AIM

8/15/19

4

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5

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17

Surveillance Systems

2.

One of the data elements transmitted by

ADS

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B is the aircraft’s Flight Identification

(FLT ID). The FLT ID is comprised of a maximum of
seven alphanumeric 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
enter it prior to flight. However, some ADS

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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

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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

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Match (CSMM) is generated and ATC automa-

tion 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

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B aircraft is assigned a unique

ICAO address (also known as a 24

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bit address) that

is broadcast by the ADS

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B transmitter. This ICAO

address is programmed at installation. Should
multiple aircraft broadcast the same ICAO address
while transiting the same ADS

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B Only Service

Volume, the ADS

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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.
Aircraft that are equipped with ADS

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B avionics on

the UAT datalink have a feature that allows them to
broadcast an anonymous 24

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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. After January 1, 2020, and in
the airspace identified in 14 CFR 91.225, the UAT
anonymous 24

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bit address feature may only be used

when the operator has not filed a 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.
Operators should be aware that in UAT anonymous
mode, they will not be eligible to receive ATC
separation and flight

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following services and will

likely not benefit from enhanced ADS

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B search and

rescue capabilities.

4.

ADS

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B systems integrated with the

transponder will automatically set the applicable
emergency status when 7500, 7600, or 7700 are
entered into the transponder. ADS

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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

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B is intended for inflight and airport

surface use. ADS

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B systems should be turned “on”

and remain “on” whenever operating in the air and
moving on the airport surface. Civilian and military
Mode A/C transponders and ADS

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B systems should

be adjusted to the “on” or normal operating position
as soon as practical, unless the change to “standby”
has been accomplished previously at the request of
ATC.

d. ATC Surveillance Services using ADS

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B 

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Procedures and Recommended Phraseology

Radar procedures, with the exceptions found in this
paragraph, are identical to those procedures pre-
scribed for radar in AIM Chapter 4 and Chapter 5.

1.

Preflight:

If ATC 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

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B avionics.

2.

Inflight:

When requesting surveillance services while air-
borne, pilots must disable the anonymous feature, if
so equipped, prior to contacting ATC. Pilots must also
ensure that their transmitted ADS

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B FLT ID matches

the aircraft identification as entered in their flight
plan.