Automatic Dependent Surveillance-Broadcast (ADS-B) Out Performance Requirements To Support Air Traffic Control (ATC) Service, 56947-56972 [07-4938]

Agencies

• Federal Aviation Administration
• DEPARTMENT OF TRANSPORTATION

[Federal Register Volume 72, Number 193 (Friday, October 5, 2007)]
[Proposed Rules]
[Pages 56947-56972]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 07-4938]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 91

[Docket No. FAA-2007-29305; Notice No. 07-15]
RIN 2120-AI92


Automatic Dependent Surveillance--Broadcast (ADS-B) Out 
Performance Requirements To Support Air Traffic Control (ATC) Service

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: This notice proposes performance requirements for certain 
avionics equipment on aircraft operating in specified classes of 
airspace within the United States National Airspace System. The 
proposed rule would facilitate the use of Automatic Dependent 
Surveillance-Broadcast (ADS-B) for aircraft surveillance by Federal 
Aviation Administration and Department of Defense air traffic 
controllers to accommodate the expected increase in demand for air 
transportation. In addition to accommodating the anticipated increase 
in operations, this proposal, if adopted, would provide aircraft 
operators with a platform for additional flight applications and 
services.

DATES: Send your comments on or before January 3, 2008.

ADDRESSES: You may send comments identified by Docket Number FAA-2007-
29305 using any of the following methods:
     Federal eRulemaking Portal: Go to https://
www.regulations.gov and follow the online instructions for sending your 
comments electronically.
     Mail: Send comments to the Docket Management Facility; 
U.S. Department of Transportation, 1200 New Jersey Avenue, SE., West 
Building Ground

[[Page 56948]]

Floor, Room W12-140, Washington, DC 20590-0001.
     Hand Delivery or Courier: Bring comments to the Docket 
Management Facility in Room W12-140 of the West Building Ground Floor 
at 1200 New Jersey Avenue, SE., Washington, DC, between 9 a.m. and 5 
p.m., Monday through Friday, except Federal holidays.
     Fax: Fax comments to the Docket Management Facility at 
202-493-2251.
    Privacy Act: We will post all comments we receive, without change, 
to https://www.regulations.gov, including any personal information you 
provide. Anyone is able to search the electronic form of all comments 
received into any of our dockets by the name of the individual 
submitting the comment (or signing the comment, if submitted on behalf 
of an association, business, labor union, etc.). You may review DOT's 
complete Privacy Act Statement in the Federal Register published on 
April 11, 2000 (65 FR 19477-78) or you may visit https://
DocketInfo.dot.gov.
    Docket: To read background documents or comments received, go to 
https://www.regulations.gov at any time and follow the online 
instructions for accessing the docket. Or, go to the Docket Management 
Facility in Room W12-140 of the West Building Ground Floor at 1200 New 
Jersey Avenue, SE., Washington, DC, between 9 a.m. and 5 p.m., Monday 
through Friday, except Federal holidays.

FOR FURTHER INFORMATION CONTACT: Vincent Capezzuto, Surveillance and 
Broadcast Services Office, Air Traffic Organization, Federal Aviation 
Administration, 800 Independence Avenue SW., Washington, DC 20591; 
telephone 202-385-8288.

SUPPLEMENTARY INFORMATION:

Comments Invited

    The FAA invites interested persons to participate in this 
rulemaking proposal by submitting written comments, data, or views. We 
also invite comments relating to the economic, environmental, energy, 
or federalism impacts that might result from adopting the proposals in 
this document. The most helpful comments reference a specific portion 
of the proposal, explain the reason for any recommended change, include 
specific rule language changes, and include supporting data. We ask 
that you send us two copies of written comments.
    We will file in the docket all comments we receive, as well as a 
report summarizing each substantive public contact with FAA personnel 
concerning this proposed rulemaking.
    Before acting on this proposal, we will consider all comments we 
receive on or before the closing date for comments. We will consider 
comments filed after the comment period has closed if it is possible to 
do so without incurring expense or delay. We may change this proposal 
in light of the comments we receive.
    If you want the FAA to acknowledge receipt of your comments on this 
proposal, include with your comments a pre-addressed, stamped postcard 
on which the docket number appears. We will stamp the date on the 
postcard and mail it to you.

Proprietary or Confidential Business Information

    Do not file in the docket information that you consider to be 
proprietary or confidential business information. Send or deliver this 
information directly to the person identified in the FOR FURTHER 
INFORMATION CONTACT section of this document. You must mark the 
information that you consider proprietary or confidential. If you send 
the information on a disk or CD-ROM, mark the outside of the disk or 
CD-ROM and also identify electronically within the disk or CD-ROM the 
specific information that is proprietary or confidential.
    Under 14 CFR 11.35(b), when we are aware of proprietary information 
filed with a comment, we do not place it in the docket. We hold it in a 
separate file to which the public does not have access, and place a 
note in the docket that we have received it. If we receive a request to 
examine or copy this information, we treat it as any other request 
under the Freedom of Information Act (5 U.S.C. 552). We process such a 
request under the DOT procedures found in 49 CFR part 7.

Availability of Rulemaking Documents

    You can get an electronic copy of rulemaking documents using the 
Internet by--
    1. Searching the Federal eRulemaking Portal (https://
www.regulations.gov);
    2. Visiting the FAA's Regulations and Policies Web page at https://
www.faa.gov/regulations_policies/; or
    3. Accessing the Government Printing Office's Web page at https://
www.gpoaccess.gov/fr/.
    You can also get a copy by sending a request to the Federal 
Aviation Administration, Office of Rulemaking, ARM-1, 800 Independence 
Avenue, SW., Washington, DC 20591, or by calling (202) 267-9680. Make 
sure to identify the docket number, notice number, or amendment number 
of this rulemaking.

Authority for This Rulemaking

    The FAA's authority to issue rules regarding aviation safety is 
found in Title 49 of the United States Code. Subtitle I, Section 106 
describes the authority of the FAA Administrator. Subtitle VII, 
Aviation Programs, describes in more detail the scope of the agency's 
authority.
    This rulemaking is promulgated under the authority described in 
Subtitle VII, Part A, Subpart I, Section 40103, Sovereignty and use of 
airspace, and Subpart III, section 44701, General requirements. Under 
section 40103, the FAA is charged with prescribing regulations on the 
flight of aircraft, including regulations on safe altitudes, 
navigating, protecting, and identifying aircraft, and the safe and 
efficient use of the navigable airspace. Under section 44701, the FAA 
is charged with promoting safe flight of civil aircraft in air commerce 
by prescribing regulations for practices, methods, and procedures the 
Administrator finds necessary for safety in air commerce.
    This proposal is within the scope of sections 40103 and 44701 since 
it proposes aircraft performance requirements that would meet advanced 
surveillance needs to accommodate the projected increase in operations 
within the National Airspace System (NAS). As more aircraft operate 
within the U.S. airspace, improved surveillance performance is 
necessary to continue to balance the growth in air transportation with 
the agency's mandate for a safe and efficient air transportation 
system.

