8900.1 CHG 569



Section 1  The Elements of Maintenance

3-591    OBJECTIVE. This section clarifies what constitutes maintenance and the differences between the elements that make up maintenance.

3-592    GENERAL. The term “maintenance” is defined in Title 14 of the Code of Federal Regulations (14 CFR) part 1, § 1.1 as “inspection, overhaul, repair, preservation, and the replacement of parts, but excludes preventive maintenance.” While this definition has been around for a long time, differences between the five elements that make up maintenance (i.e., inspection, overhaul, repair, preservation, and the replacement of parts) have not always been clearly understood. Also note that the definition of maintenance does not include the terms “rebuild” or “rebuilt.” Those functions are limited to the design approval holder (DAH) (i.e., manufacturer) with Production Certificate (PC) approval using its approved design (proprietary) data. Refer to 14 CFR part 43, §§ 43.3(j) and 43.7(d), and 14 CFR part 21, § 21.137(o). In this section we discuss key differences, the implications of those differences, and then discuss items that do not fall into these categories.

3-593    ADDITIONAL REGULATORY BACKGROUND. Part 43 identifies persons authorized to perform maintenance and the performance standards that must be followed. Regardless if maintenance, preventive maintenance, or alteration are being performed on an aircraft, engine, propeller, or appliance, each person shall use the methods, techniques, and practices prescribed in the current manufacturer’s maintenance manual or instructions for continued airworthiness (ICA) prepared by its manufacturer, or other methods, techniques, and practices acceptable to the Administrator. A manufacturer is required under § 21.50(b) to prepare a complete set of ICAs in accordance with (IAW) the applicable certification standard for the product (14 CFR parts 23, 25, 27, 29, 33, 35) that is acceptable to the Federal Aviation Administration (FAA). The purpose of the ICAs are to enable persons authorized by the FAA to maintain the continued airworthiness of the product and approve the product for return to service. The manufacturer is also required to furnish the ICA to each owner of the product and then make it available to persons requiring its use. This is how the certification rules interface with the continued airworthiness rules of part 43 and 14 CFR part 91. Also, as part of the ICAs, the manufacturer is required to provide airworthiness limitations (AWL). The FAA-approved Airworthiness Limitation Section (ALS) is required to be separate and distinct from the remainder of the FAA-accepted ICA document. All of the certification standards (e.g., parts 23, 25, 33, 35) require ICAs to have an ALS that states the following: “The Airworthiness Limitations section is FAA approved and specifies maintenance required under §§ 43.16 and 91.403 of Title 14 of the Code of Federal Regulations unless an alternative program has been FAA approved.”

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3-594    INSPECTION. There are many different types of inspections. Inspections are generally visual examinations and/or manual checks to determine the condition of an aircraft, product, or article. Inspections can range from general visual inspections, to detailed inspections involving inspection aids such as mirrors or magnifying lenses, to special detailed inspections which may require complete disassembly and/or the use of specialized techniques and/or equipment such as x ray, ultrasonic, eddy current, or magnetic particle equipment. Per the Maintenance Steering Group — 3rd Task Force (MSG-3), “general visual inspections” are a visual examination of an interior or exterior area, installation, or assembly to detect obvious damage, failure, or irregularity. “Detailed inspections” are an intensive examination of a specific item, installation, or assembly to detect damage, failure, or irregularity. And finally, “special detailed inspections” are an intensive examination of a specific item, installation, or assembly to detect damage, failure, or irregularity. It is also important to understand that inspection is only one element of maintenance; its tasks are different from other elements of maintenance that may be required as a result of performing an inspection, such as parts replacement and repair.

A.    Unscheduled Maintenance. An inspection event can also occur during unscheduled maintenance activities, which would not necessarily be associated with inspecting an aircraft under an inspection program. For example, a reported discrepancy (part 91) or mechanical irregularity (14 CFR parts 121/135).

B.    Use of ICAs. When an inspection is performed and a determination of airworthiness is required, ICAs must be used (or other data acceptable to the FAA) as stated in § 43.13. ICAs must be provided by the manufacturer IAW the applicable certification standards (e.g., parts 23, 25, 33, 35).

3-595    OVERHAUL. The term “overhaul” is mentioned in several places in the rules, but is not explicitly defined. An overhaul is comprised of several distinct maintenance activities, with the goal of restoring a product or article to a condition that will give a reasonable assurance of operation for a specified amount of time. From a regulatory perspective, § 43.2(a) states that an overhaul consists of disassembly, cleaning, inspection, repair, reassembly, and testing. However, overhaul of an article is defined as a unique maintenance activity in and of itself.

