Who Invented c/n?

A random review of images of aircraft data plates reveals that the following descriptors were in use at various times:

NUMBER
NO.
SERIAL
SERIAL NO.
MACHINE NUMBER
MAKER'S NO.
FACTORY NO.
MANUFACTURER'S SERIAL NO.
MFG. SERIAL NO.
MANUFACTURER'S NO.
MFG. NO.

A Douglas data plate for an R4D-8 delivered in 1952 records a "Manufacturers Serial No." and a "Customers Serial No." in acknowledgement of the fact that the aircraft had a serial number issued by the manufacturer as well as a serial number issued by the customer, in this case the U.S. Navy. Modern convention suggests that "Serial Number" is a purely military identifier although this was clearly not the intention when many aircraft were built. Military serial numbers of aircraft built in the USA are alternatively known as "Tail Numbers" even though the number physically painted on the tail can be a truncated form of the actual serial number. Aircraft of the United States Navy carry serial numbers allocated by the USN Bureau of Aeronautics and these are usually described as Bureau Numbers often abbreviated to BuNo.

Given the wide variety of terms used on data plates, it is clear that a central registration authority would have been faced with either adopting one of these terms or coining a new term which was devoid of any ambiguity arising from the use of the common descriptor "Serial Number". While the manufacturers continued to operate in splendid isolation, the registration authorities in the UK and the USA did achieve some degree of standardisation, although each chose a different standard terminology. It would appear that the UK opted for "Constructor's Number" and the USA adopted "Manufacturer's Serial Number".

The significant difference between "Constructor's Number" or "Manufacturer's Serial Number" and "Serial Number" is that a C/N or MSN does not change during the lifetime of a particular airframe. On the other hand, a "Serial Number" issued by the military can change if the aircraft continues in military service after being sold to another nation with a different numbering system.

As far back as 1910, the Paris International Convention on Air Navigation recognised the need for all civil aircraft to be registered. International implementation was delayed by WWI but in 1911 a Draft Air Navigation Bill was introduced in the UK stating that with effect from 20 April 1919 all British civilian aircraft must carry registration markings. As an interim measure, British civil aircraft would use a continuation of the RAF serial system beginning at K-100. A listing of these registrations published as recently as 1986 uses the term "C/N" (Constructor's Number) to define individual aircraft. It is not known if this term was used in the original document or if it was applied retrospectively by the compiler.

As an indication of what requirements had prevailed, an Australian document titled "Application for Registration of an Aircraft" issued under Aerial Navigation Regulations 1915, requires the applicant to describe the aircraft but not define the aircraft. It makes no provision for a serial number of the airframe or the engine, requiring only the year built and approximate number of miles flown.

A provisional form for "Certificate of Registration" was issued by ICAN sometime prior to 1922 and this document has provision for a "Maker's No."

When the first formal British Register came into effect on 22 July 1919, all aircraft previously registered with K series registrations were re-registered beginning at G-EAAA. A listing of these registrations published in 1986 again uses the term "C/N".

In October 1938, the British Air Registration Board printed a form titled "Nationality and Registration Marks". This appears to mark a transition from a ledger to a card system for maintaining the Register. This form has a heading "Constructor's No." The card for G-EAAA (and many others) is stamped;

"THIS ENTRY COPIED on 1st JANUARY, 1939, From FORMER REGISTER".

About 1928, Australia changed its Certificate of Airworthiness (Form C.A. 14) from a burgundy coloured card to a new four page paper CofA document while retaining the same form number. The burgundy card made provision for "Name of Constructor" and "Description of Aircraft" but made no provision for an identifying number. The revised four-page document made provision for a "Constructor's Number". This new form layout was almost identical to the UK CofA (Form 59) used in 1932 and possibly earlier.

An "Application for Certificate of Airworthiness" issued under Australian Air Navigation Regulations 1921 has a heading "Constructor's No. or Late Service No." This would appear to provide for aircraft that had a military serial number but no serial number issued by the manufacturer. In some instances, applications were submitted (and accepted!) quoting a military serial number when it should not have been too difficult for the applicant to determine that the aircraft did indeed have a "Constructor's Number". Although issued under 1921 legislation, this form does not reveal a printing date so the term "Constructor's Number" could have been introduced anytime after 1921.

Although it is suspected that Australia used the term as early as 1921, the earliest documented Australian use of the term "Constructor's Number" is 1928, although without access to the original UK Register of 1919, it remains highly likely that the term was in use in the UK as early as 1919.

Australian practice is believed to have followed British practice with the use of "C/N" until approximately 1936 when Australian documents began to use the term "Manufacturer's Serial Number". At this time there were widespread changes to Australian air navigation legislation resulting from legal action brought against the Commonwealth by the private pilot Henry Goya Henry (1901-1974).

By the fifties, data plates issued by Lockheed, Douglas and Boeing were using the term "Manufacturer's Serial Number" but this probably commenced much earlier.

To add to the mix, a Certificate of Registration of Aircraft (CA Form 71) issued by the U.K. Civil Aviation Authority on 27 February 1976 for Cameron Balloon G-BDSE registered to British Airways, provides a column headed "Aircraft Serial Number".

Therefore, it is concluded that the terms "Constructor's Number" and "Manufacturer's Serial Number" are both well established and equally valid methods of defining the same numerical descriptor used to identify an individual airframe. Today, "Manufacturer's Serial Number" (MSN) is the descriptor of choice for Airbus and Boeing.

The abbreviations for "Constructor's Number" and "Manufacturer's Serial Number" can be presented in upper case or lower case but upper case has been adopted here for consistency. Traditionally, the abbreviation for "Constructor's Number" is presented in lower case letters separated by an oblique. Some writers have used the term "Construction Number" but this variation does not appear on any official documentation sighted by the compilers. For the full expression, most official documents show the possessive apostrophe but this is sometimes omitted (notably on data plates) presumably for simplicity.

The compilers' review of readily available aircraft data plates initially revealed only one which used the term "Constructor's No." and this was for a Vampire built in Australia in 1952 (shown below). Subsequently other examples have emerged e.g. Hindustan Aeronautics. An abbreviated form, "CONS. NO." is used on some Auster fuselage frame assembly plates (see Note 7 below). Despite a wider search, the compilers were unable to find any use of the term "Constructor's Number" by an American manufacturer or agency.

MFG. NO.

Curiously, the data plate fixed to Auster VH-KBG (see below) shows the type as J5/B whereas the aircraft is actually a J1/B. It is believed that in this instance the plate has been punched incorrectly. Auster data plates are unusual in that many of them show a SERIAL NO. and a CONS. NO. This confusing situation is explained by UK Auster specialist Ian O'Neill.

An Auster airframe carries many sub-assembly identification plates. The principal plate is the fuselage frame assembly plate which carries a unique serial number (SERIAL NO.). No military Auster has a constructor's number (CONS. NO.) stamped on the fuselage frame assembly plate as it was not a military requirement. However, most but not all, military Austers were allotted a constructor's number by the manufacturer for internal company use only. Initially, post-war civilian Austers were treated similarly until circa 1951 when the constructor's number was added to the fuselage frame assembly plate. At the time of manufacture, the fuselage frame assembly plate was riveted to the square tube forming the upper part of the starboard door framework.

Fuselage Frame Plate of VH-KBG

(Picture: Ian McDonell)