---------+
|           |                      |   |   |          |           |         |
+-----------+----------------------+---+---+----------+-----------+---------+
| DRAFT     |                      |   |   |          |           |         |
+-----------+----------------------+---+---+----------+-----------+---------+
|           |                      |   |   |          |           |         |
+-----------+----------------------+---+---+----------+-----------+---------+
|           |                      |   |   |          |           |         |
+-----------+----------------------+---+---+----------+-----------+---------+
|           |                      |   |   |          |           |         |
+-----------+----------------------+---+---+----------+-----------+---------+

# Table of Contents {#table-of-contents .Front-Matter-Header}

Section Page

1\.

Introduction 1-[1](#introduction)

> 1.1 Backgound
> 2-[2](#number-range-level2number-range-level3number-range-level4-backgound)
>
> 1.2 Objective and Intended Use
> 3-[3](#number-range-level2number-range-level3number-range-level4-objective-and-intended-use)
>
> 1.3 Scope of Document
> 4-[3](#number-range-level2number-range-level3number-range-level4-scope-of-document)
>
> 1.4 Document Organization
> 5-[4](#number-range-level2number-range-level3number-range-level4-document-organization)

2\. NAS Surveillance Operational Needs and Services
6-[1](#nas-surveillance-operational-needs-and-services)

> 2.1 Air Traffic Management Operations and Limitations from
> Surveillance
> 7-[1](#number-range-level2number-range-level3number-range-level4-air-traffic-management-operations-and-limitations-from-surveillance)
>
> 2.1.1 Surface/Tower
> 8-[3](#number-range-level3number-range-level4-surfacetower)
>
> 2.1.2 Terminal (Approach and Departure Services)
> 9-[6](#number-range-level3number-range-level4-terminal-approach-and-departure-services)
>
> 2.1.3 Current En Route Operations and Limiatations
> 10-[8](#number-range-level3number-range-level4-current-en-route-operations-and-limiatations)
>
> 2.1.4 Oceanic/Remote
> 11-[11](#number-range-level3number-range-level4-oceanicremote)
>
> 2.1.5 Flight Service Stations (FSS)
> 12-[12](#number-range-level3number-range-level4-flight-service-stations-fss)
>
> 2.1.6 Traffic Flow Management (TFM)
> 13-[14](#number-range-level3number-range-level4-traffic-flow-management-tfm)
>
> 2.1.7 Special Use Airspace Operations and Limitations
> 14-[15](#number-range-level3number-range-level4-special-use-airspace-operations-and-limitations)
>
> 2.2 Flight Crew Operations and Limitations from Surveillance
> 15-[15](#number-range-level2number-range-level3number-range-level4-flight-crew-operations-and-limitations-from-surveillance)
>
> 2.2.1 Preflight
> 16-[16](#number-range-level3number-range-level4-preflight)
>
> 2.2.2 Taxi 17-[16](#number-range-level3number-range-level4-taxi)
>
> 2.2.3 Departure
> 18-[17](#number-range-level3number-range-level4-departure)
>
> 2.2.4 Cruise 19-[17](#number-range-level3number-range-level4-cruise)
>
> 2.2.5 Approach and Landing
> 20-[18](#number-range-level3number-range-level4-approach-and-landing)
>
> 2.3 Fleet and Ramp Management Operations and Limitations from
> Surveillance
> 21-[18](#number-range-level2number-range-level3number-range-level4-fleet-and-ramp-management-operations-and-limitations-from-surveillance)
>
> 2.3.1 Preflight
> 22-[19](#number-range-level3number-range-level4-preflight-1)
>
> 2.3.2 Gate Management/Pushback/Departure
> 23-[20](#number-range-level3number-range-level4-gate-managementpushbackdeparture)
>
> 2.3.3 Climb/Cruise
> 24-[21](#number-range-level3number-range-level4-climbcruise)
>
> 2.3.4 Arrival 25-[22](#number-range-level3number-range-level4-arrival)

3\. Future Operational Environment and Characteristics
26-[1](#future-operational-environment-and-characteristics)

> 3.1 Guiding Principles
> 27-[1](#number-range-level2number-range-level3number-range-level4-guiding-principles)
>
> 3.2 Overview of Future Surveillance Operational Concept
> 28-[2](#number-range-level2number-range-level3number-range-level4-overview-of-future-surveillance-operational-concept)
>
> 3.2.1 Separation Assurance
> 29-[5](#number-range-level3number-range-level4-separation-assurance)
>
> 3.2.2 Conflict Management
> 30-[9](#conflict-managementnumber-range-level3number-range-level4)
>
> 3.2.3 Collision Avoidance
> 31-[11](#number-range-level4-collision-avoidance)
>
> 3.3 Architectural Concepts and Functional Needs
> 32-[12](#architectural-concepts-and-functional-needs)
>
> 3.3.1 System Architecture
> 33-[12](#number-range-level3number-range-level4-system-architecture)
>
> 3.3.2 Data Security and Privacy
> 34-[12](#number-range-level3number-range-level4-data-security-and-privacy)

4\. NAS Surveillance Operations by Domain and/or Phase of Flight
35-[1](#nas-surveillance-operations-by-domain-andor-phase-of-flight)

> 4.1 Flight Planning Surveillance Needs
> 36-[1](#number-range-level2number-range-level3number-range-level4-flight-planning-surveillance-needs)
>
> 4.1.1 Near Term Flight Planning
> 37-[2](#number-range-level3number-range-level4-near-term-flight-planning)
>
> 4.1.2 Transition Period Flight Planning
> 38-[2](#number-range-level3number-range-level4-transition-period-flight-planning)
>
> 4.1.3 Mature State Flight Planning
> 39-[4](#number-range-level3number-range-level4-mature-state-flight-planning)
>
> 4.2 Airport Surface Surveillance Operations
> 40-[5](#number-range-level2number-range-level3number-range-level4-airport-surface-surveillance-operations)
>
> 4.2.1 Near Term Airport Surface
> 41-[5](#number-range-level3number-range-level4-near-term-airport-surface)
>
> 4.2.2 Transition Period Airport Surface
> 42-[6](#number-range-level3number-range-level4-transition-period-airport-surface)
>
> 4.2.3 Mature State Airport Surface
> 43-[8](#number-range-level3number-range-level4-mature-state-airport-surface)
>
> 4.3 Terminal Area, Approach and Departure Surveillance Operations
> 44-[9](#number-range-level2number-range-level3number-range-level4-terminal-area-approach-and-departure-surveillance-operations)
>
> 4.3.1 Near Term Terminal
> 45-[9](#number-range-level3number-range-level4-near-term-terminal)
>
> 4.3.2 Transition Period Terminal
> 46-[10](#number-range-level3number-range-level4-transition-period-terminal)
>
> 4.3.3 Mature State Terminal
> 47-[11](#number-range-level3number-range-level4-mature-state-terminal)
>
> 4.4 En Route Surveillance Operations
> 48-[12](#number-range-level2number-range-level3number-range-level4-en-route-surveillance-operations)
>
> 4.4.1 Near Term En Route
> 49-[12](#number-range-level3number-range-level4-near-term-en-route)
>
> 4.4.2 Transition En Route
> 50-[13](#number-range-level3number-range-level4-transition-en-route)
>
> 4.4.3 Mature State En Route
> 51-[15](#number-range-level3number-range-level4-mature-state-en-route)
>
> 4.5 Oceanic Surveillance Operations
> 52-[16](#number-range-level2number-range-level3number-range-level4-oceanic-surveillance-operations)
>
> 4.5.1 Near Term Oceanic
> 53-[17](#number-range-level3number-range-level4-near-term-oceanic)
>
> 4.5.2 Transition Period Oceanic
> 54-[18](#number-range-level3number-range-level4-transition-period-oceanic)
>
> 4.5.3 Mature State Oceanic
> 55-[18](#number-range-level3number-range-level4-mature-state-oceanic)
>
> 4.6 Traffic Flow Management Surveillance Operations
> 56-[18](#number-range-level2number-range-level3number-range-level4-traffic-flow-management-surveillance-operations)
>
> 4.6.1 Near Term TFM
> 57-[18](#number-range-level3number-range-level4-near-term-tfm)
>
> 4.6.2 Transition TFM
> 58-[18](#number-range-level3number-range-level4-transition-tfm)
>
> 4.6.3 Mature State TFM
> 59-[18](#number-range-level3number-range-level4-mature-state-tfm)

5\. Summary 60-[18](#summary)

Bibliography BI-[18](#bibliography)

Appendix A. Surveillance Mode Descriptions and Limitations
A-[18](#surveillance-mode-descriptions-and-limitations)

> A.1 Primary and Secondary Radars
> A-[18](#a.1number-range-level2number-range-level3number-range-level4-primary-and-secondary-radars)
>
> A.1.1 En Route Domain
> A-[18](#a.1.1number-range-level3number-range-level4-en-route-domain)
>
> A.1.2 Terminal Domain
> A-[18](#a.1.2number-range-level3number-range-level4-terminal-domain)
>
> A.1.3 Surface Domain
> A-[18](#a.1.3number-range-level3number-range-level4-surface-domain)
>
> A.1.4 Oceanic Domain
> A-[18](#a.1.4number-range-level3number-range-level4-oceanic-domain)
>
> A.2 Primary and Secondary Radar Limitations
> A-[18](#a.2number-range-level2number-range-level3number-range-level4-primary-and-secondary-radar-limitations)
>
> A.2.1 Primary Radar Limitations
> A-[18](#a.2.1number-range-level3number-range-level4-primary-radar-limitations)
>
> A.2.2 Secondary Radar Limitations
> A-[18](#a.2.2number-range-level3number-range-level4-secondary-radar-limitations)
>
> A.3 Passive Cooperative Surveillance Systems
> A-[18](#a.3number-range-level2number-range-level3number-range-level4-passive-cooperative-surveillance-systems)
>
> A.3.1 Passive Surveillance Limitations
> A-[18](#a.3.1number-range-level3number-range-level4-passive-surveillance-limitations)
>
> A.4 Airborne Surveillance Radar
> A-[18](#a.4number-range-level2number-range-level3number-range-level4-airborne-surveillance-radar)
>
> A.5 Ground and Airborne Weather Radar
> A-[18](#a.5number-range-level2number-range-level3number-range-level4-ground-and-airborne-weather-radar)
>
> A.5.1 Current Airborne Weather Radar Operational Capabilities
> A-[18](#a.5.1number-range-level3number-range-level4-current-airborne-weather-radar-operational-capabilities)
>
> A.5.2 Current and Planned Ground Based Weather Radar Capabilities
> A-[18](#a.5.2number-range-level3number-range-level4-current-and-planned-ground-based-weather-radar-capabilities)
>
> A.6 Automatic Dependent Surveillance (ADS)
> A-[18](#a.6number-range-level2number-range-level3number-range-level4-automatic-dependent-surveillance-ads)
>
> A.7 Traffic Alert and Collision Avoidance System (TCAS)
> A-[18](#a.7number-range-level2number-range-level3number-range-level4-traffic-alert-and-collision-avoidance-system-tcas)
>
> A.7.1 Limitations of TCAS
> A-[18](#a.7.1number-range-level3number-range-level4-limitations-of-tcas)
>
> A.8 Uplink of Traffic Information
> A-[18](#a.8number-range-level2number-range-level3number-range-level4-uplink-of-traffic-information)
>
> A.8.1 Limitations of TIS
> A-[18](#a.8.1number-range-level3number-range-level4-limitations-of-tis)
>
> A.9 Direction Finder (DF)
> A-[18](#a.9number-range-level2number-range-level3number-range-level4-direction-finder-df)
>
> A.9.1 Limitations of DF
> A-[18](#a.9.1number-range-level3number-range-level4-limitations-of-df)
>
> A.10 Emergency Locator Transponder (ELT)
> A-[18](#a.10number-range-level2number-range-level3number-range-level4-emergency-locator-transponder-elt)
>
> A.10.1 Limitations of ELT
> A-[18](#a.10.1number-range-level3number-range-level4-limitations-of-elt)
>
> A.11 Visual Surveillance
> A-[18](#a.11number-range-level2number-range-level3number-range-level4-visual-surveillance)
>
> A.11.1 Limitations of Visual Surveillance
> A-[18](#a.11.1number-range-level3number-range-level4-limitations-of-visual-surveillance)
>
> A.12 Voice Reporting
> A-[18](#a.12number-range-level2number-range-level3number-range-level4-voice-reporting)
>
> A.12.1 Limitations of Voice Reporting
> A-[18](#a.12.1number-range-level3number-range-level4-limitations-of-voice-reporting)
>
> A.13 Data Link
> A-[18](#a.13number-range-level2number-range-level3number-range-level4-data-link)
>
> A.13.1 Limitations of Data Link
> A-[18](#a.13.1number-range-level3number-range-level4-limitations-of-data-link)

Glossary GL-[18](#glossary)

# List of Figures {#list-of-figures .Front-Matter-Header}

Figure Page

2-1. Current Sensor-Centric Surveillance Operation for Domestic Terminal
and En Route Facility Operations
61-[1](#figure-64-1.-current-sensor-centric-surveillance-operation-for-domestic-terminal-and-en-route-facility-operations)

3-1. Mature State Information-Based Surveillance Operations for NAS Air
Traffic Services 62-[3](#section-10)

# Executive Summary {#executive-summary .Front-Matter-Header}

Surveillance is our window on the operation of the National Airspace
System (NAS). Safety and efficiency, the essentials of the operation,
are driven by the richness and clarity of our shared view. As the
demands of capacity and efficiency grow, so must our ability to surveil
the immediate and evolving operation. Safety and efficiency can move
forward when a common understanding of system participant needs and
desires are known, and appropriate procedures and technologies applied.
Surveillance plays a role not only in separation assurance, but also in
traffic flow management, fleet management, and collision avoidance. This
document discusses those needs and our opportunities to advance system
performance as they have evolved since RTCA's Task Force 3. Fundamental
to this vision is the recognition that safety is the keystone to future
enhancements. Increased levels of safety make possible both increased
efficiency and increased capacity.

In this document, **surveillance** is defined as the detection,
tracking, characterization, and observation of aircraft, targets, and
weather phenomena for the purpose of conducting flight operations in a
safe and efficient manner. The primary purpose of surveillance is for
tactical control of aircraft, situational awareness, and separation
assurance. Methods of surveillance include voice reports, visual
acquisition, radar (both primary and secondary), and other new
technologies such as automatic dependent surveillance. Surveillance
information can be used either in a ground facility or in the cockpit.
In addition, surveillance may be used to support functions such as fleet
monitoring and management in a dispatch office, traffic flow management,
and search and rescue operations. The quality of surveillance can be
described in terms such as the target update rate, position accuracy,
velocity (speed and heading) accuracy, identification, intent,
integrity, reliability, and availability.

This surveillance concept of operations is intended to serve as a
starting point on the journey to Free Flight. It is part of an overall
government/industry activity to look at the evolution of surveillance
services and of the surveillance architecture. A companion document will
focus on the surveillance technology and architecture needed to achieve
the operational concept described herein. Along the way, evaluation of
procedures, technologies, advances in Human Machine Interface (HMI), and
domestic and international policies will shape the final outcome. In
addition, there are other efforts currently underway in international
fora, such as Eurocontrol and International Civil Aviation Organization
(ICAO), to promote a global airspace, which provides increased capacity,
efficiency, cost effectiveness, and safety.

The approach described herein transitions from the current
radar/interrogator baseline of surveillance to a digital informational
environment that encompasses air and ground operations. This approach
focuses on shared real-time information, which is applied by service
providers using automation to manage aircraft separation in all air
operations. Information requirements and revised procedures will be
derived from the concept of operations, providing increased capacity,
and, where appropriate, reduced separation standards while maintaining
or increasing safety.

This document focuses on these operational needs, so that there can be a
common understanding of the aviation community's expectations for
surveillance and so that the investment decisions in the NAS
architecture can be validated against defined operational needs. Because
surveillance plays a role in separation assurance, collision avoidance,
flight planning, traffic flow management, and collaborative
decision-making, an operational concept is needed that clarifies the
extent of surveillance information needed, its required quality, and the
system-wide treatment of differing levels of surveillance. In many
cases, new operational benefits are anticipated based on improved
operations. For many of these operations, extended surveillance
information is required to meet increased needs of service providers and
users. Each domain, ground, terminal, en route, oceanic and ramp, has
individual and interconnecting needs. These needs transcend traditional
service provider and user requirements to serve as the basis for
creation of a future system wherein the asset operators have greater
control of the operational outcome. The intent of this concept is to
document these needs in a technology-independent manner.

Within this document, a number of principles form the foundation of the
operational concept for the role of surveillance, especially with
respect to separation assurance. These key principles, as outlined
below, are essential.

-   The overriding premise in managing air traffic is safety.

-   The operational objectives of new concepts include improved capacity
    and efficiency in all weather and visibility conditions, to
    accommodate increasing demands.

-   The surveillance system provides uniform availability of shared,
    rich, and reliable data to service providers and users of the NAS.

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-   Training, supporting, and developing roles are performed in a
    nonpunitive culture rather than one focused on punitive regulatory
    enforcement aspects or decertification.

-   Common, consistent separation standards are applied based on total
    system performance, rather than by airspace designation.

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-   User equipage is benefits driven and is not forced by mandate or
    additional restrictions on airspace access.

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-   New means of achieving separation objectives do not fundamentally
    change the nature of interactions between pilots and service
    providers

Key surveillance related concepts in the evolution of the NAS to allow
greater user flexibility are the following:

-   Separation assurance is the responsibility of the service provider.
    In the future, for specifically certified and approved operations,
    separation responsibility may be delegated to the pilot, who uses
    on-board capabilities to both monitor and assure separation.

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-   Airborne and ground situation awareness is enhanced by new
    surveillance technology. This is especially significant for allowing
    positive control in non-radar environments.

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-   The oceanic environment evolves to more closely resemble the en
    route environment in terms of waypoints, surveillance, airspace
    structure, and communications.

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```
-   Improved surveillance information is provided in a timely and
    consistent manner across the NAS for planning and decision making.
    This information is available through various audible, graphical,
    and textual means designed to meet the needs of the human-centric
    tasks involved. This information enables decisions to be based on a
    shared common view of situations, even as conditions are changing.
    It is envisioned that the sharing of this information will be
    facilitated via a NAS information system.

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-   It is envisioned that NAS improvements with more detailed, more
    accurate, and more timely surveillance information, will provide
    decision makers with the basis for improved operations, reduced
    separations, and also provide the key data source to automation
    aids. It will also provide improved situational awareness.

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-   The future airspace environment will include aircraft operating
    without people onboard, which will have special surveillance
    information requirements. Likewise, because of these aircraft, other
    users and operators in the system may also have special surveillance
    information requirements.

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-   In order for Special Use Airspace to be used by all system users
    more efficiently, the capability for common status and surveillance
    information about that airspace to be shared between the Department
    of Defense (DoD) and other system participants will be required.

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-   Equipage for all users will be benefits based.

    In summary, new cockpit capabilities that build on improved
    surveillance provide pilots and controllers additional tools to
    achieve separation objectives. However, they do not fundamentally
    change the nature of interactions between pilots and controllers.
    The FAA continues to be responsible for establishing new procedures
    and ensuring that the tools supporting them are operationally
    suitable. These new procedures support greater flexibility,
    increased safety, and increased capacity. These essential new
    procedures are codified as a set of Electronic Flight Rules (EFR).
    Some of these procedures result in delegation of separation
    responsibility to the pilot. In all cases, controllers continue to
    have the discretion of when to issue what clearances; pilots will
    continue to have discretion in requesting or accepting procedures.
    The development of improved surveillance capabilities and the
    critical EFR procedures to employ them are essential to user safety,
    flexibility, and traffic growth.

# Section 63Number range Level1Number range Level2Number range Level3Number range Level4Number range FigureNumber range Table {#section-63number-range-level1number-range-level2number-range-level3number-range-level4number-range-figurenumber-range-table .Section-Heading}

# Introduction {#introduction .Section-Header}

Surveillance is our window on the operation of the National Airspace
System (NAS). Safety and efficiency, the essentials of the operation,
are driven by the richness and clarity of our shared view. As the
demands of capacity and efficiency grow, so must our ability to surveil
the immediate and evolving operation. Safety and efficiency can improve
when a common understanding of system participant needs and desires are
known, and appropriate procedures and technologies applied. Surveillance
plays an integral role in the NAS, not only in separation assurance, but
also in traffic flow management, fleet management, and collision
avoidance. This document discusses those needs and our opportunities to
advance system performance as they have evolved since RTCA's Task
Force 3. Fundamental to this vision is the recognition that safety is
the keystone to future enhancements. The road to increased safety
provides an opportunity to also increase both efficiency and capacity.

In this document, **surveillance** is defined as the detection,
tracking, characterization, and observation of aircraft, other targets,
and weather phenomena for the purpose of conducting flight operations in
a safe and efficient manner. The primary purpose of surveillance is for
tactical control of aircraft, situational awareness, and separation
assurance. Methods of surveillance include voice reports, visual
acquisition, radar (both primary and secondary), and other new
technologies such as automatic dependent surveillance. Surveillance
information can be used either in a ground facility or in the cockpit.
In addition, surveillance may be used to support functions such as fleet
monitoring and management in a dispatch office, traffic flow management,
and search and rescue operations. The quality of surveillance can be
described in terms such as the target update rate, position accuracy,
velocity vector (speed and heading) accuracy, identification, intent,
integrity, reliability, and availability.

This surveillance concept of operations is intended to serve as one
essential element on the journey to Free Flight. It is part of an
overall government/industry activity to look at the evolution of
surveillance services and of the surveillance architecture. A companion
document will focus on the surveillance technology and architecture
needed to achieve the operational concept described herein. Along the
way, evaluation of procedures, technologies, advances in Human Machine
Interface (HMI), and domestic and international policies will shape the
final outcome. In addition, there are other efforts currently underway
in international fora, such as Eurocontrol and International Civil
Aviation Organization (ICAO), to promote a global airspace, which
provides increased capacity, efficiency, cost effectiveness, and safety.

## 63.1Number range Level2Number range Level3Number range Level4 Backgound

With the completion of RTCA's Task Force 3 on Free Flight, a number of
goals were established for [NAS Modernization. Chief among these goals
was the elimination of restrictions to flight operations, and the
recognition of economics as a critical factor in both user and system
equipage decisions\[1_1\].]{.mark} The NAS Architecture is the Federal
Aviation Administration\'s (FAA's) plan to modernize the NAS in support
of these goals, with priorities for improvements based on budget
considerations, benefits, technical development, and other factors. Some
evolving surveillance concepts are undergoing operational evaluation as
part of Safe Flight 21. These activities, in addition to those of RTCA
Special Committee 186 on Automatic Dependent Surveillance Broadcast
(ADS-B), lay the foundation for actual implementation of surveillance
improvements.

In this document, the concept for the near term reflects the initial
Free Flight capabilities as envisioned by Task Force 3 and as outlined
in the RTCA *Government/Industry Operational Concept for the Evolution
of Free Flight*, as well as the RTCA *Free Flight Action Plan*. The
transition period describes the incremental steps toward Free Flight,
with additional capabilities across a wider area of the NAS. This
timeframe coincides with the completion of the National Airspace Review,
the replacement of the Host automation system, the transition to
satellite navigation, and the broadened use of automatic dependent
surveillance in the near term, and its broader use in the mid term. This
conjunction of capabilities creates the opportunity for service
providers to make fundamental changes in how NAS services are delivered.
The mature state captures more advanced concepts and capabilities that
will require more definition. Each of these timeframes is consistent
with the operational concepts defined in the RTCA Task Force 3 report.

This surveillance operational concept was developed by the Select
Committee on Free Flight Implementation to respond to government and
industry desires to ensure that the NAS architecture truly reflects the
most appropriate path for the evolution of surveillance capabilities in
the NAS. In addition to the development of an overall operational
concept for the role of surveillance in air traffic operations, a number
of new concepts are being evaluated through the Safe Flight 21 program,
which builds on the Free Flight Operational Enhancements recommendations
from the Select Committee in August 1998. A significant number of these
new concepts build on improved surveillance in both the cockpit and on
the ground. This operational concept is consistent with the specific
operational concepts being explored via Safe Flight 21.

The approach described herein transitions from the current
radar/interrogator baseline of surveillance to a digital informational
environment that encompasses air and ground operations. This approach
focuses on shared real-time information, which is applied by service
providers using automation to manage aircraft separation in all air
operations. Information requirements and revised procedures will be
derived from the concept of operations, providing increased capacity,
and, where appropriate, reduced separation standards, while maintaining
or increasing safety.

## 63.2Number range Level2Number range Level3Number range Level4 Objective and Intended Use

Because surveillance plays a role in separation assurance, collision
avoidance, flight planning, traffic flow management, and collaborative
decision-making, an operational concept is needed that clarifies the
extent of surveillance information needed, its required quality, and the
system-wide treatment of differing levels of surveillance. In many
cases, new operational benefits are anticipated based on improved
operations. For many of these operations, extended surveillance
information is required to meet increased needs of service providers and
users. Each domain, ground, terminal, en route, oceanic and ramp, has
individual and interconnecting needs. These needs transcend traditional
service provider and user requirements to serve as the basis for
creation of a future system wherein the asset operators have greater
control of the operational outcome. This document focuses on these
operational needs, so that there can be a common understanding of the
aviation community's expectations for new surveillance functionality,
and so that the investment decisions in the NAS architecture can be
validated against defined operational needs. The intent of this concept
is to document these needs in a technology-independent manner.

