The Sum of All Parts

Sum"Grumman" G-44 (USCG J4F-1) serial no. 1228 - restored as N1340V

A model G-44 Widgeon – serial no. 1312 (N13122) which really is a “Grumman” aircraft – as opposed to the SCAN Type 30 license-built copies manufactured in France under license.

The Sum Of All Parts

Written by Dave Marion – It may be that most people in aviation do not think that much or even enough about it, but the proper identification of an airplane is predicated on three simple parameters – make, model, and serial number. As simple as that sounds, there is a lot of evidence out there that some folks do not understand what those terms actually mean. I recently wrote an article that focused on the too often misunderstood or unappreciated significance of model designations in particular. Here I want to discuss the meaning of “make” instead.

“Make” refers to the manufacturer or builder of a particular aircraft. Contrary to popular opinion however, that does not necessarily mean the original designer, original TC Holder, or if it has ever been sold or transferred, a subsequent or “current” owner of the type certificate at the time the particular aircraft in question was built. As clearly specified under 14 CFR §45.13(a), “make” refers to whomever actually built the aircraft – and it is an individual criterion independent of any similar aircraft. If that builder also happens to be the original designer or TC holder, that fact is no more than coincidental as far as the FAA and its formal identification are concerned.

In that context, there can be no such thing as a legitimate “data tag rebuild” – at least there should not be according to the Federal Aviation Regulations. Anyone who so completely “rebuilds” an aircraft that the only “original” part left on or in it is the original manufacturer’s data tag, then that data tag is in fact no longer valid according 14 CFR §45.13(a). Since it matters much less who actually fabricates the parts – as long as they are made per approved processes and with approved materials (manufacturers often use subcontractors to fabricate parts) then it is easy to see that the term “build” also can be legitimately interpreted more simply as “assemble.”

“Grumman” G-44A Widgeon serial no. 1473 (N244GW)

Even if 100% OEM* spare or “new old stock” (NOS) parts are used in the process, when anyone assembles (builds) or even re-assembles (rebuilds) a particular aircraft, it is no longer appropriate or correct to continue to identify that aircraft as a product of the nominal OEM. Unless the new “builder” actually has some kind of formal FAA manufacturing or production approval under Part 21 – a production certificate (PC) or an approved production inspection system (APIS) – or he is in fact the TC holder (i.e. owner) of the type certificate under which the aircraft is certified, then that builder is technically speaking just an amateur builder and the airplane he has built is no more than an amateur-built “copy” of the original. In other words, such a “data tag rebuild” would effectively transform a “real” and inherently valuable historic aircraft into a much less valuable “replica” of one.

(*Original Equipment Manufacturer)

As such, even though it may still be identified by its original model designation – assuming the requisite conformity to type design (regardless of whether or not that design is approved and certificated) the airplane in question should be formally re-identified and registered henceforth using the new builder’s name in relation to its “make” and a new and unique serial number that is different than its original one since it is by FAA definition no longer the same aircraft. In fact, in regard to the new serial number, FAA standards require that an amateur builder or any builder for that matter other than the OEM must use a unique serial number that is even formatted differently from all of the original manufacturer’s serial numbers so that it specifically cannot be confused with an original production serial number or OEM-built aircraft.

This G-21A Goose is in the early stages of restoration – but does this degree of work qualify as a “repair” or as “rebuilding” it? If it is “rebuilt” by someone other than Grumman, per the FARs it would no longer be a “Grumman”

Aircraft certificated in the Experimental category, as long as they were not previously certificated under another category, as is the case with most so-called “warbirds”, are specifically excluded from the nominal requirements of Part 43. Even so, many if not most aircraft mechanics and others involved in warbird restorations in particular seem not to understand or appreciate the difference between “maintenance and alteration” under 14 CFR Part 43 and manufacturing or building (or rebuilding as applicable) certificated aircraft and parts for them under 14 CFR Part 21 and they improperly apply Part 43 maintenance standards and policies to rebuilding and restoration, which are really in effect manufacturing processes.