Table of Contents

I. Background
    A. Vision of the Future
    B. The Century of Aviation Reauthorization Act and NextGen
    C. Today's Radar Environment
II. The ADS-B System
    A. General
    B. Ground Infrastructure
III. Summary of the Proposal
IV. The Proposal for ADS-B Out
    A. Advantages of ADS-B Out
    B. Avionics
    1. 1090ES and UAT Broadcast Links
    2. Broadcast Link Requirements for Different Flight Levels
    3. Part 91 Appendix H Message Elements
    4. Navigation Position Sensor and the Accuracy and Integrity of 
the ADS-B Message
    5. ADS-B Antenna Diversity and Transmit Power Requirements
    6. Latency of the ADS-B Out Broadcast Message Elements
    7. Maintenance
    C. Operational Procedures
    1. Applicability
    2. Airspace
    3. Pilot Procedures
    4. Backup Surveillance Strategy

[[Page 56949]]

    5. Compliance Schedule for ADS-B Out Requirements
V. ADS-B In
    A. Avionics
    B. Applications and Services
VI. FAA Experience with ADS-B
    A. Capstone
    B. Gulf of Mexico
    C. UPS--Louisville
    D. Surveillance in Non-Radar Airspace
VII. ADS-B in Other Countries
VIII. Alternatives to ADS-B
IX. Rulemaking Notices and Analyses

I. Background

A. Vision of the Future

    The demand for air travel is growing in the U.S. and around the 
world. The FAA's forecasts project a doubling in U.S. airline passenger 
traffic by 2025. The forecasts also show strong growth for general 
aviation, especially with the advent of very light jets. By the end of 
this decade as many as 400-500 of these small jets could join the fleet 
each year. With the new small jets and other growth, the active general 
aviation fleet is projected to grow from 230,000 aircraft today to 
275,000 aircraft in 2020.
    That is the demand from piloted aircraft. The development and use 
of unmanned aircraft systems (UAS) is one of the next big steps forward 
in aviation's evolution. The FAA is working across government and 
industry to ensure the safe authorization of these aircraft to fly in 
civil airspace.
    The good news is U.S. air travel and related use of the National 
Airspace System (NAS) will grow. That growth will bring challenges 
since the present U.S. air traffic system--the world's largest and 
safest--is not designed to absorb this level of growth. Today's system 
is limited by outmoded technology--such as the constraints ground-based 
radar places on the distance aircraft must be separated and the limits 
caused by having to transmit information by voice between aircraft and 
the ground.
    The solution to managing the anticipated growth in the use of the 
NAS is the Next Generation Air Transportation System, or NextGen, which 
will assure the safe and efficient movement of people and goods as 
demand increases. NextGen will use technology to allow precise 
navigation, permit accurate real-time communication, and vastly improve 
situational awareness. The goal: A system flexible enough to 
accommodate safely whatever number, type and mix of aircraft there will 
be in U.S. skies by 2025.
    NextGen will be an aircraft-centric system with performance-based 
requirements. The future system will describe performance for 
navigation, communications, and surveillance.
    For navigation, the aviation community is already seeing the 
benefits of performance-based navigation with the use of Required 
Navigation Performance (RNP) as well as Area Navigation (RNAV) 
procedures at many U.S. airports. RNP and RNAV are examples of 
procedures that use improved navigational accuracy as compared to 
traditional procedures. The new procedures are being implemented 
consistent with the ``Roadmap for Performance-Based Navigation.'' The 
benefit of performance-based navigation: Enabling aircraft to fly 
precisely defined flight paths with unprecedented accuracy.
    For communication, NextGen will be built on a more comprehensive 
and capable information network than has been previously available. It 
will ensure the right information gets to the right person at the right 
time. With performance-based navigation and internet-like access to 
critical information--including nearly real-time weather--pilots will 
be able to make precision landings at airports that have no control 
towers, radar, or Instrument Landing Systems. Attaining the goal of 
performance-based communications will depend on technology, such as 
datalink, which would transmit key instructions directly to aircraft 
flight management systems, which would speed receipt of critical 
information and prevent errors that can come from manual data entry.
    The third element--performance-based surveillance--relies on 
technology that permits knowing the exact location of other aircraft in 
the air and of other aircraft and ground vehicles on the airport 
surface. The aviation community's experience with ADS-B, which 
periodically broadcasts an aircraft's location--both horizontal and 
vertical position and horizontal and vertical velocity--will lead 
directly to the performance requirements. When displayed in the 
cockpit, information obtained through ADS-B greatly improves 
situational awareness in the en route segment, in the terminal area 
during approaches, and on the airport surface. For additional 
information on ADS-B activities, see Section VI, FAA Experience with 
ADS-B later in the preamble.
    This rulemaking is important because ADS-B is an essential NextGen 
building block. Improving surveillance requires advanced onboard 
equipment with backup capability. Most, if not all, of the surveillance 
capability as well as the navigation and communications capabilities 
should be onboard the aircraft so the required capabilities will go 
wherever the aircraft goes. As part of the rulemaking effort, the FAA 
established an Aviation Rulemaking Committee under Order 1110.147. This 
committee has been chartered to deliver a report on how to optimize 
operational benefits of the ADS-B system and to provide recommendations 
to the FAA on the rulemaking after the NPRM is published. The scope of 
the ARC membership is designed to provide the widest range of inputs 
into the development of the NextGen strategy. The FAA will put the ARC 
recommendations in the docket established for this rulemaking.
    It is this combination of onboard capability and performance 
expectations that will enable aircraft in the future to fly safely and 
efficiently despite ever-increasing demands on the airspace.

