Aircraft operating with a Mode-S transponder (most common transponder installed on aircraft) will emit an identifying ICAO address (most commonly known as a hex code) through an ADS-B message. This hex code is required to match, one-to-one, to your aircraft registration and can easily be used to identify an aircraft registrations.
To address privacy concerns, the FAA has created the Privacy ICAO Address (PIA) program, which allows operators to use alternate, temporary ICAO addresses that are not tied to an operator in the Civil Aviation Registry (CAR). With this alternate ICAO address, while operating your aircraft, it will be tracked using the tail number associated to the alternate ICAO address and not to your actual tail number.
