I believe a change of spinner (to another PMA spinner) and bulkhead can be considered a minor alteration.
I would like to use a composite spinner approved by stc for later models of my type, along with the spinner bulkhead that was used in the later model from the factory.
My parts book shows the spinner and bulkhead separate from the propeller assembly.
I understand it is the AP's primary function to determine whether it is major or minor; that a later IA might disagree and not sign off on the annual inspection; that at anytime the FAA might disagree; and that it might be appropriate to ask for a field approval anyway.
Analysis:
1. 14 CFR Part 1, Section 1.1 defines a "Major Alteration" as an alteration:
"(1) That might appreciably affect weight, balance, structural strength, performance, powerplant operation, flight characteristics, or other qualities affecting airworthiness; or
(2) That is not done according to accepted practices or cannot be done by elementary operations."
(I submit a spinner is done to accepted practices by elementary operations, so (2) is not an issue)
Of course, there is no definition of "appreciable". Weight and balance are not affected, powerplant operation will not be affected, the new composite spinners appear to be more durable than the original equipment aluminum ones, no effect of the basic airframe structure. Could it affect flight characteristics or other qualities? I doubt it, but on a quantum mechanics level everything affects everything.
2. Part 43, Appendix A, lists items that are definitely considered to be major alterations.
Since the spinner and bulkhead are considered airframe parts, I need only be concerned with the language in Part 43, Appendix A(a)(1) "Airframe major alterations", and not (a)(2) "Powerplant major alterations" nor (a)(3) "Propeller major alterations".
The "Airframe major alterations" does not contain any specific reference to a spinner or bulkhead. Neither does the powerplant or propeller sections contain any specific reference to a spinner or bulkhead.
Therefore the only basis I see for a spinner change to be a considered major alteration under Appendix A would be "(xii) Changes to the basic...cooling...system". But I think that is a stretch to consider a spinner as being a part of the cooling system.
3. So if the spinner is part of the cooling system, we fail the minor alteration test.
4. If the spinner is not part of the cooling system, then we only have to consider the "appreciably affect" test of Part 1, Section 1.1 in order to be a minor alteration.
5. Enter the Vintage Aircraft Parts Substitution AC 23-27. Assuming basic qualification of the aircraft (pre 1980, fixed wing, unpressurized, recip engine, less than 12500 pounds gross).
Section 1.a. states that the "You may use the date in this AD as "approved" data for substantiating parts,,, substitutions to vintage aircraft."
Section 8.c. (4) states "You may use previously approved (per STC or field approval) part/material substitutions on like kind aircraft. If the part/material is installed with previously approved parts or material, PMA, Technical Standard Order (TSO), NAS, etc., and if it is completed in a similar manner with a previous field approval or STC, you may use those approvals as the basis for approval on your aircraft." (Additional recordkeeping details omitted.) I don't see any definition of "like kind" but surely a model on the same Type Certificate must somewhere be defined as like kind.
AC 23-27 contains an apparent inconsistency. In Section 13 it discusses documenting a minor alteration with simply a log entry, a major alteration with a 337, with no mention of the intervention of an Aviation Safety Inspector. However, in Section 1.b. it states that "the Aviation Safety Inspector (ASI) makes the final determination of any approvals."
In particular, note Section Appendix 1, Section 6.a., deeming it a minor alteration to swap engine parts from one model to another even though not specifically approved for that model engine.
Argument:
A spinner/bulkhead is just a spinner/bulkhead and doesn't appreciably affect airworthiness.
A spinner/bulkhead isn't part of the cooling system, and therefore is not a per se major alteration.
Therefor, a change of spinner/bulkhead to the later model (same TCDS) spinner/bulkhead is a minor alteration. As such, only a logbook entry is necessary.
In addition, AC 23-27 is the approval basis to use the later model spinner/bulkhead as a major alteration, which I understand would require a 337 and IA signoff, since there is now APPROVED DATA, but no requirement of a field approval, and not sure if the ASI has to be involved.