B. The Century of Aviation Reauthorization Act and NextGen

    The ``Century of Aviation Reauthorization Act'' was enacted on 
December 12, 2003 (Pub. L. 108-176) (the ``Act''). This law set forth 
requirements and objectives for transforming the U.S. air 
transportation system to meet the needs of the 21st Century. Section 
709 of the Act required the Secretary of Transportation to establish in 
the FAA a joint planning and development office (JPDO) to manage work 
related to NextGen. Among its statutorily defined responsibilities, the 
JPDO coordinates the development and utilization of new technologies to 
ensure that when available, they may be used to the fullest potential 
in aircraft and in the air traffic control system.
    The FAA, the National Aeronautics and Space Administration (NASA) 
and the Departments of Commerce, Defense, and Homeland Security have 
launched an effort to align their resources to develop and further 
evolve NextGen. The goals of NextGen, as stated in the Act, that are 
addressed by this proposal are:
    (1) Improve the level of safety, security, efficiency, quality, and 
affordability of the NAS and aviation services;
    (2) Take advantage of data from emerging ground-based and space-
based communications, navigation, and surveillance technologies;
    (3) Be scalable to accommodate and encourage substantial growth in 
domestic and international transportation and anticipate and 
accommodate continuing technology upgrades and advances; and
    (4) Accommodate a wide range of aircraft operations, including 
airlines,

[[Page 56950]]

air taxis, helicopters, general aviation, and UAS.
    The JPDO was also charged with creating and carrying out an 
integrated plan for NextGen. The Act mandates that the NextGen 
Integrated Plan (the ``Plan'') be designed to ensure that the NextGen 
system meets the air transportation safety, security, mobility, 
efficiency, and capacity needs beyond those currently included in the 
FAA's Operational Evolution Plan.\1\ As described in the Plan \2\, the 
current approach to air transportation, where ground based radars track 
flights along congested airways, and pass information among the control 
centers for the duration of the flights, is becoming operationally 
obsolete. The current system is increasingly inefficient, and large 
increases in air traffic will result in mounting delays or limitations 
in service for many areas in the NAS.
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    \1\ The Plan was submitted to Congress on December 12, 2004.
    \2\ A copy of the Plan has been placed in the docket for this 
rulemaking.
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    As detailed in the Plan, the demand for air travel is expected to 
double within the next 20 years. Current FAA projections are that by 
2025, operations will grow to more than half a million departures and 
arrivals per year at approximately 16 additional airports. The present 
air traffic control system will be unable to handle this level of 
growth. Not only will the current method of handling traffic flow not 
be able to adapt to the highest volume and density for future 
operations, but the nature of the new growth may be problematic, as 
future aviation activity will be much more diverse than it is today. A 
shift of 2 percent of today's commercial passengers to very light jets 
that seat 4-6 passengers would result in triple the number of flights 
necessary to carry the same number of passengers.\3\ Furthermore, the 
challenges grow with the advent of other non-conventional aircraft, 
such as the UAS.
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    \3\ Very light jets may revolutionize the industry by permitting 
more individuals and corporations to own aircraft. It addition, many 
airports that are too small for large jet operations should benefit 
because they can support very light jets.
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    The future of air transportation contemplated in the Plan is 
complex, and the FAA believes that ADS-B technology is a key component 
in achieving many of the goals set forth in the Plan. This proposed 
rule embraces a new approach to surveillance performance requirements 
that can lead to greater and more efficient use of airspace. The Plan 
articulates several large transformation strategies to create the 
NextGen System. This proposal is a major step toward strategically 
``establishing an agile air traffic system that accommodates future 
requirements and readily responds to shifts in demand from all users.'' 
ADS-B technology will assist in the transition to a system with less 
dependence on ground infrastructure and facilities, and would provide 
for more efficient use of airspace.

C. Today's Radar Environment

    In the U.S., Air Traffic Control (ATC) surveillance and aircraft 
separation services are provided by the use of primary and secondary 
surveillance radar systems. While radar technology has advanced, it is 
essentially a product of 1940s World War II technology. Both primary 
and secondary radars are very large structures that are expensive to 
deploy and maintain; they also require the agency to lease land for 
site installation.
    Primary radar is a passive detection method that requires no 
special equipment aboard the aircraft. It is a technology that 
transmits a beam that is reflected by a target. This reflection forms a 
return signal that is translated into an aircraft position by ATC 
automation systems. Primary radar, however, is not always able to 
distinguish aircraft from other objects that reflect radar beams, such 
as birds or severe weather, which can result in ``clutter'' on the ATC 
radar scope. In addition, with primary radar, ATC is provided only with 
an aircraft's position relative to time. It does not provide any other 
information about the aircraft.
    Primary radar measures both the range and bearing of a particular 
aircraft. Bearing is measured by the position of the rotating radar 
antenna when it receives a response to its signal that is reflected 
from the aircraft. Range is measured by the time it takes for the radar 
to receive the reflected response. Detecting changes in an aircraft's 
velocity requires several radar sweeps that are spaced several seconds 
apart. Because the antenna beam becomes wider as the aircraft travels 
farther away from the radar, the accuracy of the radar is a function of 
range, and the accuracy decreases as the distance between the aircraft 
and the radar site increases. Consequently, aircraft on the outer 
fringes of radar coverage or in non-radar areas are separated by 
greater distances, directly affecting efficiency and ultimately 
capacity in the NAS.
    A Secondary Surveillance Radar (SSR) system consists of antennas, 
transmitters, and processors installed in ATC facilities, and radio 
transponder devices that are installed in aircraft. This system 
enhances primary radar by improving the ability to detect and identify 
aircraft. An SSR transmits interrogation pulses that elicit responses 
from transponders on board the aircraft. A transponder installed on the 
aircraft ``listens'' for the interrogation signal and sends back a 
reply that provides aircraft information. The aircraft is then 
displayed as a tagged icon on the air traffic controller's radar 
screen.\4\
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    \4\ An aircraft without an operating transponder may still be 
observed by ATC using primary radar, but the aircraft will not have 
an identifying tag.
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    Each transponder category has unique characteristics, operating 
functions, and requirements. A transponder with Mode A functionality 
requires the pilot to input a discrete code. If the same transponder is 
connected with an encoding device then it will also report the 
aircraft's altitude (Mode C). Most aircraft operated in general 
aviation have Mode A/C transponders. Any aircraft required to have 
Traffic Alert and Collision Avoidance System (TCAS) II, or that 
voluntarily has TCAS II installed must also be equipped with a Mode S 
Transponder. (This generally includes aircraft operated under parts 
121, 125, 129 and some aircraft operated under part 135.) Mode S 
transponders transmit both aircraft altitude and aircraft 
identification information. Both Mode A/C transponders and Mode S 
transponders require interrogation to provide information.
    To accommodate the projected level of traffic without increasing 
delay, more comprehensive surveillance in the NAS, including more radar 
sites in certain areas, would be necessary. Even if more radar sites 
were commissioned, however, there are many areas in which radar 
coverage is not feasible, either geographically (e.g., mountainous 
areas) or in a cost-effective manner (e.g., remote areas). Furthermore, 
simply increasing the number of radars in the NAS does not solve the 
inherent limitation of radar technology, and would not allow the FAA to 
reduce current separation standards.\5\ Consequently, the future of air 
traffic surveillance cannot be based solely on the use of radar. Radar 
technology also lacks the capability to provide services on the flight 
deck. However, the FAA is planning to maintain its current network of 
primary radars, and expects to be able to reduce a percentage of its 
secondary radars. This NPRM does not propose to reduce primary radar 
sites.\6\

[[Page 56951]]

