A question for the screeners and editors: if you check the FAA database (registry.faa.gov), all US registrations have a prefix of N. The prefixs NX
and NR are optional, to indicate types of certification. X is experimental, R is restricted and I can't remember what C is, but I think once was commercial. Hence, the correct registration for the Spirit of St. Louis would be N211, not NX211.
This begs the question as to what the standard is for airliners.net. I have some pictures in the database with the two letter prefix and some where I have dropped the second letter. Which is correct?