## 63.3Number range Level2Number range Level3Number range Level4 Scope of Document

This document focuses on NAS operations that build on the use of
surveillance information. The primary role of surveillance is in
separation assurance; thus, much of this document discusses concepts for
separation assurance and how improved surveillance information provides
operational benefits. Weather detection and data dissemination, while
obviously forms of surveillance, are treated here only to the level the
information would affect operations. General flight planning and
management services, including search and rescue, also involve
surveillance information exchange, although the requirements are
generally less demanding than those for separation assurance. Flight
planning and management services are also outlined, but in lesser depth.

This document focuses on the operational use of surveillance, not the
technical or architectural aspects of providing the information to those
needing it. As such, this document includes needs for the human-computer
interface and for tools that substantially build on surveillance. This
document does not address which surveillance technologies can meet any
particular need. A basic assumption is that equipage of new capabilities
is voluntary, based on the delivery of new user benefits.

Because future concepts for separation assurance involve the potential
adjustment in roles and responsibilities, with implied needs for
surveillance to support these new operations, this document also
addresses separation responsibility and the roles of pilots and
controllers. In addition, functional dependencies and needed information
are indicated.

## 63.4Number range Level2Number range Level3Number range Level4 Document Organization

Section 2 describes an overview of NAS surveillance needs and services,
and a description of how surveillance is integral to the function of the
NAS.

An overview of the future NAS environment is provided in Section 3, with
related surveillance operational concepts.

Then, in order to convey a meaningful concept of operations, Section 4
is organized according to recognizable operations that users would
follow in preparing and conducting a flight through the Air Traffic
Management (ATM) system.

-   **Section 4.1** Flight Planning Surveillance Needs

-   **Section 4.2** Airport Surface Surveillance Operations

-   **Section 4.3** Terminal Area, Approach and Departure Surveillance
    Operations

-   **Section 4.4** En Route Surveillance Operations

-   **Section 4.5** Oceanic Surveillance Operations

-   **Section 4.6** Traffic Flow Management Surveillance Operations

The operational concepts are presented in an evolutionary format, where
only the changes envisioned for each time period (near term, transition,
and mature state) are described. Concepts common to all users are
presented first, followed by unique user concepts where appropriate for
each phase of flight.

Supporting material for the needs of Section 2, descriptions of today's
surveillance capabilities, is found in the Appendix.

Terms used in this document are listed in the Glossary.

A Bibliography provides information on documents referenced here as well
as other documents relevant to this surveillance concept of operations.

# Section 64Number range Level1Number range Level2Number range Level3Number range Level4Number range FigureNumber range Table {#section-64number-range-level1number-range-level2number-range-level3number-range-level4number-range-figurenumber-range-table .Section-Heading}

# NAS Surveillance Operational Needs and Services {#nas-surveillance-operational-needs-and-services .Section-Header}

In Section 2.1, overall NAS operations are outlined, focusing on the use
of surveillance, its impact, and its limitations. The next section
describes the ways that the surveillance modes are implemented from the
perspectives of the flight crew. Finally, the last section depicts fleet
and ramp management operations and limitations from surveillance.

An overview of current surveillance modes is found in the Appendix to
this document.

## 64.1Number range Level2Number range Level3Number range Level4 Air Traffic Management Operations and Limitations from Surveillance

Today's ATM system is based around the display of traffic to a
controller, who is responsible for assuring separation of aircraft from
one another and from hazards such as mountains and obstructions such as
towers or antennae. Figure 2-1 shows the role of surveillance in today's
operations.

![](media/image1.wmf)

###### Figure 64-1. Current Sensor-Centric Surveillance Operation for Domestic Terminal and En Route Facility Operations

As shown in the diagram, primary radars use signal reflections to
identify the positions of all aircraft within range. In addition,
co-located secondary radars interrogate the aircraft with Mode-S or
Mode-C transponders to obtain aircraft identification. Mode-S provides
the capability to increase capacity, but is not fully achieved because
of ATCRBS limitations..

The surveillance information is transferred to the facility to which the
radar is linked; one shortcoming is that only limited data is shared
with any other facility. The facility's Host computer processes the
surveillance data, and displays the tracks on the controller's display.
The controller must use mental faculties to assess the positions,
headings, and speeds to determine whether there might be a conflict
between any of the aircraft in the future. Because this is such a
mentally labor-intensive task, structured routes were established to
reduce the randomness of track intersections, and therefore, reduce the
problem complexity. This helps to assure safety, but reduces the ability
of users to fly their preferred route, reducing system flexibility and
efficiency.

Surveillance system differences among various facilities and the lack of
data-sharing networks cause a surveillance information gap among
controllers. Traffic management restrictions are put in place, among
other reasons, to compensate for these system problems. These
artificially-induced inefficiencies prohibit ever utilizing today's
legal separation minima, and affect every departing aircraft everyday.
Saving even as little as 30 seconds on each departure flight would
equate to significant improvements in service.

Today's surveillance infrastructure is predicated on the economic
considerations associated with the deployment of costly radar systems.
Because physical limitations in many areas prohibit the installation of
radar, there is no surveillance coverage in certain mountainous regions,
including parts of the Rocky Mountains and Alaska, and in oceanic
airspace. Low altitude airspace, as well, is often without surveillance
coverage. As a result, increased separations are implemented to assure
safety, therefore reducing capacity and user flexibility.

The NAS currently relies on a sole centralized individual (controller)
to process information with few automation aids to control multiple
aircraft and resolve conflicts. Capacity and flexibility are, as a
result, limited by the cognitive skills of the individuals today who
take responsibility for separation assurance within their assigned area
of jurisdiction.

The primary source of surveillance data is from radar. Other sources of
surveillance data can not be processed for display at the control
position. In order to take advantage of future surveillance upgrades,
the system must be adapted to accept data from other surveillance
sources, and remove dependencies on specific surveillance sensors. For
example, en route automation (e.g., the Host computer) can only accept
surveillance from en route radars at a ten-to-twelve-second update rate,
using ATCRBS formats.

As the current surveillance systems age, with the result that accuracy
and reliability are degrading. To compensate, controllers institute
increased separations to assure safety, which again reduces capacity.

There is a lack of procedures and capabilities to accommodate weather
conditions and still maintain capacity. Therefore, capacity in IFR
conditions is reduced.

Airspace design is dependent upon many factors, including the direction
of flow of traffic, volume of traffic, complexity factors such as number
of crossing streams, and the degree of surveillance capability. In
airspace where NAS knowledge of aircraft position is imprecise, such as
areas lacking radar, greater procedural separation standards are
imposed. This results in higher controller workload, limiting the number
of aircraft a service provider can safely manage, thereby reducing
airspace capacity. Separation standards are greatest in oceanic
airspace, making this the least efficient airspace. In the continental
United States, mountainous areas with poor radar coverage also are
inefficient. The number of aircraft a controller can manage is directly
related to workload, airspace complexity, surveillance accuracy, and
separation standards.

The NAS includes some aircraft operating without an onboard crew. These
aircraft are often small and difficult to be seen. Because of these
aircraft, other users and operators in the system may also have special
surveillance information requirements.

Other general issues are those of potential power source failures for
surveillance and automation and the availability of backup sources.
Stable power sources, free of surges and other aberrations, are required
to provide reliable power distribution to solid state systems currently
operating in the NAS. Power failures have been occurring more frequently
because of the old and unreliable power supply systems, which lack the
needed new technology to supply adequate power to the new technology
systems that have been operating in the NAS. More sophisticated
equipment is more sensitive to power fluctuations, so existing power
conditioning is insufficient for this new equipment.

These issues are described in detail by operational domain in the
sections that follow.

### 64.1.1Number range Level3Number range Level4 Surface/Tower

One of the major bottlenecks of the ATM system is congestion at busy
airports. In the control tower, controllers primarily use visual
observation, flight strips, the D‑BRITE (Digital Bright Radar Indicator
Tower Equipment), and voice reports from the pilots as their methods for
surveillance and situational awareness of the airport surface and
surrounding airspace. Further, flight progress strips are generally used
by the tower controllers and arranged on the tower console in such a way
as to portray the activity of aircraft under the tower's control. The
controllers use this surveillance information, along with their
knowledge of aircraft performance characteristics, to sequence the
aircraft within their airspace.

The most obvious operational limitations which result from the use of
visual observation as the means of surveillance is the loss of
surveillance information in poor visibility conditions or when the line
of sight in interrupted by obstacles such as hangars and terminal
buildings. The controllers have limited surveillance information, often
having to rely on solely visual means for surveillance of aircraft, and
are not able to identify aircraft by call sign, resulting in increased
controller workload associated with procedural separation. Therefore,
low visibility requires the application of increased separation on the
ground, because the controller must rely on pilot reports rather than
visual cues to determine aircraft position.

In low visibility, controller workload is increased, aircraft movement
operations are slowed, and the tempo of operations is reduced,
diminishing system capacity. Relying on visual acquisition also allows a
greater opportunity for aircraft misidentification, degrading system
safety. As a result, airport throughput is reduced, with reduction of
50% or more of airport capacity in low visibility conditions.

A variety of controller aids are currently available to assist the tower
controllers in providing separation and ground movement instructions.
Where available, these capabilities provide improvements over unaided
visual observations. However, each has limitations. The capabilities and
their limitations are described in the following paragraphs.

Certain airports provide a radar display in the control tower, which
presents the controller with the primary and secondary radar returns of
airborne aircraft in the vicinity of the airport. This system is called
D-BRITE, and is usually connected to the radar and automation system of
the host terminal approach control facility. D-BRITE displays primary
and secondary radar information with data blocks for each aircraft on
the traffic display, improving the controller's awareness of airborne
traffic over mere visual observations. Controllers use the display to
make decisions for sequencing of aircraft for arrival and departure, as
well as allowing controllers to provide improved traffic advisory
information to aircraft in the airport's area. Additionally, D-BRITE is
not deployed at all towers.

Airport Surface Detection Equipment (ASDE) is another tool used to
enhance the controller's awareness of the position and movement of
aircraft on the airport's surface. It presents the controller with a
primary radar display of the position of targets on the surface. This
capability is used by the ground controller to aid in managing the
movement of aircraft.

ASDE has a number of limitations, including the following:

-   ASDE, as a primary radar, has no ability to present identification
    information of the targets it detects.

-   ASDE, while very helpful to the controller, is labor intensive, in
    that its information must be interpreted and then applied by the
    controller.

-   The controller must convey the ASDE-derived information to the
    pilot, which may not be immediately possible for a variety of
    reasons, including congestion on the communication channel. In the
    case of runway incursions, delays in alerting departing crews to the
    danger of a conflict are unacceptable.

-   ASDE identifies non-aircraft entities, which include tracking flocks
    of birds, reflected radar returns, rain, and false targets.

-   The ASDE radar system is most susceptible to these problems during
    periods of reduced visibility, such as heavy rain, which is when
    controllers need the equipment most.

-   As earlier ASDE equipment ages, its performance degrades, resulting
    in more false targets, reduced target detection capability, and
    system outages. As the reliability of aircraft detection equipment
    is diminished, controllers must compensate with procedural increased
    separation to ensure the current level of safety. This reduces the
    acceptance rate of the airport, which may cause downstream delays
    for arriving aircraft, in addition to delaying departing aircraft.

-   When traffic increases to the point of requiring two tower
    controllers, it is difficult for both to use the single ASDE
    display; this reduces safety of operations.

-   Relying on visual acquisition of aircraft limits system capability
    and allows greater opportunity for aircraft misidentification,
    degrading system safety.

In addition to airport surface resource utilization being the single
most significant factor in determining system capacity, the fact is that
approximately 70% of fatalities and hull losses occur on the airport
surface. The Airport Movement Area Safety System (AMASS) is the FAA's
first generation endeavor to automate warning of potential collision
threats on the runway. One of the benefits of the AMASS system is the
ability to transfer arriving aircraft identification from ARTS to the
ASDE displays, providing positive aircraft identification to the
controller. This function is the first step in providing an enhanced
safety net and operational advancement much needed in the tower
environment.

Unfortunately, AMASS is limited by the sources of its data. Ground Radar
Targets are received from the ASDE-3 radar system, and flight
information on arriving aircraft is transferred from the ASR radar
surveillance automation systems. The aforementioned ASDE problems can
cause an extremely high number of nuisance alerts. Because of the
limitations of data sources, AMASS is not operational at any of the
sites at which it has been installed.

Another tower capability, Surface Movement Advisor (SMA), provides
departure and arrival scheduling. It also provides the controller with
conflict advisories. It facilitates information sharing among air
traffic, airline, and airport operations entities, and thereby augments
surface movement decision-making. The benefit of SMA is that it reduces
delays and helps to optimize airport capacity.

SMA has only been tested as a proof of concept. The first operational
system is not scheduled to be installed until FY2000.

Additional surveillance problems affect the controller's ability to
manage traffic safely and efficiently on the airport surface.
Controllers currently do not have reliable vehicle position and velocity
information. At those airports without D-BRITE or ASDE, controllers use
visual means to identify and control aircraft. The ability of the
controller to accomplish this is limited by the atmospheric conditions.
Low visibility requires the application of increased separation on the
ground because the controller must rely on pilot reports rather than
visual cues to determine aircraft position. This reduces the acceptance
rate of the airport, which may cause downstream delays for arriving
aircraft, in addition to delaying departing aircraft.

Human factors issues still need to be addressed, including reduction of
false alerts. The time it takes the controller to determine the validity
of the alert and a course of action subjects the controller to increased
workload.

In the case of actual problem situations, there is a delay from the time
the situation is apparent and the controller recognizes it, to develop a
resolution, communicate it to the pilot, and the time the pilot responds
and initiates a maneuver. This delay subjects the aircraft, crew, and
passengers to unnecessary and unacceptable risk, which could be averted
by improved surveillance capabilities that notify controller and pilot
to the danger earlier than current systems.

Under low-visibility conditions, or instances where the pilot is
unfamiliar with the airport, pilots can request progressive taxi
instructions from the service provider. This would require the service
provider to have knowledge of the aircraft location, which he may not
have, and it consumes controller time by having to provide progressive
taxi instructions, thus limiting controller productivity and airport
throughput.

### 64.1.2Number range Level3Number range Level4 Terminal (Approach and Departure Services)

In the terminal approach control facilities, primary and secondary radar
are essential tools for the safe and efficient control of aircraft
within the facility's airspace. Typically, a single terminal approach
control receives surveillance information from a single primary and
secondary surveillance radar site. In some cases, larger terminal
facilities receive surveillance information from additional radar
systems. In either case, the surveillance information from these radars
is not typically shared with any other approach control facility and
only the data from one radar site is used at a time. The surveillance
information, as a source of position information to the air traffic
automation system, allows the controller to effectively separate and
sequence aircraft within the assigned airspace. The current terminal
area radar separation standards (3 miles between aircraft within 40
miles of the radar site, and 5 miles beyond 40 miles) were established
historically through experience with a variety of factors. These include
pilot and controller performance, aircraft and ground automation
performance, communication system performance, and surveillance system
performance. Empirical observations of the current system suggest that
these standards provide a sufficient level of safety. However, no
quantitative analysis exists to support the specific standards in use
today.

Visual separation procedures are also used in the terminal environment.
The example of clearing aircraft for visual approaches to follow other
aircraft and maintain separation from that aircraft illustrates this.

Operational limitations that result from the current surveillance
capabilities include the following:

-   Loss of surveillance information when aircraft fly directly above
    the radar antenna

-   Line of sight characteristics of the radar, which limit the radar's
    ability to capture aircraft in mountainous areas

-   Satellite airports served by the terminal facility, where a single
    approach control provides radar service to many satellite airports
    from a single radar site at the primary airport, do not have
    adequate surveillance coverage to assure that aircraft have landed
    or departed; this delays any other aircraft from using the runway,
    decreasing system capacity

Loss of surveillance information results in a reliance on increased
procedural separation standards, which increases controller workload and
decreases the system's capacity. Further, radar identification requires
target acquisition within one mile of the departure end of the runway.
Failure to acquire a target within this limitation increases controller
workload by requiring the application of an additional technique for
radar identification. Prior to establishing radar contact, non-radar
separation must be applied, impacting all other aircraft in the
vicinity. Also, while five mile separation is used in the terminal
environment for wake turbulence avoidance, it is only required between
specific types/sizes of aircraft. This reduces capacity unnecessarily.

Transitioning from terminal to en route requires the terminal controller
to provide separation in excess of the three mile requirement.

In limited visibility, the lack of shared position information on
aircraft can limit the times when this procedure can be used, as well as
hindering the pilot's understanding of the aircraft picture around the
airport.

The area above the radar antenna (where aircraft cannot be acquired by
the radar) has the potential to create a safety problem when tower
positions are split. This gap in surveillance requires the controllers
to rely on verbal coordination to maintain situational awareness.

The Precision Runway Monitor (PRM) is an electronically-scanned
secondary surveillance radar. Because the antenna does not rotate,
targets can be interrogated at a variable rate, as fast as twice per
second. Accuracy is better than 1.0 milliradian. The system is intended
for terminal area surveillance, and thus the range is about 40 nmi.

PRM has a capacity of 35 aircraft at a 1-second update rate. Targets are
presented to the controller on a high-resolution 20 x 20-inch color
display.

PRM was originally developed to support simultaneous approaches to
closely spaced parallel runways, for which the high accuracy and high
update rate were critically important. Other applications have since
been identified, including monitoring simultaneous offset approaches (at
St. Louis) and monitoring departures (at Hong Kong).

PRM is no replacement for an ASR-9. PRM is a specialized tool for
precise monitoring on final approach or initial departure, rather than a
general area surveillance system. So an ASR is still needed in addition
to PRM. Also, a one-way ARTS interface is needed to get aircraft
identification information. To date, the PRM data has not been fed back
to ARTS.

### 64.1.3Number range Level3Number range Level4 Current En Route Operations and Limiatations

In the en route control facilities, accurate surveillance information is
also essential for the safe and efficient control of aircraft within the
facility's airspace. Unlike in a terminal facility, a single en route
control center receives surveillance information from a number of
primary and secondary surveillance radars. However, as with terminal
facilities, the surveillance information from these radars is not
typically shared with another en route control facility. Therefore,
there is a lack of consistency between the terminal facility's view and
the en route facility's view of traffic, which could have an impact on
safety and operations. Additionally, NAS automation can only process
radar data from twenty-two sites.

Unlike the terminal area's three-mile separation standards, en route
separation is currently five miles, which reduces the capacity of the en
route system.

The surveillance information, as a source of position information to the
air traffic automation system, allows the controller to effectively
separate and sequence aircraft within the assigned airspace. However,
there is not sufficient quantity or quality of surveillance information
to allow for the creation and dissemination of a consistent traffic
picture. This lack of consistent traffic picture, which can be
recognized as valid and used by all system users and participants,
limits the system's efficiency and capacity. Lack of surveillance
information and/or the lack of controller confidence in the quality of
the information have a negative impact on the system's capacity and
efficiency within the en route domain. Further, the lack of additional
information (such as near and long-term intent information) from the
surveillance systems, coupled with the current controller displays,
automation systems, and decision support tools, limit opportunities to
improve the air traffic management system's safety, efficiency, and
capacity.

Lack of surveillance information in those areas where there is no
electronic surveillance capability limits the systems' capacity and
efficiency. It hinders the creation and use of more low-altitude IFR
routes. This is because the use of IFR routes where there is no
surveillance information is very workload intensive to the controller.
In such areas, non-radar separation standards are applied, a workload
intensive activity. Creation and use of such routes is not feasible in
certain sectors where the increase in workload would be unacceptable.
Similarly, in areas such as the offshore areas of the Caribbean Sea and
Gulf of Mexico, the lack of surveillance information also brings with it
the need to use non-radar separation standards. The transition from
radar to non-radar standards is workload intensive. These gaps may be
fairly small, but seriously diminish system capacity. Another area where
the lack of surveillance information impacts the system is at
non-controlled airports. The lack of location information for arriving
and departing aircraft limits the IFR capacity of the airport to a
one-in/one-out process. For example, once an aircraft has been given an
IFR clearance to land at the airport, no other aircraft can be given an
IFR clearance to land or depart the airport until the landing pilot
notifies the controller that the aircraft has landed and cleared the
runway.

Lack of controller confidence in the quality and timeliness of
surveillance information, the way it is processed by the automation
system and the way it is displayed to the controllers cause other
operational limitations. Lost radar data, target jumps, and other
reliability issues are system limitations commonplace in the en route
domain. Target jumps in particular are common. As aircraft transitions
from one radar sort box to another, tracks often shift. This shift may
activate an alert, indicating erroneously that an operational error has
occurred. The Operational Errors and Deviations (OE/D) program records
this action. Controllers are sensitive to this program and, therefore,
often employ greater than minimum separation in these situations to
ensure against the possibility of such an erroneous recording. In this
way, unreliable surveillance information impacts the controller's
ability to apply minimum separation standards. Thus, use of the minimum
five-mile separation between aircraft is rare due to the failure of the
radar display processor to provide consistently accurate track
information.

Additional operational limitations, which result from the current
surveillance capabilities, include the requirement for higher separation
standards as a result of the current use of a mosaic of data from
several radar sites. Mosaic radar provides greater coverage, but less
accurate data than a single radar. This less accurate surveillance
information results in separation standards of five miles rather than
the terminal area's three miles, reducing en route capacity.

Additionally, due to the relatively slow update rate of the radar
information, the en route system has a greater lag than the terminal
system in displaying an aircraft's track, speed, and altitude. These
lags cause the en route controller to delay issuing clearances to other
aircraft, as many procedures rely on observed information. For example,
when applying vertical separation, an altitude may be issued to an
aircraft only when another aircraft previously at that altitude reports
leaving it. Mode C may be considered a valid report of altitude
departure, but is subject to considerable lag, often resulting in the
controller obtaining a verbal report for expedience. This increases
workload on both pilot and controller, and increases frequency
congestion.

Special Use Airspace (SUA) surveillance information is not consistent
between the FAA and the Department of Defense. This inconsistency
includes not only the availability of surveillance data in the different
facilities, but also the manner in which it is displayed to the
respective controllers. There is limited or no sharing of surveillance
data between FAA and DoD control facilities. The lack of common and
consistent surveillance information hinders the effective use of SUA
when it is not being used by the DoD.

The lack of quality surveillance information and a common air picture
results in limited use of user-preferred trajectories. The current
system relies on the controller for separation assurance. This reliance
translates into controller workload to issue instructions and observe
compliance. When the controller's workload is high, use of workload
intensive user-preferred trajectories is therefore decreased. There is
currently no capability to share surveillance information, and a lack of
procedures and rules to allow the sharing of the separation assurance
responsibility between controller and pilot.

Controllers have limited ability to provide services to low-end general
aviation and other VFR users of the system. Services to VFR users are
provided by controllers on a workload-permitting basis. High controller
workload limits their ability to provide any services. This limitation
decreases the overall level of system safety.

Primary radar is the only method available to detect non-transponder
aircraft. Some of the reasons for non-transponder aircraft include
equipment or electrical failures as well as the failure of pilots to
activate the equipment. The effects on safety and efficiency include
increased separation minima, increased pilot reporting and controller
coordination workload, and prohibitively large separation requirements
for direct off airway or similar routings.

Weather information available to en route controllers is currently
dependent upon primary long range radar's limited ability (relative to
National Weather Service radars) to detect weather information and the
ability of the current automation system to display it. Controllers in
areas served only by ATCRBS do not have any weather data displayed on
their scope. Aircraft encountering hazardous weather maneuver around the
area. A controller without weather data is unable to anticipate changes
in flow or fully utilize available system capacity. In addition, lack of
current weather information may result in inadvertent vectoring of
aircraft to areas not suitable for the user's operation. Weather
deviations significantly lower the capacity of a given sector. Sector
saturation delays all aircraft on routes that transition the sector. The
ability to plan for weather deviation is essential to maintaining the
current level of safety in the ATC system. Accurate weather information
not only ensures a level of safety, but also allows strategic planning
to improve system capacity.

Lastly, the current en route automation and display systems limit the
enhancement of system capacity and efficiency. The currently used
information technology and modes of displaying information to
controllers produce human-machine interface problems. Separate weather
and traffic displays make it difficult for the controller to associate
weather with traffic positions. These problems introduce additional
workload for the controllers and limit the amount of information the
controllers can efficiently use. The result is an artificial capacity
limit in a given sector, and a reduced ability of the controller to
handle additional information in a crisis situation. Today's manual
method of assessing situations will not handle the expected traffic
growth.

