What is ADS-B Out, and on which two frequencies does it operate in the U.S.?

4-5-7. Automatic Dependent Surveillance -Broadcast (ADS-B) Services
a. Introduction.
1. Automatic Dependent Surveillance -Broadcast (ADS -B) is a surveillance technology deployed
throughout the NAS (see FIG 4- 5-6). The ADS-B system is composed of aircraft avionics and a ground
infrastructure. Onboard avionics determine the position of the aircraft by using the GNSS and transmit its
position along with additional information about the aircraft to ground stations for use by ATC and other ADS-B
services. This information is transmitted at a rate of approximately once per second. (See FIG 4-5-7 and
FIG 4-5-8.)
2. In the United States, ADS-B equipped aircraft exchange information on one of two frequencies: 978 or
1090 MHz. The 1090 MHz frequency is also associated with Mode A, C, and S transponder operations. 1090
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MHz transponders with integrated ADS-B functionality extend the transponder message sets with additional
ADS-B information. This additional information is known as an "extended squitter" message and is referred to
as 1090ES. ADS-B equipment operating on 978 MHz is known as the Universal Access Transceiver (UAT).
3. ADS-B avionics can have the ability to both transmit and receive information. The transmission of
ADS-B information from an aircraft is known as ADS-B Out. The receipt of ADS-B information by an aircraft
is known as ADS-B In. All aircraft operating within the airspace defined in 14 CFR § 91.225 are required to
transmit the information defined in § 91.227 using ADS-B Out avionics.
4. In general, operators flying at 18,000 feet and above (Class A airspace) are required to have 1090ES
equipment. Those that do not fly above 18,000 may use either UAT or 1090ES equipment. (Refer to 14 CFR §§
91.225 and 91.227.) While the regulations do not require it, operators equipped with ADS -B In will realize
additional benefits from ADS- B broadcast services: Traffic Information Service - Broadcast (TIS -B)
(paragraph 4-5-8) and Flight Information Service - Broadcast (FIS-B) (paragraph 4-5-9).
FIG 4-5-6
ADS-B, TIS-B, and FIS-B:
Broadcast Services Architecture
b. ADS-B Certification and Performance Requirements.
ADS-B equipment may be certified as a surveillance source for air traffic separation services using ADS-B Out.
ADS-B equipment may also be certified for use with ADS -B In advisory services that enable appropriately
equipped aircraft to display traffic and flight information. Refer to the aircraft's flight manual supplement or Pilot
Operating Handbook for the capabilities of a specific aircraft installation.
c. ADS-B Capabilities and Procedures.
1. ADS-B enables improved surveillance services, both air-to-air and air-to-ground, especially in areas
where radar is ineffective due to terrain or where it is impractical or cost prohibitive. Initial NAS applications
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of air-to-air ADS-B are for "advisory" use only, enhancing a pilot's visual acquisition of other nearby equipped
aircraft either when airborne or on the airport surface. Additionally, ADS-B will enable ATC and fleet operators
to monitor aircraft throughout the available ground station coverage area.
FIG 4-5-7
En Route - ADS-B/ADS-R/TIS-B/FIS-B Service Ceilings/Floors
FIG 4-5-8
Terminal - ADS-B/ADS-R/TIS-B/FIS-B Service Ceilings/Floors
2. One of the data elements transmitted by ADS-B is the aircraft's Flight Identification (FLT ID). The FLT
ID is comprised of a maximum of seven alphanumer ic characters and must correspond to the aircraft
identification filed in the flight plan. For airline and commuter aircraft, the FLT ID is usually the company name
and flight number (for example, AAL3432), and is typically entered into the avionics by the flight crew during
preflight. For general aviation (GA), if aircraft avionics allow dynamic modification of the FLT ID, the pilot can
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enter it prior to flight. However, some ADS-B avionics require the FLT ID to be set to the aircraft registration
number (for example, N1234Q) by the installer and cannot be changed by the pilot from the cockpit. In both
cases, the FLT ID must correspond to the aircraft identification filed in its flight plan.
ATC automation systems use the transmitted ADS-B FLT ID to uniquely identify each aircraft within a given
airspace, and to correlate it to its filed flight plan for the purpose of providing surveillance and separation
services. If the FLT ID and the filed aircraft identification are not identical, a Call Sign Mis-Match (CSMM) is
generated and ATC automation systems may not associate the aircraft with its filed flight plan. In this case, air
traffic services may be delayed or unavailable until the CSMM is corrected. Consequently, it is imperative that
flight crews and GA pilots ensure the FLT ID entry correctly matches the aircraft identification filed in their flight
plan.
3. Each ADS-B aircraft is assigned a unique ICAO address (also known as a 24 -bit address) that is
broadcast by the ADS-B transmitter. This ICAO address is programmed at installation. Should multiple aircraft
broadcast the same ICAO address while transiting the same ADS-B Only Service V olume, the ADS-B network
may be unable to track the targets correctly. If radar reinforcement is available, tracking will continue. If radar
is unavailable, the controller may lose target tracking entirely on one or both targets. Consequently, it is
imperative that the ICAO address entry is correct.
4. Aircraft that are equipped with ADS-B avionics on the UAT datalink have a feature that allows them to
broadcast an anonymous 24-bit ICAO address. In this mode, the UAT system creates a randomized address that
does not match the actual ICAO address assigned to the aircraft. The UAT anonymous 24-bit address feature
may only be used when the operator has not filed an IFR flight plan and is not requesting ATC services. In the
anonymity mode, the aircraft's beacon code must be set to 1200 and, depending on the manufacturer's
implementation, the aircraft FLT ID might not be transmitted. Pilots should be aware that while in UAT
anonymity mode, they will not be eligible to receive ATC separation and flight following services, and may not
benefit from enhanced ADS-B search and rescue capabilities.