A.    Overhaul From a Certification Perspective. All of the certification standards (in their applicable appendixes) require the manufacturer to identify in their ICA the items requiring overhaul and their recommended overhaul periods. Parts 23 and 25 for aircraft certification standards only require maintenance manuals and do not require overhaul manuals. For parts 33 and 35 (engine and propeller products), the manufacturer is required to provide acceptable data in the form of an ICA to provide for the continued airworthiness of all engine and propeller parts to include overhaul and recommended overhaul intervals. Overhaul manuals are required and the content requirements are found in parts 33 and 35. Appendix A in parts 33 and 35 require both engine and propeller overhaul manual contents to contain “Details of repair methods for worn or otherwise substandard parts and components along with the information necessary to determine when replacement is necessary.”

B.    Overhaul Actions. Several FAA legal interpretations have stated that all of the actions listed in § 43.2(a) are not necessarily required for a maintenance action to be considered an overhaul. As stated, the FAA’s legal position is 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. However, the performance standards of § 43.13 must still be complied with. Specifically, unless using other methods, techniques, and practices acceptable to the Administrator, the overhaul process (e.g., methods, techniques, and practices) prescribed in the current manufacturer’s overhaul manual (i.e., ICA), must be followed when performing an overhaul.

C.    Regulatory Requirements. Since part 91 operators are not required to comply with a manufacturer’s entire maintenance program, overhauls are not mandatory for part 91 operators who operate strictly under part 91 (with some possible exceptions for part 91 subpart K (part 91K) in most situations. While the concept of part 91 operators not having to comply with certain overhaul intervals is well known, the reasons behind it have not been well documented. It should be noted, however, that Advisory Circular (AC) 20-105, Reciprocating Engine Power-Loss Accident Prevention and Trend Monitoring, has included a statement to this effect since at least 1998. From a regulatory perspective, part 91 operators are required to have an “inspection program.” The program could either be a 100-hour, annual, manufacturer’s recommended inspection, or one of the operator’s own design, depending on aircraft type. However, under other operating rules such as part 135, nine or less operators must have both an inspection program (part 135, § 135.419) and a program that covers additional maintenance requirements (§ 135.421). It is this extra mention of compliance with the manufacturer’s recommended maintenance programs (or a program approved by the Administrator) in § 135.421 that makes certain overhaul intervals required for part 135 (and similar operational rules), but not for part 91. As stated earlier, the definition of maintenance “…means inspection, overhaul, repair, preservation, and the replacement of parts, but excludes preventive maintenance.” In the definition, overhaul and inspection are separate elements, which shows that they are both unique forms of maintenance. Overhauls are a maintenance process.

1)    All of this notwithstanding, it is possible that an Airworthiness Directives (AD) could be issued that would require compliance with a specific overhaul limit. That would make that particular overhaul required regardless of the type of operation.
2)    Also, a reference to an overhaul in the ALS of the ICAs would make it mandatory. However, overhauls are typically not listed in the ALS because an overhaul process is a continued airworthiness function, not an AWL.

3-596    REPAIR. This function is a procedure executed IAW appropriate technical data to restore an aircraft, airframe, engine, propeller, appliance, or component part at least equal to its original or properly altered condition.

A.    Repair by Fabrication. When the replacement of a part involves complex operations such as riveting or welding, this is actually classified as a repair, not a part replacement. This can be seen in the language defining “airframe major repairs” in part 43 appendix A, paragraph (b) that states: “…repairs to the following parts of an airframe and repairs of the following types, involving the strengthening, reinforcing, splicing, and manufacturing of primary structural members or their replacement, when replacement is by fabrication such as riveting or welding, are airframe major repairs.” While the rule is specifically talking about airframe major repairs, note that part replacements involving riveting or welding would still be considered a repair even if they were determined to be a minor repair.

B.    Materials. If materials are substituted for the original materials, then there should be an equivalency determination made. If it cannot be determined that the materials are equivalent, then the repair might not be returning the aircraft or part at least equal to its original or properly altered condition. If that is the case, it may be an alteration rather than a repair.

C.    Technical Standard Orders (TSO). Simply repairing something to a TSO standard may not be returning the part at least equal to its original or properly altered condition. A TSO Authorization (TSOA) is an FAA design and production approval issued to the manufacturer of an article that has been found to meet a specific TSO. The TSO is a minimum design performance standard, not a repair standard. While the TSO is used by a TSOA holder to produce a part, there may be other characteristics to the part that are not defined in the standard. This design data may be proprietary to the manufacturer and it may not be possible to obtain the repair data without an agreement with them. Alternately, persons or maintenance organizations can develop their own repair data, but this can be costly depending on the regulatory requirements for the part in question.