### 64.1.4Number range Level3Number range Level4 Oceanic/Remote

Currently, many oceanic ATS functions are performed manually by
controllers using supporting automation that consists primarily of a
visual display, conflict probe, and logic checks of surveillance data.
Paper flight strips provide the information required for surveillance,
separation, and memory trigger functions for the controllers. Strips are
also used to manually record flight information, such as actual or
proposed flight profile changes, clearances, requests, estimates,
progress reports, and aviation advisories. Although most flight data is
electronically transmitted, stored and processed, many data updates are
manually calculated and documented by controllers. The data recorded on
paper flight strips furnish the primary means by which controllers
monitor and ensure separation.

Surveillance information from radar systems is not usually available to
the controller in an oceanic airspace environment and (by definition) in
remote continental airspace. In oceanic areas, surveillance information
usually comes to the controller in the form of hourly pilot position
reports relayed to the oceanic automation system via a third party. In
some regions and on some routes, equipped aircraft can provide
surveillance reports based on pilot estimates of position via data link
to the oceanic automation system. Since the reports are widely spaced
and may be delayed in transit, there is a reduced certainty as to the
actual position of the aircraft between reports. The accuracy of the
aircraft navigation equipment also affects the accuracy of the
aircraft's position on the controller's display.

As is the case in the radar environments described above, oceanic
separation standards are related to the characteristics of the
surveillance reports, primarily their latency, accuracy, and frequency.
Surveillance can also be degraded by HF communications system congestion
and the limitations on the timeliness and reliability of communications
between the controller and the pilot for aircraft that are not data link
equipped. Coupled with the extensive controller workload needed to
monitor flight progress using paper strips, the controller's ability to
intervene in conflict situations is reduced even further, increasing
required separation minima.

Operational limitations, which result from the current surveillance
capabilities, include the inability of controllers to independently
validate the pilot's position reports. The process of using a relatively
inflexible route structure is also necessary as a result of current
deficiencies in surveillance and navigation tools, and real-time,
automated data communication exchanges. The controller's ability to
grant pilot requests and allow dynamic route changes is also limited due
to the uncertainty of aircraft position. Because of limitations of the
current oceanic system, airspace users are frequently unable to achieve
maximum fuel efficiency, minimum travel times, preferred takeoff times,
and flight paths that are free of severe turbulence.

### 64.1.5Number range Level3Number range Level4 Flight Service Stations (FSS)

Weather service and surveillance for aviation is a joint effort of the
National Weather Service (NWS), the FAA, military weather services, and
other aviation groups or individuals. The NWS maintains an extensive
surface, upper air, and radar weather observing program; a nationwide
aviation weather forecasting service; and provides limited pilot
briefing service. However, FAA personnel at Automated Flight Service
Stations provide the majority of pilot weather briefings. Aviation
routine weather reports (METAR) are taken manually by NWS, FAA,
contract, or supplemental observers.

The FAA maintains a nationwide network of Automated Flight Service
Stations (AFSS/FSS) to serve the weather needs of most pilots. FSSs are
currently the primary source for obtaining preflight briefings and
in-flight weather information for general aviation, military, and public
service flights. Pilot briefings are available 24 hours a day through
the use of a toll free number. In recent years, the FAA has contracted
to provide basic weather information over the Direct User Access
Terminal System (DUATS); allowing all users the capability to access
weather information by personal computer. Flight Service Specialists are
qualified and certified by the NWS as Pilot Weather Briefers. They are
not authorized to make original forecasts, but are authorized to
translate and interpret available forecasts and reports directly into
terms describing the weather conditions. In addition, NWS meteorologists
are assigned to most ARTCC facilities as part of the CWSU. They provide
Center Weather Advisories (CWA) and gather weather information to
support the needs of the FAA and other users of the system.

After weather, the most essential normal use of the FSS (and its DUATS
connection) is as the only interface with the NAS for filing, opening,
and closing VFR flight plans, and as the primary and only reliable
interface by which general aviation, military, and public service
flights can file IFR flight plans. These flight plans, especially the
VFR flight plan, are instrumental in initiating Search and Rescue (SAR)
operations. For VFR aircraft that are simply lost, the FSS on request
can provide assistance through its Direction Finding (DF) equipment
(usually located at the FSS). Through the use of directional antennas,
the system receives the Very High Frequency (VHF) voice transmissions
from aircraft and provides the FSS specialist with a magnetic bearing to
the aircraft. This crude form of surveillance allows the FSS specialist
to aid a pilot who has lost bearing. The FSS specialist can give the
pilot a heading and help the pilot regain situational awareness.

SAR is a lifesaving service provided through the combined efforts of the
federal agencies signatory to the National SAR Plan and the agencies
responsible for SAR within each state. To carry out these
responsibilities, the Coast Guard and the Air Force have established
Rescue Coordination Centers (RCCs) to direct SAR activities within their
regions. For aircraft emergencies, distress, and urgency, information is
passed to the appropriate RCC through an ARTCC or FSS.

ARTCCs and FSSs alert the SAR system when information is received from
any source that an aircraft is in difficulty, overdue, or missing. The
loss of radar contact with an aircraft on an IFR flight plan without
service termination notice is considered to be a possible emergency. A
filed flight plan is the most timely and effective indicator that an
aircraft is overdue.

Surveillance related limitations of the FSS primarily fall into the
categories of weather dissemination, finding lost aircraft, and the lack
of adequate surveillance information to initiate SAR operations in a
timely manner. These limitations are explained in the following
paragraphs.

Currently, the only way to relay weather surveillance information from
the FSS to the aircraft is VHF voice. This is cumbersome, and verbal
descriptions are difficult to visualize. The FSS needs a way to get this
weather information into the cockpit in easily understood graphics.

Providing DF instructions to a lost pilot is cumbersome and time
consuming. To augment today's DF data, the FSS needs modern surveillance
data about aircraft in their respective area of responsibility in order
to provide efficient, effective service to these aircraft before they
get into more serious trouble.

With respect to saving human life, when SAR operations are needed, it is
imperative that the FSS have modern surveillance data, especially when
following aircraft on VFR flight plans. At present, the only method the
FSS has for surveillance is verbal voice reports over VHF
communications. And, due to the awkwardness involved in providing these
reports, they are seldom made. Currently, no phone checks are made until
the aircraft is at least 30 minutes overdue in closing the flight plan.
A similar 30-minute waiting period is applied when an aircraft released
for an IFR departure fails to check in with the first control sector
over voice communications or appear on radar. To exacerbate the
situation, since a VFR aircraft is not surveilled during the flight, SAR
participants do not know where to begin to look unless the Emergency
Locator Transmitter (ELT) and its associated antenna work properly. Even
if the aircraft adhered to the flight plan, it could be anywhere along a
path sometimes many hundreds of miles long over all kinds of terrain.
For downed aircraft that are following either VFR and IFR flight plans,
this 30 minute waiting period and lack of adequate surveillance
information on the actual aircraft location loses valuable time when
lives are at stake.

### 64.1.6Number range Level3Number range Level4 Traffic Flow Management (TFM)

Traffic Flow Management (TFM) today consists of the combined efforts of
one national entitythe Air Traffic Control System Command Center
(ATCSCC)and multiple Traffic Management Units (TMUs), one at each
Center and at large TRACONs. It is the responsibility of these combined
TFM entities to ensure that air traffic flows smoothly across the
system, and that congested airspace and hazardous weather are avoided.

The Command Center begins activities early each morning, examining the
predicted weather forecast for the day, and developing traffic flow
strategies for the day that avoid any predicted hazardous weather and
that balance demand. These strategies may be in the form of flow
restrictions, ground holds, or adjusted traffic flow routes. Throughout
the day, these strategies may be adjusted, or new ones initiated, to
accommodate changing environmental conditions. In addition, the Command
Center may receive calls throughout the day from any TMU requesting flow
strategies to alleviate over-capacity conditions in that Center. The
Command Center coordinates among all affected Centers to accommodate the
needs of all involved and to assure the most efficient strategy.

Each Center's TMU monitors the predicted traffic and environmental
conditions such as weather for that Center. If traffic exceeds capacity
thresholds and requires a strategy, such as a restriction, on traffic
entering from another Center, the TMU calls the Command Center for
approval of the necessary strategy. If the traffic or weather conditions
can be handled by strategies solely within the Center, the TMU sets
these and notifies the appropriate controller(s).

Although the current process works for the most part, some problems do
exist. Because there is currently no capability to assess the effects of
any strategy prior to implementation, the development of strategies is
based on previous experience. Therefore, sometimes unnecessary or
excessive strategies are implemented. Users want reduced flow
restrictions and fewer ground delays.

Sometimes weather predictions are inaccurate, and unnecessary ground
holds or reroutes are instituted to avoid weather that never
materializes. Winds shift, and gain or lose strength. As a result,
aircraft sometimes fly into turbulence, which might have been avoided
with better information. Better surveillance of weather is needed, with
incorporation of this information into controllers' traffic displays, to
allow controllers to provide improved services, resulting in a more
efficient NAS.

Finally, at the Command Center, the weather section and the Eastern U.S.
desk and Western U.S. desk do not coordinate plans, sometimes leading to
contradictory strategies.

### 64.1.7Number range Level3Number range Level4 Special Use Airspace Operations and Limitations

Surveillance in special use airspace is conducted primarily by the U.S.
military using primary and secondary surveillance radars. The primary
radars used include both short-range radars (similar to the ASR-8/9) and
long range radars (similar to the FAA FPS and ARSR radars). The
secondary radars used are similar in performance to the FAA ATCBI-4/5.
These radars provide surveillance information to military radar units
that control participating aircraft within the airspace. These military
radar units, unlike military radar approach controls, are not staffed by
FAA-certified air traffic controllers, and are not authorized to control
IFR traffic within their assigned airspace. Therefore, these facilities
may not participate in the air traffic surveillance system modernization
programs in which the military air traffic control facilities
participate.

For the most part, the surveillance information used by the U.S.
military to control operations within special use airspace is not shared
with the FAA. The resultant surveillance information gap places
limitations on the ability of non-military air traffic control to
control non-participating traffic in special use airspace, even when
that airspace is not being used by the military.

## 64.2Number range Level2Number range Level3Number range Level4 Flight Crew Operations and Limitations from Surveillance

The term flight crew addresses a wide range of users. This section
provides a general overview, by operational phase, of operations and
limitations.

Users who need surveillance information include the pilot/cockpit crew
and those who conduct flight planning and aircraft fleet management
activities. The lack of surveillance information has a negative impact
on their ability to operate safely and efficiently within the system.
Lack of situational awareness is first and foremost a safety issue.
There is no sharing of the surveillance information of proximate
aircraft between the air and the ground. Lack of situational awareness
induces a secondary problem of reduced system capacity and efficiency.
Without a common air picture between the air and the ground,
communications between the air and ground about traffic situations is
more complicated. If there were a common shared air picture, this
communication could be done rapidly and effectively with reduced voice
communications, thereby decreasing controller workload and allowing more
controller time to perform other tasks, with a resultant overall
increase in system capacity. Part 121 aircraft cannot operate in areas
of forecast weather without onboard weather radar. Although air carriers
have excellent weather information, airborne aircraft do not usually
have access to this graphic information.

### 64.2.1Number range Level3Number range Level4 Preflight

During the preflight, comprised of walk-arounds, system checks, weight
and balance determinations, and so forth, it is not necessary to have
rapidly-updated surveillance information, weather, and traffic.
Currently, this information on traffic and weather is passed along to
the cockpit either by voice or data link according to the class of user,
and is fairly limited. There is no additional surveillance information
that would be considered essential to improving safety, but there are a
few items that might affect planning and efficiency for subsequent
phases of flight. These would include improved access to predictions of
traffic demand at major airports for users without AOCs, and an
indication of the status and use of Special Use Airspace (SUAs).

### 64.2.2Number range Level3Number range Level4 Taxi

Currently, taxi operations are conducted solely by visual means,
augmented by verbal instructions and whatever mental picture can be
garnered from the "party-line" communications. The limitations of this
method constitute considerable limitations on flight operations in low
visibility, and can be a constraint under any conditions when a pilot
unfamiliar with the airport asks for progressive taxi instructions. A
pilot cleared to follow an aircraft cannot positively identify that
aircraft. The lack of surveillance information increases the need for
communication between the pilot and controller.

Under conditions of low visibility and nighttime operations, airport
capacity is degraded, and surface operations can sometimes be
compromised. Pilots taxi aircraft at a slower rate, taking longer to
traverse the airport surface. Taxiing aircraft sometimes blunder onto
runways or taxiways for which they have not been cleared. This may
result from lack of familiarity with the airport surface, or simply the
inability of the pilot to visually identify the cleared surface route.
These problems reduce both safety and airport capacity.

Users do not currently have departure sequencing information. Pilots
need this information for planning and executing engine and other
on-board preparations.

### 64.2.3Number range Level3Number range Level4 Departure

Before commencing the departure roll, pilots currently perform a visual
scan for traffic and listen to radio reports from other aircraft. Once
the aircraft commences roll for take-off, the controller may not have
time to relay instructions to avoid sudden incursions. The pilot has the
final responsibility for avoiding runway incursions. Under good
visibility, this usually poses minimal problems, but in low visibility
conditions, the pilot has no tools with which to see other aircraft.
Some aircraft have TCAS, but it is not designed to be operationally
useful on the airport surface. On the surface during taxi, the currently
recommended procedure is to have the transponder in standby mode. Action
in the cockpit is the final place for collision prevention resulting
from a runway incursion.

Lack of accurate wake vortex information is a key capacity limitation
for departing aircraft. Departure procedures add buffers for wake
vortices in the absence of accurate surveillance to detect them,
reducing capacity. Airborne departures would encounter surveillance
needs similar to any aircraft in flight.

### 64.2.4Number range Level3Number range Level4 Cruise

At cruising altitudes, the capabilities of the various categories of
aircraft diverge considerably. The well-equipped airliners and business
aircraft have systems like EGPWS, TCAS, weather radars, and lightening
detectors to provide surveillance information. An owner/operator of a
piston single engine aircraft operating under VFR may only have a VHF
communications radio to call a Flight Service Station for weather, or to
obtain flight following services from ATC. Visual scanning for airborne
traffic is inadequate. ATC is the sole source of surveillance
information for GA pilots; if controller workload is high, this
precludes providing radar advisories and flight following services to GA
pilots. Furthermore, smart procedural design could increase the ability
of GA to fly in controlled airspace, such as Class B airspace. The small
aircraft operator community currently has very limited access to weather
and traffic information in flight. This segment of the aviation
community, however, is most susceptible to the presence of adverse
weather and other traffic. In addition, the status of SUAs is not
available on a timely basis, limiting the use of that airspace by public
users.

### 64.2.5Number range Level3Number range Level4 Approach and Landing

During approach and landing, the pilot is almost entirely dependent on
the ground system and visual acquisition of traffic. In low visibility
conditions, the pilot in final approach cannot see traffic on the
airport surface, sometimes leading to runway incursions. Also, because
arrival rates are based on visual acquisition of traffic, which is not
always easily accomplished, greater separations are used to assure
safety, thereby reducing system capacity. A pilot cleared to follow a
specific aircraft often cannot positively identify that aircraft. Low
visibility conditionssuch as weather, night time operations, and
hazeall have a negative impact on operations and capacity. Finally, the
lack of surveillance information increases the need for communication
between the pilot and controller, affecting system capacity.

Thus, there is a need for an improved set of surveillance data for
safety and to increase airport capacity.

## 64.3Number range Level2Number range Level3Number range Level4 Fleet and Ramp Management Operations and Limitations from Surveillance

Currently, air carrier involvement with surveillance by airline
personnel on the ground (hereafter referred to as "airline operations")
is based primarily around three objectives:

1.  Basic flight following capability mandated by FAR (Part 121.99,
    121.533, 121.535, et al.).

2.  Meteorological information required for dispatch release, alternate
    planning, and safety of flight (FAR Part 121.599, et al.).

3.  Monitoring of aircraft locations for commercial purposes (e.g.,
    information needed to design, maintain, and revise schedules to
    maximize economic performance).

The surveillance timeliness and accuracy requirements for airline
operations are generally relaxed compared with ATC surveillance
requirements. The major exception to this statement is in ramp
operations (i.e., operations on the non-movement area of the airport),
where ATC does not provide any separation services.

Air carriers rely on several means to obtain aircraft position
information, both government and non-government owned. The primary
FAA-sourced surveillance asset is the Enhanced Traffic Management System
(ETMS)/Aircraft Situation Display, which provides the dispatch center
with one-to-four minute updates in the CONUS from ARTCC host data of
position, speed, altitude, and ground track. The FAA has given a new
name to the Aircraft Situation Display (ASD): Traffic Situation Display
(TSD). In addition, the ETMS feed also provides a rudimentary ETA
capability; however, most carriers have found that this information is
not accurate enough for gate and ramp management.

In addition to the ETMS feed, airlines sometimes use secondary
surveillance radars, either through a direct link to the radar, or by a
passive listening scheme (i.e., PASR). This information is typically
only gathered by particular airlines at their hub airports. Further, the
surveillance information from ASDE is not shared with non-FAA entities
around the airport. Therefore, operators do not have accurate
information on aircraft location between landing and arriving at the
parking spot. Often aircraft must hold out away from the parking area.

Non-government methods for obtaining flight information are also used by
airlines. Most notably are automatic Out-Off-On-In (OOOI) reports
generated by avionics onboard the aircraft. Some airlines have
programmed their aircraft avionics to periodically send position reports
to the dispatch office at an interval of 5 to 30 minutes, and include
use of SATCOM resources as a link for global coverage. Airlines want to
manage aircraft and gates to optimize operations, and provide connecting
information to passengers. They currently don't get enough timely
information to manage these, sometimes resulting in diversions of
aircraft, gates, or crews.

Currently, air carriers generally obtain meteorological information from
private weather service providers. There are sometimes discrepancies
between this and NAS meteorological data, leading to differences in
plans. Some carriers retain certified meteorologists on staff to provide
forecasts tailored to routes and regions of particular interest to that
carrier. Finally, some air carriers have programmed their aircraft
avionics to send periodic weather observations while in flight.

Of increasing concern to global air transport is the surveillance and
reporting of volcanic ash. The FAA and NWS, using the geostationary
operational environmental satellite (GOES) satellite capability,
cooperate in tracking volcanic ash. Occasionally, pilots are the first
to see volcanic activity, and are expected to deliver the first warning
of the activity through a Pilot Report or Air Report. Continuing
volcanic ash information is distributed in the system via SIGMET, NOTAM
(ASHTAM), and PIREP. The VAFTAD is developed and distributed as
necessary by NOAA/NWS/NESDIS.

The following paragraphs describe fleet management surveillance
operations and limitations by phase of flight for air carrier
operations.

### 64.3.1Number range Level3Number range Level4 Preflight

About two hours prior to flight, a dispatcher begins planning the fuel
and route for that flight using commercially-provided weather products
and/or staff-provided weather information. The weather information
received is generally adequate for the United States, and is usually
acceptable for the rest of North America and parts of Europe and the
Asia/Pacific region.

The dispatcher must compensate for several limitations. Meteorology data
for locations without weather radar coverage or surface observations
(oceanic and remote areas) is inadequate. The quality of en route winds
aloft and turbulence information is inadequate. This information is
currently based on computer models with limited inputs (e.g.,
radiosondes), and is inaccurate, reducing safety. Freezing precipitation
is a danger to aircraft. AWOS does not provide horizon-to-horizon
evaluation of the weather situation.

For commercial flights, an aircraft is assigned to a scheduled flight.
The aircraft assigned to this flight is generally known well in advance
(24 hours or more), but delays and cancellations of previous flight legs
could be cause for reassignment of an aircraft to other flights. This
information is typically calculated by internal airline computer
resources, based on OOOI information; however, an abnormal operation
with multiple delays, diversions, or cancellation may force a real-time
reassignment of aircraft based on ETA information of aircraft in flight.
In cases of abnormal operations, dispatch also uses knowledge of
weather, forecasts of airport demand, and FAA flow control programs to
determine whether to delay or cancel outbound flights.

A significant problem for the airlines is the fact that ETA information
from aircraft in flight is generally not very accurate; a more accurate
prediction of "On" times would allow dispatchers to make decisions with
higher confidence.

It should be noted that AOCs' decisions are also limited by their own
internal ground systems. For example, it has been noted that at one
carrier, connection information sent to aircraft in flight to inform
passengers is based on the original scheduled landing time, and not the
actual landing time after experiencing a departure delay--"stale"
information is sometimes perpetuated by the internal AOC ground system.

### 64.3.2Number range Level3Number range Level4 Gate Management/Pushback/Departure

Traffic and fleet managers must be provided accurate surveillance
information if an airport's limited runways, gates, and other resources
are to be effectively used. SMA provides very useful arrival information
and has demonstrated the potential to aid controllers in efficiently
queuing aircraft for departure.

The Estimated Time of Departure (ETD) is assigned by the gate agent for
the flight (in conjunction with other personnel), based on incoming
aircraft ETA and observation of the readiness of ground service
personnel and flight crew, but is still largely a matter of personal
experience.

Limitations are evident in that the accuracy of the ETD is highly
dependent on the gate agent's ability to account for a variety of
factors including maintenance, baggage loading, refueling, cleaning,
catering, passenger loading, flight crew prep, and other, often
non-quantifiable factors.

Sometimes the gate agent and dispatch use ETAs of inbound flights to
make a decision on whether to delay another flight to connect passengers
or crew members, or to make alternate passenger arrangements, and use
reserve pilots and flight attendants. However, inaccurate ETA data can
lead to a faulty decision to hold or depart a flight.

Ramp control uses ETA and ETD information to predict future gate
availability and assign gates to incoming flights. This information is
passed on to the land-side operation so that gate information is kept
up-to-date for passengers checking in or connecting.

Once again, inaccurate ETA/ETD information can lead to gates and other
ground resources not being used efficiently, which in turn can lead to
collateral delays. For example, otherwise ready aircraft may be unable
to push back due to congested ramp space.

When the aircraft has been pushed back from the gate, an automatic "Out"
report is sent via ACARS. This is used by the airlines to identify that
the gate is now available. The existing Out report is generally
considered to be accurate enough.

Once the aircraft lifts off from the runway, an automatic "Off" report
is sent via ACARS. This report is used to start a second clock for
flight time, which is used by maintenance to schedule periodic checks on
airframes. Flight time is also used by flight crews to log flight hours.
The existing Off report is generally considered to be accurate enough.

The aggregated difference between Out and Off information is used to
estimate taxi time and fuel usage, and to make changes to schedules.

### 64.3.3Number range Level3Number range Level4 Climb/Cruise

Once airborne, dispatch starts getting ETMS and/or ACARS position
updates for each aircraft. The dispatcher monitors flights that may be
affected by weather en route and possibly require rerouting. Wind and
turbulence information sent by in-flight aircraft is used by ATC and
dispatch to update wind forecasts and route plans. Good aircraft and
weather surveillance is vital to the safe handling of rerouting.
However, for international traffic, the quality of surveillance
information outside of CONUS is degraded compared to domestic ETMS data.

ETA can be predicted more accurately once airborne: for example, it has
been noted that adding the flight plan Estimated-Time-En route to the
ETMS departure time yields a more accurate arrival time than ETMS by
itself. Increased accuracy of predicted "On" times have the potential to
greatly improve efficiency of airline operations during ground turns.

### 64.3.4Number range Level3Number range Level4 Arrival

Users do not currently have arrival sequencing information. As a flight
enters radio range of the destination, the ETA prediction becomes much
more accurate.

The lack of accurate ETA information sufficiently in advance of the
aircraft's arrival impedes efficient operations. Without accurate and
timely ETA information, airlines cannot effectively manage ramps, gates,
service personnel, passenger connections, and flight crew connections.
This becomes especially critical when business or safety factors are
affected, such as flight crews exceeding FAA maximum time limits, or
fuel reserves approaching standard minimums.

Once the aircraft has touched down, an automatic On report is sent to
allow organization of resources for gate arrivals and to inform the
public of the status of the flight through the Flight Information
Display System (FIDS). The current On report is generally considered
adequate.

Operators do not have accurate information on aircraft location between
landing and arriving at the parking spot. Often aircraft must hold out
away from the parking area/gate. ASDE information, when coupled with
identification tags, would be of great value to all parties, but is not
currently available. As traffic increases, asset management becomes even
more dependent on the most current information. Operators' efficient
gate and aircraft management can complement surface movements by
avoiding unnecessary delays on congested taxiways and hold pads. The
sharing of future ASDE presentations, or like data, with ramp towers and
fleet managers leads to greater customer satisfaction, asset management,
and reduced time-consuming inquiries between control towers and
operators.

Once the aircraft is parked at the gate, an automatic In report is sent
to stop logging of block time for crew labor calculation, as well as
estimating future taxi-in and block-hour schedules. The existing In
report is generally considered adequate.

# Section 65Number range Level1Number range Level2Number range Level3Number range Level4Number range FigureNumber range Table {#section-65number-range-level1number-range-level2number-range-level3number-range-level4number-range-figurenumber-range-table .Section-Heading}

# Future Operational Environment and Characteristics {#future-operational-environment-and-characteristics .Section-Header}

This section presents the guiding principles that were the foundation of
the surveillance operational concept, building on improved surveillance
information. An overview of the concept is then described. Note that in
the rest of this document, the term "controller" is replaced by "service
provider" to indicate an evolution of tasks from today's largely manual
system to the future NAS.