Please critique the above. Don't be shy. Thank you.
I would like to use a composite spinner approved by stc for later models of my type, along with the spinner bulkhead that was used in the later model from the factory.
My parts book shows the spinner and bulkhead separate from the propeller assembly.
I understand it is the AP's primary function to determine whether it is major or minor; that a later IA might disagree and not sign off on the annual inspection; that at anytime the FAA might disagree; and that it might be appropriate to ask for a field approval anyway.
Analysis:
1. 14 CFR Part 1, Section 1.1 defines a "Major Alteration" as an alteration:
"(1) That might appreciably affect weight, balance, structural strength, performance, powerplant operation, flight characteristics, or other qualities affecting airworthiness; or
(2) That is not done according to accepted practices or cannot be done by elementary operations."
(I submit a spinner is done to accepted practices by elementary operations, so (2) is not an issue)
Of course, there is no definition of "appreciable". Weight and balance are not affected, powerplant operation will not be affected, the new composite spinners appear to be more durable than the original equipment aluminum ones, no effect of the basic airframe structure. Could it affect flight characteristics or other qualities? I doubt it, but on a quantum mechanics level everything affects everything.
2. Part 43, Appendix A, lists items that are definitely considered to be major alterations.
Since the spinner and bulkhead are considered airframe parts, I need only be concerned with the language in Part 43, Appendix A(a)(1) "Airframe major alterations", and not (a)(2) "Powerplant major alterations" nor (a)(3) "Propeller major alterations".
The "Airframe major alterations" does not contain any specific reference to a spinner or bulkhead. Neither does the powerplant or propeller sections contain any specific reference to a spinner or bulkhead.
Therefore the only basis I see for a spinner change to be a considered major alteration under Appendix A would be "(xii) Changes to the basic...cooling...system". But I think that is a stretch to consider a spinner as being a part of the cooling system.
3. So if the spinner is part of the cooling system, we fail the minor alteration test.
4. If the spinner is not part of the cooling system, then we only have to consider the "appreciably affect" test of Part 1, Section 1.1 in order to be a minor alteration.
5. Enter the Vintage Aircraft Parts Substitution AC 23-27. Assuming basic qualification of the aircraft (pre 1980, fixed wing, unpressurized, recip engine, less than 12500 pounds gross).
Section 1.a. states that the "You may use the date in this AD as "approved" data for substantiating parts,,, substitutions to vintage aircraft."
Section 8.c. (4) states "You may use previously approved (per STC or field approval) part/material substitutions on like kind aircraft. If the part/material is installed with previously approved parts or material, PMA, Technical Standard Order (TSO), NAS, etc., and if it is completed in a similar manner with a previous field approval or STC, you may use those approvals as the basis for approval on your aircraft." (Additional recordkeeping details omitted.) I don't see any definition of "like kind" but surely a model on the same Type Certificate must somewhere be defined as like kind.
AC 23-27 contains an apparent inconsistency. In Section 13 it discusses documenting a minor alteration with simply a log entry, a major alteration with a 337, with no mention of the intervention of an Aviation Safety Inspector. However, in Section 1.b. it states that "the Aviation Safety Inspector (ASI) makes the final determination of any approvals."
In particular, note Section Appendix 1, Section 6.a., deeming it a minor alteration to swap engine parts from one model to another even though not specifically approved for that model engine.
Argument:
A spinner/bulkhead is just a spinner/bulkhead and doesn't appreciably affect airworthiness.
A spinner/bulkhead isn't part of the cooling system, and therefore is not a per se major alteration.
Therefor, a change of spinner/bulkhead to the later model (same TCDS) spinner/bulkhead is a minor alteration. As such, only a logbook entry is necessary.
In addition, AC 23-27 is the approval basis to use the later model spinner/bulkhead as a major alteration, which I understand would require a 337 and IA signoff, since there is now APPROVED DATA, but no requirement of a field approval, and not sure if the ASI has to be involved.
Please critique the above. Don't be shy. Thank you.
