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Posted 6 years 123 days ago ago by Admin


Note: For brevity, the following article paraphrases select passages and embeds hyperlinks to specific reference documents. All links open to the faa.gov or ecfr.gov websites. Several links consist of search results that offer additional reading.

Ever had someone sneak up behind you while twisting a wrench and inquire if you were doing it “by the book”? Ever wonder what book they were referring to?

What follows is my own unconventional interpretation. I’m by no means an expert. However, after years of practicing I think I can get this as mixed up as the best of them.


In the beginning, there were no books. The early years of aviation had no documentation as we know it today, for aviation wasn’t regulated until 1926. And the first aircraft Approved Type Certificate was not awarded until March 1927. This left common sense, a wrench, and what became the Type Certificate Data Sheet (TCDS) as the only requirements to keep things flying. Yes, these were the original good old days.

The push to standardize aircraft documentation began in the years prior to World War II. This was followed by numerous military and government initiatives, culminating in the Federal Aviation Act of 1958, which in turn created the FAA and the basic regulatory system we know. Following 1967, with the establishment of the National Transportation Safety Board (NTSB), we complete the regulatory players who influence our maintenance documentation.

During this same period, manufacturers (OEMs) and owner/operators developed their own documentation, but only at the behest of regulating authorities. Initially these two groups regulated themselves, all the while enjoying vast influence on all aspects of aviation, including documentation—or lack thereof.

And here it is 2016. We have maintenance reference documents coming out of every possible orifice from an unlimited number of providers: FAA, OEM, owner/operators, STC holders, vendors, suppliers ...  the list goes on and on. So the $64,000 question is: What documentation must we follow?


The quick answer—only regulatory documentation need be followed. Now wasn’t that easy! Unfortunately, FAA regulations (FARs) themselves can create confusion. The explanation of why can be a little tricky.

Since we are focusing on maintenance, I’ll begin with its official FAA definition. FAR Part 1 defines maintenance as “… inspection, overhaul, repair, preservation, and the replacement of parts, but excludes preventive maintenance.”

Our next step is to find a reference to perform those tasks. Lo and behold, we find our first reference in FAR Part 43: Maintenance, Preventative Maintenance, Rebuilding, and Alteration.


While Part 43 is the primary reference for mechanics in maintaining an aircraft, sub-section Part 43.13(a) addresses maintenance reference documents. To simplify, I’ll break down paragraph (a) into three segments.

The first segment states that each person shall use current OEM maintenance manuals (MM) or Instructions for Continued Airworthiness (ICA) when performing maintenance, alterations, or preventative maintenance. Note how quickly we gained two other qualifiers to our maintenance references: alterations and preventative maintenance. So much for the official definition.

The next segment describes the use of tools, equipment, and test apparatus to ensure completion to accepted industry standards, with a note to use any OEM recommended special equipment. We now have “industry standards” intermixed with OEM instructions and recommendations.

The final segment focuses on specific elements of Part 43.13(a): “…or other methods, techniques, and practices acceptable to the Administrator…or its equivalent acceptable to the Administrator.” These blanket statements allow the use of any acceptable reference or equipment a mechanic can get his hands on to complete the task.



Well, if a mechanic wants to use the term “rebuilt” in his maintenance entry he will need to follow guidance in Part 43.2. It is similar in tone to Part 43.13(a), but it includes several specific requirements … yet another twist.

Part 43.2 also includes overhauling, which is inclusive to the Part 1 definition of maintenance. So on face value, if a mechanic wishes to “overhaul” an item, but not use that term in his maintenance entry, he would follow guidance in Part 43.13(a). However, if the mechanic indicates “overhaul” in the paperwork, he must follow Part 43.2.

Still with me? Here we have the mechanic’s most fundamental maintenance reference, and in one paragraph we are given three far-reaching options to cover a somewhat expanded definition of maintenance. It’s flexibility and confusion at its best … or not. Can you imagine what the FARs would look like if they listed every possible option?


