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AIM

10/12/17

4−5−17

Surveillance Systems

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 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−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 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−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

Volume, 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.

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. After January 1, 2020, and in

the airspace identified in 14 CFR 91.225, the UAT

anonymous 24−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−following services and will

likely not benefit from enhanced ADS−B search and

rescue capabilities.

4. 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. ADS−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−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−B −

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−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−B FLT ID matches

the aircraft identification as entered in their flight

plan.

2/28/19

AIM