What are the repercussions of flying an aircraft with an invalid N number on the side?
As a controller, if it's a correctly constructed N-number, I'd know nothing. and wouldn't do anything. If you file a flight plan, however, the N-number you use will go into the FAA's database. Keep in mind that if you ask a controller for flight following, a Mode C check, etc., there will be a record, even if it's only &quot;on the tape&quot;.
I have no idea whether they would flag an unregistered number, but I can give you some history on an aircraft that flew with an INVALID N-number.
In 2006 (or so, why is this stuff so long ago?), I was working the high altitude sector in the LBF (North Platte, NE) area. I received a handoff on an aircraft with a call sign similar to, but not exactly &quot;N1EP2D&quot;, which is an illegal construct (see https://www.faa.gov/licenses_certificates/aircraft_certification/aircraft_registry/forming_nnumber/)
I alerted my supervisor, who directed me to question the pilot. As it turned out, the pilot had filed this deliberately, and on a whim.
The FAA does not do &quot;whimsical&quot;.
I instructed the pilot to submit the correct N-number, which he did, and I amended the flight plan. I also instructed the pilot to NOT use the invalid number, and to call our Operations Manager for further instructions.
I heard it was a six-month suspension, although I had no official follow-up.