What is the tail number of a flight?
It’s the unique identification number for the aircraft. Every aircraft has one. US aircraft have tail numbers beginning with N; other countries it’s something else.
General aviation craft are only known by tail number for flight planning, air traffic control, and flight tracking. (There is no other ID to use.)
Aircraft from airlines and other large fleets all have tail numbers too, but don’t use them for ATC and tracking. Instead they use flight numbers assigned by the company.
This is not 100% true, depending on what you consider general aviation. The definition I use is that general aviation is any aviation that is not military and is not commercial*. That said, there is a sizable amount of general aviation that uses flight numbers. Some examples are Quest Diagnostics, NetJets, and Walmart.
For information on who is assigned a flight ID see the FAA Contractions publication available here.
*Commercial aviation includes scheduled and charter carriers and consists of passenger and cargo operations.
http://www.airlinecodes.co.uk/reglinks.asp?type=Official This might help?
University of North Dakota uses flight numbers on their planes too as I’m sure other big flight schools do.
UND call sign is “Sioux” and I think the flight number would be the last 2 numbers in the reg, ie: N371ND would be Sioux 71.