## 65.1Number range Level2Number range Level3Number range Level4 Guiding Principles

Within this document, a number of principles form the foundation of the
operational concept for the role of surveillance, especially with
respect to separation assurance. These key principles, as outlined
below, are essential.

-   *[The overriding premise in managing air traffic is
    safety]{.underline}*. Therefore, any recommendations with respect to
    the operational applications of surveillance information is aimed at
    raising the target levels of safety, concomitant with the projected
    increases in air traffic levels. Changes in separation methods,
    roles, and responsibilities to increase system performance occur
    only if they are demonstrated, certified, and proved to materially
    enhance system safety. Merely replicating the current ground-based
    system safety achievement in an airborne system is not a goal of
    future operations.

-   *[The operational objectives of new concepts must include improved
    capacity and efficiency in all weather and visibility conditions, to
    accommodate increasing demands]{.underline}*. Current technology can
    support this via the application of new procedures, while still
    maintaining safety. In addition, new capabilities being developed
    have increased capacity and efficiency as a primary goal.

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-   *[The surveillance system provides uniform availability of shared,
    rich, and reliable data to service providers and users of the
    NAS]{.underline}*. Surveillance data performance and quality,
    coupled with the necessary access and interface methods, supports
    unambiguous, timely, and reliable applications for safe separation
    of aircraft in all flight regimes.

-   *[Development of procedures and training of controllers are
    extensive]{.underline}*. New procedures are developed to take
    maximum advantage of all available surveillance data. Controllers
    are thoroughly trained in these procedures, allowing their
    implementation to maximize system efficiency.

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-   *[Training, supporting, and developing roles are performed in a
    nonpunitive culture rather than one focused on punitive regulatory
    enforcement aspects or decertification]{.underline}*. This is
    applied both to service providers as well as to pilots. Tools that
    provide cues to service providers or to pilots are used as means to
    provide feedback and improve performance and are not used as a
    trigger for disciplinary action.

-   *[Common, consistent separation standards are applied based on total
    system performance, rather than by airspace
    designation]{.underline}*. The future system infrastructure supports
    a common minimal separation standard across all domains. This
    dictates a commonality of surveillance information across domains.
    The goal of applying a common separation standard between terminal
    and en route airspace could serve as the important initial step in
    demonstrating the efficacy of reduced separation minima. There is a
    distinct difference between the targeted separation (e.g., 3 miles)
    and an explicit safety margin; service providers and pilots are
    aware of the safety margin, and if the targeted separation varies
    but the safety margin is still maintained, then there is no negative
    repercussion.

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-   *[User equipage is benefits driven]{.underline}*. However, in some
    airspace, as today, users are restricted from operating unless they
    can support a minimum level of surveillance performance (either from
    a ground or cockpit perspective). This airspace may include separate
    "arrival" streams, tracks (e.g., in oceanic airspace), or entire
    blocks of airspace (e.g., Class A is restricted to IFR). To get the
    increased airspace access and performance benefits, general
    aviation, corporate, and commercial operators are tasked to support
    the level of surveillance equipage required for enhanced operations
    within these areas of NAS.

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-   *[New means of achieving separation objectives do not fundamentally
    change the nature of interactions between pilots and service
    providers]{.underline}*. The FAA continues to be responsible for
    establishing new procedures and ensuring that the tools supporting
    them are operationally suitable. These new procedures may support
    greater flexibility, increased safety, and increased capacity. Some
    of these procedures result in delegation of separation
    responsibility to the pilot. In all cases, service providers
    continue to have the discretion of when to issue what clearances;
    pilots continue to have discretion in requesting or accepting
    procedures.

## 65.2Number range Level2Number range Level3Number range Level4 Overview of Future Surveillance Operational Concept

The future concept for Free Flight in the NAS capitalizes on
surveillance improvements as one of the foundations for removing
restrictions. These, by nature, go beyond traditional ground-based
radar. Surveillance continues to be used in functions such as separation
assurance, conformance monitoring, collision avoidance, and fleet
management. Improved surveillance information, combined with enhanced
tools for the people who interact with the NAS, has a role in improving
safety, reducing separation standards, improving performance of
automation and decision support tools, and enhancing a common awareness
among members of strategic and tactical traffic situations.

Use of improved surveillance information in the cockpit and on the
ground evolves incrementally as operational experience is gained and as
confidence increases in the system performance. Figure 3-1 presents the
future surveillance system's role in a modernized NAS.

###### ![](media/image2.png){width="6.4in" height="4.5in"}

###### 

###### 

###### To be supplied

###### 

###### 

###### 

###### 

###### Figure 65-1. Mature State Information-Based Surveillance Operations for NAS Air Traffic Services

Traditional primary and secondary radar are still in use. However, this
is supplemented by aircraft position reporting via datalink. These, plus
any future modes of position reporting that may be developed, are
transferred through a LAN that makes the data available to any facility.
The surveillance data from all sources, independent of sensor location
or type, is processed and integrated into a single view of each sector's
airspace for display to that service provider. The resulting target
locations are more accurate, thereby improving the accuracy of predicted
aircraft positions and predicted problems. There are fewer missed alerts
and fewer unnecessary safety-induced avoidance maneuvers. Consequently,
the combination of modernized surveillance capabilities along with
problem prediction and resolution allow a shift in the service
provider's role from a tactical one to that of more strategic planning.
Additionally, the more accurate location of aircraft allows reduced
separation standards, and therefore increased capacity. For the users,
the benefit of this fusion of capabilities is increased user-preferred
routing.

To reiterate the safety imperative, any universally implemented
operational application is fully developed, certified, and approved. As
an example, the initial use of Multi-Functional Displays (MFD) in the
cockpit are expected to be informational, providing pilots with an
improved situational awareness and enhancing safety and their ability to
operate the aircraft according to current operations (both IFR and VFR).
This improved cockpit surveillance information is shared with the ground
systems. As confidence is gained, some procedures are expected to
require pilot and service provider agreement to use information to aid
in the execution of a maneuver, such as a passing instruction. However,
no maneuver is ever performed at less than an approved separation safety
margin standard. "See and avoid" is not considered a separation
standard. Progressively, certified and approved separation standards for
EFR are expected to be developed. Ultimately, in some airspace,
ground-based dynamic management of operations under EFR is minimal.
Separation management is accomplished by procedure design and user
compliance. For larger air carriers, the procedures are assumed to
operate at a high level of safety, such as is achieved by a safety net
provided by an active Airborne Collision Avoidance System (ACAS). No
procedure relies on a single fault failure strategy. Aircraft
capabilities provide improved conflict management and situational
awareness capabilities to increase overall safety, flexibility, and
efficiency.

In this operational concept, the role of surveillance is highlighted for
a number of functions. Some of these functions are performed only by
pilots or by aircraft systems; other functions are performed only by
service providers. Airborne collision avoidance, for example, remains a
function performed in the cockpit. Conflict management functions include
the prediction of conflicts and the generation of strategies to avoid
the predicted conflict. The latter function is generally referred to as
conflict resolution. For airborne conflict resolution, however, this
function is denoted as *flight path deconfliction* to minimize confusion
with the resolution advisory function of a collision avoidance system.

The rest of this section elaborates further on the three key functional
areas Collision Avoidance, Conflict Management, and Separation
Assurance. These fundamental concepts are then integrated into Section
Four, which details the transition from near-term to mature-state
operations in different domains of flight management.

### 65.2.1Number range Level3Number range Level4 Separation Assurance 

Separation assurance is the primary task of ensuring safe flight
operations. Separation assurance involves the maintenance of a safe
interval between aircraft and any vehicles operating in the same areas.
This is in contrast to collision avoidance (see section 3.2.3), which
provides a "safety net": an immediate response to a potential collision.

The concept for separation assurance takes into account that NAS users
conduct sometimes widely disparate operation, and that military
operations often require segregation from the civil air traffic. In
addition, new cockpit capabilities building on improved surveillance
provide pilots and service providers additional tools to achieve
separation objectives. However, they do not fundamentally change the
nature of interactions between pilots and service providers. The FAA
continues to be responsible for establishing new procedures and ensuring
that the tools supporting them are operationally suitable. Future
procedures support greater flexibility, increased safety, and increased
capacity. Some of these procedures result in delegation of separation
responsibility to the pilot, codified as a set of EFR. In all cases,
service providers continue to have the discretion of when to issue what
clearances; pilots continue to have discretion in requesting or
accepting procedures. These separation assurance responsibilities are
summarized in Figure 3-2.

![](media/image3.wmf){width="5.99375in" height="4.2131944444444445in"}

**Figure 3-2. Separation Management**

#### 65.2.1.1Number range Level3Number range Level4 Separation Management

The Separation Manager is the person who is currently responsible for
assuring separation for the current flight operation, and for
identifying conflicts and resolving them. Separation Management, as
illustrated in Figure 3-2, is the process of designating responsibility,
applying separation assurance measures, and as appropriate, transferring
responsibility to a new separation manager. Traditionally, the service
provider acts as the separation manager for instrument flight rules
(IFR) operations in controlled airspace. In this case, the transfer of
responsibility occurs between service providers as an aircraft crosses
sector boundaries. In VFR operations, the pilot is generally responsible
for separation management[^1]. Normally, there is no transfer of
separation responsibility for a VFR aircraft unless the pilot elects to
request IFR services. Separation responsibility may also be temporarily
delegated by the service provider to the pilot in certain procedures,
such as visual approaches.

*Separation Assurance* is the application of specific measures to ensure
a separation standard, or minimal distance (lateral, longitudinal, and
vertical) between an aircraft and other potential hazards, or between an
aircraft and protected airspace. The separation assurance process
involves three key steps:

-   The separation manager uses available surveillance and tools (e.g.,
    procedures, automation, and guidelines) to predict potential
    conflicts between the aircraft and other aircraft, obstacles,
    terrain, weather, airspace containing potential hazards, and other
    restricted or prohibited airspace.

-   The separation manager determines one or more actions to ensure
    adequate separation, and communicates this with affected flight
    crews and service providers. If a flight crew cannot accept one of
    the needed actions, the separation manager determines an alternate
    action.

-   The separation manager monitors the execution of the action, and
    provides corrective action as necessary.

The separation standard applied to the aircraft may depend on a number
of factors, including aircraft navigation quality, the ability of the
separation manager to monitor the situation and to predict conflicts,
and the expected intervention time, which can be affected by factors
such as aircraft speed. Navigation quality of the aircraft and of other
aircraft in the nearby airspace (for example, actual navigation
performance \[ANP\]) is the basis for determining how much uncertainty
there is in their expected position. Monitoring is affected by the
quality of both the surveillance information (such as the uncertainty of
reported position, update period, etc.) and the utility of displays.
Conflict prediction capability may either be performed mentally or
through the use of conflict prediction tools, with various look-ahead
times. Look-ahead time is dependent upon the needed time for the
separation manager to intervene and apply corrective measures, if a loss
of separation is anticipated. Critical to this is the quality of the
communications between the affected parties (including speed of
communication).

As indicated in the previous paragraph, the quality of surveillance
information is a key factor (but not the only one) in predicting
potential conflicts and in monitoring the execution of a pilot action.
For example, aircraft operating in oceanic airspace without radar
coverage have higher separation minima than aircraft operating in a
radar-controlled terminal environment with much more accurate
surveillance data.

It should be noted that current separation standards are based on
historical experience with a variety of factors. These include pilot and
service provider performance, limited aircraft and ground automation
performance, voice communication systems performance, and radar
surveillance system characteristics. Empirical observation of current
operations suggests that these standards provide a sufficient level of
safety. A change to separation standards in the future requires an
analytic study of the affected existing system elements. Then, any
suggested change to separation standards based on improved surveillance
or other system elements must be analyzed to show that an improved level
of safety will exist with the modified standards.

New cockpit and ground automation capabilities, building on improved
surveillance, provide pilots and service providers with additional tools
to achieve separation assurance objectives, but does not fundamentally
change the nature of the separation management process or the
interactions between pilots and service providers. The FAA continues to
be responsible for establishing new procedures and ensuring that the
tools supporting them are operationally suitable. These new procedures
support greater flexibility, increased safety, and increased capacity.
Some of these procedures result in temporary delegation of separation
responsibility to the pilot for either pair-wise operations or for
general responsibility that takes place under a codified set of extended
flight rules. In all cases, service providers continue to have the
discretion of when to issue a clearance to apply new procedures building
on new tools; pilots continue to have discretion in requesting or
accepting procedures involving these new tools.

Under EFR, separation management is performed by the pilot, with
additional monitoring performed by the service provider. If the service
provider anticipates that the complexity of the situation may be too
difficult for EFR conventions to resolve predicted conflicts, the
service provider can issue instructions to transfer separation assurance
responsibility and resume the role of separation manager.

#### 65.2.1.2Number range Level3Number range Level4 Application of Separation Standards 

The future system infrastructure supports a common minimal separation
standard across all domains. This is supported by a commonality of
surveillance information across different flight management domains. One
of the first steps in reaching this goal is the elimination of
artificial differences in separation between terminal airspace and en
route airspace; efficiencies gained through the use of 3 nmi separation
standards is extended past traditional terminal airspace areas and is
applied in en route airspace. The reduction of separation minima (while
maintaining safety), provides both service providers and pilots more
options in maintaining overall objectives for managing flight operations
and results in fewer restrictions, fewer changes from user-preferred
routes, and reduced workload.

Application of improved surveillance data to separation standards is
focused first on improving methods of separating aircraft from aircraft
while requiring fewer restrictions on aircraft for airspace access.
Next, the surveillance information is used to the fullest to develop the
policies, procedures, and tools to attain the current separation
standards by engendering the operating confidence and capability to
safely reduce the separation between aircraft to that standard. An
explicit difference is made between identifying the target separation
standard and the minimal allowable separation, or safety margin.

Because there is a difference between the target separation standard and
the safety margin, both service providers and pilots become more
confident in their ability to achieve efficiency and capacity
objectives. In particular, tools are provided that maintain awareness of
aircraft operating near the safety margin, providing progressive cues
when margins are close to being exceeded. These tools, however, are not
used as means of enforcement or for discipline on performance, and
results are not used to decertify either pilots or service providers.
The change in the use of tools to an advisory nature, in addition with
other incentives, encourages users and service providers to support
overall system capacity and efficiency objectives. These objectives are
understood, however, to maintain overall system safety and do not
compromise the ability of service providers or pilots to respond to
situations where safety needs must be addressed.

### 65.2.2 Conflict ManagementNumber range Level3Number range Level4 

In most airspace, users are authorized by the service provider to
perform self-separation functions. In less dense airspace,
free-maneuvering is the primary mode of operation, and pilots and
service providers use a common set of EFR that provide bounds on the
movements and on the resolution of conflicts between aircraft. The
increased safety and flexibility of free maneuvering under EFR results
in an increased user participation in the system; fewer users fly under
VFR since EFR provide equivalent or nearly-equivalent flexibility with
greater protection.

With separation standards in en route airspace reduced to three nmi and
1000 feet in all airspace, users have more opportunity to fly at
preferred routes and altitudes. The reduction in separation standards,
in addition, reduces the likelihood of conflicts, allowing fewer
diversions from the user's optimal flight path.

Service providers operate primarily in a monitoring role, but still
provide separation assurance services to the few aircraft that are not
equipped or authorized for self-separation, or for those users who
prefer to receive separation services from the air traffic control
facility.

Improved conflict prediction and resolution are crucial to a safe and
efficient ATM that is able to satisfy the demands of the future air
traffic. Improved trajectory modeling systems manage flows of aircraft
and more accurately predict conflicts. Improved conflict resolution
capabilities reduce service provider workload and increase the safety of
the system. Improved user interfaces are efficient and intuitively
apparent, and provide a wide suite of capabilities that allow the
service provider to safely and efficiently manage the airspace.

**Self-separation** and **free maneuvering** are Free Flight techniques
that can be employed to meet user goals in optimizing their operation
and maintaining flexibility. In this operational concept,
self-separation refers to the use of cockpit tools and procedures for
separation assurance during which separation responsibility is delegated
to the pilot under a precisely defined set of EFR. Delegation of
separation authority to the pilot is done by a positive transaction
between the pilot and the service provider, much as is currently done
with an IFR clearance. In some environments, free maneuvering may not be
an option. Some busy terminal airspace, for example, may require more
structured operation as the default mode.

Free maneuvering refers to the ability for pilots to make adjustments in
speed, heading, or altitude without prior approval from the service
provider, but within a constrained subset of EFR. Free maneuvering is
only authorized as long as the aircraft remains conflict free with other
aircraft, restricted airspace, or other hazards. Free maneuvering may be
performed with either the pilot or the service provider acting as the
separation manager. It is expected that for initial operations, the
service provider continues to maintain separation responsibility.

In a given airspace, self-separation or free maneuvering is authorized
or "cleared", provided the service provider and pilot agree that the
situation can be handled safely. It is critical that during the period
of operation, both pilot and service provider agree that the complexity
of the operation can be managed, and that a positive statement and
acceptance of the clearance is transacted Tools are needed to predict
changes in dynamic density (situation complexity). These tools generate
an alert well in advance of an overly complex situation occurring. With
the receipt of an alert, service providers issue amended clearances to
the pilots engaged in self-separation or free maneuvering, resulting in
an orderly transition back to ground-based IFR separation assurance and
responsibility.

Both self-separation and free maneuvering require that the pilot have a
surveillance capability in the aircraft that supports situational
awareness and provides the capability to easily predict conflicts. In
addition, some aircraft may also include flight deconfliction tools to
manage longer-range potential conflicts with other aircraft. This
requires a conflict probe capability in the aircraft plus a surveillance
capability with intent[^2] extending over 100 nmi to ensure that
conflicts can be corrected with minor changes in course, altitude, or
speed.

During the period that pilots are free maneuvering, EFRs are employed,
so that each user can predict the behavior of others, and determine
their own appropriate action. At a minimum, all aircraft must be
detectable to other aircraft that have a collision avoidance function,
and must support ground surveillance requirements. Aircraft not
participating in self-separation or free-maneuvering continue to be
provided separation assurance services from service providers; aircraft
that are free-maneuvering are required to go around "less-capable" ships
and those operating under VFR following well defined and validated EFR.

Self-separation is used when all necessary steps have occurred to ensure
that the operation is safe; this is implicit in the set of EFRs. This
includes the explicit clearance for transfer of responsibility from the
service provider, acceptance by the pilot, definition of appropriate
separation standards and procedures, assurance that adequate cockpit
tools are in place, that both pilots and service providers are
adequately trained, completion of necessary risk analyses, and
definition of failure mode responses. In addition, self-separation
operations are associated with a minimum required total system
performance (RTSP), not just the surveillance performance of aircraft.
Total system performance includes communications performance, navigation
performance, and any decision support tool capability deemed necessary
in both the cockpit and in the ground facility that is responsible for
monitoring the operation.

### 65.2.3 Number range Level4 Collision Avoidance

Collision avoidance capabilities are, and continue to be, essential
elements of safe aircraft operation. Collision avoidance is defined as
the function required to provide an immediate response to a potential
collision between two aircraft.

Advice to maneuver from an aircraft's collision avoidance function still
takes precedence over a conflict management capability. All pilots
continue to be required to perform visual scanning. Regardless of the
automation and surveillance on-board, visual scanning continues to serve
as a means to verify information and to assess potential threats not
identified by surveillance means. In addition, some classes of users are
required to carry certified collision avoidance equipment that provides
an increased level of safety. In addition, in much of the airspace, as
is today, aircraft are required to carry equipment enabling them to be
detectable to these collision avoidance systems.

While operating in civil airspace, unmanned vehicles or remotely
operated vehicles are required to participate in collision avoidance and
must be "visible" to allow detection and collision avoidance. In
addition, these vehicles must have either an on-board or remote
capability to "see and avoid" other aircraft.

Low-end users, especially those operating under VFR flight rules, have
enhanced situational awareness through capabilities that provide
improved traffic situational awareness and awareness of potential
conflicts, but do not necessarily have equipment certified as collision
avoidance equipment. Although this service does not support collision
avoidance needs, the displays providing increased situational awareness
does provide increased effectiveness of visual scanning, and provides
alerts of possible short term conflicts, giving pilots more time to
assess and respond to situations.

## 3.3 Architectural Concepts and Functional Needs

The NAS of the future evolves from today's ground-based radar system to
one that is information-based, with a common surveillance picture shared
among all participants in the NAS. This common surveillance picture
allows all participants to improve decision-making, making the system
safer and more efficient.

### 65.3.1 Number range Level3Number range Level4 System Architecture

The future system concept and architectural requirements ensure that
surveillance and separation functions accommodate all normal and
non-normal operational conditions and provide rapid recovery for
scenarios where major service upset cannot be completely prevented.
Automation data requirements and processing are major drivers in the
surveillance concept for the future. Automation significantly enhances
the ability of the users of the data to assimilate, interpret and apply
collaborative decision making capabilities. The human-machine interface
(HMI) and decision support automation are designed to ensure that
improved workload, cognitive response, and decision processes result
from the enhanced information, whether airborne or on the ground.
Uniform availability of information is expected to drive the level of
automation, processing, and HMI requirements for data type,
availability, performance, etc.

Interoperability of separation methods and surveillance equipment and
tools are maintained on an international basis.

### 65.3.2 Number range Level3Number range Level4 Data Security and Privacy

The NAS has evolved as an immense confederation of disparate systems
that have arisen independently without integrated information security
controls. As the NAS itself is modernized, changes to operations and
supporting systems address user and service provider needs for both
physical and information security.

Security issues for surveillance data that must be addressed include
spoofing, jamming, and passive targeting.

Another data security concern is that of privacy. VFR users currently
maintain some level of privacy while still participating in the ATC
system through the use of transponders with the "1200" code. This allows
others to be aware of their presence while preserving individual
privacy. New operations and systems related to surveillance need to
maintain this model. For example, when using ADS-B, privacy issues must
be mitigated by the use of unique alternatives to broadcasting the
24-bit International Civil Aviation Organization (ICAO) identifier that
contains specific, universally available, aircraft identification data.
Authentication by the crew at predeparture helps alleviate repudiation
concerns.

***{NOTE - WILL BE GETTING INPUT FROM AOPA)***

There are also privacy needs for other classes of users. Corporate
flights, for example, may be participating in the ATC system but may
wish to keep their identity undisclosed to parties outside of the
system. As collaborative decision making increases, and there is more
data sharing between the Air Traffic Control and AOC systems, there may
be requirements to shield proprietary data from other carriers, while
maximizing the exchange of surveillance information supporting CDM.
Access to surveillance data has at least as stringent requirements as
that for Flight Data Recorders (FDRs).

System-level security issues for surveillance are being readdressed with
the consideration of new technology. Some of the security issues that
have been identified with surveillance information are:

-   Availability: sending, receiving, and processing surveillance
    information within the required time limit

-   Privacy: providing adequate protection against information misuse

-   Integrity: providing correct data to qualified users

-   Repudiation: rejecting claim of ownership

# Section 66Number range Level1Number range Level2Number range Level3Number range Level4Number range FigureNumber range Table {#section-66number-range-level1number-range-level2number-range-level3number-range-level4number-range-figurenumber-range-table .Section-Heading}

# NAS Surveillance Operations by Domain and/or Phase of Flight {#nas-surveillance-operations-by-domain-andor-phase-of-flight .Section-Header}

The concepts presented in the previous section are amplified here by
domain or phase of flight: flight planning, airport surface, terminal,
en route, oceanic, and TFM. Each domain presents unique challenges to
achieving the future concept; these are satisfied via the implementation
of integrated capabilities and procedures that empower the achievement
of needed benefits.

## 66.1Number range Level2Number range Level3Number range Level4 Flight Planning Surveillance Needs

This operational concept applies to the broad spectrum of aviation
during the pre-flight planning phase as well as in flight. During the
flight planning phase, airlines with AOCs and GA with AOC-like
capabilities are able to file ICAO-formatted Filed Flight Plans (FPL)
using the en route automation system.

The Flight Information Service (FIS) provides needed flight planning
information for users of the NAS. FIS is defined as the non-control,
advisory information needed by pilots to operate more safely and
efficiently in the NAS and in international airspace. Flight Information
Services provide to pilots the necessary weather graphics and text, SUA
information, notices to airmen (NOTAMs) and other information. The goal
for FIS in the cockpit is to use digital data link to deliver
information to the pilot, to improve safety, reduce costs to users and
increase the utility, efficiency and capacity of the NAS. The timely
provision of high quality, accurate, and consistent information is
essential to support sound operational decisions by pilots, service
providers, and dispatchers.

The concept of autonomous aircraft operations requires greater access to
FIS information than is currently available to the user community. For
example, part of the concept requires the availability of accurate
weather observation and forecast information that can be transmitted to
aircraft in flight to allow Flight Management Systems (FMS) to optimize
fuel consumption.

For general aviation, it is important to emphasize the need for low-cost
equipage and avionics that enables, and thus encourages, participation
of this user in the future free flight vision. Therefore, a broadcast
data link system for FIS information is preferred, based on anticipated
lower equipment costs and ease of operation, which allows FIS data link
dissemination to the widest range of users. Finally, the limited cockpit
resources in a single pilot operation demand that the operating
procedures for the data link system be intuitive and easy to understand
and use.

