Gig 601XL Builder wrote:

According to the AIM...

Pilots operating under provisions of 14 CFR Part 135 and not having an FAA
assigned 3-letter designator, are urged to prefix the normal registration
(N) number with the letter "T" on flight plan filing; e.g., TN1234B.

But lots of folks never do it.



There was a time right after the controller strike that the FAA
gave preference to airlines and 135 operators. People heavily
used TANGO-NOVEMBER to make sure they got their precedence.