Excerpts from 23-27 and related FAA guidance:
AC 23-27
Section 1.a. says “. . . You may use the data in this AC as approved data for substantiating parts . . . substitutions . . .”
Section 4 says “This AC intends to . . . expedite the field approval process . . .”
Section 5: “Examples of substituted parts include . . . wheels and brakes.”
Section 5.e. discusses current industry standards, of which the TSO is surely a candidate.
Section 5.f. discusses the need for data if the part might affect safety if it failed. It would seem that the TSO addresses that data.
Section 7.c.(3) suggests that if one can establish that the part is at least equal in performance and safety to the part it replaces, then substitution is possible.
Section 8.c. defines a standard part as one manufactured in complete compliance with acceptable standards for such parts.
Section 8.e. says that a field approval is the standard way of authorizing installation, and:
Section 9.d.(3) states that a PMA is not required for a TSO part.
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Excerpts from Order 8900.1 Vol 4 Chapter 9
4-1185
[h=4]A. Major Alterations. The list in Figure 4-68, Eligibility Considerations For Field Approval, describes methods of approval for typical major alterations. This list is not all-inclusive; examine each project on a case-by-case basis. If an alteration is not on the list, it may be eligible for a field approval; however, each alteration must be evaluated on a case-by-case basis. Items not listed should be treated as Evaluation (designated by the letters “EVL”). Alterations on transport category aircraft with 30 or more passenger seats or operating under part 121 should be considered Engineering (designated by the letters “ENG”) and must be coordinated with the RO.[/h]
4-1191 References
· AC 23-27, Parts and Materials Substitution for Vintage Aircraft.
4-1192 Procedures
[h=5]4) Denial of Proposed Alteration/Repair Approval. If the applicant is unwilling or unable to comply with the requirements to obtain the requested field approval, terminate the process by notification in writing to the applicant. This notification should include the reason for denial. The applicant should be given the opportunity to make necessary corrections within a reasonable amount of time from receipt of notification.[/h]
AC 43-210
This is a straightforward AC that first denies that it is regulatory in nature, and then flat out states that if the words “shall” and/or “will” appear in an instruction, they reflect a regulatory requirement. Then, in § 102(b)(2) it says an ASI will provide a written response with reasons for denial, if a field approval request is to be denied. It gives only four reasons for denial (section c).
CAR4a
is the controlling document for all Piper Cubs prior to the PA-18. Requirements are “simply” codified, and currently available on-line.
Notably, landing gear is covered on pp 21, 26, and 27. A detailed structural discussion is held in part 4a.477, where it says wheels have to be “certified” in accordance with part 15. Part 15 is on page 1- a single paragraph covering the certification of an entire aircraft.
Brakes are interesting – they are required on transport aircraft (4a.483-T). Tailwheels are even more interesting – “may be any type or model, and are not certificated.” And yet, folks are still getting field approvals for tailwheels?
Now to Order 8300.16 CH 1
I think this replaces the earlier guidance cited above from 8900.1. Not sure . . .
This is from Chapter 4 – really difficult to follow paragraph numbering, but try
4-2.e(4):
Typically, data that meets a more stringent airworthiness standard when applied to an alteration requiring a less stringent airworthiness standard is normally acceptable
That little excerpt would seem to indicate, for instance, that a Cleveland wheel and brake assembly that meets certification requirements of CAR 3 would be more than sufficient for the less stringent CAR 4a. See Type Certificate 1A2 for approved Cleveland wheels and brakes on a CAR 3 Cub-type aircraft.
8-5.b - Analysis as Part of a Data Package. In many cases, the analysis may have been accomplished as part of a data package for an STC or other approval that is being used as the basis for an alteration. In these cases, it is not necessary that it be done again provided it is appropriate to the alteration in question. Like the entire field approval process, the goal is to ensure operational safety and aircraft airworthiness
From the Appendix:
Substantiating Data. Technical data used to show that an article complies with the applicable airworthiness standards. Compliance may be shown by tests, analysis, experience, and/or computations appropriate to the maintenance, alteration, or continue-in-service condition of the article being evaluated. Substantiating data shown to comply with the applicable airworthiness standards is acceptable to the Administrator. This is because it establishes that the article meets the regulatory requirements and would be returned to its original or properly altered condition by use of this data.
[emphasis mine - bob]