### 66.1.1Number range Level3Number range Level4 Near Term Flight Planning

Flight planning for the near term remains much as it is today. However,
if an aircraft is properly equipped, users are able to file
user-preferred routes from departure airport Instrument Departure
Procedures (DP) to arrival airport Standard Terminal Arrival Routes
(STAR) or direct routings between airports applying user defined
waypoints or similar. Furthermore, all users can probe against system
constraints such as hazardous weather, SUA, flow restrictions (airspace
facility demands), and infrastructure outages so that the flight planner
has an improved awareness of conditions along the proposed route and
whether the flight may need to be rerouted after departure.

Collaborative flight planning begins as the air traffic service provider
and the AOCs use visual collaboration media supported by automation
capabilities to exchange real-time information regarding airspace or
flow restrictions. This information is used by the AOC to prepare flight
plans resulting in reduced reroutes. The user is able to obtain a
complete weather briefing for the proposed route via AOC computer. In
addition, system wide information is obtained through the AOC computer.

For the majority of GA pilots, flight planning and filing require access
to an air traffic service provider, who can provide the weather and
system briefings necessary for the flight. Some users, however, have
access to system wide information through a personal or Fixed Based
Operator (FBO) computer and can print the appropriate information on an
attached printer. This service is not much different than services
available today, except for the ability to probe flight plans against
system constraints.

Initial FIS products for delivery to the cockpit include information on
the status of the NAS, such as Notices to Airmen and Special Use
Airspace, as well as meteorological information, both in textual as well
as graphical format. This new service is dependent on a public/private
partnership to provide affordable FIS products. The FAA utilizes the
private sector's FIS capabilities to the maximum extent possible to
bring FIS services and products to the aviation community quickly and
efficiently. Therefore, future FIS services are multi-tiered, with
certain services and products being provided by the Government and
others by the private sector.

In the near term, DoD continues to use flight plans to describe their
intended route and altitude for a flight within the NAS.

### 66.1.2Number range Level3Number range Level4 Transition Period Flight Planning

It is useful to separate FIS needs into two general classifications of
meteorological data and facility/traffic information. Weather
information, such as winds aloft or precipitation data, is fairly well
defined in content and is separable into many independent information
elements. The content of facility and traffic information, such as
runway conditions, facility availability, SUA, or traffic flow reports,
is quite variable in content and still in development.

The flight planning process includes the improvements made in the near
term with capabilities further enhanced due to real time sharing of
information regarding system demand on the NAS. Service providers move
to a collaborative interaction with the user, where both reveal
strategies and constraints and mutually develop solutions to problems.

Users have the information, tools, and an interactive capability
necessary to create a flight profile that can be as simple as the user's
preferred route or as detailed as a time-based trajectory, including
preferred climb and descent profiles. The user supplies the service
provider with the flight profile that best meets requirements. This
flight plan information is automatically available electronically to all
service providers until the termination of the flight. Information such
as runway preferences and aircraft weight, or information to support
flight following, can be added during the planning phase.

As the user generates the profile, information regarding current and
predicted weather conditions, traffic density, restrictions, and status
of SUAs is available. When the profile is filed, it is automatically
checked against these conditions and any static constraints such as
terrain and advisories. Potential problems are displayed automatically
to the user for reconciliation. Upon filing, the flight profile created
at the initiation of planning is updated as are all affected projections
of NAS demand.

For all users, an enhanced flight plan is available that provides a much
larger data set, including preferred trajectory, aircraft weight, runway
preference for departure and arrival, gate assignment, and cross-border
issues for international flights. The information within this flight
profile can be updated throughout the flight, providing a common source
of information to users and service providers.

Air traffic service providers maintain a continuously updated database
of airspace and flow restrictions. The AOC and Air Traffic (AT)
computers share this information. Using this data, the AOC flight
planner prepares a proposed flight plan, performing a probe for active
or scheduled SUAs, weather, and airspace and flow restrictions. The AOC
flight planner uses this information to file the final flight plan. As
conditions change during the planning phase or during the flight, the
user is able to interactively determine the impact of the changes on the
flight and modify the flight plan as necessary.

The status of active and proposed flights, as well as real-time updates
to reflect more realistic departure times (e.g., the latest planned
departure times) are available to NAS users. This results in more
accurate predictions of traffic load, and increased flexibility due to
the imposition of fewer restrictions. Current information is also
available on the status of the NAS infrastructure. Availability of
flight planning information and NAS infrastructure information
facilitates more effective collaborative decision making between the AOC
and AT. This increased collaboration and information exchange between
the user and the service provider provides a baseline of planning for
traffic loading.

In the transition period, the GA user has the capability to access the
same flight data used by all other system users and service providers
via personal computer, FBO, or service provider computer. Those users
connecting through personal computer are able to enter a command and be
transferred to a service provider for clarification of the information.
Depending on the user's equipment, this dialog can be by voice or
through electronic messaging.

VFR flight plans, once filed, are available to all ATC service
providers. This enhances the ability of the pilot to receive and the
service provider to provide VFR flight following services.

These surveillance improvements allow the roles and responsibilities of
the controllers and FSS specialists to stay as they are now. However, it
is possible that it would be more appropriate to reassess this division
of functions within the NAS. If the NAS were restructured to give
greater and more direct access to services on an equal basis to all air
carrier, general aviation, military, and public service aircraft, then
the lost aircraft, flight plan interface, and SAR functions could be
removed from the responsibilities of the FSS and its operations reduced
to providing improved weather information to the user during preflight
and while airborne. If it is felt that such a reorganization would
overload the existing system as designed primarily for air carriers,
then perhaps thought could be given to developing a coordinated system
that gives the FSS more jurisdiction over general aviation, military and
public service aircraft for flight following. With improved onboard
systems it is even possible to consider the FSS managing a true Free
Flight system. However, since it is unlikely that such bold creative
steps will be taken at this juncture, the legacy constraints of the NAS
dictate that the FSS at least needs the surveillance improvements
listed.

DoD flight planners have no unique capabilities above those already
mentioned, although flight planning continues to be performed by
Military Base Operations (BASEOPS).

### 66.1.3Number range Level3Number range Level4 Mature State Flight Planning

The mature state uses the enhanced programs and procedures during the
transition period. Interactive flight planning capabilities have been
fully implemented. User preferred routing from airport-to-airport is
available to all properly-equipped aircraft for domestic and
international flights.

An interactive flight planning capability is available for all
properly-equipped aircraft to aid in filing airport-to-airport flight
plans with user-preferred routings. Interactive flight planning also
allows users to better monitor fleet activities during routine and
non-routine operations, which results in better resource utilization and
cost savings.

Interactive flight planning information is available to all GA pilots.
Interactive flight planning is available for pilots of properly-equipped
aircraft to aid in filing airport-to-airport flight plans with
user-preferred routings.

The DoD user has real-time interactive flight planning capabilities,
which enable more effective flight planning with respect to NAS
resources.

## 66.2Number range Level2Number range Level3Number range Level4 Airport Surface Surveillance Operations

This section identifies the pilot and service provider capabilities and
procedures necessary to safely increase the capacity of surface
operations during all weather conditions. An evolution is described from
today's visibility-dependent surface operations to a mature state
supported by improved surveillance, advanced decision support tools, and
avionics.

Safety is increased via a capability that provides the pilot with
graphical information in the cockpit depicting proximate traffic and the
taxi routes to be taken, thus eliminating blunders into another
aircraft's path. This same capability also increases taxiing efficiency
by eliminating the uncertainty that occurs in low visibility, thereby
allowing the pilot to taxi safely with minimal service provider
assistance. A capability that provides the tower service provider with
aircraft positions and associated IDs on the surface and on short final
to the runways aids efficiency and safety in the future with a potential
for reducing runway incursions.

Increasing public demand for air travel causes increased demand on
airport resources. Since airports are limited in their ability to
increase the number of runways and other surface areas, more efficient
use of these resources is made. Surveillance is seamless, with no gaps
in coverage.

Improved efficiency on the airport surface is provided by several
factors. Improved cockpit capabilities and safety capabilities free the
service provider to do planning of aircraft routing on the surface, and
sequencing of aircraft for departure. This results in more efficient
queuing and sequencing, reducing taxi times and fuel usage.

### 66.2.1Number range Level3Number range Level4 Near Term Airport Surface

In the near term, CDTI is available in some aircraft, providing an
increased situational awareness of other equipped aircraft and ground
vehicles in the movement area, as well as in the traffic pattern. This
gives the flight crew decision support information to eliminate the
potential for runway and taxiway incursions and ramp incidents,
especially at night and in low visibility conditions.

The same surveillance information provides the service provider with a
flight ID associated with those ground targets on the tower display.

This information cannot be used to change procedures unless all
necessary traffic can be displayed in the cockpit of an equipped
aircraft on an appropriate service provider display.

Locations of uncharted or temporary obstructions in and around some
airports are marked by broadcast transmitters for better obstruction
avoidance.

Service providers have an integrated display of both aircraft on final
approach and the movement of vehicles and aircraft on the airport
surface. These aircraft are identified on the display. In the near term,
prediction and resolution of runway incursions remains primarily the
responsibility of service providers using current tools to augment
existing procedures.

As traffic increases, asset management becomes even more dependent on
the most current information. Operators' efficient gate and aircraft
management can complement surface movements by avoiding unnecessary
delays on congested taxiways and hold pads.

A capability that provides the pilot with graphical information in the
cockpit depicting the taxi routes to be taken, increases safety by
eliminating blunders into another aircraft's path, and increases taxiing
efficiency. A capability that provides the tower service provider with
aircraft positions and associated IDs on the surface and on short final
to the runways aids efficiency and safety in the future with a potential
for reducing runway incursions.

### 66.2.2Number range Level3Number range Level4 Transition Period Airport Surface

In the transition period, timely and current flight information,
together with the integration of service provider surveillance and
surface automation with departure and arrival automation, provides the
ability to establish an efficient use of runways, taxiways, and ramps
for departures, arrivals, and surface traffic. This results in the
reduction of taxi times, takeoff delays, and idle time spent on the
airport surface.

Also during this time, a surface management information system is
fielded at some airports to facilitate coordination between
decision-makers at all levels of the airport operation. This system's
processes and displays provide complete data connectivity between the
service provider, flight deck, airline operations center, ramp, airport
operator, and airport emergency centers. The system provides access to
airport environmental information, arrival, departure, and taxi
schedules, airborne and surface surveillance information, flight
information, ATIS and other weather information, and traffic management
initiatives. These data are shared among users and service providers.
The sharing of data at the airport allows the service providers to
coordinate local operations with airline ramp and airport operators,
improving overall airport operations. At sites where the surface
management information system is not fielded, ad-hoc site adaptations
can provide basic intra-airport connectivity.

The tower service provider is aided by integrated surveillance and
automation systems. Airport traffic, including ground vehicles as well
as aircraft, are identified and displayed to the service provider on an
airport map that includes runways, taxiways, hold areas, ramp areas, and
gates, as well as obstacles on the airport surface. Landing aircraft
approaching the runway are also identified. Conformance monitoring and
problem prediction capabilities in the tower, supported by accurate
surveillance data, notify the service provider of any problems among any
of the aircraft or other vehicles or obstructions. The service provider
can therefore provide safe separation in all visibility conditions,
including low visibility or nighttime conditions, without significant
degradation of services.

During the transition period, airport surveillance is enhanced with the
continuing growth of ADS-B equipage. Cockpit surveillance systems offer
an alternative that can serve as an immediate safety alerting system.

For aircraft on the airport surface, new surveillance systems, used in
conjunction with CDTI, improve safety and efficiency. Under conditions
of low visibility, taxiing aircraft require assistance to safely
traverse ramp areas, taxiways, and runways. The NAS provides this
assistance in the form of surveillance as well as navigation and
communication capabilities. While ATC continues to provide separation
services and pilots continue to maintain visual vigilance in collision
avoidance, pilots begin to rely on surveillance means for conflict
avoidance. The pilot has a moving map display of the airport surface,
with the aircraft's current location, location of other aircraft, and
obstacles displayed. This improved situational awareness of traffic
allows the pilot to accomplish the following:

-   Identify runways, taxiways, and other airport surface areas, thereby
    allowing the pilot to comply with service provider instructions
    efficiently

-   Identify and avoid potential incursions and conflicts, improving
    safety on the airport surface

Pilot familiarity with the airport is enhanced with a moving map display
that leads to better planning and increased safety during surface
operations. Cockpit capabilities for some users include appropriate
conflict prediction logic, which, in conjunction with an airport moving
map display to monitor present position, allows for safer operations,
especially in low-visibility conditions. Properly-equipped aircraft are
authorized for lower Runway Visual Range (RVR) operations than those
that are not equipped. Cockpit display of position information from
other aircraft further contributes to better situation awareness for the
pilot, resulting in increased safety.

Ramp service providers, who manage aircraft in non-movement areas of an
airport, are able to sequence and meter aircraft movement at gates and
on ramp areas using situation displays that interface with decision
support systems and personnel in the control tower. Safety is enhanced
by these situation displays, which include airborne and surface traffic
as well as information from the local information system. This
information aids in preparing for gate operations and in sequencing gate
arrivals and departures in concert with the ground taxi planning system.

Most of the enhancements described above do not require the addition of
new procedures; these enhancements basically allow users and ATC to make
better decision of when to perform existing operational tasks (e.g.,
more realistic pushback times).

CDTI capability enhanced with conflict prediction logic may require
development of new cockpit procedures to authorize potential clearance
deviation for conflict avoidance. Consonance of these cockpit procedures
with ATC procedures must also be ensured.

Operational approval criteria and pilot procedures is necessary to
approve lower RVR-operations, where feasible.

### 66.2.3Number range Level3Number range Level4 Mature State Airport Surface

The integrated surveillance information providing improved situational
awareness is shared by all parties: service providers, pilots, ramp
operators, and crew and flight planners. This common understanding of
the current status reduces user requests for information from service
providers, again freeing service provider time for planning and
instructing pilots, resulting in more efficient operations.

In the mature state, the majority of users are equipped with data link,
surveillance and CDTI realizing safety and efficiency benefits at more
airports, particularly in low visibility conditions.

In the mature state, there is an accurate display of weather for both
user and service provider, with automatic simultaneous broadcasts of
hazardous weather alerts.

With the implementation of local augmentation corrections,
satellite-based position information is very accurate. With accurate
position information (e.g., taxi routes), a cockpit moving map with
aircraft positions, and real-time data link information, airport
operations can continue to occur at near normal visual rates in near
zero visibility conditions.

Aircraft using satellite-based navigation on the airport surface are
subject to conflict prediction checking by tower automation. Tower
automation predicts conflicts between aircraft as well as between
aircraft and vehicles. Tower automation also performs conformance
monitoring of the aircraft's taxi route to ensure that aircraft do not
enter active runways without clearance.

The mature state for airline airport surface movement potentially
includes the capability for very low visibility taxiing. These
properly-equipped aircraft and trained flight crews are authorized to
taxi and provide separation assurance solely based on electronic means
(e.g., enhanced vision moving map, CDTI, conflict prediction logic).

To support low-visibility station keeping on the airport surface, the
in-trail aircraft needs to monitor the position and speed of the lead
aircraft, and to detect changes in speed to ensure that safe separation
is maintained. The data required is identified in the *Minimum Aviation
System Performance Standards For Automatic Dependent Surveillance
Broadcast (ADS-B)*, RTCA Document No. RTCA/DO-242.

In the mature state, with the majority of aircraft having a cooperative
surveillance capability, the pilot has immediate runway intrusion
information available directly in the cockpit. This equipage enhances
safety by eliminating any time delay engendered by processing alert
information through the service provider.

## 66.3Number range Level2Number range Level3Number range Level4 Terminal Area, Approach and Departure Surveillance Operations

Systems such as TCAS and airborne wind shear detection systems help the
better-equipped aircraft, but an improved heads-up interface and
reliable wake vortex detection or prediction increases safety.

### 66.3.1Number range Level3Number range Level4 Near Term Terminal

Operations in the near term are facilitated by increased pilot
situational awareness through improved surveillance information to the
cockpit, as well as by better weather information to the cockpit and
improved understanding of the airspace environment (such as SUA and
navaid status).

Adequate CDTI and collision avoidance protection enhances safety during
the elimination of the 250 knot speed restriction for climb outs under
10,000 feet, which the service provider has been given the authority to
waive, allows flights to climb using optimum climb profiles. Increased
pilot situational awareness increases the safety and efficiency of
approaches and departures and leads to better runway utilization.

For airline type users in the near term, procedures are being developed
for reduced visual approach and departure minima with the use of
specific point in space geometries that are designed to allow for easy
visual acquisition of traffic of interest (e.g., traffic on adjacent
approach). These geometries include FMS offset approaches and departures
combined with vertical and horizontal separation between aircraft. Speed
control in relation to traffic of interest is required, but may be
obtained procedurally (e.g., assigned speeds) or in reference to CDTI
(e.g., station-keeping). Once proven in visual conditions, these types
of approach and departure procedures may be accomplished in IMC.

Safety enhancements include improved identification of other traffic
(e.g., electronic flight ID) as well as automation assistance to judge
closure rates, geometries, and wake vortex separation with other
traffic. Approach and departure visual separation spacing can also be
more accurately maintained by the pilot. With confidence in the CDTI
system, visual approaches and departures may be continued even with
momentary loss of visual acquisition, as long as the target is still
displayed on the CDTI and the flight crew assesses that it is still a
safe situation.

### 66.3.2Number range Level3Number range Level4 Transition Period Terminal

In the transition period, building on improved area navigation
capabilities and the growing number and increasing quality of cockpit
displays, all users have the capability to display weather and
surrounding traffic in the cockpit. Also, a common data link is
available that provides current weather information and hazardous
weather alerts, in addition to the more routine message traffic. With
the improved accuracy and display of the weather information on the
service provider's display, users and providers share a common
situational awareness.

With the introduction of a global standard for satellite-based
navigation and surveillance, aircraft position is provided to ATC and
other users to provide a common traffic picture to pilots and ATC
service providers. Such a concept must account for any potential
navigational failure in order to maintain a robust operational system.
In addition, provisions must be made to ensure that equipped aircraft
have a complete picture of all surrounding traffic in the terminal area,
including unequipped aircraft or aircraft with an equipment failure.

For the airline category user in the transition period, real time
weather information and maps are received in the cockpit. The
improvement of real-time wake turbulence visualization in the cockpit is
available. The addition of enhanced collision avoidance logic based on
satellite-based navigation and surveillance information has improved
collision avoidance capabilities to provide protection to the ground,
including on closely spaced parallel approaches.

As now, service providers remain informed on distant weather conditions
in order to anticipate changes to the daily traffic flow, and requests
from other facilities. This is especially important when working with
tower service providers to manage runway configuration changes.

With the capability for the crew to see the surrounding aircraft,
modifications to service provider ATM procedures, and the improvements
in turbulence and wake vortex avoidance, reduced or time-based
separation standards can be implemented and more direct routes through
the terminal airspace can be flown. This could help improve the traffic
flows in the terminal area as a result of the streamlining of the
aircraft command and control functions, particularly in airspace without
radar surveillance.

As satellite-based navigation and surveillance capabilities expand, the
routine 250 knot speed restriction is lifted by service providers in
more Class B airspace for both departures and arrivals within
environmental constraints. Uses of data link and cockpit displays are
developed to the point that the pilot cannot only monitor all the
surrounding traffic but current meteorological data and automated
hazardous weather alerts as well.

Also, improved service provider automation and displays and the use of
cockpit situation displays enhance traffic situational awareness and
allow for enhanced approaches and departures. Dependent and independent
approaches and departures in IMC may be performed at many airports
between properly-equipped aircraft and by a properly trained flight
crew. As a result, increased capacity and greatly reduced delays during
IMC are realized at airports with closely-spaced parallel runways.

### 66.3.3Number range Level3Number range Level4 Mature State Terminal

In the mature state, surveillance systems and automation automatically
send some messages directly to the pilot and service provider to further
increase safety by eliminating the time necessary for a human to relay
the message. Examples of such messages are wind shear alerts (generated
either by airborne or ground equipment), airborne collision resolution
advisories, and instructions to go around in a runway incursion
scenario.

At this point, the equipage with improved surveillance information
sharing capability is fundamentally complete and all aircraft provide
their position to ATC and other users. For airline type users, free
maneuvering operations in low density areas are being performed. In high
density areas, ATC provides sequencing and primary separation assurance;
however, some cockpit self-separation is assigned to the flight crew by
ATC when operationally advantageous.

Using CDTI based on the mature state surveillance capabilities, together
with ATC decision support systems and data link, new procedures use area
navigation capabilities to reduce congestion over waypoints, thus
improving the utility and safety of the system for all users.

## 66.4Number range Level2Number range Level3Number range Level4 En Route Surveillance Operations

Based on each aircraft owner's and/or operator's evaluation of the
benefits to be gained, aircraft within the NAS begin to be installed
with equipment that provide new or improved surveillance capabilities.
The improvements and benefits described here attempt to address the
system shortcomings discussed in Chapter 2 of this document. Those
shortcomings include, but are not limited to, the lack of surveillance
information in controlled airspace and the inconsistent quality of
surveillance information. These shortcomings result in the operational
impacts discussed in Chapter 2.

### 66.4.1Number range Level3Number range Level4 Near Term En Route

In the near-term, techniques for establishing metering spacing provide
the crew the flexibility to efficiently manage their flight with respect
to aircraft performance, crew preferences, and ATC considerations. It
also allows aircraft to stay on route in cases were ATC would otherwise
have to vector the aircraft off route to achieve the desired spacing due
to service provider workload and today\'s pilot-ATC tactical control
loop. While vectoring of aircraft is a high workload item both for
service providers and pilots, only one clearance is given for this
metering spacing technique. Also, the option to stay on route is
typically more fuel and time efficient. The AOC monitors the status of
the NAS and relays status information to pilots. Aircraft not equipped
to operate in a Free Flight environment are handled as they are today.

Aircraft begin to equip with systems that improve the crew's airborne
situational awareness. Situational awareness in the cockpit is improved
through the equipage of avionics that displays other craft in proximity
to the aircraft. This new avionics could either do the detection
autonomously or in conjunction with systems on the ground which provide
the information to the avionics for display to the crew. Extensive human
factors testing determines the most appropriate form to present this
information to the crew, as well as the best way for the crew to
interact with the display. Further, procedures have been developed in
conjunction with all appropriate oversight and regulatory agencies which
define how the improved situational awareness can be converted into
benefits for the airspace users.

Although the ultimate separation assurance responsibility remains with
the service provider on the ground, based on this improved situational
awareness in the cockpit, procedures are developed and employed which
allow for the transfer of separation responsibility from the ground to
the cockpit for specific and well-defined situations. These
self-separation procedures have been well tested and simulated prior to
their introduction into the system, and both aircrews and service
providers have received extensive training to ensure the procedures are
safe and well understood by all parties. Initially, self-separation
(with the concomitant transfer of separation responsibility) occurs only
for the limited time duration necessary for the participating aircraft
to achieve its desired benefit(s). (See the Cross-Cutting Concepts
discussion on Self-Separation.)

Airborne collision avoidance continues to be provided, using collision
avoidance systems and technology. More users, primarily military
passenger aircraft and high-end GA aircraft, become equipped with
collision-avoidance capabilities. While not a collision avoidance
system, low-end users have enhanced situational awareness through the
limited delivery of radar information on surrounding traffic.

For GA users, multi‑function displays begin to appear in GA aircraft,
including weather and traffic information superimposed on a moving map.
Those DoD aircraft equipped with a cockpit display of traffic
information have better situational awareness throughout the cruise
phase of flight.

Surveillance information presented to the air traffic service provider
continues to be provided by ground-based long-range primary radar and
ground-based secondary surveillance radars. This radar-provided
surveillance information is used with new service provider displays to
enhance the service providers' understanding of the air picture within
their assigned sector. New service provider automation tools, such as a
conflict probe capability, use the surveillance information to enhance
efficiency of the air traffic flow, reduce unnecessary vectoring and
improve service provider-to-service provider coordination.

Concerted efforts are made to achieve the minimum separation standards
currently in effect. This is achieved, primarily, using existing
surveillance information in conjunction with the new service provider
displays. Removal of the Operational Errors and Deviations program from
the ground automation system encourages the service providers to utilize
their assigned airspace most efficiently, while continuing to achieve
the existing levels of safety.

### 66.4.2Number range Level3Number range Level4 Transition En Route

During the transition period, accommodation is made for both legacy and
new technology surveillance systems, both on the ground and onboard
aircraft. Plans for the phased elimination of ground-based long-range
primary radars continues and becomes more sharply focused. Initiation of
long-range primary radar elimination can begin only after other
surveillance systems can be shown to meet the necessary level of
performance. This level of performance is determined after a thorough
analysis of the performance issues, and the cost and performance
tradeoffs involved. Until consensus can be achieved on this analysis and
its implications vis-à-vis primary surveillance radar, there will be a
continuing need for non-cooperative independent surveillance.