Instead, this NPRM would transfer future aircraft surveillance to newer 
and more advanced onboard avionics that provide more accurate and 
timely aircraft information. ADS-B has been identified as the 
technology to facilitate that goal.
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    \5\ The FAA currently separates aircraft by 5 NM in the en route 
environment and 3 NM in the terminal environment.
    \6\ While the FAA expects to be able to reduce a significant 
percentage of the national secondary surveillance radar 
infrastructure, primary radars will not be decommissioned as a 
function of this proposal. Primary radar will serve a role in 
surveillance during the transition period of ADS-B avionics 
equipage.
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II. The ADS-B System

A. General

    The ADS-B system is an advanced surveillance technology that 
combines a satellite positioning service, aircraft avionics, and ground 
infrastructure to enable more accurate transmission of information 
between aircraft and ATC. The system enables equipped aircraft to 
continually broadcast information, such as identification, current 
position, altitude, and velocity. ADS-B uses information from a 
position service, e.g. Global Positioning System (GPS), to broadcast 
the aircraft's location, thereby making this information more timely 
and accurate than the information provided by the conventional radar 
system (which has a latency factor since it is based on interrogation 
and reply). ADS-B also can provide the platform for aircraft to receive 
various types of information, including ADS-B transmissions from other 
equipped aircraft or vehicles. ADS-B is automatic because no external 
interrogation is required, but is ``dependent'' because it relies on 
onboard position sources and onboard broadcast transmission systems to 
provide surveillance information to ATC and ultimately to other users.
    Implementation of an ADS-B system would not completely replace the 
primary radar or SSR at this time. In addition, ADS-B does not replace 
the requirement for transponders. Transponders are still necessary for 
SSR, which is the FAA's backup strategy in case of ADS-B failure. For 
more information on the backup strategy, see section IV.C.4, Backup 
Surveillance Strategy.
    The performance requirements for ADS-B avionics proposed in this 
NPRM would ensure that the aircraft is broadcasting the requisite 
information with the degree of accuracy and integrity necessary for ATC 
to use that information for surveillance.\7\ This enhanced surveillance 
would provide ATC with the enhanced ability to surveil and separate 
aircraft so that efficiency and capacity could increase beyond current 
levels to meet the predicted demand for ATC services while continually 
maintaining safety. Incremental developments in capacity, efficiency, 
and air traffic control procedures based on radar technology cannot 
accommodate the anticipated increase in demand for surveillance and 
separation services, which could result in delays that would far exceed 
those experienced today. Without ADS-B, the increase in demand could 
result in increased congestion and the denial of ATC service to some 
users of the NAS.
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    \7\ An aircraft equipped for ADS-B Out would transmit the 
aircraft's position, velocity and other specified, proposed message 
elements once per second. Radar data, on the other hand, is 
generated approximately once every 3-12 seconds for display to the 
air traffic controller depending on whether the aircraft is in the 
en route or terminal environment.
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    ADS-B technology already has been demonstrated successfully in 
Alaska via the Capstone program.\8\ In Alaska, radar coverage is either 
very limited or non-existent. ADS-B provides a level of surveillance 
performance that previously did not exist and has resulted in increases 
in both efficiency and capacity.
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    \8\ For additional information on Capstone, see Section VI. 
later in the preamble. It should be noted that Special Federal 
Aviation Regulation No. 97, Special Operating Rules for the Conduct 
of Instrument Flight Rules (IFR) Area Navigation (RNAV) Operations 
Using Global Positioning Systems (GPS) in Alaska (68 FR 14072; March 
21, 2003), would remain in effect to supplement the requirements in 
this proposal as it applies to Alaska.
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    ``ADS-B Out'' refers to an appropriately equipped aircraft's 
broadcasting of various aircraft information. ``ADS-B In'' refers to an 
appropriately equipped aircraft's ability to receive another aircraft's 
ADS-B Out information. This proposal only seeks to require ADS-B Out; 
the FAA is not proposing to require ADS-B In at this time.\9\
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    \9\ See Sections IV. later in the preamble for a detailed 
discussion of ADS-B Out and V. for a detailed discussion of ADS-B 
In.
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B. Ground Infrastructure

    Implementing ADS-B in the NAS to provide surveillance requires 
avionics, ground infrastructure, automation, and data. This NPRM 
addresses the performance requirements for the avionics and the 
necessary data that must be broadcast from the aircraft in order for 
ATC to use that information for surveillance and separation. The ground 
infrastructure involves the installation of a multitude of ground 
stations throughout the NAS that first receive the ADS-B Out 
transmissions from an aircraft, then relay real-time information based 
on those transmissions to ATC facilities. The exact number of ground 
stations needed to provide broadcast services across the NAS will be 
negotiated as part of the national broadcast service contract. The 
preliminary estimate approved by the FAA's Joint Resource Council call 
for 548 ground stations to provide coverage NAS-wide and in the Gulf of 
Mexico.
    On August 30, 2007, the FAA awarded a performance-based service 
contract to a consortium led by ITT Corporation. The contract is to 
provide ADS-B surveillance uplink (ground-to-air) and downlink (air-to-
ground) services and Automatic Dependent Surveillance Rebroadcast (ADS-
R), Traffic Information Services--Broadcast (TIS-B) \10\, and Flight 
Information Services--Broadcast (FIS-B) \11\ services. The vendor will 
install and maintain the ground equipment necessary to provide ADS-B 
uplink and downlink services to ATC. On November, 30, 2006, the FAA 
issued a Screening Information Request to determine which vendors 
understand the contract requirements well enough to proceed in the 
acquisition process. The FAA's schedule for ADS-B Out calls for all 
ground infrastructure, including the provision of broadcast services, 
to be in place and available where current surveillance exists by the 
end of fiscal year 2013. This schedule will provide reasonably ample 
time for operators to equip their aircraft for ADS-B Out and meet the 
proposed compliance date of 2020 in this notice.
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    \10\ Traffic Information Services--Broadcast (TIS-B) is a 
ground-based uplink report to a pilot of proximate traffic that is 
under surveillance by ATC but is not ADS-B-equipped. This service 
would be available even with limited ADS-B implementation. The 
combinations of the surveillance and TIS-B services can enable 
pilots to have enhanced visual acquisition of other aircraft. Having 
traffic and other flight obstacles on a cockpit display will enable 
pilots to more quickly identify safety hazards and communicate with 
ATC if necessary. Aircraft that are equipped with ADS-B can be 
monitored through a direct reception of their ADS-B signals in an 
air-to-air environment.
    \11\ Flight Information Services--Broadcast (FIS-B) is a ground-
based uplink of flight information services and weather data. Other 
flight information provided by the FIS-B service includes Notices to 
Airmen and Temporary Flight Restrictions.
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III. Summary of the Proposal

