----[Please read http://ercoupers.com/disclaimer.htm before following any advice in this forum.]----
In a message dated 5/2/2004 3:10:53 PM Eastern Standard Time, [EMAIL PROTECTED] writes:
Can you give reference to the regulatory prohibition
I think we're loosing sight of the real issue here. The hose spec'd for the Ercoupe application is still Mil-6000. The reason is that it's the correct hose for the application and fittings spec'd. To arbitrarily choose to use something else, 303 for example is totally without regulatory precidence. As pointed out, there are significant dimentional differences between the various hose types and that alone should tell you that substitution is fraught with peril.
A quick check of part 43, appendix A of the regs shows that a modification to the fuel system of a certificated aircraft is a major modification and as such requires a field approval or an STC. It further states that any repair involving "substitution of materials" constitutes a major repair and requires the same level of authorization. There doesn't have to be a specific prohibition in light of the fact that there is no basis for authorization.
The fact that the parts manual lists the size of the hose is not meant to imply that size is the only detereminate of what constitutes an acceptable part. The fact that there is a part number indicates that the part is specified elsewhere as to material, size, tolerances, etc. Only by reference to that data can the determination be made as to what constitutes an acceptable part.
You may not realize this, but the words "better" and "exceeds" are red flags for the FAA. Any change that involves making something "better than original" or where the change "exceeds the performance of the original" is by definition a modification and falls under the appropriate level of scrutiny and beauracracy. Keep that in mind as you go through life.
Lest you think this is all a bunch of hot air, think about this. Suppose you have a hard landing and the subsequent inspection turns up a bunch of popped rivits in a skin somewhere. To make the repair "better than new" you elect to use bigger rivits. "I'll never have to fix this again." Next time you have a hard landing, those rivits hold just fine and the inspection turns up no damage. Now you're feeling really smart. You made the plane stronger than new. But a hidden crack developes in a bulkhead next to your alteration. A couple of days later you have a gear collapse on a normal landing.
Similar things happen when folks decide to use .040 stock to make a doubler on a cracked .032 skin. The added stiffness of the .040 just moves the weak point out to the edge of the doubler. Cracks develop all around the patch and the whole panel fails. (Rule: aviod abrupt changes in cross sectional area...)
This is not to say that making hoses for an Ercoupe fuel system from 303 and the appropriate fittings is going to make your plane fall out of the sky. On the contrary, I can't think of a single technical reason not to do it. However, bear in mind that an insurance adjuster's job is to find a reason not to pay and an FAA inspector's job (he thinks) is to find a reason to ground you.
(Stepping down from soap box now)
John
============================================================================== To leave this forum go to: http://ercoupers.com/lists.htm Search the archives on http://escribe.com/aviation/coupers-tech/