Additional information intent and aircraft performance data is provided
to ground-based decision support systems, thus improving the accuracy of
trajectory predictions. This includes intent and aircraft performance
data, improved information on SUA activation/deactivation, and
information on current and projected weather. This information is
integrated on the service provider's display. Since there are different
separation standards depending on the flight's equipage and the quality
of the positional data, service provider displays indicate the quality
of the resulting aircraft positions and the appropriate equipage
information. Reduced or time-based separation standards are developed
based on technology and aircraft capability, further increasing system
capacity and safety.

Collision avoidance capability continues to be an essential element of
safe aircraft operation. Additional airspace users equip with an
airborne collision avoidance capability, due to availability of more
affordable avionics for low-end users. The use of lateral as well as
vertical maneuvers become available as a potential method for collision
avoidance (see the discussion in the Collision Avoidance section).
Further, harmonization activities with civil aviation authorities around
the world ensure that different collision avoidance systems can safely
and effectively interact. Civil mandates for collision avoidance
equipage are based on performance requirements, and not a specific
equipage solution, thus eliminating the need for equipage of redundant
capabilities.

Cockpit technology improvements allow more user-preferred routings, SID
to STAR or airport-to-airport. This increase is underpinned by decision
support systems that assist in conflict prediction and resolution. This
reduces mental workload and gives the provider more time for other tasks
such as responding to user requests. Improving the service provider's
ability to efficiently and accurately identify conflicts also reduces
the number of occasions when there is unnecessary intervention, allowing
the user to fly the trajectory proposed with higher frequency.

A common surveillance picture is shared among all ATM participants:
service providers, pilots, and planning agencies. Based on this common
surveillance information and the capability to accurately display the
information to both the service providers and cockpit crews, separation
standards are reduced. Any separation standard reduction is based on
performance-based operational criteria such as RSP, RNP, RCP and RTSP,
rather than an equipage-specific technological solution.

Increased collaboration between the airline AOC and the ATM system
occurs as the AOC interactively probes proposed route changes. Modified
routes can be developed collaboratively between the AOC, pilot and the
service provider and then data linked to the cockpit and downstream ATC
facilities. In addition, working with TFM specialists, the AOC helps
define and implement TFM initiatives to relieve airspace congestion.
Collaboration is extended as AOCs have an expanded role in determining
the landing sequence of company flights. Also, since the AOC can
interactively probe proposed flight changes, more point-to-point
routings are allowed to more runways.

The use of aircraft-derived position data satellite-based navigation and
surveillance data has not only increased on-board capabilities ranging
from cockpit display of traffic and enhanced collision avoidance
capabilities, but it is also used by ground-system automation for
enhanced conflict probe and alerting. Monitoring all surrounding traffic
with cockpit display of traffic information increases pilot situational
awareness. Display of information such as other aircraft flight ID and
closure rate is used intrinsically in metering activities. Many of these
aircraft have a navigational capability coupled to an FMS.

As GA users begin to equip with traffic displays, safety is enhanced as
the potential for midair collisions is reduced. In most busy terminal
areas, transition through Class B or C airspace is facilitated by the
design of routes and procedures that allow for direct VFR and IFR
flights through the airspace. Enhanced surveillance compliments
continuous earth referenced navigation systems Satellite-based
navigation and augmentation systems greatly expand IFR access to low
altitude airspace, enhancing operations outside of radar coverage.

VFR flight following services are enhanced. For aircraft automatically
reporting their satellite navigation-derived positions, the inclusion of
that information, coupled with access to the VFR flight's data, reduces
the workload associated with providing traffic advisories to
uncontrolled aircraft and increases the availability of VFR flight
following services.

DoD users benefit from cockpit traffic displays that allow random and
flexible air refueling tracks.

### 66.4.3Number range Level3Number range Level4 Mature State En Route

The final decision on the future of ground-based radar for surveillance
in the en route domain has been made and implemented. Surveillance of
the entire en route domain is achieved, potentially by more than one
technology. Surveillance information is cross-flowed between and among
the cognizant agencies and facilities to allow the creation of a common
and consistent recognized air picture. This allows all decision-makers
access to all of the surveillance information necessary for each
decision-maker to efficiently perform his/her function.

All aircraft that conduct IFR free-flying operations require a collision
avoidance capability with at least a traffic advisory capability. This
collision avoidance capability could be achieved using any appropriate
technology or group of technologies. Likewise, the extent of the
collision avoidance capability could be different for different classes
of users, such as general aviation, the military, and regional, national
and international air carriers. Harmonization has continued between
global aviation authorities to ensure that civil mandates for collision
avoidance equipage is based on performance requirements and not a
specific equipage solution. Panel-mounted multi-function displays and
data link capabilities become commonplace in all but the low-end GA
aircraft, where hand-held units remain the equipment of choice. In
addition, satellite-based surveillance systems that enable robust
multi-function capabilities begin to appear in GA cockpits.

The increased surveillance information coverage and common surveillance
aspects of the mature stage of free flight also allows the attainment of
certain benefits and efficiencies:

Procedural changes are implemented to allow low altitude direct routes
for aircraft and powered lift vehicles, greatly benefiting regional,
business, general aviation, and other users. Use of the ground based
conflict probe has been modified to allow for airborne procedures to
resolve most conflicts, thus allowing maximum routing flexibility with
the least restrictions. Both the airborne and ground-based conflict
probes include the ability to account for weather systems, including
their movement and growth or decay, and avoidance of Special Use
Airspace, taking into account the time of activation/deactivation of
such airspace relative to the future position of the aircraft.

Airlines and high-end GA frequently perform free maneuvering operations
in low-density areas. In high-density environments, the oversight from
ATC for sequencing and primary separation assurance is still required.
However, some cockpit self-separation is assigned to the flight crew by
ATC when operationally advantageous. Display of intended route of own
and other aircraft, the use of trend vectors and aircraft positions at
the time of closest predicted approach, along with cockpit automation,
helps the pilot self-separate. Point-to-point routings are routinely
flown, i.e., from SID to STAR or from airport-to-airport, and airborne
holding is adjusted to maximize airport capacity. Aircraft not equipped
to operate in a Free Flight environment are handled as they are today.

SUA still exist in the mature stage of Free Flight. However, SUA is
managed more dynamically. When determined by the DoD to be feasible,
control of SUA is transferred to the FAA for use by non-participating
aircraft. This allows more tactical control of SUA and increased
approval of user-preferred routes, increasing system efficiency.

For GA users, in all busy terminal areas, transition through Class B or
C airspace is facilitated by the design of routes and surveillance
procedures that allow for direct VFR flights through the airspace.

## 66.5Number range Level2Number range Level3Number range Level4 Oceanic Surveillance Operations

Based on each aircraft owner's and/or operator's evaluation of the
benefits to be gained, aircraft within the NAS continue to be equipped
with new or improved surveillance and communication capabilities. There
are some benefits realized by all aircraft, not just those that equip,
due to near-term infrastructure improvements. The improvements and
benefits described here attempt to address the system shortcomings
discussed in Chapter 2 of this document. Those shortcomings include, but
are not limited to, the lack of frequent, timely, and verifiable
surveillance, and the inconsistent quality of surveillance information.

FAA initiatives are focused on separation reductions that can be
implemented independently of a new ground automation infrastructure or
service provider-pilot data link communications and automatic dependent
surveillance. These include phased implementations of 50 nautical miles
(nmi) lateral separation, reduced vertical separation minima (RVSM).
Details of these activities can be found in the *Separation Plan for
Oceanic Airspace Enhancements and Separation Reductions.*

### 66.5.1Number range Level3Number range Level4 Near Term Oceanic

During the near-term, experience gained with new procedures and expanded
use of improved avionics results in improved oceanic airspace management
and increased overall capacity. Coupled with the deployment of advanced
ground automation, more timely and accurate surveillance data allows
implementation of improved separation standards. There are separation
reductions to 50 nmi longitudinal, to seven or eight minutes
longitudinal in specified airspace, and 30 nmi lateral and longitudinal
in oceanic areas for RNP-4 approved aircraft. This reduction in
separation standards, coupled with workload efficiencies, greatly
increases capacity in oceanic airspace, allowing more user-preferred
routing. Improved communication and distribution of data on the ground
allows more efficient collaborative decision-making in support of DARP.
This allows users to choose more desirable route profiles and utilize
more flexible tracks and user-preferred profiles (UPPs).

Service providers move from a labor-intensive paper flight strip, manual
calculation environment, where data must be continuously reviewed and
updated to maintain surveillance, into an environment where many of
these manual tasks are performed through the use of automation. Flight
data that was previously marked on strips is readily accessible to the
service provider via automation. Flight progress monitoring is oriented
toward dealing with data that is an exception to the expected aircraft
progress, rather than based on the receipt of data within conformance.
Aircraft waypoint/position reports do not require service provider
action or acknowledgment, unless the automation detects an aircraft is
out of conformance with its cleared flight plan. Situations detected by
the automation that require service provider action are brought to the
service provider's attention. The service provider is able to focus on
cognitive tasks such as analyzing traffic, granting user requests, and
monitoring changing air traffic situations.

Integration of flight data processing (FDP), Radar Data Processing
(RDP), ATS Interfacility Data Communications (AIDC), data link
communications, automatic dependent surveillance (ADS), and display
capabilities enable service providers to minimize workload associated
with data input and rudimentary computations while maintaining sector
situational awareness. Display capabilities enable the service provider
to visualize airspace, aircraft progress, and intent; to confirm times
and distances between aircraft; to review and amend flight plan data;
and to analyze the impact of projected and actual changes in aircraft
flight profiles. In addition, display capabilities enable the service
provider to identify, analyze and resolve potential or actual
aircraft-to-aircraft, aircraft-to-airspace, and aircraft-to-terrain
conflicts. One of the major improvements to the ground automation is
better prediction of future aircraft position based on knowledge of
pilot intent. This contributes significantly in subsequent phases to
generating capacity and providing increased flexibility.

Better surveillance and navigation tools and real-time, automated data
communication capabilities facilitate the transition from tracks toward
trajectories for oceanic airspace. Changes in airspace structure (based
on weather, demand, and user preferences) are coordinated with affected
national and international service providers and airspace users via
electronic data transfer. During this period, the modernized oceanic
surveillance capability maintains, as needed, levels of interface with
other FAA surveillance systems. This includes the ability to interface
with, process, and display primary and secondary (mode A/C) surveillance
radar, Mode S, ADS, and voice or data reported surveillance data.
Surveillance data from a variety of sources (e.g., radar,
satellite-relayed data position reports, high frequency \[HF\] or
satellite voice \[SATVOICE\] relayed position reports) are integrated to
enable the service provider to apply proper separation standards.
Integration of available surveillance products and capabilities provides
a more accurate picture of the traffic situation to service providers,
offers FAA an opportunity to increase the capacity of its airspace, and
supports automated tools that allow more route flexibility.

Aircraft equipped with data link and ADS-A are able to downlink position
reports at specified intervals, as well as times at a specified waypoint
and estimated times for the next and next plus one waypoints. It is
estimated that in the near term approximately two thirds of the aircraft
in the Pacific and half of the aircraft in the Atlantic are equipped for
this capability. Automated conformance monitoring of the position
reports by the ground system enables the service provider to focus
attention on exceptional situations, rather than the routine flight
progress monitoring. This provides more time for strategic activities,
allowing more UPPs, and granting more user requests. Current
longitudinal separation standards between suitably equipped aircraft are
reduced to 30 nmi in some areas by using the ADS-A reports, in
conjunction with automated service provider tools.

Also during this near term, some aircraft begin to equip with broadcast
ADS (ADS-B) in support of air to air communications between aircraft.
The better pilot situational awareness obtained from use of ADS-B and
cockpit display of traffic information (CDTI) enables procedures and
rules to be developed to conduct operations like cruise-climb flight
profiles, in-trail climb maneuvers, and limited stationkeeping between
pairs of equipped aircraft.

### 66.5.2Number range Level3Number range Level4 Transition Period Oceanic

The transition period continues to see expansion of the near-term
capabilities, as most aircraft are equipped to support data link and
ADS. Both service providers and airspace users become confident in the
use, accuracy, and reliability of these new technologies. There is
increased use of DARP and UPPs during this period. Aircraft can fly
direct via National Route Program (NRP) to oceanic routes. The
transition period sees full-scale use of the new communication,
navigation and surveillance (CNS) technologies, as well as the ground
and airborne automation display systems, implemented in the near-term.
This environment provides the framework for further reductions in
lateral and longitudinal separation standards, expanded use of dynamic
routings, significantly improved frequency of aircraft being able to
"fly as filed" and the migration towards the mature state of oceanic
free flight.

The use of air/ground data link communications in oceanic airspace
expands to include additional types of data link (e.g., aeronautical
telecommunications network or ATN) and additional capabilities (e.g.,
expanded message sets) in order to provide data link service to a larger
variety of airspace users. This enables a seamless air/ground data link
environment and better surveillance for aircraft flying between U.S. and
international flight information regions (FIRs) and between oceanic and
domestic airspace, as well as a common approach to air/ground data link
communications for oceanic and domestic service providers.

Enhanced automation assists the service provider with selection of the
most operationally effective resolution option. Conflict resolution
options for aircraft encountering SUA or severe weather are available to
the service provider. These suggested resolutions are displayed on the
service provider workstation and may utilize reroutes, real-time
restrictions, or (for appropriately equipped aircraft) radar-like
control techniques, such as vectoring, speed control, and monitored
climbs and descents.

Automation helps to determine dynamic traffic densities. Airspace
planners receive several types of non-flight-specific information that
enables them to assess traffic demand in oceanic airspace. The
automation measures and predicts the traffic density at all sectors.
Dynamic measurements and near-term predictions of each sector's traffic
density are available for each sector. This provides the traffic
planners with awareness of predicted demand levels and the affect on
traffic operations in order to allocate service provider workload more
effectively.

The increased use of ADS-A and air-air ADS-B, along with the display of
conflict resolution advisories to the service provider, allow
improvements in airspace and route design to allow sectors and routes to
be better aligned so as to reduce the complexity of conflict situations.
Route structures are defined in three dimensions and allow free-routing
to increase airspace users flexibility, reduce flight time and reduce
aircraft emissions. The role of the airspace planner is to define those
airspace boundaries (in collaboration with the airlines flight planners)
for corridors where the equipped aircraft operate as a "free flight", in
addition to establishing tracks for any unequipped aircraft. Based on
the flight plans, the airspace planners also determine projected traffic
densities in various airspace segments and use automated tools to
allocate service provider workload equitably. In those situations where
projected traffic density exceeds allowable corridor thresholds,
aircraft continue to be metered or restricted to assure that separation
criteria are met.

Corridor users are equipped with ADS-B and are able to view relevant
aircraft on their CDTI. These airspace users are responsible for
maintaining situational awareness and can perform limited tactical
resolutions after notifying the service provider of their intent and
receiving appropriate service provider instructions. For example, a
pilot sees on the CDTI a tactical situation that improves the flight's
performance and coordinates via air to air voice with the other aircraft
involved (to assure a near term strategic understanding of that
aircraft's plans). The pilot then uses data link to request a clearance
from the service provider to execute a self-separation procedure. The
request identifies the other aircraft involved, current relative
position information, and the planned maneuver, including final relative
position information. The service provider assesses the situation and,
if appropriate, grants the request with notification to the other
aircraft involved. The pilot notifies the other aircraft of his
intentions via air to air voice and the pair of aircraft are responsible
for maintaining their separation. The service provider maintains
responsibility for separation between the pair and other aircraft and
also notifies the pair immediately of any out-of-conformance situations
and any necessary maneuvers. Conformance monitoring is performed
automatically by the ground automation. Longitudinal separation may be
reduced to 15 nmi for aircraft operating under self-separation within
corridors.

### 66.5.3Number range Level3Number range Level4 Mature State Oceanic

In the mature state, separation standards, procedures for flight
planning, coordination, and transfers in U.S. domestic and oceanic
airspace evolve in concert with updates to ICAO standards and
recommended practices enabling seamless transitions between en route,
oceanic, and non-U.S. airspace. Differences between separation
standards, data processing protocols, surveillance operations, and other
technological issues, are harmonized to better ensure seamless
transitions from a global perspective.

Service providers and airspace users have gained confidence during the
transition period in the ability of the ground-based and airborne
communications and automation equipment to support timely and accurate
data link communications, and ADS-A air-ground and ADS-B air-air
surveillance. Virtually all aircraft in oceanic airspace are now
equipped with these technologies. Service providers are confident in the
capabilities of automated tools to predict and suggest resolution
options for conflict situations. This enables oceanic airspace users to
take advantage of benefits through greater flexibility, increased
user-preferred routes and climbs, and greater capacity.

Dynamic random routing for individual user-preferred trajectories is the
norm; oceanic fixed routes have been eliminated. Use of cockpit
self-separation and free maneuvering operations are being performed in
more complex situations, such as merging and crossing situations. ATC
oversight is still required for sequencing and separation assurance, but
collaborative decision making has greatly increased among the service
provider, AOC, and the aircraft.

Airspace users use surveillance data via ADS-B air-air, Airborne
Collision Avoidance System (ACAS) and Cockpit Display of Traffic
Information (CDTI) to identify, accurately measure distance from other
aircraft and efficiently resolve conflicts. However, in order to prevent
situations from developing which could be too difficult for realizing
air-derived separation assurance, the ATM system provides appropriate
information to the aircraft on future traffic situations, and meters
aircraft through some very complex or high-density traffic situations.
Potential conflicts may be uplinked to the cockpit, to advise the pilot
of traffic of concern.

The oceanic ATM system makes effective use of airborne surveillance
information in monitoring aircraft conformance to the intended flight
profiles. Flight progress monitoring and conformance checking is
automated, allowing service providers to focus on addressing the
exceptional situations. The ground system has full and accurate
knowledge of the aircraft's intent, there is a fast and reliable
communication link between the ground and airborne systems, and there is
immediate notification of any change intent. Therefore, the service
provider only has to respond to changes in the situation or exception
situations, not constantly monitor every movement.

With the reduction of computational and communications barriers,
airspace design and supporting sector configurations are no longer
constrained by predefined geographic boundaries. Using automated tools
and procedures to evaluate airspace structure, anticipated traffic
flows, and weather changes in real-time, sector boundaries are
dynamically adjustable in order to allocate workload efficiently and
permit greater use of flex tracks, random routes, and corridors.

Pilot self-separation is applied where it can reduce traffic-driven
restrictions on user-preferred routings or improve airspace efficiency
by allowing more timely and precise aircraft maneuvering.
Self-separation is dependent upon aircraft equipage (i.e., ADS-B and
cockpit display of traffic information) and is implemented by as yet
undefined procedures using further reduced separation minima. In
general, self-separation requires the imposition of horizontal and
vertical deviation limits, airspace-sensitive system conformance
checking, and requirements for pilot intent information. Pilots are
cleared for self-separation between their flight and a single opposing
flight identified by the service provider. The service provider notifies
the pilot of any traffic of which he needs to be aware. Types of
situations in which self-separation are used include a flight performing
station-keeping (either laterally or in trail) within a traffic flow, an
aircraft operating at or through another flight's altitude, and an
aircraft separating itself from a flight in an interacting traffic flow.

## 66.6Number range Level2Number range Level3Number range Level4 Traffic Flow Management Surveillance Operations

Improved surveillance capabilities and shared information help the
system to become more efficient. Downlinking of winds and temperatures
aloft provide a more accurate picture of current conditions, allowing
aircraft to avoid turbulence and other adverse weather conditions.
Improved weather surveillance and prediction capabilities allow
institution of the minimum flow strategies to handle the conditions.
Improved surveillance capabilities, including downlinking of aircraft
position and intent provide more accurate tracking and projection, with
implementation of reduced separation standards, thereby increasing
capacity of the system. This increased capacity reduces the need for
ground delays. Sharing information with users provides the means to
collaborate in the decision-making process, increasing the accommodation
of user preferences.

A common situational awareness among all NAS participants is critical
for strategic planning. Expanded FAA/Industry data exchange allows the
FAA to share estimated en route flow constrained areas, projected sector
densities and fix saturation with the NAS operator. These constraints
are made available in order to allow the NAS operator to modify his
intent. The traffic flow management service updates the constraint
information and disseminates it.

Increased universal situational awareness is achieved as a result of
common data shared by all NAS users. Actual and planned flight planning
information are available to improve the prediction of airport demand,
arrival and departure fix loading, and flow constraints. Access to real
time flight plan data coupled with improved trajectory models aid in the
prediction of traffic congestion. Collaborative technologies and
client/server architectures facilitate the interaction between user and
service provider making it possible to share intent and constraint
information as part of strategic planning.

Mechanisms for allocating resources are available, allowing the NAS
operator the flexibility to modify and exchange routing plans during
planned flow constrained events.

Initial models for resource allocation are in place. Specifically,
aggregate departure and arrival lists set the stage for improved
predictability of the system. This in turn leads to improved routing
plans. Information on possible diversions resulting from a specific
initiative and "off the gate but on ground hold" flights is made
available for procedural resolution. Automated resource allocation
mechanisms and algorithms are available to produce routing allocations
and departure runway balancing solutions.

Traffic flow management services provide the ability to rapidly assess
proposed routing strategies for impact on pre-existing conditions.
Post-operation evaluation capabilities allow FAA/Industry to analyze
results from traffic flow management strategies used in dealing with en
route congestion, and also allow analysis of candidate strategies.

Deployment of collaborative decision-making capabilities provide the
users with increased flexibility and predictability, while providing the
FAA with the control required to monitor and resolve efficient NAS flows
through collaborative routing. The functional and data requirements
listed below contribute to collaborative management of resources.

-   Flow Constraint Area Determination and Dissemination\
    Defined by weather and projected traffic are collected, processed,
    and disseminated to FAA facilities and NAS service providers in a
    timely manner to provide the foundation for collaborative decision
    making in traffic flow management.\
    Output: Dissemination of airspace volume parameters affected by
    known constraints.

-   Projected Traffic Processing and Display\
    Defined by projecting aggregate intent information to determine
    predicted congestion. This information is the basis for one case of
    flow constrained area definition.\
    Output: Predicted traffic congestion.

-   Weather Forecast Processing and Display\
    Defined by weather forecast information to determine weather
    avoidance. This information is the basis for one case of flow
    constrained area definition.\
    Output: Predicted weather avoidance airspace volumes.

-   Flight Planning Intent Processing\
    Defined by the ability to collect actual and planned flight planning
    intent information for processing by traffic management services.\
    Output: Simultaneous display of actual and planned flow status of
    the NAS.

-   Real Time Status of Impacted Flights\
    Provides status of impacted flights, particularly those affected by
    a flow management strategy or event.\
    Output: Impacted flights.

-   Resource Allocation Mechanisms\
    Provides procedural and logical distribution of constrained
    resources based on agreed upon "business rules."\
    Output: Fair and efficient allocation of resources for planing and
    re-planning purposes.

-   Impact Assessment Tools\
    Evaluates a proposed traffic flow management strategy given
    knowledge of flow-constrained areas and aggregate flight planning
    information.\
    Output: Real time evaluation of proposed flow strategies.

-   Post Operational Assessment Tools\
    Evaluates traffic flow management strategies based on archived
    operational data.\
    Output: Post operational evaluation of executed flow strategies.

### 66.6.1Number range Level3Number range Level4 Near Term TFM

TFM is the strategic view of the NAS. It includes long-term planning
done to assure proper staffing and locations on a seasonal basis, daily
planning at the national level, and local planning on an hourly basis.
TFM does not directly require surveillance data. It does require
information that is timely, accurate and available to all parties
involved in flow decisions. Increased accuracy, coverage, and
distribution of surveillance data help provide a complete and more
accurate basis for planning.

Information exchange and collaboration continue to be critical
components of traffic management in the near term. Improved information
exchange among users and service providers enables shared insight about
weather, demand, and capacity conditions and allows for improved
understanding of NAS status and TFM initiatives. Users are key
participants in the planning process of traffic flow initiatives. As
users receive better knowledge of the intent of traffic flow
initiatives, they may arrange their own resources to help solve the flow
problems.

### 66.6.2Number range Level3Number range Level4 Transition TFM

TFM employs the philosophy of problem resolution at the appropriate
level. Local service providers have access to the projected demand
information for the day, as well as tools to strategically identify
areas and times of higher density; many TFM issues can be efficiently
resolved at the local level. Improvements in surveillance data gathering
and distribution increases the effectiveness of this planning. Service
providers at the national TFM level monitor traffic, weather, and
infrastructure across the NAS, manage and implement traffic restrictions
of a broader scope, facilitate coordination among other domestic and
international service providers, and interact with AOC facilities and
other NAS users. National TFM service providers also monitor NAS
performance and adjust traffic management strategies as needed.

### 66.6.3Number range Level3Number range Level4 Mature State TFM

Interactive assessment capabilities are available to any user with the
technology to execute them. These capabilities allow the TFM and users
to create, evaluate, and adjust traffic management strategies
interactively in real time. Therefore, the needs of all NAS participants
can be satisfied in the most efficient manner.

