The Elements of Aircraft Maintenance – Part 2

The Elements of Aircraft Maintenance – Part 2
An article by our Guest Blogger and SAS Instructor and Consultant  Kevin Rookes

Welcome to the second part of a four-part series that explains what constitutes maintenance from an FAA perspective and what are the differences between the elements that make up maintenance!

This article considers what makes up overhaul, repair and preservation.


An overhaul includes several separate maintenance activities to restore a product or article to a condition that will give a reasonable assurance of operation for a specified amount of time. The term “overhaul” is mentioned in several places in the FAR’s but this article uses the definition in 14 CFR section 43.2(a), which states that an overhaul consists of disassembly, cleaning, inspection, repaired as necessary, reassembly, and testing.

Overhaul from a Certification Viewpoint

All FAA certification standards require the manufacturer to identify in their Instructions for Continued Airworthiness (ICA) the items requiring overhaul and their recommended overhaul interval. 14 CFR parts 23 and 25 for aircraft certification standards only require maintenance manuals and do not require overhaul manuals. 14 CFR parts 33 and 35 (engine and propeller products), require the manufacturer 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 in the form of an overhaul manual. Appendix A in parts 33 and 35 require the overhaul manual 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.”

Interpreting Overhaul Requirements

Several FAA legal interpretations have stated that all the tasks listed in § 43.2(a), i.e. disassembly, cleaning, inspection, repair, reassembly, and testing are not necessarily required for a maintenance action to be considered an overhaul. 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 FAA, the overhaul process published in the current manufacturer’s overhaul manual must be followed when performing an overhaul.


A repair is a procedure carried out in accordance with appropriate (FAA-accepted or FAA-approved) technical data to restore an aircraft, airframe, engine, propeller, appliance, or component part at least equal to its original or properly altered condition.

Repair by Fabrication

When the replacement of a part involves complex operations such as riveting or welding, this is classified as a repair, not a part replacement. This can be seen for “airframe major repairs” in part 43 appendix A, paragraph (b) which 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.

Material Substitution

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.

Technical Standard Orders (TSO)

Repairing to a TSO standard may not be returning the part to 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.

Fabrication of Parts

Fabrication of parts is often seen as a maintenance activity. Technically, though, fabrication of parts is a manufacturing activity. In some 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 repair agency is not performing maintenance when actually fabricating parts, so the maintenance and airworthiness provisions of rules under part 43 or part 145 do not apply to these activities. However, it is a maintenance activity when the fabricated parts are installed onto an article or an aircraft. It is also a maintenance activity when the product or article is being repaired through fabrication methods such as riveting or welding.


Preservation is a specific set of maintenance actions that are accomplished to maintain the integral design capabilities of the product or article. There are many forms of preservation including lubrication (oils and grease), and the application of preservative or protective coatings. 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 non-structural 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.

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