I'm looking for some of the same answers and so will add my research to the pile.
Lacking sufficient qualifications and experience, I will avoid (where possible) attempts to definitively address the meanings of the terms as they apply to MANUFACTURING a product.
However, some of the previously posted answers could inconvenience you, or worse, get you into trouble, if used after the product has been manufactured, so I'll try to address them from a MAINTENANCE perspective.
After a product has been manufactured under USA FAA CERTIFICATION (and is being MAINTAINED under USA FAA rules) the following should apply:
OVERHAUL is defined in 14 CFR 43.2(a):
"No person may describe in any required maintenance entry or form an aircraft, airframe, aircraft engine, propeller, appliance, or component part as being overhauled unless-
(1) Using methods, techniques, and practices acceptable to the Administrator, it has been disassembled, cleaned, inspected, repaired as necessary, and reassembled; and
(2) It has been tested in accordance with approved standards and technical data, or in accordance with current standards and technical data acceptable to the Administrator, which have been developed and documented by the holder of the type certificate, supplemental type certificate, or a material, part, process, or appliance approval under part 21 of this chapter."
A practical distinction of OVERHAULING a product, versus the more extensive REBUILDING, is that when OVERHAULING, the product must merely meet "serviceable" limits and tolerances as opposed to having to meet "new" tolerances.
Generally, the manufacturer controls the issuance of the data that is published to define what is "serviceable" and what constitutes "new."
[If interested in REBUILDING, then 14 CFR 43.2(b) is worth looking at.]
REPAIR - DICTIONARIES
Obviously REPAIR is defined in dictionaries, but when meanings really count, we are often hoping for something more specific. In spite of this, it is notable that dictionary definitions of REPAIR are very broad. A quick review in the dictionaries before we go deeper can be helpful, and especially in this case, the reason for doing so will hopefully become apparent later in this post.
Dictionary.com definitions of REPAIR include variations on HEALING, MENDING, PREPARING FOR REPAIR, RESTORATION, STRENGTHENING, and in some contexts, ADDING TO (Ref. Dictionary.com).
The New Oxford American Dictionary 3rd Edition adds FIXING.
Black's Law Dictionary 8th Edition is silent on the matter of REPAIR. This hints that in law, the meaning might not differ much from the more generic meanings used throughout general society and provided in general dictionaries. The 9th Edition exists, but I don't have it yet.
The Cornell University Law School's free (donation supported) WEX online dictionary lists 16 examples of REPAIR used in law and in various legal terms. Notably, there is no standalone listing for the word REPAIR. Further, none of the 16 examples seems to indicate a use of the word REPAIR that conflicts appreciably with the more general definitions of the word REPAIR that are provided in general (non-law) dictionaries.
The above findings form a generally wide basis for the meaning of the word REPAIR. There is little in the way of maintenance activities that could be excluded if we use those definitions of the word REPAIR.
In fact, the above definitions are actually a bit too broad and need a little narrowing to be of good use on aviation products - especially those maintained under FAA rules. So let's explore some more.
REPAIR - INTERNATIONAL
Like most Aviation Authorities, FAA generally works within the framework of what is internationally agreed to by almost all nations via the international laws that authorize the International Civil Aviation Organization (ICAO). The USA is a signatory to the relevant international laws that authorize ICAO's existence and authority, so ICAO's meanings have some influence.
Going a little further below the surface, REPAIR is defined in ICAO Annexes 8 & 6.
However, there are occasional FAA exceptions and differences, so caution is warranted, but let's have a go at it anyway. The ICAO definitions include:
ICAO Annex 8 - REPAIR: "The restoration of an aeronautical product to an airworthy condition as defined by the appropriate airworthiness requirements."
ICAO Annex 6 - REPAIR: "The restoration of an aeronautical product to an airworthy condition to ensure that the aircraft continues to comply with the design aspects of the appropriate airworthiness requirements used for the issuance of the type certificate for the respective aircraft type, after it has been damaged or subjected to wear."
It should now be obvious that ICAO generally equates REPAIR to RESTORATION.
REPAIR - USA FAA REGULATIONS (IN THE USA CODE OF FEDERAL REGULATIONS [CFR])
Let's dig a little deeper and look at the local USA variations on the meaning of REPAIR.
On products maintained under FAA certification, FAA regulations generally use the word REPAIR in a somewhat broad context that includes almost everything involved in fixing a product, except for a few activities.
The FAA general definition of MAINTENANCE includes REPAIRS, amongst other things. This puts REPAIRS on an equal footing with other such separate things as INSPECTION, PRESERVATION, REPLACEMENT OF PARTS, and the previously discussed OVERHAULS. REPAIRS and all of those other activities are listed as being included in the definition of MAINTENANCE (Ref. 14 CFR 1.1).
Now that we have established that REPAIRS are included in the definition of MAINTENANCE, let?s look at something that isn't usually included in REPAIRS or MAINTENANCE. That is ALTERATIONS. Note that ALTERATIONS weren't included in the definition of MAINTENANCE, noted above, either.
Although, in a practical sense ALTERATIONS are closely related to MAINTENANCE and REPAIRS, and are often performed at the same time, FAA lists separate definitions of MAJOR REPAIRS, MAJOR ALTERATIONS, MINOR REPAIRS, and MINOR ALTERATIONS (again, Ref. 14 CFR 1.1).
Careful study of the definitions and the use of the words throughout the 14 CFR series reveals that those 4 items (MAJOR REPAIRS, MAJOR ALTERATIONS, MINOR REPAIRS, and MINOR ALTERATIONS) are often used in a manner that makes them exclusive of each other.
In other words, a REPAIR is different from an ALTERATION, and vice versa. Unfortunately, life cannot be so easy and there are exceptions.
