Sources of parts

[Ed Haywood]

I am currently doing a bare frame restoration of my '78 Decathlon, which is basically an exercise in parts gathering. I am leveraging multiple sources for parts, including TC/PC, PMA, TSO, STC, Standard, and Owner Fabricated. That has pushed me to learn the regs in greater detail, so that I don't waste my supervising IA's time.

AC 20-62 has been a huge help in clarifying terminology. Discussion forums and articles on the internet are rife with vague terms like "aircraft grade" which are meaningless for actually determining whether parts are eligible. The AC lays out the different categories of eligible parts and provides information on how to verify them.

Take electrical crimp terminals, for example. Now I know that crimp ring terminals are a standard part which is produced to a published specification. Checking AC 43.13-1B tells me that terminals should meet MIL-T-7928. Now I can check the manufacturer and product line to verify that the terminals I am buying meet that specification. If I really wanted to dig, I could read the identification requirements in the specification, which probably specifies some sort of stamp on the terminals and/or label on the packaging. If I really really wanted to be fussy, I could request traceability documents to prove the terminals I bought were actually made by the labeled manufacturer.

So here is my question: now I know how to find out if a part is eligible to install. But I'm still unclear on the process for determining whether an eligible part can be installed on a particular TC aircraft. Is there a similar product that rolls up all the regs into an easy to understand summary or flow?

Right now my general understanding is that step 1 is determining whether an alteration or repair is minor or major.

If major, then approved data must be used. That approved data could come from a TC, STC, field approval, or other (what?). Approved data would normally include a parts list with instructions and drawings necessary to comply. Any deviation from the parts list would not be approved data.

If minor, then acceptable data must be used. The primary source of acceptable data would be AC 43.13-1B, which is probably not titled "acceptable methods" by accident. So if I use acceptable methods to install approved or acceptable parts, then I am in compliance with regulations.

But obviously there are a lot of holes in my understanding. A big one concerns installation of TSO products. I understand that a TSOA is a production approval, and establishes that the product meets performance specifications in the TSO. I also understand that a TSO is not an installation approval. So where does the installation approval come from?

Not so hypothetical example: I want to replace my fuel pressure gauge. The FP gauge is required equipment per my AFM. The TC holder has approved specifications for several gauges such as the EI FP-5. The EI also is produced under TSOA, and has an STC with AML. So I see that I have 3 possible paths to justify installation:

1. Approved data via TC specification.
2. Approved data via STC AML.
3. Determination of minor alteration and use of acceptable data. (?????)

The 3rd one is the most confusing. The EI FP installation instructions say the following:

If your aircraft is not covered on our STC (found at the back of this manual), you must perform the flow and pressure tests in FAA document A.C. 23.955-1 (Substantiating Flow Rates and Pressures in Fuel Systems of Small Airplanes) to insure safe and proper operation.

I assume what they are saying is that the TSO plus AC 23.955-1 provides acceptable data?

So in general terms, what is the process for obtaining acceptable data on whether a TSO gauge (or other product) can be installed as a minor alteration? Is it a matter of comparing the TSO performance specifications meet the requirement? If 2 gauges meet the same TSO, would that be acceptable data to replace one with the other?

 

[Bell206]

So here is my question: now I know how to find out if a part is eligible to install. But I'm still unclear on the process for determining whether an eligible part can be installed on a particular TC aircraft. Is there a similar product that rolls up all the regs into an easy to understand summary or flow?

No, on the summary route. The reason there’s not one is there are too many variables to offer a single guide. Even AC 20-62 is a general guide which mostly addresses replacement parts. To use your ring terminal example above, there are a number of other acceptable published industry specifications (ASM, ASTM, SAE, etc) that these ring terminals are produced under which can be used on TC aircraft. Best practice is to purchase your standard parts from a reputable source which usually ensures traceability to an industry specification.

Right now my general understanding is that step 1 is determining whether an alteration or repair is minor or major.

Read over AC 43-210A, then see what questions you have on this topic.

I want to replace my fuel pressure gauge.

You’re getting ahead of yourself. First question, are you replacing the existing OEM fuel press indicator with a different one that is not an OEM alternate indicator for your S/N aircraft?