Although the term “rebuilt” is not specifically defined under 14 CFR Part 1 (Definitions and Abbreviations) it is defined for all practical purposes under 14 CFR §43.2(b) where it states that “No person may describe in any required maintenance entry or form an aircraft, airframe, aircraft engine, propeller, appliance, or component part as being rebuilt unless it has been disassembled, cleaned, inspected, repaired as necessary, reassembled, and tested to the same tolerances and limits as a new item, using either new parts or used parts that either conform to new part tolerances and limits or to approved oversized or undersized dimensions.”

The subject of what constitutes a rebuilt engine in particular is also specifically addressed in 14 CFR §91.421(c) and FAA Advisory Circular no. AC 43-11 (Change 1 dated March 29, 2007) in which it is stated that “for the purposes of this section, a rebuilt engine is a used engine that has been completely disassembled, inspected, repaired as necessary, re-assembled, tested, and approved in the same manner and to the same tolerances and limits as a new engine with either new or used parts. However, all parts used in it must conform to the production drawing tolerances and limits for new parts or be of approved oversized or undersized dimensions for a new engine.”

Pretty much the same thing goes for this P-51 Mustang – the work it needs goes well beyond the typical scope of “maintenance” and “repairs” under Part 43 – but if it is “rebuilt” it will no longer be a “North American” P-51.

By those same tokens and for the sake of this argument, a “rebuilt” aircraft would be “a used aircraft that has been completely disassembled, inspected, repaired as necessary, re-assembled, tested, and approved in the same manner and to the same tolerances and limits as a new aircraft with either new or used parts. However, all parts used in it must conform to the production drawing tolerances and limits for new parts or be of approved oversized or undersized dimensions for a new aircraft.”

Even though the issues of rebuilding and who is or is not authorized to do it are all addressed under Part 43, what is written there about it essentially puts the subject of “rebuilding” back under the purview of Part 21. Authority to “rebuild” an “aircraft, airframe, aircraft engine, propeller, appliance, or component part” is for the most part explicitly excluded from being done by anyone other than a “manufacturer” as noted under 14 CFR §43.3(j) and qualification as a manufacturer is and can be done only under Part 21. If you build or rebuild an aircraft, you are a builder, not a mechanic – and if you also happen to have the requisite approval under Part 21, then you actually may qualify as a manufacturer too. Otherwise, you are just an amateur builder and the aircraft that you built (or rebuilt) would be eligible only for an Experimental certificate of airworthiness.

Similarly, mechanics are authorized to perform maintenance, preventive maintenance, and alterations, but they are not authorized to build or rebuild anything per se. Furthermore, maintenance done under Part 43 must be accomplished with “reference to data acceptable to the Administrator.” That typically means the use of service or maintenance manuals, service letters or bulletins, or other applicable Instructions for Continued Airworthiness (ICA) – none of which is ever so comprehensive as to serve as a valid basis for the assembly or manufacture of a complete aircraft. One very strong clue that should be taken into consideration by warbird owners and restorers is that once you get into the realm of engineering drawings and blueprints as your approved technical references, you are no longer talking about “maintenance.”

A flight of three Experimental Thorp T-18 aircraft.

All of this is consistent with another, more well-known and commonly understood segment of general aviation – Experimental “home-built” aircraft. Small, non-certificated, “kit” aircraft are a distinct segment of the general aviation market and they exist not only because of their appeal to “do-it-yourselfers” but also as an alternative to more expensive, fully type-certificated, production or factory-built aircraft. They also usually offer certain advantages in terms of simplicity and/or performance.

In contrast to the “warbird” community, almost everybody in the “home-built” community seems to understand that when someone builds a “kit” airplane such as a Thorp T-18 or any of the Vans RV series (for two common examples) the finished aircraft is not a “Thorp” T-18 or a “Vans” RV-whatever. An experimental Thorp T-18 built by amateur-builder “John Smith” would be formally identified, certificated for airworthiness (if not actually type design) and registered by the FAA as a “John Smith T-18” because per 14 CFR 45.13(a) that is who actually built it and as what. And typically too Mr. Smith would choose, because he is required to do so, his very own unique serial number for it, such as “JS-1” for another example.

An example of a Vans RV-8 kit-built aircraft.