To get back on track, I think we can agree on what OEM references are, but what about “industry standards” and “acceptance by the Administrator.” For the first one, unfortunately no single book of industry standards exists. Furthermore, Part 43.13(a) doesn’t even state the use of aviation industry standards. If you dig deeper into the FAA website you can see various examples of standards used: Society of Automotive Engineers (SAE), Radio Technical Commission for Aeronautics (RTCA), and National Aerospace Standards (NAS), to name a few.

As for “acceptance by the Administrator,” we see this reference throughout the FARs. But in the case of Part 43.13(a) the burden of proof falls on the FAA to determine if a mechanic’s reference is not acceptable. Several Letters of Interpretation (LOI) issued by the FAA Chief Counsel’s office indicate a mechanic’s reference is acceptable, unless that reference has been changed or invalidated by FAA.

So far so good, but what if a mechanic has to perform a task not found in the available OEM maintenance documentation? Say the Velcro is missing from the cabin overhead trim panel on a Bell 206B. Mechanic A reviews the Bell MM and can’t find a single reference on Velcro replacement. Undaunted, he goes to FAA AC 43.13-1B. Likewise, no reference. (OMG!) He ponders getting a Letter of No Technical Objection from Bell, or developing his own procedure and getting it “approved” by Bell.

However, Mechanic B gets off break and sees the Velcro is missing. He procures a length of new Velcro and glues it to the trim panel using 3M Contact 10. He finishes by making a logbook entry describing replacement of the Velcro and signs his name and certificate number.

So who’s right? They both are. While you may challenge this example as being too basic, it does illustrate how the regulation works.

What if the local FAA aviation safety inspector (ASI) comes by and questions the sign off on the Velcro replacement? Mechanic B has two options: (1) He can state he followed the “hook and pile tape” replacement instructions in the Airbus AS355 MM, an FAA acceptable reference; or (2) He used Velcro and glue of equal OEM quality as referenced under Part 43.13(b).


Part 43.13(b) is not technically a maintenance reference. Rather, it’s more a performance regulation on how a mechanic carries out maintenance. It gave Mechanic B above the option of using manners and materials of such quality to ensure the aircraft is “at least equal to its original or properly altered condition.”

I know, big gray area. And some even contest its general use outside of “aerodynamic function, structural strength, resistance to vibration and deterioration, and other qualities affecting airworthiness.”

On the other hand, regulations and other reference documents are there for the purpose of assisting and supporting mechanics in maintaining aircraft to minimum requirements and airworthiness—especially when mechanics are confronted with a minor repair or alteration. So, if it’s good enough for a major item like aerodynamic function, you can bet it’s a good reference for Velcro replacement.


Part 43.13(c) applies to the majority of helicopter mechanics: those working for Part 135 operators. A special provision contained in this paragraph allows holders of an Air Carrier Certificate (Part 121, 129, 135) to use the maintenance portion of their required Air Carrier manual(s) as a means of compliance for Part 43.13.

This is why a number of helicopter mechanics are not exposed to Part 43.13(a) and (b) on a regular basis. Under an Air Carrier Certificate, mechanics are required to use those associated manuals as their main maintenance reference. Although these air carrier manuals may indicate use of OEM MMs, they often contain sections on specific consumables, or alter existing OEM practices to something more specialized to the operator. They may even contain a procedure to replace Velcro on any aircraft under the Air Carrier Certificate … making life all the merrier.

Remember, not every task is in OEM or operator documentation. Part 43.13(a) and (b) are applicable to air carrier operations. Simply because mechanics work for a Part 135 operation doesn’t mean they have to exclude other regulatory options. It’s quite the opposite.

The regulations work from the bottom up. For maintenance it’s Part 43 to Part 91 to Part 135 ... to whatever. Each associated FAA regulation builds on or interacts with its previous applicable regulation. To demonstrate this we will bring inspections into our reference jungle when we return in Part Two of this article. Stay tuned!

About Scott Skola: After 32 years maintaining helicopters in various capacities, Skola concluded a full-time career with a major operator in 2014. When not pursuing future writing projects, he can still be seen around the flight line providing third-party maintenance oversight, audit assistance, litigation support, and technical research/writing services. Scott can be contacted at [email protected].

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