1. Purpose of This Notice. This notice clarifies the differences between overhaul processes and the inspections that make up required inspection programs
under Title 14 of the Code of Federal Regulations (14 CFR) part
2. Audience. The primary audience for this notice is Flight Standards District Offices (FSDO), certificate management offices (CMO), and Airworthiness
aviation safety inspectors (ASI) with oversight responsibilities for certificate holders operating under part
secondary audience includes Federal Aviation Administration (FAA) headquarters (HQ) and Flight Standards Service (AFS) divisions and branches in the regions.
4. Background. There have been several recent issues surrounding the interpretation of whether compliance with the manufacturer’s recommended
time between overhaul (TBO) intervals are required under part
5. Discussion. The term “maintenance” is defined in 14 CFR part
“Maintenance means inspection, overhaul, repair, preservation, and the replacement of parts, but excludes preventive maintenance.” While this definition has been around
for a very long time, differences between some of the elements that make up maintenance (such as inspection and overhaul) have not always been clearly understood. In this notice, we
discuss the key differences between inspection and overhaul and the implications of those differences.
a. Inspections. Inspections are visual examinations and/or manual checks to determine the condition of an aircraft or component. An inspection can range
from a routine visual examination to a detailed inspection involving complete disassembly and/or the use of complex inspection aids, such as X-ray, ultrasonic, eddy current, or magnetic
(1) Inspection Program Content. Not all tasks classified or described as “inspections” are part of the inspection “program.” Inspection
programs refer to a list of scheduled inspection items and associated intervals whose main purpose is to determine the condition of the aircraft and its components (airframe, engines,
propellers, rotors, appliances, survival equipment, and emergency equipment). In other words, they are scheduled items done at a defined interval to check for hidden damage and continued
serviceability. Typically, unscheduled inspections constitute a maintenance action, such as when damage is known and a discrepancy must be cleared. These inspections are event-driven from
a known malfunction or discrepancy, such as a hard landing or prop strike. The intent of these inspections is to determine the level of damage
so that maintenance actions may be taken to restore the aircraft to a known good
condition. Similarly, inspections that are part of a larger maintenance process, such as inspections performed during an overhaul, are also classified as a maintenance action and not a
part of an inspection program for the reasons stated above.
(a) Inspection Programs vs. Maintenance Programs. Maintenance personnel should not confuse an inspection program with the elements that make up a more extensive
maintenance program. An inspection program will only capture a list of scheduled inspections whereas a maintenance program will encompass many elements, to include inspections, overhaul
requirements, repair schemes, Corrosion Prevention and Control Programs (CPCP), and the scheduled replacement of parts.
(b) Overhauls are Maintenance. By definition, overhauls are a form of
maintenance, not inspection, and are not included in an inspection program. Overhauls
are part of the maintenance program. Part
are not required to comply with a manufacturer’s entire maintenance program; as such, overhauls are not mandatory for part
(c) Part Replacements. Scheduled replacement of parts (such as filters, seals, etc.) are also maintenance. Part replacements is a part of the overall maintenance
program and are not to be included in an inspection program. However, if an inspection of an item is destructive in nature and mandates the replacement of the part after the inspection, it
is still appropriate to include these items in the inspection program.
(d) Type Certificate Data Sheet (TCDS) Notes. FAA legal interpretations state TCDS notes containing overhaul limits are not mandatory under our regulations. TCDS
notes define the design of the aircraft and how that design meets the certification basis it is certificated under, not to define how it is maintained. Some manufacturers have attempted to
put information into a TCDS that defines requirements for continuing maintenance of their aircraft; however, such information is not regulatory and is outside the purpose of the TCDS notes.
Information not specifically referencing the design and configuration of an aircraft, such as ongoing maintenance requirements, is inappropriate and not binding on the owner/operator in a
regulatory sense. The Aircraft Certification Service (AIR) has published FAA Order
Certificate Data Sheet (TCDS) Notes, that explains the intent and design of TCDS notes in greater detail, including descriptions of appropriate content.
(e) Differences Between Operating Rules. Although we have focused on part
it is prudent to mention that many other operating rules do require compliance with some form of a maintenance program (beyond the inspection program requirements). Title 14 CFR part
or fewer) requires compliance with at least the manufacturer’s recommended maintenance program. (Refer to part
or more) and 14 CFR part
a Continuous Airworthiness Maintenance Program (CAMP), which includes a more extensive maintenance program. (Refer to §§
135.443; and part
only form of scheduled maintenance required under 14 CFR part
compliance with the manufacturer’s recommended overhaul periods. (Refer to part
are only required to comply with scheduled maintenance items if they elect to develop their own CAMP under part
are only required to comply with overhaul limits if included in their CAMP program developed per §
Note: Certain part replacements (life-limited parts, parts affected by Airworthiness Directives (AD), etc.) remain mandatory for aircraft operated under part
to other regulatory requirements, even though they are not part of the inspection program.