D.    Fabrication. Fabrication of parts is often viewed as a maintenance activity. Technically, though, fabrication of parts is a manufacturing activity. In a few limited instances, owners and repair agencies are authorized to fabricate parts under the rules. These are defined in § 21.9(a)(5) and (6) which state: “(a) If a person knows, or should know, that a replacement or modification article is reasonably likely to be installed on a type-certificated product, the person may not produce that article unless it is—…(5) Produced by an owner or operator for maintaining or altering that owner or operator’s product; or (6) Fabricated by an appropriately rated certificate holder with a quality system, and consumed in the repair or alteration of a product or article in accordance with part 43 of this chapter.” It is important to understand that a mechanic or agency is not performing maintenance when fabricating parts, so the maintenance and airworthiness provisions of rules under part 43 or 14 CFR part 145 do not apply to these activities. However, it is still a maintenance activity when the fabricated parts are installed onto an article or into an aircraft. It is also a maintenance activity when the product or article is being repaired through fabrication methods such as riveting or welding.

3-597    PRESERVATION. Preservation is a specific set of maintenance actions that are accomplished for the purpose of maintaining the inherent design capabilities of the product or article. There are many forms of preservation. This includes everything from lubrication, such as oils and grease, to the application of preservative or protective coatings. However, not every type of preservation is classified as maintenance because some tasks have been specifically identified as items of preventive maintenance in part 43 appendix A, such as:

    Cleaning and greasing of landing gear wheel bearings;

    Lubrication not requiring disassembly other than removal of nonstructural items such as cover plates, cowlings, and fairings; and/or

    Applying preservative or protective material to components where no disassembly of any primary structure or operating system is involved, and where such coating is not prohibited or is not contrary to good practices; this could be interpreted to include painting.

NOTE:  Depending on the size of the area to be painted, or what is being painted, there may be additional maintenance tasks required such as balancing flight control surfaces or reweighing the aircraft.

3-598    REPLACEMENT OF PARTS. The final element of maintenance is the replacement of parts. Parts replacement is the removal and/or installation of parts on a product or article. At first glance, the replacement of parts seems simple and straightforward, and logically a maintenance action. But there are a couple of specific cases that require further explanation.

A.    Removing and Reinstalling the Same Part. While not explicitly addressed in the rule (the rule uses the term “replacement”), reinstallation of the same part that was removed would still be classified as maintenance. If this was not the case, you could conceivably remove an entire engine and then reinstall it and not call the action maintenance. Without classifying it as maintenance, there would be no requirement to record the activity, no need to follow the manufacturer’s instructions, etc. In this case, the word “replacement” is not interpreted as changing the part out for something new, but rather the placement, or installation, of a part on the product.

B.    Components Designed for Simple Removal and Replacement. Removal and replacement/reinstallation (R&R) of some parts designed to be easily swapped, such as those with quick disconnects, may not be considered maintenance; even more so if it does not require any form of hand tools. This includes obvious things like removing a fuel cap or opening an access panel with quick release latches to facilitate fueling of the aircraft. However, this can also include more complex actions like replacing a medical oxygen bottle (in limited situations) or an air ambulance litter. But this is a complicated topic and it is best to err on the side of caution. For example, if the component is part of a critical aircraft function such as an item of avionics, then the R&R of that component would still be considered maintenance even though the avionics box is mounted in a tray and only secured with thumb screws (i.e., not requiring tools to remove it). The same would hold true for the removal and reinstallation of fuses, control yokes, and certain doors on helicopters and/or aircraft, even though designed for easy removal without tools.

3-599    FUNCTIONAL CHECKS. Per the MSG-3, “function” is the normal characteristic of an item, and “functional checks” are a quantitative check to determine if one or more functions of an item performs within specified limits.

A.    Classification. Functional checks are not one of the defined elements of maintenance. Additionally, while it may seem that they are logically a form of inspection, they really should be classified under the element of maintenance from which they are called out. For example, when performed as a check after a part replacement, the functional checks are part of the part replacement element of maintenance; when performed after a repair, then they are part of the repair. Specifically, if a maintenance procedure calls for a functional check, then that check is part of that maintenance procedure and must be completed by, or at the very least performed under the supervision of, a mechanic or entity authorized to perform the maintenance procedure.