Another aspect of experimental “home-built” aircraft is that the FAA standard for qualifying as the “builder” of such an aircraft is based on who assembles the simple majority of the aircraft, i.e. 51% or more. That standard is nominally tied to the operation of amateur-built “aircraft the major portion of which has been fabricated and assembled by persons who undertook the construction project solely for their own education or recreation” per 14 CFR §21.191(g). The 51% figure is not mentioned there, but rather in a relatively recent Advisory Circular AC 20-27GCertification and Operation of Amateur-Built Aircraft” which was issued by the FAA in September 2009.

There does not seem to be any comparable standard for the manufacture of new aircraft explicitly defined in the regulations. Even so, by that same standard, anyone who even just “repairs” a historic warbird by replacing 51% or more of its parts legally should be considered its new “builder” and that fact too would alter its official identification accordingly. Common sense would dictate that replacing that much or more of an aircraft’s structure is not a restoration or repair, but rather the rebuilding of the whole aircraft.

A “restored” P-51D Mustang that may or may not still qualify as a “North American Aviation” product.

While it seems not be noticed or appreciated as such, there are numerous examples of such warbirds. Currently there are something like 76 P-51D Mustangs on the US civil registry that are no longer pure “North American Aviation” aircraft; they are listed instead as “North American / Aero ClassicsP-51D Mustangs. An old forum thread on the Warbird Information Exchange (WIX) suggested without much conviction or apparently any particular knowledge or expertise on the subject that it may have been the result of the fact that a company called Aero Classics was simply the TC Holder at the time that the Mustangs in question were certified. However, that should not have been the case according to all of the aforementioned regulations. It is valid and proper to identify an aircraft as such if and only if the named entity was actually responsible for and directly involved in building (or rebuilding) the aircraft in question.

If that was not the case and Aero Classics did not in fact actually build or rebuild those 76 Mustangs, or they were built or rebuilt by someone else only while Aero Classics was simply the current TC Holder at the time, then some misguided owners and/or FAA bureaucrats misidentified the aircraft in question, at least as far as the regulations are concerned. Such mistakes certainly have happened at other times and in regard to other aircraft too.

A “Cessna” 305 series (Army L-19 or O-1) “Birddog”

Conversely, there are some twenty “Cessna / Ector” model 305A aircraft (better known as their military designations as the L-19 or O-1Birddog”) that are on the US civil registry. There are also nine similar “Cessna / Air Repair” model 305F aircraft on the registry too. The aircraft in these cases were not built by Cessna, but are examples of a specific type that was designed, certificated, and originally built by Cessna. These particular examples however were built instead by the Ector Aircraft Co. of Odessa, Texas or rebuilt by Air Repair Inc. of Cleveland, Mississippi respectively using either NOS military surplus spare parts that were originally fabricated by Cessna in support of their original production for the military or that were fabricated new by these subsequent builders.

Accordingly, these aircraft have serial numbers distinctly different than original 305 series aircraft actually built in Cessna’s own factory. Whereas the Cessna-built model 305 series aircraft have serial numbers 21001 & up, the Ectorbuilt aircraft have serial numbers in the 2001 & up range and the Air Repair rebuilt aircraft have serial numbers AR-1 through AR-9. In spite of the fact that Ector and Air Repair built their own examples of the Cessna 305 series, they could not identify those aircraft as actual “Cessna” aircraft. Nobody is ever authorized to build an aircraft and then identify it as having been built by someone else, even the original designer or TC Holder.

Basically it all boils down to this; production and manufacturing are governed under Part 21 and maintenance, preventative maintenance, and alterations are all governed under Part 43. The term “rebuild” is officially defined by the FAA – and by that definition it actually falls under the purview of Part 21, under which most aircraft mechanics do not have any authority to operate or function. However, the terms “restore” or “restoration” are not similarly defined, but in general use the operations to which they refer are actually manufacturing or production operations – to “make like new again” – which are the functions of a manufacturer or builder, not of a mechanic. At some point, the warbird community needs to catch on to that fact and differentiate such aircraft accordingly.

Dave Marion is the Technical Content Editor at As A&P and IA with 29 years of experience in aircraft maintenance, he is also a Commercial Pilot with Airplane, Single & Multi-Engine, and Instrument ratings. He has a BA from Colgate University in 1984 and also graduated cum laude from Embry-Riddle Aeronautical University (DAB) with a BS in Aviation Technology in 1990. He can be reached along with all of the editors via E-Mail: [email protected]