5. ADS-B systems integrated with the transponder will automatically set the applicable emergency status
when 7500, 7600, or 7700 are entered into the transponder. ADS-B systems not integrated with the transponder,
or systems with optional emergency codes, will require that the appropriate emergency code is entered through
a pilot interface. ADS-B is intended for inflight and airport surface use. Unless otherwise directed by ATC,
transponder/ADS-B systems should be turned "on" and remain "on" whenever operating in the air or on the
airport surface movement area.
d. ATC Surveillance Services using ADS-B - Procedures and Recommended Phraseology
Radar procedures, with the exceptions found in this paragraph, are identical to those procedures prescribed for
radar in AIM Chapter 4 and Chapter 5.
1. Preflight:
If A TC services are anticipated when either a VFR or IFR flight plan is filed, the aircraft identification (as entered
in the flight plan) must be entered as the FLT ID in the ADS-B avionics.
2. Inflight:
When requesting surveillance services while airborne, pilots must disable the anonymous feature, if so equipped,
prior to contacting ATC. Pilots must also ensure that their transmitted ADS -B FLT ID matches the aircraft
identification as entered in their flight plan.
3. Aircraft with an Inoperative/Malfunctioning ADS-B Transmitter:
(a) ATC will inform the flight crew when the aircraft's ADS-B transmitter appears to be inoperative or
malfunctioning:
PHRASEOLOGY-
YOUR ADS-B TRANSMITTER APPEARS TO BE INOPERATIVE/MALFUNCTIONING. STOP ADS-B TRANSMISSIONS.
(b) ATC will inform the flight crew if it becomes necessary to turn off the aircraft's ADS-B transmitter.
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PHRASEOLOGY-
STOP ADS-B TRANSMISSIONS.
(c) Other malfunctions and considerations:
Loss of automatic altitude reporting capabilities (encoder failure) will result in loss of ATC altitude advisory
services.
4. Procedures for Accommodation of Non-ADS-B Equipped Aircraft:
(a) Pilots of aircraft not equipped with ADS-B may only operate outside airspace designated as ADS-B
airspace in 14 CFR §91.225. Pilots of unequipped aircraft wishing to fly any portion of a flight in ADS -B
airspace may seek a deviation from the regulation to conduct operations without the required equipment.
Direction for obtaining this deviation are available in Advisory Circular 90-114.
(b) While air traffic controllers can identify which aircraft are ADS-B equipped and which are not, there
is no indication if a non -equipped pilot has obtained a preflight authorization to enter ADS -B airspace.
Situations may occur when the pilot of a non-equipped aircraft, without an authorization to operate in ADS-B
airspace receives an ATC-initiated in-flight clearance to fly a heading, route, or altitude that would penetrate
ADS-B airspace. Such clearances may be for traffic, weather, or simply to shorten the aircraft's route of flight.
When this occurs, the pilot should acknowledge and execute the clearance, but must advise the controller that
they are not ADS-B equipped and have not received prior authorization to operate in ADS -B airspace. The
controller, at their discretion, will either acknowledge and proceed with the new clearance, or modify the
clearance to avoid ADS-B airspace. In either case, the FAA will normally not take enforcement action for
non-equipage in these circumstances.
NOTE-
Pilots operating without ADS-B equipment must not request route or altitude changes that will result in an incursion into
ADS-B airspace except for safety of flight; for example, weather avoidance. Unequipped aircraft that have not received a
pre-flight deviation authorization will only be considered in compliance with regulation if the amendment to flight is
initiated by ATC.
EXAMPLE-
1. ATC: "November Two Three Quebec, turn fifteen degrees left,  proceed direct Bradford when able, rest of route
unchanged."
Aircraft: "November Two Three Quebec, turning fifteen degrees left, direct Bradford when able, rest of route unchanged.
Be advised, we are negative ADS-B equipment and have not received authorization to operate in ADS-B airspace."
ATC: "November Two Three Quebec, roger"
or
"November Two Three Quebec, roger , turn twenty degrees right, rejoin Victor Ten, rest of route unchanged."
2. ATC: "November Four Alpha Tango, climb and maintain one zero thousand for traffic."
Aircraft: "November Four Alpha Tango, leaving eight thousand for one zero thousand. Be advised, we are negative ADS-B
equipment and have not received authorization to operate in ADS-B airspace."
ATC: "November Four Alpha Tango, roger"
or
"November Four Alpha Tango, roger , cancel climb clearance, maintain eight thousand."
REFERENCE-
Federal Register Notice, Volume 84, Number 62, dated April 1, 2019.
e. ADS-B Limitations.
The ADS-B cockpit display of traffic is NOT intended to be used as a collision avoidance system and does not
relieve the pilot's responsibility to "see and avoid" other aircraft. (See paragraph 5-5-8, See and Avoid). ADS-B
must not be used for avoidance maneuvers during IMC or other times when there is no visual contact with the
intruder aircraft. ADS-B is intended only to assist in visual acquisition of other aircraft. No avoidance maneuvers
are provided or authorized, as a direct result of an ADS-B target being displayed in the cockpit.
f. Reports of ADS-B Malfunctions.
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Users of ADS-B can provide valuable assistance in the correction of malfunctions by reporting instances of
undesirable system performance. Since ADS-B performance is monitored by maintenance personnel rather than
ATC, report malfunctions to the nearest Flight Service Station (FSS) facility by radio or telephone, or by sending
an email to the ADS-B help desk at adsb@faa.gov. Reports should include:
1. Condition observed;
2. Date and time of observation;
3. Altitude and location of observation;
4. Type and call sign of the aircraft; and
5. Type and software version of avionics system.