B.    Check Flights. An operational check flight is a type of functional check. When prescribed in the ICA, a mechanic can provisionally approve an aircraft for return to service limited to the performance of an operational check flight. A pilot can then perform the flight. A mechanic may or may not need to accompany the pilot on the flight depending on what needs to be checked, but no unnecessary persons should be allowed on the flight. After the flight, the mechanic can make any necessary adjustments, call for the operational check flight to be repeated, or finalize the maintenance procedure and approve the aircraft for return to regular service.

C.    Operational Checks. An operational check is a task to determine that an item is fulfilling its intended purpose. Checks that are part of a pilot’s pre or postflight procedures, as defined in the Aircraft Flight Manual (AFM), are operational checks and not functional checks and are therefore not items of maintenance. Similarly, Extended Operations (ETOPS) verification flights, which are required after maintenance on a primary system, are also a form of operational check. Verification is accomplished by the flightcrew and not observed by maintenance. And finally, ADs sometimes prescribe “checks” and specifically authorize pilots to perform them. In these cases, these would be considered operational checks and not items of maintenance, by the same logic.

D.    Inclusion in Inspection Programs. Since functional checks are not classified as inspections, by extension, they should not be considered part of the manufacturer’s inspection program. Only checks that are specifically called out for in the inspection program should be classified as inspections.

3-600    ACTIONS NOT CLASSIFIED AS MAINTENANCE. It is mistakenly believed that if something has the potential to cause harm to the aircraft or its operation, the activity should be covered as a maintenance activity. That perception probably has ties to the language that is used in the definition of a “major repair” in § 1.1: “Major repair means a repair: (1) That, if improperly done, might appreciably affect weight, balance, structural strength, performance, powerplant operation, flight characteristics, or other qualities affecting airworthiness….” This has led people to improperly classify some activities that could affect the airworthiness of the aircraft, if done improperly, as maintenance. These activities include:

A.    Preventive Maintenance. Specifically excluded from the definition of maintenance, preventive maintenance applies to a special category of items that have been identified and defined in the regulations as not rising to the level of maintenance. Preventive maintenance is defined in § 1.1 as “…simple or minor preservation operations and the replacement of small standard parts not involving complex assembly operations.”

1)    Part 43 appendix A, paragraph (c) contains a limited and very specific list of items the FAA has defined as preventive maintenance. This special category could be thought of as the exceptions to the maintenance rule and are not necessarily “preventive” in nature. Even though the rule language says preventive maintenance is limited to the items in the list, in a legal interpretation by Rebecca B. MacPherson to David Coleal, the FAA concluded that the list is not and should not be taken as all inclusive (refer to https://www.faa.gov/about/office_org/headquarters_offices/agc/practice_areas/regulations/Interpretations/data/interps/2009/coleal%20-%20(2009)%20legal%20interpretation.pdf). Items of preventive maintenance can include:

    Replenishing aircraft oxygen systems through a single servicing port (except when fittings, other than a cap, need to be disconnected and reconnected);

    Replenishing medical oxygen systems that can be removed and filled without tools, or aircraft mounted systems that can be serviced without tools (except when fittings, other than a servicing port cap, need to be disconnected and reconnected);

    Adding air and/or oil to landing gear shock struts;

    Replenishing hydraulic fluid in the hydraulic reservoir; and

    Replacing or servicing batteries.

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2)    Paragraph 3(b)(1) of AC 43-12, Preventive Maintenance, also cautions that “because of differences in aircraft, a function may be preventive maintenance on one aircraft and not on another.” The above reference to changing and repairing landing gear tires illustrates this maxim. The FAA may agree that the pilot of a small General Aviation (GA) airplane may change and repair its landing gear tire, but the agency would not consider the changing and repair of a landing gear tire on a transport category airplane to be preventive maintenance that a pilot could permissibly do. The distinction here can be made due to the definition of preventive maintenance in § 1.1 as being limited to “simple or minor preservation operations” and it “not involving complex assembly operations.” Even though the task might be listed in part 43 appendix A, paragraph (c), it does not mean that every iteration of that task would be considered preventive maintenance. As with the other paragraphs of appendix A (i.e., on major repairs and major alterations), the preventive maintenance list is better viewed as examples of the tasks in each category; they cannot be considered all‑inclusive.
3)    The legal interpretation from Rebecca MacPherson to David Coleal above also reiterates differences in who is able to perform preventive maintenance. “Accordingly, a pilot operating that aircraft under the operating rules of 14 C.F.R part 91 may, in accordance with the provisions of 14 C.F.R 43.3(g), perform daily landing gear tire pressure checks. Under the same regulation, however, a pilot of that aircraft operating under 14 C.F.R part 135 may not perform that task.” However, § 43.3 is clear on who is allowed to perform preventive maintenance and who is not.

