strut replacement documentation

[Guest]

Re: strut replacement documentation

"You can also build a part that can be installed under a STC, which requires that you complete a form 337. This is the way Alaska Airframes does their struts.
Both are FAA/PMA approved parts. I am not really sure why Alaska Airframes chose a different route for approval from the other two."

Because of the major change (?) from OEM strut dimensions, weight, strength, and possibly material noted previously, perhaps this is why.

"Product" refers to the aircraft.

"Major Change": Change to an aircraft, engine, or propeller which appreciably affects weight, balance, strength, reliability, operational characteristics, airworthiness characteristics, power, noise characteristics, or emissions.

5. Who Needs A PMA?
a. General Requirements. Title 14 of the Code of Federal Regulations
(14 CFR) § 21.303(a) requires any person producing replacement or modification parts for sale for installation on a type-certificated product to get a PMA. A PMA is a combined design and production approval for replacement parts. Also we may use a PMA for the production of modification parts from supplemental type certificates (STC). The prior STC approves the design and installation of these modification parts in products. However, if any replacement part alters a product by introducing a major change, then 14 CFR § 21.113 requires an STC for the approval of these parts. See FAA Order 8110.4, Type Certification, for STC procedures.

Gary

Hi Gary,

No, I don't think its that.

Those dimensions changing do not constitute a major difference.

There is some other reason that is yet hidden from us and I suspect that because of two STC's that I have on my Aeronca.

One of the STC's is for the addition of two inspection covers in the leading edge that allow inspection of the top of the front spar of each wing. Simple little inspection covers.

Another is for the replacement of the spar. The difference between the STC'ed spar and the OEM spar is that the plywood plates on the STC spar are not rectangles like the OEM spar. AC43.13-1B tells us not to make rectangular plates. This is not a major issue either.

Thirdly (I don't have this one but I am aware of it) there is an STC for Aeroncas to use#4 screws to hold the ribs on instead of nails. Is that a major issue? I don't think so.

My supposition is that there is some commercial/economic reason for using the STC.

For example; one can sell the simple inspection covers or screw kits to others if there is an STC. I don't object to that it is very convenient however without the STC it is not legally possible. Not sure how that works for spars or struts.

One thing additionally is true about the strut scenario though. Once you install the struts on the plane with the STC those struts are married to that plane and cannot be moved to another plane as a used serviceable part. STCs go with a particular airplane by serial number.

Dave R

[PA1195]

Re: strut replacement documentation

Hi Dave and thanks for the perspectives. We may never know the why of the STC in this case. I could call Lee Budde the originator of STC for these Taylorcraft struts, who was/is maybe still is, a Taylorcraft owner but probably won't bother. He sold the Airframes package to the current owners some time back. They can be reached at (907) 331–4480 if folks want to learn more.

My aircraft is included in the AML and the 2007 STC SA02300AK is for my aircraft as you note. It's described on the STC as a design change, that's why I mentioned it may have been major, but perhaps only in the FAA's view. Noted on the STC and available are a master drawing list, installations instructions, and instructions for continued airworthiness. Their webpage also provides instructions: http://www.airframesalaska.com/Default.asp

Edit: An article about the strut AD and Airframes, Inc's initial involvement: https://generalaviationnews.com/2007...opportunities/

Gary

[Guest]

Re: strut replacement documentation

Gary,

I had an interesting discussion with an engineer from an ACO office today.

I called to discuss the quality system requirements and afterwards I asked him why people get STCs for installing what is essentially a repair part.

We had a nice discussion and 3 thoughts emerged.

First thing he came out with and very quickly was what he thought was the most common reason. Some countries do not accept PMA replacement part certification from the US but they do accept STC certification. So if you want to sell to foreign locations STC has an advantage. He used an acronym for it, something like "EUFA".

Secondly was what I mentioned above, the ability to market some parts that the STC can provide.

Thirdly was that some folks merely apply for the STC because they are convinced in the their own minds that they need engineering approval so the pursue it.

Dave R

[PA1195]

Re: strut replacement documentation

All good ideas Dave. I can see another...eventually tiring of the business and marketing the value of the STC vs PMA should the originator decide to do so. Can I assume both can be sold or transferred? Like...here's my STC or here's my PMA for sale. Some do that as it may (???) end the originator's liability while offering profit from a buyout. Not sure about this just speculating but would be interesting to know nonetheless.

It's been -30-40F below here for several days but clouds are coming to Interior Alaska and it's time to dig my plane out of 3' of snow and install skis.

Gary

[Guest]

Re: strut replacement documentation

All good ideas Dave. I can see another...eventually tiring of the business and marketing the value of the STC vs PMA should the originator decide to do so. Can I assume both can be sold or transferred? Like...here's my STC or here's my PMA for sale. Some do that as it may (???) end the originator's liability while offering profit from a buyout. Not sure about this just speculating but would be interesting to know nonetheless.

It's been -30-40F below here for several days but clouds are coming to Interior Alaska and it's time to dig my plane out of 3' of snow and install skis.

Gary

Excellent point on market value of STC, that makes it an investment.

I would not survive there I don't like to walk to my second garage/shop when its +40.

Dave R