    The FAA is proposing ADS-B Out performance requirements for all 
aircraft operations in Class A, B, and C airspace areas in the NAS, and 
Class E airspace areas at or above 10,000 feet mean sea level (MSL) 
over the 48 contiguous United States and the District of Columbia. This 
proposal also would require that aircraft meet these performance 
requirements in the airspace out to 30 nautical miles (NM), from the 
surface up to 10,000 MSL, around certain identified airports that are 
among the nation's busiest. In addition, this proposal if adopted would 
require that aircraft meet ADS-B Out performance requirements to 
operate in

[[Page 56952]]

Class E airspace over the Gulf of Mexico from the coastline of the 
United States out to 12 nautical miles (NM), at and above 3,000 feet 
MSL.
    The FAA proposes to require aircraft flying at or above Flight 
Level 240 (FL240) to have ADS-B Out performance capabilities using the 
1090 Extended Squitter (1090ES) broadcast link. Aircraft flying in the 
designated airspace below FL 240 would have to use either the 1090ES or 
Universal Access Transceiver (UAT) broadcast link. These proposals 
would affect all U.S. commercial air carrier operations, foreign-flag 
carriers operating in the designated classes of U.S. airspace, air 
charter operations, air cargo operations, and a significant portion of 
the general aviation fleet operating in the NAS.
    The implementation of ADS-B requires two datalinks to support the 
full set of applications. UAT is intended to support applications for 
the general aviation user community that are not needed by air carriers 
because air carriers have weather radar, fly at high altitudes, and 
have other aeronautical links. UAT-equipped general aviation aircraft 
are not generally equipped with weather radar and would be flying at 
low altitudes. The 1090ES link is the internationally agreed upon link 
for ADS-B, and is intended to support applications for air carriers and 
other high-performance aircraft. The 1090ES broadcast link does not 
support applications available from FIS-B, like weather and related 
flight information. This is because of the bandwidth limitations of the 
1090ES link for transmitting the large message structures required by 
FIS-B. Weather and flight information for 1090ES-equipped aircraft is 
generally provided by commercial products.
    As described in the Plan, large increases in air traffic would 
result in mounting delays or limitations in service for many areas if 
the current surveillance system is not modified. An environment in 
which aircraft meet the proposed ADS-B Out performance requirements 
would result in greater capacity and efficiency in the NAS, maintain 
safety, and provide a flexible, expandable platform to accommodate 
future traffic growth while avoiding possible system delays and 
limitations in service.
    In moving forward with a performance-based surveillance system, the 
FAA believes that communication with the affected industry is critical. 
The FAA hosted several Industry Days to brief the technology, the 
rulemaking and procurement processes and associated milestones to 
interested parties, including manufacturers and affected operators. As 
with any rulemaking, the FAA invites comments on the various elements 
of this proposal, and all comments will be carefully considered. If 
this proposal is adopted as a final rule, it may be modified in view of 
the submitted comments.

IV. The Proposal for ADS-B Out

A. Advantages of ADS-B Out

    ADS-B Out, as proposed in this notice, would enhance surveillance 
and broadcast services in both the en route and terminal environments 
and provide ATC with more accurate information to safely separate 
aircraft in the air.
    In today's radar surveillance environment, accuracy and integrity 
of radar information is a function of range and decreases as the 
distance between the radar antenna and the aircraft increases. Unlike 
radar, both the accuracy and integrity of ADS-B Out is uniform and 
consistent throughout the service area. A comprehensive, national 
surveillance system that utilizes ADS-B Out would provide ATC with the 
ability to accurately identify and locate aircraft that are either far 
away from the ATC facilities or at the outer boundaries of ground 
station service volume.
    If ATC had more precise aircraft position information, it could 
position, separate, and provide speed and direction instructions to 
aircraft with improved precision and timing. This would result in the 
use of optimal flight paths and altitudes. This transmission of 
information would enable improvement of airspace capacity throughout 
the NAS. Additionally, with ADS-B Out, ATC would receive updated 
information broadcast by aircraft more frequently than with radar, and 
would be able to track a more closely monitored flight path. This would 
result in ATC providing fewer instructions to pilots, thus having more 
time to accommodate additional aircraft within the allotted airspace. 
These improved efficiencies for ATC ultimately should accommodate the 
increased number of aircraft able to operate in the NAS. In addition, 
we expect a reduction in aircraft fuel burn because better surveillance 
provides for more efficient use of the airspace, provides for optimal 
aircraft routing, and addresses the limits currently experienced with 
radar.
    In the terminal radar environment today, ATC may have to request 
pilots to provide aircraft speed, heading, and in some cases, aircraft 
identification. Neither the primary radar nor SSR systems provide all 
that information. With ADS-B, ATC is automatically provided aircraft 
speed, heading, and other identifying information, including aircraft 
size, which are necessary to safely position and separate aircraft more 
rapidly than is possible today.
    While more precise ADS-B derived aircraft position information 
improves ATC efficiencies under current separation standards, the 
potential for significantly greater capacity and efficiency gains may 
be realized by reducing separation standards between aircraft. 
Therefore, this rulemaking is expected to help achieve a level of 
surveillance accuracy that would support reducing aircraft separation 
standards. ADS-B is an essential component of the NextGen platform and 
is necessary to achieve a level of capacity in the NAS commensurate 
with future growth.

B. Avionics

    This discussion first addresses the broadcast message links 
necessary to transmit aircraft information to the ground stations and 
the specific message elements that would be broadcast by the aircraft 
comprising the ADS-B Out transmission. Next we discuss the navigation 
position sensor and the necessary accuracy and integrity of the ADS-B 
message. Finally, we explain the necessary requirements for antenna 
diversity on the aircraft, and the required latency of the data in the 
ADS-B transmission from the aircraft.
1. 1090ES and UAT Broadcast Links
    In 2002, the United States determined that two frequencies would be 
appropriate for ADS-B: 1090MHz and 978MHz. To broadcast the necessary 
data elements for ADS-B Out transmission under this proposal, aircraft 
would have to be equipped with either 1090ES or UAT that meet the 
latest version of either Technical Standard Order (TSO)-C166a or TSO-
C154b, respectively.\12\ Today, operators of air carriers and many 
private/commercial aircraft already are primarily equipped with 
avionics designed under TSO-C112, Air Traffic Control Radar Beacon 
System/Mode Select (ATCRBS/Mode S), which are required to function with 
the Traffic Alert and Collision Avoidance System

[[Page 56953]]

