Identification Definition
Identification refers to the process where a specific aircraft’s position is displayed and confirmed on a situation display. This confirmation is known as radar contact, where the radar position of the aircraft is also recognized. According to ICAO Doc 4444 PANS-ATM, the goal of identification is to clearly match a flight in the air with its visual representation on the situation display. In simpler terms, air traffic controllers must ensure that they know which aircraft corresponds to a specific symbol shown on their screens.
Identification is vital for providing air traffic services (ATS). Before offering surveillance service to an aircraft, controllers must first identify it and inform the pilot. Maintaining this identification is crucial until the surveillance service ends. If identification is lost—perhaps due to fading radar signals—the pilot needs to be notified. When the aircraft symbol reappears, it must be re-identified, and the pilot should be updated accordingly.
Identification Procedures
The methods used for identification depend on the type of surveillance sensors involved:
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Primary Surveillance Radar (PSR): Identification relies on the returns received by the PSR.
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Secondary Surveillance Radar (SSR) or Multilateration (MLAT): Both systems use transponder replies to determine aircraft position, so their identification methods are similar—based on data from the aircraft transponder.
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Automatic Dependent Surveillance-Broadcast (ADS-B): Here, identification comes from the aircraft’s ADS-B transmitter.
Automated ATS systems typically indicate the types of sensors supplying information about a target. Different symbols help distinguish between PSR, SSR/MLAT, and ADS-B data. Additionally, combo symbols may show that multiple data types are available, helping controllers understand which identification procedures apply. Each procedure has limitations designed to prevent misidentification, and it is the controller’s job to select the appropriate method. If a chosen method fails, an alternative must be used.
PSR Procedures
Position Reporting
When a pilot reports their aircraft’s position, the controller compares this report with the observed PSR blip. If they match closely and there are no other unidentified blips nearby, identification is successful. The position report can reference a geographical point or specify a distance and direction, like “15 MILES SOUTH OF POINT”.
Departing Aircraft
For departing aircraft, controllers receive reports and compare them with PSR blips within one nautical mile from the runway’s end. Care is taken to avoid confusion with aircraft holding or overflying the airport or those using adjacent runways.
Vectoring
Controllers may issue heading change instructions (30 degrees or more) and then compare the movement of a PSR blip to the expected maneuvers. Often, a single turn suffices, but if multiple targets are on the screen moving similarly, additional vectors may be necessary.
Transfer of Identification
This common method applies to all sensors and will be detailed further below.
SSR/MLAT Procedures
Recognition of Aircraft Identification
The identification process begins with recognizing the aircraft’s callsign in the label. This requires a successful correlation between the SSR code and the callsign.
Assigned Discrete Code
For this method to function, there must be a reliable system for unique code assignment. Only discrete codes (not ending in “00”) can be used. If an aircraft squawks a conspicuity code, other identification methods must be employed.
Direct Recognition
This applies to Mode S-equipped aircraft, provided that crews input the correct callsign into the transponder. Mismatches can complicate identification.
Compliance Observation
Controllers can instruct pilots to change the SSR code and monitor this change. They can also ask pilots to squawk IDENT and observe the response. Controllers must be cautious of garbling, which can lead to false IDENT indications.
Transfer of Identification
Refer to the dedicated subsection below for details.
ADS-B Procedures
Direct Recognition
This is akin to the direct recognition of Mode-S aircraft identification, with the key difference being that ADS-B receivers provide the data instead of radar/MLAT.
Compliance Observation
Similar to the SSR process, controllers can instruct pilots to transmit ADS-B IDENT and observe the response.
Transfer of Identification
See the dedicated subsection below for details.
Transfer of Identification
Generally, the transfer of identification is applicable for all sensors. However, many options are limited to specific ones:
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Designating the position indication automatically (all sensors).
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Notifying the aircraft’s discrete SSR code or address (SSR, MLAT).
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Indicating the aircraft is SSR Mode S-equipped when coverage is available (SSR+Mode S, MLAT+Mode S).
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Notifying that the aircraft is ADS-B-equipped when compatible coverage is available (ADS-B).
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Directly pointing to the position indication, applicable when displays are adjacent or shared (all sensors).
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Referring to the position indication concerning a geographical position or navigational facility accurately shown on both displays, along with the track of the observed position if the aircraft’s route is unknown to both controllers (all).
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Instructing the aircraft to change SSR code and observing this change (SSR, MLAT).
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Instructing the aircraft to squawk/transmit IDENT and observing this response (SSR, MLAT, ADS-B).
Phraseology
Examples of phraseology related to identification procedures include:
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“IDENTIFIED” or “RADAR CONTACT” – indicating to the pilot that the aircraft has been identified.
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“IVB3011, FOR IDENTIFICATION TURN RIGHT HEADING 060” – a vectoring instruction used during PSR vectoring procedures.
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“DVK1208, SQUAWK 1234” – instructing a change in the SSR code.
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“SQUAWK IDENT” (for SSR/MLAT) or “TRANSMIT ADS-B IDENT” (for ADS-B) – directing the operation of the IDENT feature on board.
Similar Terms
Aircraft Identification
While this term may sound similar to “identification of aircraft,” they differ significantly. Aircraft identification refers to the string of letters and numbers (callsign), while identification is an ATS procedure.
Correlation
Both terms involve matching an aircraft to its flight data, but identification occurs in the controller’s mind, while correlation happens in software. A flight may be correlated without being identified, and vice versa. For instance, an automated ATS system might link a flight plan to a track with an incorrect SSR code. Conversely, an unidentified aircraft might establish radio communication with a controller, allowing for identification while remaining uncorrelated for some time due to missing flight plan information. Nonetheless, surveillance service can still be offered since identification is the key requirement.
