So, lets say that a part is listed as an optional item for your serial number. But lets say the part was not installed on your aircraft when new.
Scenario (A)
Cessna still makes the part and can sell it to you.
Scenario (

Cessna will not make the part but will sell you the drawing to make yourself.
Scenario C)
Cessna will do neither of the above but your buddy has one and you want to use it as a jig to build your own part.
Which of the above is:
1) Able to be installed with only a logbook entry
- A, B, or C are possible depending on the complexity of the part - structural, cosmetic, required, option2) Requires a Major Alteration/Repair 337 Form
- A, B, or C are possible depending on the complexity of the part - structural, cosmetic, required, option - major or minor repair or alteration3) Requires an FAA Field approval in conjunction with form 337.
If the part was not listed as an option, or if there are no instructions for installation after production, then more than likely yes.4) Is not an approved part for installation on your aircraft under any circumstances.
- Could be the case in all.Now. lets pretend that the item was not a factory option for you airplane.
In scenarios A, B, C above, which 1, 2, 3, 4 items are eligible materials for use in a field approval or STC application (approved parts, in other words, even without a PMA/TSO?)
- If the item was not listed as an option for installation on your particular serial number, then some type of approval would be required for installation, field approval, DER approval, etc. If the part has no approvals, FAA, PMA, TSO, etc, or documentation of approved installations on like products, then you will need to apply for either a field approval or STC for installation.