(TCAS II) or ACAS.\13\ Many TSO-C112 Mode S Transponders can be 
modified or are designed to provide 1090ES functionality under TSO-
C166a. Most other general aviation aircraft, typically small aircraft 
operated in non-commercial service (that are not required to have TCAS 
II), would likely use the UAT broadcast link for ADS-B Out, which 
operates on the 978MHz frequency. Today, a small number of aircraft are 
equipped with UAT ADS-B In and are capable of receiving TIS-B and FIS-B 
services. While the 1090ES link does not support FIS-B, it does support 
TIS-B.
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    \12\ A TSO is a minimum performance standard issued by the 
Administrator for specified materials, parts, processes, and 
appliances used on civil aircraft. TSO-C166a sets the minimum 
performance standards for Extended Squitter Automatic Dependent 
Surveillance--Broadcast (ADS-B) and Traffic Information Service 
Broadcast (TIS-B) Equipment Operating on the Radio Frequency of 1090 
MHz. TSO-C154b sets the minimum performance standard for Universal 
Access Transceiver (UAT) Automatic Dependent Surveillance-- 
Broadcast (ADS-B) Equipment.
    \13\ Airborne Collision Avoidance System (ACAS) is comparable to 
TCAS II and is specified for use in Europe.
---------------------------------------------------------------------------

    In December 2006, RTCA \14\ published RTCA/DO-260A, Change 2, 
``Minimum Operational Performance Standards (MOPS) for 1090 MHz 
Automatic Dependent Surveillance--Broadcast (ADS-B).'' This change 
revised RTCA/DO-260 1090ES MOPS. The major differences between RTCA/DO-
260 and RTCA/ DO-260A are refinements of the Navigation Integrity 
Category (NIC), Navigation Accuracy Category (NAC), and Surveillance 
Integrity Level (SIL) parameters, which significantly improve the 
overall performance and interoperability of the ADS-B Out broadcast 
link. These modified parameters (NIC, NAC, and SIL) provide a level of 
accuracy and integrity with respect to the information transmitted in 
the ADS-B Out message that would enable ATC to provide improved 
surveillance and separation services based on the information it 
receives from the aircraft.
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    \14\ RTCA, Incorporated is a not-for-profit corporation formed 
to advance the art and science of aviation and aviation electronic 
systems for the benefit of the public. The organization functions as 
a Federal Advisory Committee and develops consensus-based 
recommendations on contemporary aviation issues. The organization's 
recommendations are often used as the basis for government and 
private sector decisions as well as the foundation for many TSOs.
---------------------------------------------------------------------------

    After RTCA issued its updates in December 2006, the FAA 
subsequently issued TSO-C166a, which adopted the recent modifications 
specified in change 2 to RTCA/DO-260A, and characterizes the parameters 
of NIC, NAC, and SIL.\15\ There are some aircraft equipped today with 
legacy 1090ES ADS-B systems. Operators of these aircraft would need to 
modify their broadcast link equipment to meet the proposed requirements 
defined in TSO-C166a. This modification could include hardware, 
software, or both depending upon other avionics installed on the 
aircraft.
---------------------------------------------------------------------------

    \15\ TSO-C166a superseded TSO-C166.
---------------------------------------------------------------------------

    The transition to TSO-C166a and TSO-C154b has been identified as a 
requirement for use of ADS-B in the required airspace. The United 
States faces unique challenges in air traffic control due to its high 
density airspace and stringent safety requirements. In order to 
maintain safety and capacity, given a state of increased air traffic, 
advanced surveillance technologies will be necessary. The earlier 
standards in RTCA/DO-260 do not provide the performance standards 
necessary to meet the requirements of the NAS. RTCA/DO-260a provides a 
means to transmit the Secondary Surveillance Radar beacon codes that 
currently service the NAS and will continue to be required as a backup 
to ADS-B. RTCA/DO-260 does not provide that compatibility.
    The International Civil Aviation Organization (ICAO) is in the 
process of updating the 1090ES Standards and Recommended Practices 
(SARPs) published in ICAO Annex 10, Amendment 77, to include those 
requirements identified in the publication of RTCA/DO-260A, Change 2. 
These updated SARPs are expected to become effective in November 2007.
    Operators may, under this proposal, also choose to equip with dual 
link avionics, i.e. 1090ES and UAT, which would provide the capability 
to transmit and receive information on both broadcast links at the same 
time.
    If an aircraft is to operate at or above FL240, which is discussed 
further in section IV.b.3. of this preamble (``Broadcast Link 
Requirements for Different Flight Levels''), the aircraft's broadcast 
link capabilities would have to meet the minimum performance 
requirements of TSO-C166a, (i.e., be equipped with 1090ES). 
Consequently, those aircraft operating at or above FL240 with Mode A/C 
transponders would need new transponders. Aircraft with Mode S 
transponders without compatible extended squitter capability installed 
would need to be reequipped with those providing 1090ES functionality, 
or supplement them with 1090ES to operate at or above FL240.
    In December 2006, RTCA also issued RTCA/DO-282A, Change 1 for UAT, 
which clarified the definitions of the NIC, NAC, and SIL similar to 
those specified for 1090ES discussed above. TSO-C154b adopted the 
requirements of RTCA/DO-282A and clarifies performance parameters 
capable of ensuring interoperability with ground stations deployed to 
support the Capstone program in Alaska, and to provide for future NAS 
interoperability assurances. Aircraft equipped with UAT must meet the 
minimum performance standards in TSO-C154b, or later version. There are 
very few aircraft equipped with legacy UAT equipment. Operators of 
those aircraft would need to modify their equipment to meet the 
performance standards of TSO-C154b.
2. Broadcast Link Requirements for Different Flight Levels
    The FAA proposes to require that aircraft flying at or above FL240 
have ADS-B Out performance capability using the 1090ES broadcast link. 
For operations below FL240, operators could equip their aircraft with 
either the 1090ES or UAT broadcast links. Some general aviation 
aircraft are already equipped with the UAT broadcast link, and most 
general aviation operators are expected to equip with UAT under this 
proposal in order to have TIS-B and FIS-B services. Larger aircraft, 
particularly the transport category aircraft, generally operate at 
higher altitudes and are already equipped with 1090ES that meets TSO-
C166 (which would require modification to upgrade to TSO-C166a under 
this proposal) or have equipment installed that uses the 1090 broadcast 
link. Furthermore, the international aviation communities, and for the 
most part, foreign-flag aircraft operating in the U.S., tend to operate 
large transport category aircraft that also operate at the higher 
altitudes. Having a single broadcast link at higher altitudes would 
enable aircraft equipped for ADS-B In to benefit from potential future 
applications such as aircraft merging and spacing, and self-separation. 
These applications are enabled by having aircraft identify each other 
on the same data link without the need to employ ADS-R, which would 
increase the latency of the transmission. The FAA believes that the 
approach articulated in the proposal to require 1090ES for operations 
at and above FL240 is largely consistent with how those affected 
operators would choose their respective broadcast link. While this NPRM 
does not require equipage for ADS-B In, we fully recognize that 
operators may choose to equip for that capability and that it is 
reasonable to lay the foundation so that operators may be able to take 
advantage of future applications if they so choose.
3. Part 91 Appendix H--Broadcast Message Elements
    The FAA is proposing to add an appendix to 14 CFR part 91 to 
specify the broadcast message elements necessary for ADS-B Out. These 
message elements contain the data necessary for ATC to support aircraft

