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Many references below are hyperlinked in Rotorcraft Pro’s digital editions. It’s another good reason to visit RotorcraftPro.com and also download our free mobile apps from Amazon, Apple, and Google.

The March/April 2016 issue carried Part 1 of this series. Back then we left off with FAA Part 43.13 as our primary reference in performing maintenance on aircraft. We now dive a little deeper by introducing inspections to the work flow.


Though inspection is part of the FAA definition of maintenance, I kept it separate for three reasons:

One, inspections have their own set of performance rules in Part 43. Two, in the course of aircraft maintenance, other than inspection, the mechanic selects the reference. In the case of an inspection program, the owner/operator selects the reference under authority in Part 91. And three, once an inspection program/reference has been selected, the mechanic is required by regulation to follow that reference.

I’m sure everyone agrees the inspection process is an expensive recurring cost in maintaining an aircraft. And although it would be unwise for an owner/operator not to consult with a mechanic prior to selecting an inspection program, it happens. Even though a mechanic may know a more efficient program to follow, Part 43.15 mandates the mechanic to follow the selected inspection program.

PART 43.15

This part directs each person who performs an inspection to meet all applicable airworthiness requirements and follow instructions set forth in the inspection program. There are no options of OEM recommendations, industry standards, or the administrator. This part also includes inspection requirements for rotorcraft, annual/100 hour inspections, and progressive inspections.

Furthermore, Part 43.15 states if an inspection is under Part 135 or Part 121, the mechanic shall follow the instructions and procedures listed under the air carrier program. Part 43.15 also gives Part 135 operators the authority to use non-company mechanics and repair stations to accomplish air carrier aircraft inspections.

So, when a mechanic is assigned to comply with an inspection, it is Part 43.15 directing him to follow a specific inspection; not the applicable Part 91, 121, or 135 under which the inspection was selected by the owner/operator.

Now, it gets a tad tighter under the next part.

PART 43.16

Welcome to the wonderful world of FAA-approved references. Prior to this part, our reference documents fell under the FAA acceptable category. The actual FAR (Part 43.13) is regulatory, but the references it mentions in general (e.g., MM, ICA, industry standards, etc.) are only acceptable.

At the FAA approval level, everyone must obey the rule. Part 43.16 is specific and mandatory to the word. Any requirement listed in an airworthiness limitations section of any OEM MM or ICA shall be complied with as indicated.

Part 43.16 does allow for an owner/operator to include these limitations in their FAA-approved Part 135/Part 121 operation specifications (OpSpec) or FAA-approved inspection program under Part 91.409(e), but that’s the only exception. Percentage-wise, few of our references are approved by the FAA. For example, although chapter 4 is approved in a Bell MM, the remaining MM chapters are only acceptable.

This finishes what I call the reference foundation. A mechanic can maintain an aircraft using the guidance solely from Part 43. No question. But what about the other available maintenance references?

The Other Books

Whereas industry standards are governed by their respective associations, all other maintenance reference documentation falls under FAA oversight. This article—let alone the entire magazine—is not large enough to list every FAA acceptable reference available to a mechanic.

To complicate matters, there is no FAA definition of “acceptable.” In place of an official definition, I’ll use a comparison of minor repair to major repair as an analogy. A minor repair is any repair which is not a major repair. So by my definition, an acceptable reference is any reference which does not need FAA approval.

In general, if a reference is used within the aviation industry, it is acceptable. It is similar to a document from the SAE; an acceptable reference simply needs a verifiable origin. Using Uncle Louie’s handwritten Huey notes from his days in Da Nang may not pass the acceptable test … that is, unless they were copied from a verified source. (That would be a stretch!)

Numerous references exist: service bulletins, alert service bulletins, service letters, FAA advisory circulars, component manuals, standard practices manuals, and installation instructions, to name a few. Other lesser known or seldom used references are also acceptable: military specifications, FAA Form 337s, non-aircraft OEM documentation, and even the Standard Aircraft Handbook. Specific examples include Whelen lighting instructions, Honeywell VXP manuals, and even instructions on a glue can listed in the MM consumable section. Remember, if you’re not sure a reference is acceptable you can always call your local, friendly ASI for guidance.

When Current Is Not Current

We now enter the dark side of this topic. A path so obscure even the feds get lost. It’s the esoteric underground in working with regulations and references. OK, I’m exaggerating, but sometimes you have to wonder what they were thinking!

Part 91.409(f)(3) gives us a prime example:

(3) A current inspection program recommended by the manufacturer.”

No mixed words there. We learned the owner/operator selects the inspection program and a mechanic shall follow it. We see a current program must be used.


The word “current” has several different meanings within the FAA as opined by the FAA chief counsel. LOI Mgr. AFS is one of several LOIs which explains this legal opinion.

For example, Owner A purchased a new Bell 206 in 1975 and selected to use Bell’s then-current inspection program. The aircraft comes in for its 100 hour inspection in 2016. The mechanic prints out a current copy of Bell’s program per Part 43.15 and Part 91.409(f)(3). All good, but ... the owner requires you use his 1975 Bell forms. Who’s right?

Per the chief counsel, the owner is. In this and similar cases, the definition of “current” is backdated to the program current at the time of purchase. The LOI even extends this definition to include current OEM maintenance instructions referenced in Part 43.13(a)! (Like I’ve always said, “Knowledge is king.”) Now, if Owner A sells the 206 to Owner B in 2016, the new owner will have to use the Bell inspection program current at the time of his 2016 purchase.

Is this too much? Understand that no entity except the FAA, through the Administrative Procedure Act (APA), can make new rules on the flying public. Allowing an OEM to change their inspection program at will without oversight could be burdensome to an owner/operator using that program. Imagine the repercussions if an OEM decided to require replacement of all exterior hardware every 100 hour inspection?

Also, the word “current” has different regulatory meanings when applied to a rotorcraft flight manual and certain documentation required by air carriers and repair stations. Thankfully, that is another topic for someone else to write.

Just when you thought we had a handle on this by-the-book thing, it’s now time for a word from our sponsor...

Mandatory References

We have built a solid infrastructure of maintenance references. We’re on the downhill side heading for the hangar. But, wait! Which parts do you consider mandatory? Go ahead, guess. (You don’t have to use the word “current.”)

I’ll quote direct from FAA Order 8620.2, Applicability and Enforcement of Manufacturer’s Data:

“…However, unless any method, technique, or practice prescribed by an OEM in any of its documents is specifically mandated by a regulatory document, such as Airworthiness Directive (AD), or specific regulatory language such as that in § 43.15(b); those methods, techniques, or practices are not mandatory.”

The Order goes on to define TCDS information and notes. So to sum it up, unless your reference is in the form of specific regulatory language (FAR), an Airworthiness Directive (AD), or part of an FAA-approved airworthiness limitations section, none of our previous references are mandatory nor enforceable by the FAA.

There you have it. The proverbial “By the Book 101.” We began at the bottom and circled right back to our acceptable reference roots. It’s not rocket science. (That would be FAA Part 400 through 460.) So the next time you’re asked which book you’re following, turn around and give their chain a yank by inquiring which book they think it should be.

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. Contact him at [email protected].

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