 

[Ed Haywood]

You’re getting ahead of yourself. First question, are you replacing the existing OEM fuel press indicator with a different one that is not an OEM alternate indicator for your S/N aircraft?

Yes, exactly.

I have a 1978 Bellanca Decathlon. My existing OEM fuel pressure indicator is a Stewart Warner 2 1/16" mechanical fuel pressure gauge. AFM states instrument is required equipment, and specifies range marking of green arc from 14 to 45 PSI.



I would like to convert to a 2 1/4" electrical gauge and sender to get the fuel line out of the cockpit. Here are the current TCDS approved instruments.



I do not like the FP-5 and the FS-450, and do not want to mess with installing a transducer in my fuel hose. The United 6335 is no longer in production, and is a mechanical gauge.

I would like to install a UMA electric gauge and sender. It is TSO and can be custom range marked. Ignore the photo, actual gauge range is 0-60 PSI.



So what is the process flow for making this alteration?

 

[Bell206]

AFM states instrument is required equipment

What document in the AFM states its required? Did we discuss this swap before?

So what is the process flow for making this alteration?

What documentation is available with the UMA indicator and sending unit?

 

[Ed Haywood]

What document in the AFM states its required? Did we discuss this swap before?

Installed Equipment List, which is an appendix at the rear of the AFM. The list has an index indicating whether each item is Required for FAA certification, Standard, Optional, or Not installed. FP gauge is listed as Required. That is consistent with FAR 23 certification basis, which at the time required a pressure indicator for all pump-driven engines. FAR 23 has since been amended to allow fuel flowmeters.

IA says he'll approve if TSO. I'm just trying to understand the regulatory logic trail. In particular, trying to understand the significance of TSO vs non-TSO to an installer.

I reviewed AC 43-210A like you suggested, and followed the flow chart at figure 3-1 and 3-2. I think it is a minor alteration, and thus does not require approved data.

In that case, does TSO provide acceptable data to an installer that a product meets performance and environmental requirements for a specific application? For example, TSO C47 is for fuel, oil, and hydraulic pressure instruments. All it does is reference SAE standard AS408C. So if I find a gauge that is produced under TSOA for C47, meets the range specifications in the AFM and my old gauge, and can be installed with accepted practices and elementary methods, does that constitute "acceptable data" for a minor alteration?

 

[Ed Haywood]

What documentation is available with the UMA indicator and sending unit?

Poked around and found install instructions for the UMA gauge.

Still, am more interested in TSO and what that specifically means to an installer, especially as compared to non-TSO for a minor alteration.

 

[Bell206]

Still, am more interested in TSO and what that specifically means to an installer, especially as compared to non-TSO for a minor alteration

In general, theres no simple answer as you can have one minor alteration where use of a TSO part is moot but another that may require use of a TSO part. For example your fuel press indicator. Since it appears the indicator is a required primary instrument that is part of the approved type design then the indicator needs to be approved as well. So you would have to get your non-TSO ind approved in some manner. Now if the indicator was not required for certification then you could use the non-TSO part similar to how non-TSO comm radios can be installed.

So if you use the TSO UMA indicator you take care of the type design requirement and after reviewing Part 43 Appx A(a)(1)(xii) which deals with alterations to the basic fuel system design, even with the use of a sending unit vs a wet line, I think you might still be within a minor alteration. However, given you have an acrobatic aircraft I'm sure there might be some additional checks that need to be addressed. I dont know and would defer that call to your APIA.

Or... you could take your non-TSO indicator and its installation and see if your local blue badge will field approve all of it.

Regardless, given the OEM does offer the EI option to get the fuel lines out the cockpit, you might want to at least sit down with your mechanic and work out the pros/cons of going with the UMA. Thats what I would do.

 

[Ed Haywood]

Regardless, given the OEM does offer the EI option to get the fuel lines out the cockpit, you might want to at least sit down with your mechanic and work out the pros/cons of going with the UMA. Thats what I would do.

That's is exactly what I will do. Actually already did it over the weekend. Pros to the EI are that it is factory spec and provides fuel flow. Cons are that it is twice the cost and is butt ugly. We both agree that we like the UMA better, but it looked like the correct range is never in stock. Found out from UMA today that it is always in stock; they produce and drop ship after order. Based on that, leaning hard towards the UMA.