Legal Interpretation of 135.421(b), in particular the term "required maintenance instructions."

The FAA has published a  Legal Interpretation Memorandum as a response for a request defining the interpretation of 14 C.F.R. § 135.421(b), in particular the construction of the term "maintenance instructions."  The full Memoransum is attached below but here is the text from the document

This responds to your January 6, 2017 request for an interpretation of 14 C.F.R. § 135.421(b), in
particular the construction of the term "maintenance instructions." First, you asked what
constitutes "maintenance instructions" as the term is used in the regulation. Second, you asked
whether "manufacturer's (engine, propeller, rotor, and each item of emergency equipment)
service bulletins, service letters, service instructions, etc., that specifically address a maintenance
procedure [are] considered to be part of the 'manufacturer's maintenance programs' and thus
mandatory under this rule?"

As to your first question, i.e., what would constitute maintenance instructions, we believe that, in
the absence of a regulatory definition, the term should be given its plain meaning-something
that would instruct (teach) how to perform a maintenance task or procedure. To borrow from
your second question, these could include any or all of your examples. This could encompass
various documents issued by a manufacturer, such as a maintenance manual, service bulletins,
service letters, service instructions, etc.

Your second question asks whether, in the context of § 13 5 .4 21 (b ), those foregoing documents
that specifically address a maintenance procedure are considered to be part of the manufacturer's
maintenance programs [referenced in paragraph (a) of the regulation] and thus mandatory for the
part 135 operator that chose the "manufacturer's recommended maintenance programs" in lieu of
the alternative option of a program approved by the administrator. The answer is yes, because
paragraph (b) provides that a manufacturer's maintenance program [which is made mandatory by
paragraph (a) for operators who choose that option] 1 "is one contained in the maintenance manual
or maintenance instructions set forth by the manufacturer ... for the aircraft, aircraft
engine, propeller, rotor, or item of emergency equipment."

You provided two factual scenarios for our office to consider in answering the questions.

Scenario #1: The Part 135 certificate holder adopts the manufacturer's
maintenance program/instructions on a specific date and will maintain their
aircraft to that program up to that date only. In this scenario, would the
certificate holder only be required to accomplish the maintenance related
service bulletins (SB), service letters (SL), or service information (SI) that
is included in the manufacturer's maintenance program up to the date they
adopted this maintenance program? Or would the certificate holder have
to continue to adopt future SB, SL, or Sis?

Answer: The certificate holder would be required to follow the maintenance procedures
contained in those manufacturer's documents that were in effect on the date the certificate holder
adopted the maintenance program. Our reasoning is explained in previous legal interpretations
issued by this office. 2 While those interpretations addressed different regulations, the same
reasoning applies. Under§ 135.42l(a), the certificate holder has the option of selecting either a
manufacturer's recommended maintenance program for the aircraft's engine, propeller, rotor,
and each required item of emergency equipment, or a program for those items approved by the
FAA. If the certificate holder chooses the first option, he or she is adopting a known
maintenance program then in existence, with knowledge of what it entails. With that adoption,
the certificate holder agrees to be bound by that existing program, in lieu of developing a
different program and seeking FAA approval.

Whereas the two referenced legal interpretations dealt in part with the application of the word
"current" in the respective regulations, the same legal principles apply here even though
§ 135.421(a) does not use that term. It is implicit that if a certificate holder adopts a
manufacturer's maintenance program, it is the one in effect (hence current) at the time of
adoption. Manufacturer's often make revisions to their recommended maintenance programs,
including issuing future SBs, SLs, and Sls, but under the circumstances set forth in Scenario # 1,
a certificate holder is not obligated to follow these later-issued procedures. As we observed in
our December 5, 2008 legal interpretation, if certificate holders were required to follow newlyissued
changes to their maintenance programs, these new requirements could impose financial
and other burdens on them for which they did not bargain. The exception would be if the
maintenance program selected by the certificate holder included a clause stating that the
program, if selected, necessarily includes all future-issued SBs, SLs, and Sis, etc.
2 See, e.g., Legal Interpretation of 14 C.

Moreover, if such compliance were required, this would be tantamount to private entities
issuing "rules" of general applicability without meeting the notice and comment
requirements of the Administrative Procedure Act (APA) (5 U.S.C. § 553), and the
public would not have had an opportunity to comment on these future requirements.
An interpretation of the regulation that would allow manufacturers unilaterally to issue
changes to their recommended maintenance programs that would have future effect on
owners of their products would not be legally correct. This would run afoul of the AP A.
It would mean that our regulations effectively authorize manufacturers to issue
"substantive rules," as that term is used in the AP A, i.e., it would enable them to impose
legal requirements on the public. This would be objectionable for at least two reasons.
First, and most significantly, 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. This reasoning is discussed in greater detail in our December 5, 2008
legal interpretation.

Scenario #2: The Part 135 certificate holder adopts the manufacturer's
maintenance program/instructions and state[ s] that they [sic] will maintain
their [sic] aircraft to the current manufacturer's program/instructions, without
a set date. In this scenario, would the certificate holder be required to accomplish
all maintenance related SB, SL, and Sis past, present, and future?

Answer: The certificate holder would be required to follow the maintenance procedures
contained in those manufacturer's documents that were in effect on the date the certificate holder
adopted the maintenance program, plus all the above-referenced later-issued maintenance-related
documents. That would be the maintenance program selected by the certificate holder, and
therefore it would be mandatory until such time that the certificate holder rejects that program by
(1) either electing to adopt the program in effect on that date of decision, or (2) by selecting the
second option provided by paragraph (a) of the regulation, i.e., developing its own program and
obtaining FAA approval of it.

You also attached five examples of Service Bulletins and Service Instructions that contain
maintenance procedures that are part of Lycoming's maintenance program/instructions, and ask
whether they are required to be accomplished by the certificate holder under§ 135.421(b). In
that regard, all three attached Service Bulletins are labeled MANDATORY by Lycoming.
Consistent with our answers above, if these documents are applicable and included in
Lycoming's maintenance program at the time a certificate holder adopts Lycoming's program
for its engine, the certificate holder would be obliged to follow them. A certificate holder would
not be required to follow any of them that are issued after the date of adoption of the program,
except as noted above. The fact that Lycoming has labeled the Service Bulletins as mandatory
has no regulatory effect unless they are already included in the engine maintenance program as
adopted by the certificate holder, or the FAA has issued an Airworthiness Directive or other rule
incorporating the service bulletin by reference.

Nevertheless, because Lycoming is probably in the best position to provide maintenance advice
on its products, a certificate holder would be well-served to follow the procedures in these
recommended documents even if they are not part of the adopted maintenance program. For
example, we note that Lycoming's Mandatory Service Bulletin No. 533C addresses actions that
should be taken in the event of a sudden engine stoppage. The Service Bulletin's Subject is:
"Recommended Action for Sudden Engine Stoppage, Propeller/Rotor Strike or Loss of
Propeller/Rotor Blade or Tip." We note that, although the procedures in the bulletin may not be
mandatory from an FAA regulatory perspective, following them would be an acceptable means
of addressing the damage at issue. Doing nothing after one of the listed damage events would
not be acceptable to the FAA, and doing something else would run the risk that the FAA would
find the attempted maintenance unacceptable.

This response was prepared by Edmund Averman, an attorney in the Regulations Division of the
FAA's office of the Chief Counsel, and coordinated with the Aircraft Maintenance Division
(AFS-300). If you have further questions concerning this response, please contact Mr. Averman
at 202-267-3073.

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