Note: While scheduled items of maintenance (other than inspections) are not required to be included in the inspection program, they become mandatory if
the operator chooses to include them in an Approved Inspection Program (AIP), such as one developed under §
However, items of scheduled maintenance, that are not inspection tasks,
which the manufacturer has inserted in its inspection programs are not mandatory to operators utilizing a program under
(2) Manufacturer’s Inspection Programs. Recently, there have been questions surrounding what is specifically required under §
what constitutes a program recommended by the manufacturer. First, consider what an aircraft manufacturer is required to provide as part of the certification process in the certification
rules, which includes instructions for continued airworthiness (ICA). All certification rules have nearly identical wording, which specifies the ICA must be in the form of a manual or
manuals that must provide for a practical arrangement. For example, 14 CFR part
G specifies the requirements for the ICA, prepared by the aircraft manufacturer. Additionally, the ICA must contain the following information:
“(b) Maintenance instructions. (1) Scheduling information for each part of the airplane and its engines, auxiliary power units,
propellers, accessories, instruments, and equipment that provides the recommended periods at which they should be cleaned, inspected, adjusted, tested, and lubricated, and the degree of
inspection, the applicable wear tolerances, and work recommended at these periods. However, the applicant may refer to an accessory, instrument, or equipment manufacturer as the source of
this information if the applicant shows that the item has an exceptionally high degree of complexity requiring specialized maintenance techniques, test equipment, or expertise. The
recommended overhaul periods and necessary cross reference to the Airworthiness Limitations section of the manual must also be included. In addition, the applicant must include an
inspection program that includes the frequency and extent of the inspections necessary to provide for the continued airworthiness of the airplane.”
Being a program created by the aircraft manufacturer, an owner or operator does not need to research every engine, propeller, appliance, and equipment manual
for potential inspection items. The certification rules requires the aircraft manufacturer provide ICA for their aircraft, which includes required inspection programs for those aircraft,
including installed equipment. Additionally, modifying the aircraft, such as through a Supplemental Type Certificate (STC) or field approval, does not make a manufacturer’s inspection
program inappropriate. In such cases, the owner/operator must comply with the inspection program recommended by the manufacturer as well as any identified inspection program items from
the ICA of aftermarket equipment and/or modifications. This is no different than compliance with additional inspections called out in applicable ADs.
(3) Approved Inspection Programs (AIP). There are several rules requiring aircraft to have an AIP, but the programs are basically identical in structure and
required content. For example, we typically refer to an inspection approved under §
an Approved Aircraft Inspection Program (AAIP), while we call an inspection program approved under §
an AIP. While the terminology may vary slightly, the intent and design are the same. The same can be said for §§
If the rule requires the inspection program to be approved, it can all be
generically referred to as the AIP for that aircraft. Note, though, some
operating rules also require operators to comply with a maintenance program,
which are either the manufacturer’s recommended items or something developed by the operator (depending on the rule). This is in addition to the
inspection program requirements. Finally, we have rules that allow, or require, a CAMP. These are all-inclusive programs that have even more requirements that the basic maintenance and
inspection program requirements required elsewhere.
(4) Functional Checks. Functional checks are a form of an inspection and can be called for in a number of different situations, which can make classifying
them difficult. They can be included in an inspection program, which would make them a mandatory inspection. Or they can be performed as part of the return to service after a specific
maintenance activity, which makes them part of the maintenance procedure and excludes them from the inspection program. Additionally, they could be part of a pilot’s pre- or
post-flight procedure and not classified as maintenance items at all. Perhaps the best way to classify functional checks is to reference the source document. If it is listed in the
inspection program, it is a Required Inspection Item (RII). If it is listed in an Aircraft Maintenance Manual (AMM), it is an item of maintenance; and if it is listed in an Aircraft
Flight Manual (AFM) or pilot’s operating handbook (POH), it is an operation item.
b. Overhaul. The term “overhaul” is mentioned in
only a few places in the rules, and is not really defined. Title 14 CFR part
states that an overhaul consists of disassembly, cleaning, inspection, repair, reassembly, and testing. However, several FAA legal interpretations have stated all of these steps are not
necessarily required for a maintenance action to be an overhaul. In fact, the words “as necessary” appear after repair, and it is not clear in the text if that applies
only to the word “repair,” as it would seem, or to all previous listed items. In any case, the FAA has taken the position that only the steps that can logically be performed would be
required to call an item “overhauled.” For example, a part that cannot be disassembled without destroying it, such as a turbine blade, can still be considered overhauled
if following the manufacturer’s overhaul instructions.
(1) Mandatory or Not. While the concept of part
not having to comply with manufacturer’s TBO limits is well known, the reasons behind it have not been very well documented, although, Advisory Circular (AC)
Engine Power-Loss Accident Prevention and Trend Monitoring, has provided
guidanmce since 1998. The regulations require that part
have an “inspection program” of some sort. The program could be a 100-hour, annual, manufacturer’s recommended inspection program, or one of the operator’s own
design, depending on aircraft type. However, part
or fewer) operators must have a “maintenance and inspection program.” It is this extra mention of a “maintenance” program that makes TBOs required in part
some other operational rules), but not for part
the definition of maintenance, “Maintenance means inspection, overhaul, repair, preservation, and the replacement of parts, but excludes preventive maintenance.” In the
definition, “overhaul” and “inspection” are separate items, showing overhauls cannot be inspections, rather they are both unique forms of maintenance. Remember,
overhauls are a maintenance process, not an inspection process.
