Radial Engine Stinson History

Early Aircraft Registration and Type Certification background

This might help explain some of the early “N” numbers used and how aircraft in the 20’s and 30’s were certified.

History behind “N” numbers

The U.S. received the “N” as its nationality designator under the International Air Navigation Convention, held in 1919. The Convention prescribed an aircraft-marking scheme of a single letter indicating nationality followed by a hyphen and four identity letters (for example, G-REMS). The five letters together were to be the aircraft’s radio call sign.

In the original 1919 allotment, most of the nations shared first letters. Only U.S. and four other nations were assigned a unique first letter to be followed by any combination of four letters. In each case, that first letter was the same as a radio call letter that had been previously assigned to that nation by an evolving series of international agreements. As of April 1913, for example, Great Britain had complete rights to the radio letters B, G, and M, while sharing certain other letters. Not surprisingly, Great Britain received G as its aircraft nationality identifier under the 1919 agreement.

During this era, the U.S. had complete rights to the radio letters N and W, and to combinations of K from KDA to KZZ. Why these particular letters? The assignments of W and K appear to have been arbitrary, according to articles on early radio call signs by Thomas H. White. In the case of N, Whites notes that the U.S. Navy had used this radio letter since November 1909.

This still leaves the question of why N was chosen over W for the U.S. aircraft identifier. The answer may lie in the fact that the Government had reserved N for itself, while assigning combinations beginning with K and W to various radio stations along geographic lines. N would therefore be less confusing as a single national marking for aircraft.

No mention of N numbers appeared in the initial Air Commerce Regulations placed in effect by FAA’s first predecessor agency in December 1926. The letter markings that this original set of rules specified were C (commercial), S (state), and P (private), which were to precede the numbers assigned to licensed aircraft. Unlicensed aircraft had numbers, but no letters, at this time.

The earliest legal requirement for the N marking is found in the first general amendments to the Air Commerce Regulations on March 22,1927. These amendments mandated that U.S. aircraft engaged in foreign air commerce display the N at the beginning of its identification markings. Later, this requirement was extended to all U.S. aircraft, regardless of whether they operated beyond the Nation’s borders.

A second letter indicating the aircraft’s airworthiness category followed the N and preceded the identification numbers. These airworthiness indicators were; “C” for standad, “R” for restricted, “X” for experimental, and later an “L” for limited, (for example, NC1234). This was standard until December 31, 1948, when aircraft registered for the first time were required to display identification marks consisting of only the Roman capital letter “N” followed by the registration number. Existing aircraft operated solely within the United States could continue to display an airworthiness symbol until the first time such aircraft were recovered or refinished to an extent necessitating the reapplication of the identification marks. After December 31, 1950, all aircraft of United States registry operated outside of the United States were required to display identification marks consisting of the Roman capital letter “N” followed by the registration number.

Until December 31, 1960, the required location for display of nationality and identification marks for fixed- wing aircraft was the wing surfaces, and the vertical surface of either the tail or fuselage. Effective January 1, 1960, all fixed-wing aircraft were required to display identification marks on the vertical surfaces or either the tail or fuselage. Wing surface markings were no longer required.

Type Certificates and the Group 2 Approval Process

Type Certificates and the early aircraft approval process which seem to be heavily involved with the SM-1 production.   The Department of Commerce Aeronautics Branch, established in May 1926, had issued the first Air Commerce Regulations on 31 Dec 1926 which detailed how a manufacturer obtained a type certificate.  The federal government than issued the first Approved Type Certificate (ATC) on 19 March 1927. 

Although the rules seemed fairly basic and straightforward, obtaining a type certificate proved somewhat difficult. In 1927, the Aeronautics Branch suffered from limited resources in terms of budgets and staff. To simplify and expedite approvals of type certificates, in October 1927, the Branch required aircraft manufacturers to meet minimum engineering standards set forth in detail in a new handbook. However, manufacturers still had to send blueprints and engineering data to the Branch for examination by its engineering section. If the data conformed to the standards, a Branch inspector went to the factory to determine if the manufacturer adhered to the approved design and specification. If the inspector found no issues, one aircraft of the type being manufactured underwent flight tests – first by a company pilot and then by a federal inspector. If the aircraft passed the flight tests, the Department of Commerce issued a type certificate.

There were two different approval paths a manufacturer could pursue.  The  Approved Type Certificate was issued when the manufacturer intended to produce a large number of essentially the same airplane.  The second was the Group 2 Approval (or as known back then, “the -2’s”) which was a type certificate issued for a limited number of airplanes, for example a weight increase to only a few individual airplanes.  The approval process is essentially the same as that of an aircraft built under the type certificate process except that a more rigid inspection of the airplane is conducted when the factory facilities have not previously been approved.