N-Numbers, ICAO, and Your ADS-B Identity

By Scott Spangler on February 12th, 2018

6MarkingsPlacardsNumbers-4Many owners like to personalize their prized aircraft with an N-number that represents them, often with their initials. Before the advent of NextGen, painting the new number on the airplane, and professing it to ATC, covered the customization. Now, unless an airplane’s ADS-B identity matches its new N-number, a filter the FAA activated in January will likely scrub it from ATC’s scopes and the Traffic Information Services Broadcast to other aircraft with ADS-B.

Aircraft transmitting erroneous information, whose ADS-B identity doesn’t match the N-number painted on the airplane and processed to ATC, will not wander the sky at will. They will continue to receive ATC services based on secondary radar information when flying in radar coverage.

What’s this ADS-B identity, and where does one find it? Officially, it is the 24-bit ICAO address that is forever linked to an N-number, like a fraternal twin. It is otherwise known at the Mode S code, and when the N-number changes, so does the code.

Common Installation IssuesIf aircraft owners don’t have their avionics shops update their ADS-B systems with the new ICAO address (and call sign, if their aircraft officially operates with one instead of its N-number), when they get a new N-number, they will be spewing erroneous information. And should they get caught by the new filter, they will receive a notice of the errors of their ways and a request to contact the FAA’s ADS-B Focus Team, if the FAA can locate the owner of the offending airplane, that is.

When the ADS-B identity doesn’t match the physical N-number, making the aircraft registry connection to the owner is more involved. And if the FAA cannot make the connection, the offending aircraft is forever filtered without further notice.

There are several ways owners can ensure that their aircraft are broadcasting the correct ADS-B identity. They can have their avionics shop connect the appropriate test box and check all the numbers, correcting those in error. Or they can request a Public ADS-B Performance Report (PAPR), an automated online tool that emails a free ADS-B report card within 30 minutes after the conclusion of the specified flight in ADS-B airspace.


A PAPR examination highlights all of the erroneous data in red (check out the online PAPR user’s guide for all the details). If an owner requests a report but doesn’t receive one for the N-number he or she types into the online form, that means the system cannot find it in its inventory of flights, which means that the airplane’s ADS-B identity doesn’t match the number painted on its flanks.

Another common error is an improper emitter category, which identifies the aircraft size by weight. Its seven categories range from Light Airplane (max weight of 15,500 pounds or less) to Heavy (max weight of 300,000 pounds or more). It has three more definitive categories: Rotorcraft (all of them, regardless of maximum weight), High Performance (more than 400 knots true and 5 g), and Large Airplane with High Vortex (airplanes that weigh 75,000 pounds or more that generate high wake vortex; the Boeing 757 is the only current example).

There might be a third way, doing nothing. The only clue that there might be something amiss with the airplane’s ADS-B identity is a reduction of available ATC services. Equally important is the degradation of TIS-B traffic, which works in concert to mute the aircraft owner’s ADS-B investment. – Scott Spangler, Editor.


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