Long a source of confusion for researchers, the plan
for aircraft licenses and their display was actually grounded in logic,
short-sighted though it may have been. A summary, digested in
chronological form from William T Larkins' work in British Air Pictorial
in 1954, is presented in hopes of clarifying the waters a bit:
1919 = The Convention for the Regulation of Air Navigation, as part of
the October 1919 Peace Conference, created the system of international
identification still in use that sets the first letter(s) as country of
origin: N for United States, D for Germany, G for Great Britain, SE for
Sweden, etc. This system was in use for seven years before it was
formally ratified by our government.
1921 = In July the National Aircraft Underwriters Association, a service
organization for the insurance industry, established a five-letter
licensing code, but this system was voluntary with no governmental teeth
in it. Because of indifference from manufacturers (only 33 planes were
registered by the end of 1922, and it's doubtful if that number exceeded
50). It was history by 1925, but some aircraft of that period appeared
as N-ABCA, N-ABCB, etc; see below.
1926 = In May the first real attempt at organization came with the
federal Air Commerce Act that went into effect in January 1927. In this
system a class letter C, S, or P was to be added, denoting Commercial,
State, or Private. C specified approved (airworthy) airplanes used in
commerce and the air mail, but this was amended in 1930 to include any
aircraft meeting minimum government airworthiness requirements
regardless of its use. S was for state- or federal-owned planes, with
most all states requiring aircraft operated within their boundaries to
bear an NC number (Oregon, where much flying activity took place, was a
notable exception), but this was dropped in 1937. P only lasted until
March 1927 to sort out private aircraft from C and S (no example of an
NP designation was located). A limit of five numbers seemed adequate at
the time for present and future aircraft, but these were all taken by
"Identified Aircraft" was the term used to designate aircraft
that did not meet minimum airworthiness requirements, and it was
possible to register such an aircraft until March 1939. These would wear
IMA (Identification Mark Assignment) numbers, usually without the N.
1929 = A new plan was to approve three numerals, and a suffix: E, H, K,
M, N, V, W or Y. Not surprisingly, these new blocks were used up by the
end of 1934.
Class prefixes R and X for Restricted and Experimental aircraft were
established. A class prefix of G identified Gliders until it was
canceled in 1937, with sailplanes and gliders placed the same bag as
powered aircraft. The use of the letter N was optional at this time for
aircraft flown within the nation's boundaries.
1935 = Visionaries stepped in and claimed an increase to five numerals
would surely do it. This opened up a block from 10000 to 99999, but
these, too, showed signs of being gobbled up by the war years.
1938 = The Civil Aeronautics Authority (CAA) was established as an
independent agency and, in 1940, was split into two parts -- the Civil
Aeronautics Board, to handle rule making, regulation, and accident
investigation, and the Civil Aeronautics Administration, to take care of
licensing and certification, airway development, and safety enforcement.
By the outbreak of war, CAA had also assumed control of landings and
takeoffs at airports. The Federal Aviation Agency (FAA) would not arrive
until November 1, 1958.
1946 = Blocks of three and four numerals with the other letter suffixes
(except number-lookalikes I and O) were added, and 46000 to 79999 were
generally reserved for war-surplus aircraft. A class prefix L for
Limited type certification went into effect, lasting only until 1948.
1948 = Class prefixes of C, R, and X were eliminated in December, and
only the N was used.
1953 = Double suffixes with three numerals were authorized in March.
1958 = The Federal Aviation Agency (FAA) established
None of these rules was carved in marble, and exceptions were manifold.
A notable example is a de Havilland DH-4 that earned the very first
license in its duties with the Department of Commerce. It proudly wore
N1, even though to abide by its owner's rules it should have been NS1.
Because of DoC's practice of reassigning numbers after the sale,
destruction, or export of an airplane to another, N1 showed up later on
a government Northrop Alpha 2, a Ford 5-AT, a Lockheed 12-A, and a DC-3!
In other instances, a number might be borrowed temporarily by a
manufacturer from an inactive company hack for use on a prototype until
it had its own license, or a "blue-sky" number might be
painted on a new model for photographic or publicity purposes.
Special-request registrations became popular, accounting for the many
low-number- plus-suffix registrations, especially after World War Two.
If one had the $10.00 fee, one could have just about anything, as long
as it was available.
With batch allocations by CAA to regional offices for areal
distribution, numbers became cloudy as a logical reference tool,
indicating where airplanes were licensed, and not where or when they
were built. Additionally, some batches were issued to large
manufacturers, which explains how Douglas cornered the N30000 market.