# Section 67Number range Level1Number range Level2Number range Level3Number range Level4Number range FigureNumber range Table {#section-67number-range-level1number-range-level2number-range-level3number-range-level4number-range-figurenumber-range-table .Section-Heading}

# Summary {#summary .Section-Header}

The concept described in this document will provide an improved NAS that
accommodates the needs of the future, while achieving increased safety
with greater efficiency and accommodation of user-preferred routes.
Benefits will be achieved by all participantsusers as well as service
providersthus allowing the accommodation of the needs of the ultimate
customer: the flying public.

The attainment of these benefits is conditional upon resolution of
certain issues. The key concepts of separation assurance described in
Section 3 must be validated. Electronic Flight Rules (EFR) must be
defined and validated in operational trials, and the bounds for
delegation of separation management must be established.

The surveillance concept of the future will provide key improvements to
all participants. The risk of runway incursions will be reduced via
enhanced pilot and controller situational awareness. This situational
awareness also allows airport capacity under low visibility conditions
to be increased, while safety is maintained. Terminal efficiencies and
safety will be improved as a result of the implementation of new cockpit
procedures that utilize enhanced situational awareness. The common
surveillance picture shared across facility boundaries allows
utilization of current separation minima. Separation standards are
reduced, thereby providing increased system capacity. Fleet management
is improved, achieved as a result of the more accurate surveillance
picture that is shared with users.

In summary, benefits are achieved by all participants in the NAS through
the implementation of new surveillance capabilities.

# Bibliography {#bibliography .Back-Matter-Header}

1.  *Minimum Aviation System Performance Standards for Automatic
    Dependent Surveillance Broadcast (ADS-B)*, RTCA Document No.
    RTCA/DO-242, February 19, 1998, RTCA Special Committee 186 (SC-186),
    Washington, D.C.

2.  *Separation Plan for Oceanic Airspace Enhancements and Separation
    Reductions*

3.  RTCA *Government/Industry Operational Concept for the Evolution of
    Free Flight,* December 1, 1997, RTCA Select Committee on Free
    Flight, Washington, D.C.

4.  RTCA *Free Flight Action Plan,* December 10, 1998, RTCA Free Flight
    Steering Committee, Washington, D.C.

5.  *Final Report of RTCA Task Force 3 Free Flight Implementation*,
    October 31, 1995, Washington, DC: RTCA, Inc.

6.  *National Airspace System Architecture,* August 1998, Washington,
    DC: FAA Office of System Architecture and Investment Analysis
    (ASD01).

7.  *Enabling User Preferences Through Data Exchange*, Green, S.M., et
    al, AIAA-97-3682, 1997

Appendix Number range AppendixNumberNumber range Level1Number range
Level2Number range Level3Number range Level4Number range FigureNumber
range Table

# Surveillance Mode Descriptions and Limitations {#surveillance-mode-descriptions-and-limitations .Appendix-Header}

This section describes the various surveillance modes used within the
NAS today and their current operational limitations. One of the
objectives of this concept of operations is to remove or negate these
operational limitations as well as establish future needs and
requirements. These needs are introduced in Section 2. The descriptions
and limitations stated in this section are on today's mix of
ground-based, space-based, and airborne surveillance systems from
fielded prototypes to fully operational systems. No future systems are
identified by name, only by the need for their capabilities to remove
the existing surveillance limitations and by their need to increase and
enhance safety. The surveillance modes described in this section
include:

-   Primary Ground Radar (AN/FPS-117; ARSR-1, -2, -3, and -4; ASR-4, -5,
    -6, -7, -8, and -9; ASDE-3)

-   Passive Surveillance Systems

-   Secondary Ground Radar (ATCBI-3, -4, and -5; Mode S SSRs)

-   Airborne Surveillance Radar

-   Ground and Airborne Weather Radar

-   Automatic Dependent Surveillance (ADS)

-   Traffic Alert and Collision Avoidance System (TCAS)

-   Uplink of traffic information

-   Direction Finder (DF)

-   Emergency Locator Transponder (ELT)

-   Visual Surveillance

-   Voice Reporting

In today's operational environment, the use of primary and secondary
radar far exceeds the use of any other surveillance mode in the domestic
or international airspace. Since the introduction of radars into the
U.S. civil aviation system (i.e., since real-time, accurate aircraft
surveillance has been possible), the FAA has divided its surveillance
sensors by the flight domains of the aircraft being served. These
domains are en route, terminal area, and surface. Several generations of
surveillance radars have been designed and deployed for these domains.
The service provider personnel and systems that use surveillance data
have been deployed in facilities corresponding to (and generally located
nearby) the radars or radar data processing facilities from which they
obtain data.

In addition to these three domains served by radar surveillance sensors,
there is also the oceanic domain and other radar and non-radar
surveillance modes discussed later.

## A.1Number range Level2Number range Level3Number range Level4 Primary and Secondary Radars {#a.1number-range-level2number-range-level3number-range-level4-primary-and-secondary-radars .otherheading-2}

Surveillance radars fall into one of two mutually exclusive categories:
primary and secondary. Primary radars transmit pulsed electromagnetic
energy that is reflected by the desired targets (aircraft or particulate
matter associated with weather phenomena) and by undesired objects.

Secondary radars are useful only with cooperating aircraft targets. The
radar ground installation transmits electromagnetic energy, normally a
pulse pair. By international agreement, 1030 MHz is the carrier
frequency used for interrogation of the aircraft transponders. A
cooperating aircraft carries a transponder that receives the signal from
the ground and transmits a signal of its own, on 1090 MHz, which is
received by the ground radar.

Secondary radars have several advantages over primary radars: (1) they
are somewhat less costly, primarily due to the lower power that is
generated by the transmitter; (2) the data received on the ground
includes transponder and dependent altitude information; and (3) the
signal collected by the ground radar contains far less clutter than a
primary radar echo.

Secondary radars, sometimes called Secondary SSRs or beacon radars, are
the principal aircraft surveillance sensors used in the NAS today. All
aircraft operating in class A, B, or C airspace are required to carry
one or more transponders, unless otherwise authorized by ATC.

The main advantage of primary radars is that they do not require a
cooperative target. Primary radars can detect aircraft with transponders
turned off or malfunctioning and weather phenomena. This becomes
critical when aircraft have electrical or transponder and navigational
system failures. Also, it is important as a backup in the event of SSR
problems.

The description of primary and secondary radars can best be explained by
examining their use in the flight domain they serve.

### A.1.1Number range Level3Number range Level4 En Route Domain {#a.1.1number-range-level3number-range-level4-en-route-domain .otherheading-3}

Both primary and secondary radars are used today for en route
surveillance. Primary radars are termed Air Route Surveillance Radars
(ARSRs) and are often referred to as Long Range Radars (LRRs) or Long
Range Surveillance radars (LRSRs). These radars have a range of
approximately 200 to 250 nmi and transmit on 1200 to 1400 MHz. They have
large antennas (to achieve the gain necessary to detect weak echoes from
aircraft at maximum range) that rotate approximately once every 12
seconds.

The DoD provided the original en route primary radars, designated
AN/FPS-117. FAA, jointly with DoD and other government agencies, has
since developed the ARSR-1, -2, -3, and -4 radars. Each has some weather
detection capability in addition to the ability to detect aircraft. The
ARSR-4 is now being deployed around the perimeter of the United States
to replace earlier LRSRs.

Secondary radars are co-located with en route primary radars. Three
series of Air Traffic Control Beacon Interrogators (ATCBI) are currently
deployed: ATCBI-3, -4, and -5. These have the capability to operate in
Modes A and C (i.e., to determine aircraft identification, range,
bearing, and transmitted barometric altitude). Today, the ATCBI-3s have
all been in service for over 30 years. The newest ATCBI-4s have been in
service 30 years and the newest ATCBI-5s have been in service 26 years.
Commercial firms offer monopulse SSRs (MSSRs) which are similar in
functionality to the ATCBI series with and without discrete addressing
capability.

During the 1990s, deployment of Mode S SSRs was begun. Mode S radars
have four advantages over the ATCBI series: (1) improved range and
azimuth accuracy; (2) elimination of synchronous garble ("collision" of
replies from aircraft at nearly the same range and azimuth) by
interrogating aircraft individually (if the subject aircraft happen to
be equipped with Mode S transponders); and (3) air-to-ground data link
capability (if ever implemented at some point in the future); and (4)
fewer interrogations are needed due to monopulse processing. To be
backwardly compatible, Mode S SSRs also have the capability to
interrogate using Mode A and Mode C formats of the ATCBI but with the
advantage of roughly 4 times fewer interrogations due to monopulse
processing of the replies.

The MSSR and Mode S SSR's monopulse antenna is located on the same
revolving shaft, either as a "chin-mounted" antenna or immediately above
the primary radar's antenna. For example, on ARSR-4, the beacon antenna
is chin-mounted. Other beacon sites employ NADIF (NAFEC Dipole Fix)
secondary surveillance antennas, which are integral to the primary radar
antenna and use its reflector. There are also a few "beacon only" sites,
where a secondary radar is installed without an associated primary
radar.

### A.1.2Number range Level3Number range Level4 Terminal Domain {#a.1.2number-range-level3number-range-level4-terminal-domain .otherheading-3}

Terminal area primary radars are termed ASRs and are usually located
near one or more airports having air carrier service. ASRs have a usable
range of approximately 60 nmi and transmit on 2700 to 2900 MHz. To
obtain the more frequent surveillance data needed for terminal ATC, ASR
antennas rotate once every 4-5 seconds. ASR-4, -5, -6, -7, -8, and -9
units are now installed. Systems from the ASR-4, -5 and -6 series are
phased out over the next few years. The ASR-11, with integrated MSSR, is
now underdevelopment and a multi-purpose airport surveillance radar
(MP-ASR) is being researched.

A beacon radar is co-located with each ASR. These SSRs have the same
basic designs as those used for en route surveillance and are drawn from
the ATCBI-3, -4, ‑5, or Mode S series. However, since the service range
is shorter, a lower power transmitter is used.

### A.1.3Number range Level3Number range Level4 Surface Domain {#a.1.3number-range-level3number-range-level4-surface-domain .otherheading-3}

At larger airports, a primary radar termed ASDE performs surveillance of
aircraft on the surface. The ASDE-3 is the latest generation of that
series and is currently operational at many airports. Other airports
must rely on visual surveillance from the airport tower. The FAA is
investigating using smaller, low-cost X-band marine radars (terminal
ASDE-X) at airports where ASDE-3s may not be currently cost-beneficial.

### A.1.4Number range Level3Number range Level4 Oceanic Domain {#a.1.4number-range-level3number-range-level4-oceanic-domain .otherheading-3}

Today, in the oceanic domain, there is generally only procedural
separation. The only exception with radar separation in the ocean is
where there is coverage for feeder operations. Pilot position reports
are made to a commercial service via high frequency (HF) voice
communications. They are then forwarded to FAA oceanic ATC centers where
the reported positions are displayed to the service providers. Some
pilot reports are currently being transmitted from FANS-1/A-equipped
aircraft via satellite data link using service provider-pilot data link
communications (CPDLC) messages to some oceanic sectors.

**\[Debby Kirkman will check with Andy Aderegg on the communication
methods.\]**

## A.2Number range Level2Number range Level3Number range Level4 Primary and Secondary Radar Limitations {#a.2number-range-level2number-range-level3number-range-level4-primary-and-secondary-radar-limitations .otherheading-2}

A major disadvantage common to primary and secondary radars is that they
can only detect targets within line-of-sight of their respective
antennas. A radar can suffer "blind spots" at one or more azimuth angles
due to signal blockage by terrain and man-made structures. To achieve
the gain necessary to detect distant targets, primary and secondary
radar antennas can only see targets up to elevation angles of 30 to 40
degrees. There is a cone-shaped region directly above the radar ("cone
of silence") where targets cannot be detected. The curvature of the
earth imposes a minimum altitude requirement for aircraft to be visible
to a radar. Aircraft 40 nmi from the radar site must be above 1,000 feet
to be detected; aircraft 200 nmi away must be above 26,500 feet to be
seen.

The line of sight limitations of radar cause specific problems in
mountainous areas. Radar sites located in valleys only detect aircraft
within the valley; radar sites located on mountains must be focused
downward to detect low aircraft, which creates terrain-masking problems.

Low altitude aircraft are less likely to be detected by long range radar
than aircraft at higher altitudes. A greater distance between radar
sites raises the base of radar coverage. For example, aircraft over the
west coast of Florida are detected at 2,000 feet MSL. However, at the
Gulf of Mexico the base of radar coverage raises to 18,000 feet MSL.

Specific limitations to primary and secondary radars are described in
the following sections.

### A.2.1Number range Level3Number range Level4 Primary Radar Limitations {#a.2.1number-range-level3number-range-level4-primary-radar-limitations .otherheading-3}

Primary radars, and by necessity co-located secondary radars, have
siting restrictions imposed by the need to minimize clutter. Primary
radars are sited to look at aircraft against the sky as background. For
example, to operate effectively in a terminal area, an ASR radar must be
placed on or near the busiest airport, so that the propagation paths are
essentially horizontal or somewhat upward looking. Placing an ASR at an
elevated location where it would "look down" on the terminal area could
generally provide better visibility of aircraft, but would introduce
unacceptably large levels of clutter from background terrain,
structures, automobiles, etc. Similarly, en route LRRs are sited to
detect aircraft against a sky background.

In the domestic en route domain, there are surveillance tracking
problems. For example, there can be jumps in state vectors (e.g.,
position, velocity) across mosaic boundaries due to bias errors between
successive radars. There can also be a divergence of tracks (actual
versus displayed) during turns in which tracking lags can be around one
minute. There is also poor steady-state velocity tracking inherent to
primary radars of about 15 knots.

There are also difficulties associated with transitioning from en route
to terminal area domains. The terminal domain utilizes single site radar
while the en route domain relies on mosaic radar, which sacrifices track
accuracy for a greater area of coverage. Transitioning between radar
sort boxes, or from one site to another, often results in target jumps.
Terminal radar provides a faster update rate than en route radar which
gives the terminal service provider more accurate information on the
track speed and altitude of aircraft. This disparity of information
between the terminal and en route service provider leads to increased
workload through manual coordination.

There are also difficulties associated with transitioning from en route
to terminal area domains. For example, track accuracy and performance
goes from "poor to fair" in en route centers to good quality in TRACONS
due to update rate and higher accuracy of approach radars.

Finally, in the en route domain, there is a nominal 12 second data
update rate including Mode-C altitudes that may be insufficient for good
vertical tracking during climbs and descents. This results in tracker
lag and overshoot problems.

One major shortcoming of primary radar is that they do not automatically
associate an identification tag with a target. For example, where ASDE-3
radars are available at or near airports, they are primary radars and
only show images of planes. They do not include the aircraft
identification tags needed for direct communications and incursion
alerting.

Service providers can create an identification tag, often after
requesting via voice communications, that an aircraft change heading to
verify its identity. They then select the aircraft whose displayed track
changes correspondingly. However, this process is time-consuming and
increases the service provider's workload and inconvenience to the
aircraft operation. Second, despite the clutter-rejection capabilities
of modern Moving Target Indicator and Detection (MTI/MTD) circuitry,
clutter caused by precipitation and moving objects remains a problem.
Anomalous propagation, or even cars moving on a nearby highway, can
distract the service provider's attention and mask aircraft returns.
Primary radar specifications only require detection of at least 80% of
the targets in a single scan in their coverage region. Another major
shortcoming of primary radars is that they provide no usable altitude
measurement.

### A.2.2Number range Level3Number range Level4 Secondary Radar Limitations {#a.2.2number-range-level3number-range-level4-secondary-radar-limitations .otherheading-3}

Secondary radar can only detect cooperative targets carrying
transponders. Aircraft that enter the SSR coverage area without an
operating transponder are not detected. The backup radar to secondary is
primary. If you lose transponder or SSR then you lose track accuracy,
probability of detection due to clutter, and Mode C altitude. Due to its
dependence on transponders and associated altitude encoders, SSR
information my also be lost or compromised due to out of tolerance
transponders (resulting in significant range errors) and erroneous Mode
C reports (altitude errors). For an aircraft operating strictly under
VFR and with no requirement to check in with a radar equipped ATC
facility, checks to validate any of these transponder related functions
may be up to two years apart.

For the ATCBI-4, -4 and -5 equipment series, fruit, synchronous garble,
and azimuth accuracy are significant technical issues. All secondary
radars operate on the same frequencies (ground interrogation on 1030
MHz, aircraft replies on 1090 MHz). It is not unusual for an aircraft to
be within the coverage area of two or more beacon radars at the same
time, and generating replies to all ground interrogators. This situation
is further exacerbated by TCAS equipped aircraft. Every TCAS equipped
aircraft is essentially another beacon interrogator, each contributing
to the fruit rate. In high density airspace today, TCAS is designed to
limit its range so as not to degrade the performance of SSR more than
2%. Interference from both fruit and synchronous garble cause some
transponder returns to be unintelligible. The sliding window technique
(detecting sequences of target replies during the antenna dwell time)
used by the ATCBIs for measuring azimuth, requires approximately four
times more interrogation/reply pairs than does the monopulse technique
employed by Mode S. This increases the likelihood that fruit and garble
will occur. The ATCBI azimuth measurement error is twice that of the
ASR-9 (\~0.16 degree RMS) and four times that of the Mode S (\~0.068
degree RMS). However, these increased accuracies for Mode S assume that
the fixed time delays for replying in the airborne transponders are
within the specified tolerances and that the automation used for
processing and displaying the surveillance data actually use the full
precision of the generated position report. There are currently
shortcomings with both assumptions.

Although the Mode S design includes features that address some of the
shortcomings of the ATCBI radars discussed above, it is estimated that
Mode S still fails to detect up to one percent of the cooperative
targets in its coverage region per sweep. With plans for an increased
number of aircraft equipped with Mode S, the doubling of the squitter
message reply length, and the quadrupling the squitter message replay
rate, this detection rate by Mode S interrogators can only decrease.
These changes are reflected in plans for the initial implementation of
1090 MHz squitter for ADS-B. Also, due to the historical design of a
large number of ATCRBS transponders in the United States and Europe,
Mode S ground interrogators cannot fully operate according to design
intentions. They must continue to operate with ATCBI type interrogations
that do not suppress unwanted transponder replies as intended.

In final approach and initial departures, the sweep rate of the ASR
terminal radar is too slow (around 5 seconds) to monitor path deviations
and to estimate aircraft velocity vectors with much accuracy. Although
the Precision Runway Monitoring (PRM) radar with about a one-second
sweep overcomes this problem, it is only available at a few airports
with closely spaced parallel runways and is a costly system for
providing such capability.

**\[Jeff Williams to find out about the Final Monitor Aid (FMA) and
possibly add paragraph.\]**

## A.3Number range Level2Number range Level3Number range Level4 Passive Cooperative Surveillance Systems {#a.3number-range-level2number-range-level3number-range-level4-passive-cooperative-surveillance-systems .otherheading-2}

Passive cooperative surveillance systems have been developed and are
employed in special non-ATC applications. These applications include
airborne collision avoidance systems and ground based monitoring of
arrival traffic for gate coordination by airlines. These systems do not
rely on active interrogations or the data link transmission of
navigation data for position determination. In general, they operate
based on the accurate measurement of "time of arrival" of the reply
signals from an airborne transponder at a receiver. Fielded passive
surveillance systems fall into two categories: those that require a
database of the SSR site locations in the area of interest in
conjunction with one reply receiver, or those that use three or more
reply receivers at know locations to determine the position of the
replying transponder through "multilateration". Only systems requiring
knowledge of the location of the SSR interrogators are currently being
used. Passive systems do not require a transmitter. Therefore, they are
less costly to acquire and maintain than their active counterparts.

### A.3.1Number range Level3Number range Level4 Passive Surveillance Limitations {#a.3.1number-range-level3number-range-level4-passive-surveillance-limitations .otherheading-3}

Like secondary radars, passive surveillance systems as previously
defined can only detect aircraft with transponders. Also, for the
predominant systems in current usage, it is required that the detected
aircraft have to be in the coverage area of at least one SSR. This is
because the time since interrogation of the subject transponder and the
location of the interrogating SSR are part of the data needed to perform
the calculation to determine the position of the replying transponder.
Although "multilateration" systems do not use the SSR sweep or the
location of the SSR in its determination of replying transponder
position, an SSR is required to interrogate and elicit a reply from
ATCRBS transponders. Mode S transponders, with their spontaneous
"squitter" reply, do not require an interrogator in the area for a
"multilateration" system, but they do create a higher fruit environment
with which the other passive systems have to contend. All the passive
systems described have timing and geometry limitations that affect the
accuracy of position determinations.

## A.4Number range Level2Number range Level3Number range Level4 Airborne Surveillance Radar {#a.4number-range-level2number-range-level3number-range-level4-airborne-surveillance-radar .otherheading-2}

Certain military aircraft possess onboard radar systems which allow them
to surveil the airspace in their immediate vicinity. These radar systems
are capable of detecting both cooperative and non-cooperative aircraft
within the radar's service volume. This detection capability, along with
a graphic display in the cockpit, give the pilot a highly accurate
picture of his local traffic situation. This information, while it can
be shared with other appropriately equipped military aircraft, cannot be
shared with other users in the NAS.

## A.5Number range Level2Number range Level3Number range Level4 Ground and Airborne Weather Radar {#a.5number-range-level2number-range-level3number-range-level4-ground-and-airborne-weather-radar .otherheading-2}

### A.5.1Number range Level3Number range Level4 Current Airborne Weather Radar Operational Capabilities {#a.5.1number-range-level3number-range-level4-current-airborne-weather-radar-operational-capabilities .otherheading-3}

Current state-of-the-art weather radar systems support a broad range of
weather phenomena detection, alerting and display. Weather radar
supports the detection of convective weather out to 320 nmi ahead of the
aircraft. Using Doppler techniques, the radar can detect precipitation
gradients and rates and displays them in different colors depending on
the rate. The radar can detect areas of turbulence using gradient
detection algorithms and these areas are displayed in a distinctive
color. The newest feature to certified systems is predictive windshear
detection that detects windshear threats up to 5 miles ahead and +/- 30
degrees of the aircraft heading. This provides the crew warning time
ahead of the event (predictive).

The limitations to the current radar systems are detection range and
azimuth from the centerline. Since windshear detection is only used in
takeoff and landing configurations, there is a lack of clear air
turbulence detection with these systems.

### A.5.2Number range Level3Number range Level4 Current and Planned Ground Based Weather Radar Capabilities {#a.5.2number-range-level3number-range-level4-current-and-planned-ground-based-weather-radar-capabilities .otherheading-3}

In the near term, the FAA will continue its present philosophy of
detecting and displaying weather on its en route (ARSR-4) and terminal
(ASR-9, -11) primary surveillance radars.

Early LRRs were limited in their ability to accurately detect the level
and intensity of the weather. This was partially due to the fact that
weather data is detected and processed through the same path used for
aircraft detection. The ARSR-4 incorporates a completely separate
weather channel and processing path as well as separate target detection
channels (1 weather and 5 target channels). Early in 1996, the ARSR-4
weather data was validated as a viable ATC tool for use in conjunction
with the Next Generation Weather Radar (NEXRAD). Together they detect
weather contours for up to five National Weather Service classification
levels, which assist air traffic service providers. Service providers
are able to view the weather information via the primary path with new
Display System Replacement (DSR) consoles. When Weather and Radar
Processor (WARP)/NEXRAD is incorporated into DSR through the primary
path, service providers have the capability of displaying simultaneously
both the Host weather data (i.e., LRR) and NEXRAD weather data. Service
providers have a choice of which weather data to view on a user-by-user
basis. When DSR is implemented, LRRs initially provide the only source
of weather data to ATC, provided via the primary Host path and the
backup EDARC path. If the primary path fails, LRR weather data continue
to be available to ATC via the backup path.

The ASR-9 is a terminal (local) radar system that detects aircraft with
distances ranging up to 60 nautical miles. The ASR-9 is a primary
terminal radar. The ASR-9 features solid state technology; a moving
target detector to precisely track low altitude aircraft; a built in
monitoring subsystem; and a weather channel to display the National
Weather Service\'s standard six levels of weather, any two at a time.
The latest generation Airport Surveillance Radar, known as ASR-9, better
enables air traffic service providers to track aircraft in conditions of
severe ground and weather clutter. The ASR-9 can show aircraft and
weather activity simultaneously, and represents a significant
improvement over previous surveillance radars. The new radar provides
very accurate aircraft position information, even under extreme
conditions. Its advanced Moving Target Detection System reduces false
returns, providing service providers with a clear, clutter-free display.
It also displays six levels of weather intensity, helping service
providers direct aircraft around severe weather disturbances. The
state-of-the-art remote maintenance monitoring capabilities of the new
system reduces maintenance time and cost.

The ASR-11 is a Non-Developmental Item (NDI) radar, slated to replace
ASR-7s at low to medium density airports. It provides cooperative and
non-cooperative aircraft data, and six level weather reports, in a
digital format compatible with future automation systems. The
cooperative data is supplied via an integral monopulse secondary
surveillance radar.

Later, the FAA provides enhanced weather information to the Centers via
the WARP and to the terminal aviation system users via Integrated
Terminal Weather System (ITWS).

