> ![](media/image1.png){width="0.4625in" height="0.4625in"}
>
> U.S. Department
>
> of Transportation
>
> **Federal Aviation**
>
> **Administration**
>
> August 11, 2006
>
> [CERTIFIED MAIL -- RETURN RECEIPT REQUESTED]{.underline}
>
> Mr. Michael D. Busch
>
> 1127 Hetrick Avenue
>
> Arroyo Grande, California 93420
>
> Re: [Request for Interpretation of 14 C.F.R. § 43.13(a) and part 43,
> appendix D]{.underline}
>
> Dear Mr. Busch:
>
> On November 10, 2005, you requested, via E-mail, an interpretation of
> the above-referenced regulations in the context of whether a procedure
> specified as "required" in a service bulletin issued by a manufacturer
> is mandatory under the Federal Aviation Administration's (FAA)
> maintenance regulations (14 C.F.R. part 43) for an aircraft operated
> only under 14 C.F.R. part 91. In general, unless a service bulletin is
> incorporated either directly or by reference into a document that
> makes its requirements mandatory, the answer is no.
>
> Based on the information you provided, we see nothing that indicates
> the service bulletin referenced in your inquiry is mandatory under the
> FAA's regulations. Nevertheless, you opined that manufacturer-issued
> service bulletins are mandatory under the regulations if they specify
> a particular procedure or method of doing an item required by the
> regulations---in this case a cylinder compression test performed
> during an annual or 100-hour inspection required by
>
> 14 C.F.R. part 43, appendix D. In support you stated that 14 C.F.R. §
> 43.13(a) "requires that it \[maintenance, specifically, the
> compression test\] be done in accordance with manufacturer's
> instructions . . . ." You also stated: "Furthermore, 14 CFR 43.13(a)
> requires that the maintenance shall be done using methods, techniques
> and practices prescribed by the manufacturer or other methods,
> techniques and practices acceptable to the Administrator."
>
> The text of section 43.13(a), however, states in pertinent part: "Each
> person performing maintenance, alteration, or preventive maintenance
> on an aircraft, engine, propeller, or appliance shall use the methods,
> techniques, and practices prescribed in the current manufacturer's
> maintenance manual or Instructions for Continued Airworthiness
> prepared by its manufacturer, or other methods, techniques, and
> practices acceptable to the Administrator." The text of that section
> provides a person performing maintenance, alteration, or preventive
> maintenance on a product with a number of permissible options when
> performing that work. A manufacturer may legitimately incorporate a
> service bulletin into one of its maintenance manuals by reference. If
> it
>
> does so, the data specified, and the method, technique, or practice
> contained therein, may be acceptable to the Administrator. However,
> unless the method, technique, or practice prescribed
>
> by a manufacturer is specifically mandated by a regulatory document,
> such as an Airworthiness Directive, its contents are not mandatory.
>
> Your specific question concerns the application of a service bulletin
> issued by an engine manufacturer to an inspection item required by 14
> C.F.R. part 43, appendix D, "Scope and Detail
>
> of Items (As Applicable To The Particular Aircraft) To Be Included In
> Annual And 100 Hour Inspections." The inspection item at issue is at
> paragraph (d)(3) of the appendix, which states:

(d) Each person performing an annual or 100-hour inspection shall
    inspect

> (where applicable) components of the engine and nacelle group as
> follows:
>
> \* \* \* \* \*
>
> \(3\) Internal engine---for cylinder compression and . . . . If there
> is weak
>
> cylinder compression, for improper internal condition and internal
> improper
>
> tolerances.
>
> According to your inquiry, on March 28, 2003, Teledyne Continental
> Motors (TCM) issued Service Bulletin SB03-3, titled "Differential
> Pressure Test and Borescope Inspection for Cylinders." As you stated,
> the service bulletin "transmits TCM's current guidance concerning how
> differential pressure tests (compression tests) of cylinders are to be
> done on TCM engines, and supersedes TCM's previous guidance on the
> subject (service bulletin M84-15)." You note that a major difference
> between the two service bulletins is that the later bulletin requires
> that a borescope inspection be done in conjunction with the
> differential pressure test. The above-referenced paragraph of appendix
> D, though requiring an inspection for improper internal condition and
> tolerances if the compression test shows weak cylinder compression,
> does not specify a particular method for doing so, *i.e*., it does not
> require a borescope inspection as the means for determining the
> internal condition of the cylinders. Other methods could be used, for
> example, cylinder disassembly and inspection. In fact, if no weak
> cylinder compression is observed, no further cylinder inspection is
> required under that paragraph of appendix D.
>
> In your example, although it would be good practice in view of the
> manufacturer's recommendation to do a borescope inspection, its
> performance would not be required. If the borescope inspection were
> not performed, the engine inspection would nevertheless have to meet
> the criteria specified in section 43.13(a), *i.e*., it would have to
> be done in accordance with the "methods, techniques, and practices
> prescribed in the current manufacturer's maintenance manual or
> Instructions for Continued Airworthiness prepared by its manufacturer,
> or other methods, techniques, and practices acceptable to the
> Administrator." No violation of the regulation would be incurred if
> the borescope inspection were not performed provided the engine
> inspection was accomplished using methods, techniques, and practices
> acceptable to the Administrator.
>
> A contrary result would lead to serious legal objections. It would
> mean that our regulations effectively authorize manufacturers to issue
> "substantive rules," as that term is used in the Administrative
> Procedures Act (APA), *i.e.*, it would enable them to impose legal
> requirements on
>
> the public. This would be objectionable for at least two reasons.
> First, the FAA does not have authority to delegate its rulemaking
> authority to manufacturers. Second, "substantive rules" can
>
> be adopted only in accordance with the notice-and-comment procedures
> of the APA, which does not apply to manufacturers.
>
> In sum, the fact that "'TCM requires a cylinder borescope inspection .
> . . ,'" does not make the borescope inspection mandatory from a
> regulatory perspective. If TCM were to incorporate this inspection
> into its current maintenance manual or Instructions for Continued
> Airworthiness and if compliance with either of those documents were
> specifically mandated by regulation, or the FAA were to incorporate
> SB03-3 into an AD or some other regulatory document, then the
> borescope inspection would become mandatory.
>
> We hope the above answer responds to your needs.
>
> Sincerely,
>
> Rebecca MacPherson
>
> Assistant Chief Counsel for Regulations
>
> Office of the Chief Counsel