“Ident” is used to help a controller identify an aircraft’s secondary radar (transponder) return.

Scenario one. It is a method to allow a controller to identify an aircraft on radar, per section 5-3-3 of FAA Order 7110.65:

When using only Mode 3/A radar beacon to identify a target, use one of the following methods:

a. Request the aircraft to activate the “IDENT” feature of the transponder and then observe the identification display.

Scenario two. For lost communication, per section 10-4-4 of 7110.65:

Take the following actions, as appropriate, if two-way radio communications are lost with an aircraft:

c. Attempt to re-establish communication by having the aircraft use its transponder or make turns to acknowledge clearances and answer questions. Request any of the following in using the transponder:

1. Request the aircraft to reply Mode 3/A “IDENT.”