Anyone can reverse engineer the 'part' and apply for PMA for it. The
feds will accept it if the process is good...

There are a number of ways to get a PMA - don't be any means think that this
is a straight forward process. The first method is to prove to the FAA that
the part is identical to the original. The second is to provide engineering
data to prove that the part meets the applicable design standards from the
FAR that would apply to the design of that part. For something like an
engine part it will be very difficult to show that your part is identical to
the original without access to the OEM's data simply because you can never
be sure what material, processes, tolerances etc the OEM has used. Without
this sort of insight it can be very difficult to prove that your part is a
proper substitute for the original. If you produce OEM data to prove the
identical nature then the regulations (21.303) more of less imply that you
would then need to produce evidence of a licencing agreement for the use of
that data. There is no point in explaining this process further here. There
is volumes of data on the FAA web site that explain the process.


I looked at Advisory circular 21-1B all the Qaulity control standards
appear to be handled through the Production Certificate (PC), which I
guess is what you file to get your Parts Manufacturing Authority
(PMA)? Apparently having a PC, does not directly require a Type
Certificate (TC). Presumably this is intended so that subcontractors
can be regulated. By the look of it you CAN manufacture parts with the
FAA's blessing without a TC.

You do not need a PC to make parts under PMA (see 21.303 (h)). The PMA
application includes all the requirements for configuration and quality
control of the manufacturing process. The PMA is in effect a licence to
produce parts. Unlike a TC it is both a design and manufacturing approval.

Subcontractors do not hold separate PC's .... it is up to the PC holder to
document the process for the control of subcontractors in the PC process
control documents and manuals.


Refering up-thread to Steves comment, I can understand the engine belt
issue if the OEM for the belt doesn't directly have a PC. In effect
Pipers PC would have to include Quality Control (QC) for the part.

The reason you cannot buy a Gates belt from gates and use that is that it is
in effect a commercial part. Piper has probably developed a specification
for the part against which the part is conformed on delivery to Piper to
turn it into an airplane part. Same part yes but Piper has applied
additional QA oversight to ensure that it is fit for the purpose that they
intended. This may take the form of additional inspections or testing.


But
I can't emagine that the TC dictating that you can only buy part X
from vendor Y. It is more like Vendor Y must comply with FAA safety
standards (have a PC) in order to sell direct.

See previous explanation.


I am guessing Type Certificates were originally supposed to dictate an
engineering and testing standard required prior to selling the part.
But it eventually evolved so that the PC and flight testing standards
make up the the technical portion, while the TC itself just ends up
being a revision log. O-360-A1A, O-360-A1B etc. Is this fairly
accurate?

No not exactly. The TC is simple a design approval. The holder of a TC does
not really have any right to build the airplane. They simply have a design
approved by the FAA as meeting FAR 23/25/27/29/35 depending on the product
type.

There are two ways in which the holder of a TC can then produce airplanes to
that approved design.

Ref FAR 21 Subpart G - One is via a PC which basically establishes FAA
approved processes for the control of the manufacturing activities including
all testing of the product before delivery. Depending on the maturity of a
companies PC the company will be delegated certain levels of responsibility
by the FAA from very little right through to the authority to conduct final
inspections, approve flight test reports, issue CofA's etc (i.e. complete
control of the process). FAR 21.133 is quite clear - you must hold a TC or
an STC or evidence that you have the rights to manufacture a products to a
third parties TC or STC to be elligible for the issue of a PC. PMA holders
and subcontractors are NOT eligible for the issue of a PC.

Ref FAR 21 Subpart F - The other method of producing an airplane for which
you hold a TC is "production under a Type Certificate Only". Generally this
applies to companies who have recently gained a TC and who want to start
manufacturing the airplane but who have not yet got a PC. When airplanes are
made in the way the FAA is heavilly involved in the process. It does not
means that the company does not need production control processes, they do,
but these may not be sufficiently mature for the issue of a PC and
consequently the FAA is not yet in a position to delegate the company
authorities to conduct certain tasks on their behalf.