(2) Overhaul vs. Inspection. The difference between an overhaul and the inspections performed as part of an inspection program is the purpose of the action.
(a) Inspection Program. The primary purpose of an inspection program is to perform examinations to determine the condition of an aircraft or component so any
necessary repairs can be made. Essentially, inspection programs are focused on finding hidden problems that may impact airworthiness. In a typical inspection, items are not replaced unless
they are actually defective.
(b) Overhaul. The primary purpose of an overhaul is
to restore an article to a known good condition that will give a reasonable assurance of operation for a
specified amount of time, referred to as the “time between overhauls (TBO).” While inspecting individual components is an integral part of the overhaul, this is just one part
of the overall overhaul (maintenance) process. For example, during the inspection phase in an overhaul, a mechanic may be prompted to replace a part after inspecting it, even though it is
not broken and is still performing its intended function. But, the wear might be such that the manufacturer has confidence the part would not make it to the next overhaul period. These
tolerances are typically identified by the manufacturer as the “overhaul limits.”
(3) Compliance with Manufacturer’s Service Bulletins (SB). Manufacturers publish many forms of maintenance-related information, using varying names, such
as Service Bulletins (SB), Service Instructions (SI), etc. We will refer to them hereafter as SBs for simplicity. These documents
typically contain information that supplements a manufacturer’s published
maintenance manual or ICA. When determining whether a manufacturer’s SB is mandatory or not, further explanation needs to be considered before answering.
There are two parts to this issue; the timeframe that is sometimes prescribed, and the instructions themselves.
(a) Basic Part
some exceptions (as described in the following subparagraphs), compliance with manufacturer SBs
is not required to be accomplished on any specific timetable
for basic part
However, once the operator chooses to perform an SB, they must follow the methods, techniques, and practices prescribed within, unless they are using some other methods, techniques, and
practices acceptable to the FAA. Recall that SBs often provide supplemental
maintenance information, a topic addressed by §
requires that each person performing maintenance, alterations, or preventive maintenance use the methods, techniques, and practices prescribed in the current manufacturer’s
maintenance manual or ICAs prepared by its manufacturer, or other methods, techniques, and practices acceptable to the Administrator. However, note that
§ 43.13 states that the “methods, techniques, and practices” must be followed, not the specific timeframes or schedules defined by the manufacturer. Also, the rule specifically
addresses people who are “performing” maintenance, so the rule
applies only once a maintenance activity has been initiated, and the rule does not require a certain
maintenance activity to be “scheduled.” Therefore, once a maintenance action is initiated, maintenance personnel must follow the manufacturer’s instructions (or again,
some other instructions acceptable to the FAA), but basic part
can choose not to perform the SB at their discretion, unless it has been
mandated by an AD or other rule.
(b) Certificate Holders Other than Basic Part
dealing with certificate holders, determining whether a manufacturer’s SB is mandatory or not gets more complicated. For example, §
that operators comply with the manufacturer’s recommended maintenance programs, or a program approved by the Administrator. Operators who are required to comply with a maintenance
program of some type are required to comply with SBs that are explicitly defined as part of that program. Likewise, operators with a CAMP must have a program that covers maintenance,
preventive maintenance, and alterations. However, with a CAMP, the certificate holder can customize the program, to include what they have to accomplish in that program, as long as what
they propose is acceptable to the FAA. As a result, some SBs require
compliance at defined intervals, while some do not; it depends on the purpose of the SB and
whether it is
referenced as part of the required maintenance program. The important distinction here is that a maintenance program is required, unlike under
part 91, where
only an inspection program is required. See the discussion in the inspection section for more on this distinction.
(c) Other Situations. The following describe situations when compliance with the prescribed intervals of an SB would be mandatory:
1. All or a portion of an SB is incorporated as part of an AD.
2. The SB is incorporated directly or by reference into an FAA-approved inspection program, such as an AIP or a CAMP.
3. The SB is listed as an additional maintenance requirement in the certificate holder’s operations specifications (OpSpecs).
4. The SB is part of the FAA-approved Airworthiness Limitation Section (ALS) of the manufacturer’s manual or the type
certificate (TC). However, compliance with a new or revised ALS issued by a design approval holder (DAH) or other entity, as a type design change, is not mandatory for in-service aircraft
operating, per part
it is mandated by one of the other situations above. Of course, operators
can always elect to comply with the new or revised limits voluntarily.
6. Disposition. We will incorporate the information in this notice into FAA Order 8900.1 before this notice expires. Direct your questions or comments
concerning this notice to the Aircraft Maintenance Division (AFS‑300) at 202-267-1675.
ORIGINAL SIGNED by
/s/ John Barbagallo
Deputy Director, Flight Standards Service