[[Page 56954]]

surveillance by ADS-B. The message elements required support future 
NextGen air-to-air applications such as reduced horizontal separation 
and self separation. These message elements also support the capability 
for aircraft avionics to be verified during normal operations for 
continuing airworthiness in lieu of conducting ground checks of the 
avionics. We believe the message elements allow for further NextGen 
capabilities, at least to the extent we can predict those future needs 
at this time. However, in the future, additional elements such as 
predictive aircraft movement could be added to enable further 
capabilities.
    These elements would be broadcast automatically from the aircraft 
except where pilot entry is necessary. Pilot entry would be necessary 
for elements (g) through (k). The following is a description of each 
message element.
    (a) The length and width of the aircraft. This message element 
would provide ATC with quick reference to the aircraft's dimensions. On 
airport surfaces in particular, aircraft are in close proximity to each 
other and this information would facilitate ATC's ability to use the 
most appropriate landing and surface movement procedures for individual 
aircraft in managing traffic on the airport surfaces. This information 
would be pre-set when avionics equipment meeting the standards in TSO-
C166a or TSO-C154b, as applicable, is installed on the aircraft.
    (b) An indication of the aircraft's lateral and longitudinal 
position. This message element is derived from the aircraft's 
navigation position sensor \16\ and would provide an accurate position 
based on latitude, longitude, and accuracy values for the display of 
information in a format that meets ATC requirements. This information 
is critical to the safe and efficient separation of aircraft.
---------------------------------------------------------------------------

    \16\ The aircraft's navigation position sensor is discussed in 
detail in section IV.4. of this preamble.
---------------------------------------------------------------------------

    (c) An indication of the aircraft's barometric pressure altitude. 
This message element would provide ATC with the aircraft's altitude 
information. Currently, Sec.  91.217 requires Mode C and Mode S 
transponders to transmit pressure altitude. It is critical that the 
altitude transmitted by the Mode C and Mode S transponders is identical 
to that in the ADS-B transmission. Therefore, in addition to this 
proposed data element, we believe that Sec.  91.217 should be amended 
as well. Section 91.217 requires Mode C and Mode S transponders to 
transmit pressure altitude. We propose to revise Sec.  91.217 to also 
apply to the ADS-B transmission of altitude to ensure that the reported 
altitude from various avionics is consistent.
    (d) An indication of the aircraft's velocity. This message element 
is also derived from the aircraft's navigation position sensor and 
would provide ATC with the aircraft's airspeed with a clearly stated 
direction and describes the rate at which an aircraft changes its 
position.
    (e) An indication if TCAS II or ACAS is installed and operating in 
a mode that may generate resolution advisory alerts. This information 
would identify to ATC whether an aircraft is equipped with TCAS II or a 
later version or its European equivalent ACAS, and whether that 
equipment is operating in a mode that may generate resolution advisory 
alerts.
    (f) For aircraft with an operable TCAS II or ACAS, an indication if 
a resolution advisory is in progress. Both TCAS II and ACAS improve 
safety by detecting impending airborne collisions or incursions and 
issuing commands to the pilot on how to avoid the hazard by climbing or 
descending. If two aircraft get too close to each other, the aircrafts' 
TCAS II or ACAS systems will provide a resolution advisory (RA), which 
gives the pilots a command to climb or descend to avoid the other 
aircraft. The RA command is provided independent of ATC instructions. 
It is critical for ATC to know why an aircraft is climbing or 
descending, i.e., responding to an RA, ATC instruction, or a previous 
flight plan path. ATC may respond more efficiently and safely in 
managing the air traffic environment by knowing whether an aircraft is 
responding to an RA.
    (g) An indication if ATC services are requested. (Requires flight 
crew entry.) This message element would identify to air traffic 
controllers if services are requested and whether the aircraft is in 
fact receiving ATC services.
    (h) An indication of the Mode 3/A transponder code specified by 
ATC. (Requires flight crew entry.) All transponder-equipped aircraft on 
Instrument Flight Rules (IFR) flights are directed by ATC to ``squawk'' 
a unique four-digit code, commonly referred to as a ``Mode 3/A 
transponder code.'' All transponder equipped aircraft on Visual Flight 
Rules (VFR) flights are directed by ATC to squawk 1200. The assigned 
Mode 3/A transponder code is used by ATC to identify each aircraft 
operating under IFR, and the 1200 transponder code identifies aircraft 
operating under VFR.
    An aircraft equipped with ADS-B Out continually broadcasts its 
state vector (3-dimensional position and 3-dimensional velocity). It is 
critical for ATC to correlate and verify that the ADS-B Out information 
transmitted from each aircraft is displayed and identified correctly on 
the ATC radar display. Therefore, it is imperative that the ATC-
assigned transponder code be identical to the assigned transponder code 
in the ADS-B Out message. If the aircraft's avionics are not capable of 
allowing a single point of entry for the transponder and ADS-B Out Mode 
3A code, the pilot would have to ensure that conflicting codes are not 
transmitted to ATC. Operational procedures would have to be developed, 
including specific guidance, instructions, or training material 
provided by the equipment manufacturer, as well as the operator 
training programs, manuals, Operations Specifications, and Letters of 
Authorization, to ensure that conflicting codes are not transmitted to 
ATC.
    (i) An indication of the aircraft's call sign that is submitted on 
the flight plan, or the aircraft's registration number. (Aircraft call 
sign requires flight crew entry.) This message element would correlate 
flight plan information with the data that ATC views on the radar 
display and facilitate ATC communication with the aircraft. The 
aircraft's call sign or registration number broadcast in the ADS-B 
message would have to be identical to information contained in its 
flight plan.
    (j) An indication if the flight crew has identified an emergency, 
and if so, the emergency status being transmitted. (Requires flight 
crew entry.) This message element would alert ATC that the aircraft is 
experiencing emergency conditions and indicate the type of emergency. 
Applicable emergency codes would be found in the Aeronautical 
Information Manual. This information would alert ATC to potential 
danger to the aircraft so it could take appropriate action.
    (k) An indication of the aircraft's ``IDENT'' to ATC. (Requires 
flight crew entry.) ATC may request an aircraft to ``IDENT,'' to aid 
controllers to quickly identify a specific aircraft. The pilot manually 
inputs the aircraft's identity, which then highlights the aircraft on 
the ATC scope. When activated, this message element allows 
identification of the aircraft with which ATC is in communication.
    (l) An indication of the aircraft's assigned ICAO 24-bit address. 
ICAO 24-bit codes are unique and assigned to each individual aircraft. 
These codes are necessary for aircraft used for international 
operations. This code would provide the FAA with the future capability 
to identify aircraft using the

[[Page 56955]]

