Definition
In ADS-B and transponder operations, an interrogation is a radio signal transmitted by a ground station or another aircraft that requests an automatic reply containing identification, altitude, or position information from an aircraft's transponder or ADS-B equipment.
Plain English
A signal sent to your aircraft that asks it to automatically send back information about who you are, where you are, and how high you're flying.
Context Anchor
Seen in ADS-B and transponder discussions, especially when comparing older radar-based surveillance with ADS-B.
Derivation
From the Latin 'interrogare,' meaning 'to ask' or 'to question.' In aviation, the ground station or another aircraft is 'asking' your equipment a question, and your transponder automatically answers.
Why Pilots Care
Your transponder and ADS-B equipment must respond correctly to interrogations for ATC to see you on radar and for traffic alerting systems to function. If your equipment fails to reply, controllers and nearby aircraft may not know where you are.
Intuition Check
Interrogation does not mean a person is questioning the pilot here. It means an electronic system is sending a request for the aircraft’s equipment to reply.
Example Sentence 1
When the ground radar sends an interrogation, the aircraft's transponder automatically replies with its assigned squawk code and altitude.
Example Sentence 2
ADS-B allows the aircraft to broadcast its position automatically without needing an interrogation from the ground.