The WARP provides enhanced weather information to air traffic service
providers, traffic management specialists, area supervisors, and the
Center Weather Service Unit (CWSU) meteorologists who support them. WARP
receives and consolidates weather data from multiple sources, including
radar, into a single database, and then analyzes, generates and displays
specialized value-added aviation weather products to support en route
air traffic control operations. WARP is the primary tool used by the
meteorologists located at the air route traffic control centers (ARTCCs)
and the air traffic system control center (ATCSCC) to receive, process
and display weather information. The CWSU meteorologists are provided
with processing tools that integrate into a single workstation the
information that formerly resided on four different systems. The WARP
weather briefing terminals are located at the traffic management unit
(TMU) and area supervisors stations. WARP provides TMU personnel with
current and long-range forecast weather conditions for strategic
planning, and air traffic control supervisors with advance notice of
approaching/developing hazardous weather conditions for tactical
decision assistance. Future WARP upgrades allow the system to provide
next generation Doppler weather radar (NEXRAD) data for display on en
route service providers\' display consoles via the display system
replacement (DSR), replacing long-range surveillance radar weather data
with much more accurate information. WARP eventually becomes the common
source for weather information in the en route environment.

The ITWS provides terminal aviation system users with safety and
planning products that characterize current terminal weather situations
as well as forecast about 30 minutes into the future. This is achieved
by integrating data products from various FAA and National Weather
Service (NWS) sensors (e.g., Terminal Doppler Weather Radar \[TDWR\],
ASR-9, NEXRAD, Low-Level Windshear Alert System \[LLWAS\], Automated
Surface Observing System \[ASOS\], and other NWS systems). Products
generated by ITWS include windshear and microburst predictions, storm
cell and lightning information, terminal area winds aloft, runway winds,
and short-term ceiling and visibility predictions. ITWS differentiates
between real weather radar returns from those caused by anomalous
propagation. This system is the primary tool used by Terminal air
traffic management personnel to obtain, process and display current and
predictive weather information. ITWS supports the FAA\'s mission of
ensuring a safe and efficient National Airspace System.

## A.6Number range Level2Number range Level3Number range Level4 Automatic Dependent Surveillance (ADS) {#a.6number-range-level2number-range-level3number-range-level4-automatic-dependent-surveillance-ads .otherheading-2}

Automatic Dependent Surveillance (ADS) is a datalink application related
to surveillance that transmits parameters, such as position, track, and
ground speed from the subject target via a datalink at specified
intervals. Addressed ADS, or ADS-A (also some times called contract ADS
or ADS-C), transmits this information over an addressed or
point-to-point link, usually air-to-ground. Broadcast ADS, or ADS-B, is
an open broadcast of this information by the subject target for
utilization by any air and/or ground users requiring it.

## A.7Number range Level2Number range Level3Number range Level4 Traffic Alert and Collision Avoidance System (TCAS) {#a.7number-range-level2number-range-level3number-range-level4-traffic-alert-and-collision-avoidance-system-tcas .otherheading-2}

TCAS is an airborne collision avoidance system. There are two
implemented variants of TCAS; TCAS I and TCAS II. TCAS I is a pilot
warning indicator that displays proximate traffic and alerts the crew to
other Mode C transponder equipped aircraft which may become potential
near midair collision threats. TCAS II, in addition to providing a
warning indication, also provides recommended vertical escape maneuvers
to the crew to avert potential midair collisions. TCAS equipment in the
aircraft interrogates transponders on aircraft in its vicinity and
listens for the replies. TCAS II aircraft can coordinate resolution
maneuvers with other TCAS II aircraft.

### A.7.1Number range Level3Number range Level4 Limitations of TCAS {#a.7.1number-range-level3number-range-level4-limitations-of-tcas .otherheading-3}

TCAS surveillance range can be limited by design in high density
airspace as it tries to minimize interference with the ground
interrogators.

TCAS does not interrogate for aircraft identity as do ground SSR
systems. Instead it correlates successive range and altitude reports to
establish and maintain aircraft tracks. Because of this, it is not
capable of displaying the other aircraft\'s call sign.

TCAS relies mainly on range and altitude for resolution advisories due
to the coarseness of its detection capabilities in relative bearing or
azimuth.

TCAS is not able to provide surveillance on aircraft that are within 400
ft AGL or on the airport surface due to its design limitations and the
need to avoid excessive RF interference with ground-based SSR systems.
It cannot issue Resolution Advisories until its own aircraft is above
1000 ft AGL; however, it can issue Traffic Advisories against airborne
aircraft between 400 ft and 1000 ft AGL. It is anticipated that future
surveillance technologies fill the need for low-altitude and surface
surveillance.

Current TCAS type displays are generally not considered suitable for
advanced EFR operational concepts.

## A.8Number range Level2Number range Level3Number range Level4 Uplink of Traffic Information {#a.8number-range-level2number-range-level3number-range-level4-uplink-of-traffic-information .otherheading-2}

The current implementation for uplink of traffic information uses Mode S
radar-specific formats to transmit information about aircraft proximate
to the user requesting service. This is called TIS, and is available in
a limited number of locations. In development is a more capable service
that broadcasts the positions of all aircraft in the service volume
using a richer data format. This service is referred to as TIS
Broadcast, or TIS-B. The primary purpose of TIS-B is to accelerate
benefits associated with CDTI before there is widespread equipage with
the ADS-B system, providing a basic level of information that would
serve currently non-equipped aircraft as an incentive to equip.

### A.8.1Number range Level3Number range Level4 Limitations of TIS {#a.8.1number-range-level3number-range-level4-limitations-of-tis .otherheading-3}

The data sent from the Mode S SSR is derived from ground-based position
estimates, which have a nominal refresh rate of 4.8 seconds. As a
result, some lag in the reported position compared with the actual
position of the surrounding aircraft occurs. This is compounded by the
position report being relative to the aircraft track, rather than its
heading. This system is only available in areas having radar coverage
using Mode S, and is primarily intended for those airspace users that
are not equipped with TCAS or alternative traffic display systems, but
which have a Mode S transponder, a data processor, and a multi-function
display. TIS provides a maximum of eight targets to the user, and it
intended to serve only as an enhancement to visual acquisition for GA
targets. TIS-B limitations are primarily dependent on the quality of
ground surveillance that is available. The primary source of data for
TIS-B is radar; TIS-B coverage is then limited to the area having radar
coverage.

## A.9Number range Level2Number range Level3Number range Level4 Direction Finder (DF) {#a.9number-range-level2number-range-level3number-range-level4-direction-finder-df .otherheading-2}

Direction finding is either a ground or airborne capability to establish
an aircraft position based on two or more ground stations being able to
determine a relative bearing of the aircraft to the station by the
reception and plotting of a radio transmission (HF, VHF, UHF) from the
aircraft. An airborne aircraft my also determine its position by
plotting the intersection of two or more relative bearings to ground
stations. Alternatively, the aircraft can turn 90 degrees to the
station, fly for a specified speed and time, note the bearing change to
the station, and determine its position.

### A.9.1Number range Level3Number range Level4 Limitations of DF {#a.9.1number-range-level3number-range-level4-limitations-of-df .otherheading-3}

Ground stations must be equipped. Current single and dual bearing
systems yield a relatively low position accuracy. Current non-automated
techniques take a relatively long time to establish a position based on
plotting the intersection of the relative bearings.

## A.10Number range Level2Number range Level3Number range Level4 Emergency Locator Transponder (ELT) {#a.10number-range-level2number-range-level3number-range-level4-emergency-locator-transponder-elt .otherheading-2}

A device required to be carried by most aircraft that is activated in an
emergency or distress situation. It may be activated manually, by
G-forces, or sometimes upon contact with water. The device emits (VHF
and UHF) transmissions capable of being received by conventional
receivers as well as dedicated Search and Rescue Satellites (SARSAT).

### A.10.1Number range Level3Number range Level4 Limitations of ELT {#a.10.1number-range-level3number-range-level4-limitations-of-elt .otherheading-3}

Current units have limited life battery power. Activation is sometimes
accidental, and in some cases, it may not function as desired in a
crash. It requires either homing or triangulation to determine the
position of the transmitter.

## A.11Number range Level2Number range Level3Number range Level4 Visual Surveillance {#a.11number-range-level2number-range-level3number-range-level4-visual-surveillance .otherheading-2}

Visual surveillance is among the most basic forms of surveillance, as it
depends solely on the eyesight of a pilot or service provider to
determine the relative position of aircraft, terrain, weather, and other
entities in relationship to the observer. Visual acquisition of another
entity is considered the fundamental method of validating the accuracy
of other means of surveillance.

Despite apparent limitations (see below), visual operations remain a
cornerstone in today's ATC operations, in that visual approach
operations are considered to be the highest attainable throughput method
of landing aircraft today.

### A.11.1Number range Level3Number range Level4 Limitations of Visual Surveillance {#a.11.1number-range-level3number-range-level4-limitations-of-visual-surveillance .otherheading-3}

Visual acquisition of another entity is considered the fundamental
method of validating the accuracy of other means of surveillance.
However, it does have very significant deficiencies. Among these are
limited range, deterioration of service with changes in weather and
ambient light, limited ability to determine distances and velocities,
propensity for misidentification, and a relatively poor field of view
for high-resolution information.

## A.12Number range Level2Number range Level3Number range Level4 Voice Reporting {#a.12number-range-level2number-range-level3number-range-level4-voice-reporting .otherheading-2}

Voice position reports are considered another basic surveillance
capability, in that only a means of verbal communications is necessary
to obtain the information. It is, therefore, a means of dependent
surveillance. Information contained in a position report includes an
aircraft's location, altitude, and next point of navigation (i.e., next
waypoint). Despite inherent limitations to reporting via voice, this
type of reporting is typically the primary means of surveillance in
oceanic and other non-radar airspace, including airport traffic patterns
in uncontrolled airspace. Today in the oceanic domain, pilot position
reports are made to a commercial service via high frequency (HF) voice
communications. They are then forwarded to FAA oceanic ATC centers where
the reported positions are displayed to the service providers.

### A.12.1Number range Level3Number range Level4 Limitations of Voice Reporting {#a.12.1number-range-level3number-range-level4-limitations-of-voice-reporting .otherheading-3}

Due to the difficulty in mentally assimilating verbal information and
the high workload associated with transmitting and receiving reports,
voice reporting as a sole means of surveillance fundamentally limits the
service provider's ability to obtain a clear picture of a situation with
multiple aircraft. Saturation of the communications channel can make
access difficult also. Position accuracy is further degraded since the
time given in all reports is not synchronized to the same reference,
e.g., UTC.

## A.13Number range Level2Number range Level3Number range Level4 Data Link {#a.13number-range-level2number-range-level3number-range-level4-data-link .otherheading-2}

Surveillance information is also conveyed today via airline digital
communications service providers. In oceanic airspace, pilots of
aircraft equipped with the FANS-1 package can send position reports as
one of the Controller Pilot Data Link Communications (CPDLC) messages
available to them. The position reports are manually entered, and are
transmitted to the communications service provider, who then forwards
them to an oceanic sector service provider.

Airline fleet management is enhanced through the use of messages that
indicate aircraft status and intent with respect to departure and
destination points. These messages indicate whether the aircraft is Out
of the gate, Off the ground, On the ground, or In the gate; they are
referred to as a group as "OOOI". Like the CPDLC messages, these are
sent to the communications service provider, but they are forwarded to
an airline operations center.

### A.13.1Number range Level3Number range Level4 Limitations of Data Link {#a.13.1number-range-level3number-range-level4-limitations-of-data-link .otherheading-3}

The CPDLC messages for position reporting are not automatic, and
therefore do not support the same level of accuracy as would an ADS
report. Pilots basically transcribe navigation information into the
message; timing is not based on a common clock reference, adding
additional uncertainty.

OOOI messages provide a rudimentary level of intent information, but do
not help significantly with predictive needs, especially for arrival.

# Glossary {#glossary .Back-Matter-Header}

**[Definitions]{.underline}**

**Airport Movement Area Safety System (AMASS):** The Airport Movement
Area Safety System (AMASS) is the FAA's first generation endeavor to
automate the warning of potential collision threats on the runway. One
of the benefits of the AMASS system is the ability to transfer arriving
aircraft identification from ARTS to the ASDE displays, providing
positive aircraft identification to the service provider. This function
is the first step in providing an enhanced safety net and operational
advancement much needed in the tower environment.

**Airport Surface Detection Equipment (ASDE):** ASDE is a tool used to
enhance the service provider's awareness of the position and movement of
aircraft on the airport's surface. It presents the service provider with
a primary radar display of the position of targets on the surface. This
capability is used by the ground service provider to aid in managing the
movement of aircraft. ASDE, lacking secondary radar, has no ability to
present identification information of the targets it detects.

**Air Traffic Management (ATM):** ATM is a term used to describe the
collective services of the Air Traffic Service Provider. These services
include: Air Traffic Control, which concerns the safe separation of
aircraft; Traffic Flow Management, which ensures that demand for
infrastructure resources (e.g., airports, airways, sectors, centers)
does not overwhelm the capacity of those resources; and the design and
usage of Airspace, which gives the underlying structure upon which the
other two functions are performed.

The ATM system provides services that are fundamentally safe for all
users of the system, while introducing as few restrictions and
inefficiencies to user operations as possible.

\[ATM and CDM definitions: Earle Wolfe - break out separate
definitions\]

**Certification**: Avionics to be used for any new separation standards
must be both demonstrated and certified for the purpose for which it is
to be used.

**Cockpit Display of Traffic Information (CDTI):** CDTI presents
surveillance information about the surrounding traffic to the flight
crew. The information presented includes the relative position of other
aircraft in the vicinity with respect to one\'s own aircraft. Traffic
information for the CDTI may be obtained from one or more sources,
including, but not limited to, broadcast automatic dependent
surveillance (ADS-B), broadcast of traffic information, and traffic
alert and collision avoidance system (TCAS). To display traffic
information, the CDTI may use a dedicated display device or a shared
multi-function display (MFD) device. Even though a visual, graphical
presentation of the traffic on a heads-down display is most common in
the near term, other types of presentation (e.g., aural, graphical
head-up) are also possible, as long as information is conveyed
effectively. The specific information presented may vary based on the
intended operational use of the information. (From RTCA DO-243)

**Digital Bright Radar Indicator Tower Equipment (D-BRITE):** Certain
airports (Level 3 and above) provide a radar display in the control
tower, which presents the service provider with the primary and
secondary radar returns of airborne aircraft in the vicinity of the
airport. This system is called D-BRITE, and is usually connected to the
radar and automation system of the host terminal approach control
facility. D-BRITE displays primary and secondary radar information with
data blocks for each aircraft on the traffic display, improving the
service provider's awareness of airborne traffic over mere visual
observations. It aids in the sequencing of aircraft for arrival and
departure, as well as allowing service providers to provide improved
traffic advisory information to aircraft in the airport's area.

**Multi-Functional Display (MFD):** MFD is a device or system capable of
displaying a variety of data, either simultaneously or sequentially, on
a single display unit.

The MFD system may contain one or more electronic display devices
capable of presenting data in any one of several possible formats and
designed to depict navigation, communication, aircraft state, aircraft
system management, weather, traffic, and/or other information used by
the flight crew for command and control of the aircraft. The information
displayed may be combined to make an integrated display; or one set of
data may simply replace another.

**Electronic Flight Rules** **(EFR):** are an extension of VFR and IFR
discussed above, taking advantage of the surveillance data and other
capabilities available in the cockpit to better consider the economics
of flight operation, as well as the freedom of the pilots in making
maneuvers. These rules are developed, certified, and approved to
maintain and, where possible, enhance safety consistent with expected
future traffic growth. They are designed and to involve airspace users
in the ATM loop while continuing to fulfil the human-centered automation
requirements of the ATM system. Note: This set of rules is currently
evolving and does not currently exist.

**Instrument Flight Rules:** are a set of rules governing the procedures
for conducting instrument flight. Also a term used by pilots and service
providers, it indicates type of flight plan. ICAO definition: A set of
rules governing the conduct of flight under instrument meteorological
conditions (IMC).

**Search and Rescue** **(SAR):** is a lifesaving service provided
through the combined efforts of the federal agencies signatory to the
National SAR Plan, and the agencies responsible for SAR within each
state.

**Separation Responsibilities:** If the pilot has the airport in sight
but cannot see the aircraft to be followed, ATC may clear the aircraft
for a visual approach. However, ATC retains both separation and wake
vortex separation responsibility. When visually following a preceding
aircraft, acceptance of the visual approach clearance constitutes
acceptance of pilot responsibility for maintaining a safe approach
interval and adequate wake turbulence separation.

**Separation Services**: services provided to separate an aircraft in
controlled airspace from other aircraft, terrain, obstacles, and special
use airspace. These services are applied through the application of
established vertical, lateral, or longitudinal separation standards. The
current separation standards are outlined in the Air Traffic Control
Order 7110.65.

**Service Provider**: any authorized individual that provides
separation, traffic management, airspace management, and aviation
information, search and rescue, aviation assistance, or navigation and
landing services to a NAS user.

**User**: is any entity that uses the ATM system, including air
carriers, general aviation, and State aircraft.

**\[Is the following a candidate for removal? Kevin Chamness (NATCA) to
check if any problem with removing.\]**

**VFR-ON-TOP:** is an ATC authorization for an IFR aircraft to operate
in VFR conditions at any appropriate VFR altitude (as specified in FAR
and as restricted by ATC). A pilot receiving this authorization must
comply with the VFR visibility, distance from cloud criteria, and the
minimum IFR altitudes specified in FAR Part 91. Separation is provided
between all aircraft operating on IFR flight plans except during that
part of the flight, outside Class B or C airspace or a TRSA, being
conducted on a VFR-ON-TOP/VFR CONDITIONS clearance. Under these
conditions, ATC may issue traffic advisories, but it is the sole
responsibility of the pilot to be vigilant so as to see and avoid other
aircraft.

**Visual Approach:** is an approach conducted on an IFR flight plan,
which authorizes the pilot to proceed visually to the airport. The pilot
must, at all times, have either the airport or the preceding aircraft in
sight. This approach must be authorized and under the control of the
appropriate air traffic control facility. Reported weather at the
airport must have a ceiling at or above 1,000 feet and visibility of 3
miles or greater. Authorization to conduct a visual approach is an IFR
authorization, and does not alter IFR flight plan cancellation
responsibility.

**Visual Flight Rules:** are rules that govern the procedures for
conducting flight under visual meteorological conditions (VMC). The term
"VFR" is also used in the United States to indicate weather conditions
that are equal to or greater than the minimum VFR requirements. In
addition, VFR is used by pilots and service providers to indicate type
of flight plan.

**Visual Separation**:

a.  Visual separation is a means employed by ATC to separate aircraft in
    terminal areas and en route airspace in the NAS. There are two ways
    to effect this separation:

    1.  The tower service provider sees the aircraft involved and issues
        instructions, as necessary, to ensure that the aircraft avoid
        each other.

    2.  A pilot sees the other aircraft involved and upon instructions
        from the service provider, provides his own separation by
        maneuvering his aircraft as necessary to avoid it. This may
        involve following another aircraft or keeping it in sight until
        it is no longer a factor.

b.  A pilot's acceptance of instructions to follow another aircraft, or
    provide visual separation from it, is an acknowledgment by the pilot
    to maneuver his aircraft as necessary to avoid the other aircraft or
    to maintain in-trail separation. In operations conducted behind
    heavy jet aircraft, it is also an acknowledgment that the pilot
    accepts the responsibility for wake turbulence separation.

**[Acronyms]{.underline}**

**ACARS** Aircraft Communications Addressing and Reporting System

**ACAS** Airborne Collision Avoidance System

**ADS** Automatic Dependent Surveillance

**ADS-A** Automatic Dependent Surveillance-Addressed

**ADS-B** Automatic Dependent Surveillance-Broadcast

**ADS-C** Automatic Dependent Surveillance-Contract

**AGL** Above Ground Level

**AIDC** ATS Interfacility Data Communications

**AIM** Aeronautical Information Manual

**AMASS** Airport Movement Area Safety System

**AN/FPS** Air Navigation/Fixed Position Surveillance (Military Radar)

**ANP** Actual Navigation Performance

**AOC** Airline/Aeronautical Operations Center

**ARSR** Air Route Surveillance Radars

**ARTCC** Air route traffic control centers

**ASD** Aircraft Situation Display

**ASDE** Airport Surface Detection Equipment

**ASOS** Automated Surface Observing System

**ASR** Airport Surveillance Radars

**AT** Air Traffic

**ATC** Air Traffic Control

**ATCBI** Air Traffic Control Beacon Interrogators

**ATCRBS** Air Traffic Control Radar Beacon System

**ATIS** Automated Terminal Information System

**ATM** Air Traffic Management

**ATN** Aeronautical Telecommunication Network

**ATS** Air Traffic Service

**ATSCC** Air traffic system control center

**AWOS** Automated Weather Observing System

**BASEOPS** Military Base Operations

**CDM** Collaborative Decision Making

**CDTI** Cockpit Display of Traffic Information

**CFIT** Controlled Flight Into Terrain

**CNS** Command, Navigation, and Surveillance

**CPDLC** Controller-Pilot Data Link Communications

**CWA** Center Weather Advisories

**CWSU** Center Weather Service Unit

**D-BRITE** Digital Bright Radar Indicator Tower Equipment

**DF** Direction Finder

**DoD** Department of Defense

**DP** Departure Procedures

**DSR** Display System Replacement

**EDARC** Enhanced Direct Access Radar Channel

**EFR** Electronic Flight Rules

**EGPWS** Enhanced Ground Proximity Warning System

**ELT** Emergency Locator Transponder

**ETA** Estimated-Time-of-Arrival

**ETD** Estimated Departure Time

**ETMS** Enhanced Traffic Management System

**FAA** Federal Aviation Administration

**FANS** Future Air Navigation Systems

**FAR** Federal Aviation Regulations

**FAST** Final Approach Spacing Tool

**FBO** Fixed Based Operator

**FDP** Flight data processing

**FDR** Flight Data Recorders

**FFP** Firm Fixed Price

**FIDS** Flight Information Display System

**FIR** flight information regions

**FIS** Flight Information Services

**FMA** Final Monitor Aid

**FMS** Flight Management Systems

**FPL** Filed Flight Plan

**FPS**

**FSS** Flight Service Stations

**GA** General Aviation

**GOES** Geostationary operational environmental satellite

**HF** High frequency

**HMI** Human Machine Interface

**ICAO** International Civil Aviation Organization

**IMC** Instrument meteorological conditions

**IFR** Instrument flight rules

**ITWS** Integrated Terminal Weather System

**LLWAS** Low-Level Windshear Alert System

**LRR** Long Range Radar

**LRSR** Long Range Surveillance Radar

**MDCRS** Meteorological Data Collection and Retrieval System

**MEA** Minimum En Route (IFR) Altitude

**METAR** Meteorological Aviation Report

**MFD** Multifunction display

**MOU** Memorandum of understanding

**MP-ASR** Multi-purpose airport surveillance radars

**MSL** Mean Sea Level

**MSSR** Monopulse SSR

**MTI/MTD** Moving Target Indicator and Detection

**NADIF** NAFEC Dipole Feed

**NAS** National Airspace System

**NDI** Non-Developmental Item

**NESDIS** National Environmental Satellite Data and Information System

**NEXRAD** Next Generation Weather Radar

**NOAA** National Oceanic and Atmospheric Association

**NOTAM** Notices to airmen

**NRP** National Route Program

**NWS** National Weather Service

**OE/D** Operational Errors and Deviations

**OEDP** Operational Error Detection Program or Patch

**OOOI** Out-Off-On-In

**PIREP** PIlot REPort

**PRM** Precision Runway Monitoring

**RCC** Rescue Coordination Centers

**RDP** Radar Data Processing

**RMS** Remote Monitoring System

**RTSP** Required total system performance

**RVR** Runway Visual Range

**SAR** Search and Rescue

**SARSAT** Search and Rescue Satellites

**SATCOM** SATellite COMmunicaiton

**SATVOICE** Satellite voice

**SID** Standard Instrument Departure

**SIGMET** Significant Meteorological Information

**SMA** Surface Movement Advisor

**STAR** Standard Terminal Arrival Routes

**SUA** Special Use Airspace

**SSR** Secondary Surveillance Radars

**TAF** Terminal Area Forecast

**TCAS** Traffic alert and collision avoidance system

**TDWR** Terminal Doppler Weather Radar

**TFM** Traffic Flow Management

**TIS-B** Traffic information service broadcast

**TMU** Traffic management unit

**TRACON** Terminal RAdar CONtrol

**TRSA** Terminal Radar Service Area

**TSD** Traffic Situation Display

**USGS** United States Geological Survey

**UTC** Universal Time Code

**VAFTAD** Volcanic Ash Forecast Transport and Dispersion

**VAR** Volcanic Activity Reporting Form

**VFR** Visual Flight Rules

**VMC** Visual meteorological conditions

**WARP** Weather and Radar Processor

[^1]: In the rare occasions that there are IFR operations in
    uncontrolled airspace (such as occur in Alaskan airspace), the pilot
    performs separation management.

[^2]: See DO-242, ADS-B MASPS, for flight path deconfliction
    surveillance requirements.