ICAO 24-bit address. This capability addresses limits on future 
capacity due to the finite number of aircraft that can be tracked with 
discrete transponder codes.
    (m) An indication of the emitter category. If ATC knows the emitter 
category, it can determine separation minima based in part on a 
particular aircraft's wake vortex. This information would be used to 
provide air traffic controllers and ground crews with more efficient 
information regarding a particular aircraft's constraints and 
capabilities. Once the emitter category is set at installation, it 
would not change. (Refer to TSO-C166a or TSO-C154b for additional 
information.) Some examples of emitter categories to be used (as 
specified in RTCA DO-260A, DO-242A, and DO-282A) include, but are not 
limited to, the following:
     Light (ICAO)--7,000 kg (15,500 lbs) or less.
     Small aircraft--7,000 kg to 34,000 kg (15,500 lbs to 
75,000 lbs).
     Large aircraft--34,000 kg to 136,000 kg (75,000 lbs to 
300,00 lbs).
     High vortex large (i.e., B-757).
     Heavy aircraft (ICAO)--136,000 kg (300,000 lbs) or more.
     Rotorcraft.
    (n) An indication whether a cockpit display of traffic information 
(CDTI) is installed and operable. This message element would alert ATC 
as to whether an aircraft has an operable CDTI \17\ installed. A CDTI 
is necessary for aircraft to have ADS-B In capability. This message 
element would indicate to ATC which aircraft are capable of receiving 
ADS-B In services.
---------------------------------------------------------------------------

    \17\ CDTI is the function of presenting surveillance traffic 
information (e.g., airborne or surface) to the flight crew. To 
display traffic, the CDTI may use a dedicated display or a shared 
multi-function display (MFD) device. The CDTI is capable of 
displaying position information for nearby aircraft and ADS-B-
equipped airport surface vehicles. The CDTI consolidates ADS-B 
traffic targets, terrain, weather, and other products relative to 
the pilot's own aircraft or flight operation. It allows pilots to 
display textual and graphical information provided by the ADS-B 
System and Broadcast Services.
---------------------------------------------------------------------------

    (o) An indication of the aircraft's geometric altitude. The 
geometric altitude is a measure of altitude provided by a satellite-
based position service, determined mathematically, based on a three-
dimensional position in space. This message element is necessary to 
confirm accuracy or discrepancies between geometric and barometric 
altitude, which changes as a function of air pressure in the 
environment. The message element would serve as a tool for validating 
positioning services.
4. Navigation Position Sensor and the Accuracy and Integrity of the 
ADS-B Message
    ADS-B Out continuously transmits aircraft information through the 
selected broadcast data links of 1090ES or UAT. The aircraft's lateral 
and longitudinal position and velocity are proposed data elements 
transmitted in the broadcast message. The navigation position sensor is 
equipment onboard the aircraft that computes a geodetic position 
(latitude and longitude) that can be a separate sensor or integrated 
into other navigation equipment or system onboard the aircraft. 
(Examples of such equipment are LORAN C, GPS, GPS-WAAS, DME/DME and 
Inertial Reference Unit (IRU).)
    The accuracy and integrity of these broadcast message elements 
transmitted from the aircraft to the ground stations depends on the 
aircraft's navigation position sensor and the signal source from which 
the position is derived. The accuracy and integrity of the transmitted 
aircraft position and velocity are critical for use in surveillance and 
various airborne and surface applications. The accuracy and integrity 
of transmitted information expressed by ADS-B avionics is measured by 
the Navigation Accuracy Category for Position (NACp), the Navigation 
Accuracy Category for Velocity (NACv), the NIC and the SIL.
    An aircraft transmitting its position and velocity with the 
accuracy and integrity proposed in part 91, Appendix H, Section 3 (ADS-
B Out Performance Requirements for NIC, NAC, and SIL) would be more 
accurately identified by ATC than it would be in today's radar 
environment. The confidence with respect to the accuracy of the 
position and velocity reported by ADS-B Out would enable the future 
applications discussed further in this proposal that simply could not 
be provided by existing surveillance systems. While existing 
surveillance systems provide information that is sufficient for 
separation purposes and the capacity needs of today's traffic 
environment, a more responsive and versatile ATC system will need 
improved accuracy and integrity of broadcast information for future 
surveillance performance. The values proposed would ensure that the 
information ATC receives has the level of performance and the requisite 
confidence in the accuracy of that information necessary to control 
aircraft. Increasing the quality and standards for surveillance 
information presents new opportunities for efficiency and capacity 
improvements in the NAS, and the potential for future self-separation 
or air-to-air applications of ADS-B.
    The NACp specifies the accuracy of the aircraft's horizontal 
position information (latitude and longitude) and the vertical 
geometric position transmitted from the aircraft's avionics. All 
aircraft position information has a margin of error and the accuracy 
category specifies that margin. The NACp specifies with 95 percent 
probability that the reported information is correct within an 
associated allowance. (The horizontal 95% bound error allowance 
resembles an imaginary circle around the aircraft with a radius 
equivalent to the NACp defined value.) ATC and aircraft equipped for 
ADS-B In would monitor the NACp reporting to ensure that the accuracy 
supports the intended operational use. Not all navigation position 
sensors are capable of providing the necessary aircraft information 
with the accuracy and integrity needed to support certain surveillance 
applications.\18\ In order to use ADS-B Out for surveillance and 
separation, the NACp value must have a small margin of error in 
position reporting.
---------------------------------------------------------------------------

    \18\ Surveillance applications are discussed further in Section 
V of this NPRM.
---------------------------------------------------------------------------

    In today's radar surveillance environment, aircraft position 
accuracy is required to be within 0.3 NM for operations in the en route 
airspace, and 0.1 NM for operations within terminal area airspace. An 
aircraft broadcasting its position with a NACp equal to or greater than 
7 would provide a horizontal position accuracy of at least 0.1 NM with 
no specific requirement for vertical (geometric) position accuracy. 
Aircraft position reported at a NACp equal to or greater than 7 would 
meet the minimum radar accuracy requirement for terminal area 
operations and exceed radar performance for en route operations. 
Therefore, the FAA believes that the minimum accuracy requirement 
necessary to maintain an equivalent level of surveillance in the 
terminal airspace area (and provide for equivalent separation as that 
in today's radar environment) would be a NACp of 7. The FAA is not, 
however, engaging in this rulemaking simply to meet the level of 
surveillance that exists in the current infrastructure, or to establish 
a new surveillance system that would only enable separation performance 
equivalent to that realized today. ADS-B performance is intended to go 
beyond today's standards for accuracy and provide a platform for 
NextGen. In order to accomplish that goal, we propose a minimum 
accuracy value of NACp 9 in

[[Page 56956]]

all airspace areas that ADS-B would be required. This proposed accuracy 
requirement would provide horizontal position information for ADS-B Out 
equipped aircraft to within 30 meters (0.016NM) horizontally and 
vertical (geometric)