The IDENT feature is an important tool for pilots. With just a button press, it sends a special pulse added to the transponder reply. This pulse, known as the Special Position Identification (SPI), is only present if the pilot activates the IDENT feature. Ground systems, like the Secondary Surveillance Radar (SSR), receive this pulse and present it to air traffic controllers. The representation can vary based on the ATC system in use. For example, you might see a big yellow flashing X behind the IVB996 track symbol or a flashing label for DVK1208.
The primary uses of the IDENT feature are aircraft identification and assisting during communication loss. In some situations, identifying an aircraft can be tricky. For instance, if two planes approach the boundary with the same SSR code and lack Mode-S data, traditional methods like recognizing callsigns or SSR codes won’t work. In these cases, the IDENT feature serves as a quick, simple, and reliable alternative.
However, controllers need to be cautious. Garbling can occur when replies overlap, leading to confusion in the ground system’s IDENT representation. Additionally, nearly simultaneous IDENT transmissions can happen due to various reasons, such as pilots accidentally pressing the IDENT button or following another controller’s instruction.
In case of communication loss, the IDENT feature helps determine if the situation is complete or partial. If an aircraft doesn’t respond, controllers can issue further clearances, allowing the pilot to confirm by using the IDENT feature. While this procedure is valid according to ICAO guidelines, controllers should remember that the usual safety buffer of the readback-hearback sequence is absent.
Here are some examples of phraseology related to the transponder IDENT feature:
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“IVB3011, SQUAWK IDENT” is typically used to identify an aircraft.
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“IVB3011, IF YOU READ, SQUAWK IDENT” is used after multiple unsuccessful attempts to communicate.
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“IVB3011, SQUAWK OBSERVED, POSITION 10 MILES EAST OF REKRA, WILL CONTINUE TO PASS INSTRUCTIONS” informs the pilot that the IDENT has been received.
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“IVB3011, DESCEND FL 220 AND IDENT” gives instructions and clearances in case of partial communication loss.