B.    Cleaning. The cleaning we are specifically referring to is the routine removal of dirt and debris from the interior and exterior of the aircraft and not the disassembly and cleaning of individual parts, corrosion removal practices, or specialty cleaning processes that make up many maintenance procedures. While it is certainly true the selection and use of improper chemicals and/or cleaning methods could damage the aircraft and affect its airworthiness, that in and of itself does not make the activity maintenance. Nor is it even considered preventive maintenance. However, it is important to note that the manufacturer’s procedure for washing an aircraft may include tasks that might be classified as maintenance. These tasks might be required either before or after cleaning, or as the result of other maintenance tasks. Examples include pulling and tagging certain circuit breakers, the installation of protective devices to protect sensitive areas (other than simple slide-on covers), or replacement of defective or damaged gaskets or sealants found during the washing procedure.

C.    Fabrication. As discussed earlier, persons fabricating a part for the purpose of consuming the part into the next higher assembly are not performing a maintenance function. This is true insomuch as we are only talking about the function of fabricating a part, not performing repairs through fabrication methods, such as riveting and welding. This is significant because the fabrication of a part is covered under a different set of rules than maintenance (refer to § 21.9(a)(6)). However, even though the actual fabrication of the part is not considered maintenance, the installation or use of the part would be.

D.    Visual Checks. A visual check is an observation to determine that an item is fulfilling its intended purpose and that does not require quantitative tolerances. Visual checks do not include inspections that are performed as part of a scheduled maintenance activity, called for in an inspection program, or performed as the result of an associated maintenance activity (such as a part replacement, repair, or overhaul of a product or article). Those types of inspections are maintenance. However, a simple visual check, even if performed by a certificated maintenance person, is not maintenance. For example, a preflight inspection performed by a pilot is a visual check, but is obviously not a maintenance activity.

E.    Basic Servicing. This item is a little more complicated. Some forms of servicing are preventive maintenance, which have some regulatory requirements. For example, a record entry is required per § 43.9 for items of preventive maintenance performed. In broad terms, it has been generally upheld that basic servicing tasks, such as fueling and adding oil, are neither maintenance nor preventive maintenance. But even that has some caveats. When adding oil requires a precise sequence of steps or partial disassembly to gain access, then that would be considered a maintenance activity. Adding oil to an oleo strut for example, would be a maintenance activity, whereas adding a quart of oil to a GA aircraft would not.

F.    Alterations. Alterations are not maintenance. They have their own set of rules and regulations that must be followed, but altering a product or article is not a maintenance activity by definition. However, many ancillary functions that go along with performing an alteration are maintenance, but the alteration itself is not. This can be seen in many regulations where references to maintenance and alterations are listed separately in the same sentence.

G.    Rebuilding. Rebuilding a product or article is strictly an activity performed by the manufacturer of the part. The term “rebuild” is not included in the definition of maintenance. Section 43.3(a) states, in part, that “Except as provided in this section and § 43.17, no person may maintain, rebuild, alter, or perform preventive maintenance on an aircraft, airframe, aircraft engine, propeller, appliance, or component part to which this part applies.” Again, maintaining, rebuilding, altering, and preventive maintenance are all separate and unique activities. Section 43.3(j) states, in part, that: “A manufacturer may— (1) Rebuild or alter any aircraft, aircraft engine, propeller, or appliance manufactured by him under a type or production certificate; (2) Rebuild or alter any appliance or part of aircraft, aircraft engines, propellers, or appliances manufactured by him under a Technical Standard Order Authorization, an FAA-Parts Manufacturer Approval, or Product and Process Specification issued by the Administrator.” In this case, the manufacturer is the only entity identified as being allowed to rebuild a product or article. Further description of what rebuilding entails is found in § 43.2(b) as: “No person may describe in any required maintenance entry or form an aircraft, airframe, aircraft engine, propeller, appliance, or component part as being rebuilt unless it has been disassembled, cleaned, inspected, repaired as necessary, reassembled, and tested to the same tolerances and limits as a new item, using either new parts or used parts that either conform to new part tolerances and limits or to approved oversized or undersized dimensions.”

H.    Loading Software. In most cases, changing or loading software onto an aircraft component or system is a maintenance activity. One specific exemption is provided in § 43.3(k) for pilot-managed aeronautical databases. Additionally, loading of In-Flight Entertainment (IFE) system content software, defined in RTCA DO-178 as level E, is also not maintenance and is therefore excepted from § 43.9. IFE “content only” software is described as movie, music, and game programs with no effect on system operation.

RESERVED. Paragraphs 3-601 through 3-605.