Quite notably the entire 14 CFR Part 145 is titled 'REPAIR STATIONS,' and in this case the word REPAIR is obviously used quite broadly in a very inclusive sense.
To whit, appropriately rated "REPAIR" STATIONS are permitted to engage in almost all FAA defined maintenance and maintenance related activities, including PREVENTIVE MAINTENANCE, MAINTENANCE (including REPAIRS, et al), and ALTERATIONS [Ref. 14 CFR 145.201(a)(1)].
So the use of the word "REPAIR" in the term "REPAIR STATION" is very broad. Used in this context, the meaning lines up more with the general dictionary definitions of the word "REPAIR," than the separatist definitions and classifications of the word and related words defined in the 14 CFR 1.1 definitions.
In other words, the word REPAIR used in the term REPAIR STATION means almost everything related to maintenance.
Unfortunately, it cannot be left at that. Here come more exceptions: REBUILDING is generally prohibited, since this is the domain of the manufacturer... unless the repair facility is an agent of the manufacturer <sigh>.
And further, once you get down into the details of the actual content of Part 145, the wording again starts to line up with the separated 14 CFR 1.1 definitions of the 5 terms noted above. The distinctions between REPAIRS and ALTERATIONS start to come back into play. And if you go back to 14 CFR 145.201(a)(1) again, you will see that MAINTENANCE (including REPAIRS, et al), PREVENTIVE MAINTENANCE, and ALTERATIONS were indeed called out separately, thus reinforcing the separateness of their status in the eyes of the FAA.
The saving grace in all of this is that 14 CFR 43 Appendix A Par. (b)(1) has a nice description of AIRFRAME MAJOR REPAIRS that give us a good idea of what types of sub-activities might be included in a REPAIR:
"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..." <a list of airframe parts is then included>.
This defacto definition introduces the concept of a REPAIR possibly including the complete REPLACEMENT of a discrepant / non-conforming part.
REPAIR - USA FAA ADVISORIES AND OTHER GUIDANCE INFORMATION
If the regulations are vague, legalistic, contradictory and a bit messy in places, then the advisories are more of the same.
Remember when 14 CFR 1.1 listed REPAIR as a separate activity inside of the definition of MAINTENANCE and left ALTERATION out completely?
Per AC 43-210 Par. 106, "REPAIRS are intended to return the product to its original or properly ALTERED condition."
So AC 43-210 lumps REPAIRS and ALTERATIONS together, it would seem.
ACs 65-12A and 65-16A repeatedly indicate that sometimes REPAIRING an aircraft or product is accomplished by a complete REPLACEMENT of the discrepant / non-conforming item.
So ACs 65-12A and 65-16A lump REPAIRS and REPLACEMENTS together, it would seem.
So really, FAA seems to be all over the place with the meaning of REPAIR.
That is until you need to fill out an FAA Form 337 for documenting the completion of a MAJOR REPAIR or MAJOR ALTERATION. Then the instructions in AC 43.9-1F make it quite clear that a REPAIR is a separate activity from an ALTERATION. When filling out the form to notify FAA of the completion of the work, you must classify the work as either a REPAIR or an ALTERATION in Block No. 4.
REPAIR - CONCLUSION
With FAA, it seems that depending on the context, REPAIR can be used to mean just about any group of maintenance activities except REBUILDING. REBUILDING is the domain of the manufacturer.
FAA doesn't use the term REWORK in the FAA Regulations very often. There are only three instances in all of 14 CFR (where the FAA regulations reside).
The first use of the word REWORK in 14 CFR occurs in section 21.125(a)(9) with regard to the MANUFACTURING (specifically the PRODUCTION) of products:
"Materials and parts that are withheld because of departures from design data or specifications, and that are to be considered for installation in the finished product, must be processed through the Materials Review Board. Those materials and parts determined by the Board to be serviceable must be properly identified and reinspected if REWORK or REPAIR is necessary. Materials and parts rejected by the Board must be marked and disposed of to ensure that they are not incorporated in the final product."
As I hinted at the beginning of this post, my experiences in manufacturing weren't from a sufficiently expert vantage point and thus I wasn't exposed to the subtleties of the difference between the meanings of REPAIR and REWORK. What I can say is that when I was in manufacturing, I saw plenty of WORKED items on aircraft, both from a design and workmanship point of view, that didn't meet specifications or expected functionality. These discrepant items needed Engineering Dispositions to correct. Many of those dispositions included the term REWORK and occasionally I would see the word REPAIR.
In hindsight, I wish that I had paid more attention to the wording and asked more questions of the planners and engineers who managed the work and wrote the instructions.
The best that I can guess at this point is that if FAA fails to define it more clearly in an advisory or guidance document, then the production system procedures, such as the MRB procedures should define the terms clearly in a manufacturing environment.
With that, I turn my attention to the second use of the word REWORK in the FAA regulations. 14 CFR 43.10 provides for mutilation of a retirement life-limited part:
?Mutilation: The part may be mutilated to deter its installation in a type certificated produce. The mutilation must render the part beyond repair and incapable of being REWORKED to appear to be airworthy.?
And finally, 14 CFR 43 Appendix A states that:
?The following alterations of a powerplant when not listed in the engine specifications issued by the FAA, are powerplant major alterations. (i) Conversion of an aircraft engine from one approved model to another, involving any changes in compression ratio, propeller reduction gear, impeller gear ratios or the substitution of major engine parts which requires extensive REWORK and testing of the engine.?
As exhaustive as my research may seem, there are heaps of documents that due to time constraints I will not be able to immediately review. I can use all of the help I can get, so constructive criticism, corrections, and additions are greatly appreciated
Especially any references to additional FAA sources (such as any more direct FAA definitions for REPAIR and REWORK).