Another question to the mechanic guys

[SUNDBY]

I am in the long process of a complete restoration of my B model. I am about to plumb/install the pitot/static system. The question is, can I, should I, consider using newer technology nylon tubing inleu of using aluminum lines. My IA questions if that is legal? Can anyone expound on this and the legality of it. Where is the line drawn for STC or PMAed parts or components. Under advice I have ordered the hoses for the oil pressure lines, both fore and aft. All the wiring is new including CB's. Long story long, what legal issues and what language from our friends at the FAA makes these changes legal? George?, anyone? Thank you for the discussion. Sundby

[Showboatsix]

[quote="SUNDBY"]I am in the long process of a complete restoration of my B model. I am about to plumb/install the pitot/static system. The question is, can I, should I, consider using newer technology nylon tubing inleu of using aluminum lines. My IA questions if that is legal?[/quote="SUNDBY"]

My question to the IA would be, ...."Are we going to use the old cloth covered wires over too? Is it legal to use modern avaiation wiring also, if we can upgrade to the "modern wiring" why not the "modern pma tubing"?

I did N6863A 11 years ago to both with no problem from any of the A/P/IA's who have inspected my plane.

[GAHorn]

Use the new plastic tubing. (It doesn't corrode, fracture, and is easier to route around corners, etc.) It's a standard part. (Doesn't require PMA, STC, etc.) It also has a Cessna part number if your mechanic wants documentation on it. You can buy it from Aircraft Spruce.

Many substitutions are actually "minor" alterations. (See FAR 43 for definitions) Minor alterations may be made by simple logbook entry.

Otherwise, parts which are commonly known as "standard parts" do not require any additional documentaton other than traceability. An example is common AN hardware such as bolts, nuts, washers, or Aeroquip fittings, etc. (This is NOT hardware-store hardware, commonly known also as Grade 2 or 5. In other words, don't buy them from inside a guy's trench-coat on ebay-alley.)

Stangely, there are some common hardware items which are actually approved in some aircraft installations, but this response isn't going to get that deep. (Examples might be brass fuel and pnuematic fittings.)

Basically all supplies/equipment must be "aircraft quality" meaning they are traceable to either an approved aircraft mfr'g source or must be categorized as "standard" parts.

If you are altering an existing system (such as changing out fuses for circuit breakers) the wire and the cb's must be aircraft parts and the alteration should comply with AC 43.13 -1B as to methods/materials. If it's merely the replacement of existing equipment it's a repair and merely needs recordation. If it's a true alteration, then it is either minor or major. If minor, it merely needs a logbook entry. If it's major, it requires a Form 337 be completed and filed with FAA. If it's a completely new design it will require engineering approval (DER) or "Field Approval" (FAA signature in Block 3 of the Form 337) or it will require and STC.

It's my opinion that merely replacing original/existing wire with modern "tefzel" aircraft wiring, and substituting CB's for fuses, is a minor alteration. (Don't use Auto-Zone electrical connectors either. They do not comform to any standard of materials, and frequently use PVC insulation. Use aircraft grade electrical connectors, ring-terminals, etc. You can purchase all the necessary materials from Spruce 877-477-7823, or http://www.aircraftspruce.com/ )

Example: "Replace existing navigational-light wiring with new, MIL-W-22759/16 wire of same (or proper or stated) gauge. Replace existing fuse and fuse-holder with Klixon 7271-8 circuit breakers of same (or proper or stated) capacity. All materials/methods comply with AC 43.13-1B. This electrical circuit design has not otherwise changed." and the date, signature, cert. no. , of course.

[lowNslow]

What size plastic tubing is generally used for replacing the tubing in the pitot/static system? Also what sized fittings are used at the instruments?

[T. C. Downey]

What size plastic tubing is generally used for replacing the tubing in the pitot/static system? Also what sized fittings are used at the instruments?

Your instruments should be 1/4" pipe threads all the fittings can be bought at Aircraft Spruce. the line size is 1/4"

[T. C. Downey]

GA. who decides if the alteration is a major or minor?

[lowNslow]

Thanks Tom. I assume you would use 3/8"OD tubing (1/4"ID) Is there a connector to use from the metal pitot tube to the new plastic tubing?

[bagarre]

There is a fitting right where the aluminum pitot tube enters the wing. That's where you can put the first nylon fitting and replace the remaining with nylon.

You'll still need the aluminum tube that makes up the actual pitot tube that sticks into the wind as the nylon tube will not hold the required shape. The shape is detailed in the 100 series maintenance manual.

I swapped out all my static lines and fittings with nylon at the advice of the local avionics guy and we did it with a log book entry.

[T. C. Downey]

Thanks Tom. I assume you would use 3/8"OD tubing (1/4"ID) Is there a connector to use from the metal pitot tube to the new plastic tubing?

I'l stay with the 1/4" tubing, in the static or pitot systems you are not flowing any amount of air.

[cessna170bdriver]

What size plastic tubing is generally used for replacing the tubing in the pitot/static system? Also what sized fittings are used at the instruments?

Your instruments should be 1/4" pipe threads all the fittings can be bought at Aircraft Spruce. the line size is 1/4"

Vaccum instruments might be 1/4" pipe with 3/8" hose, but aren't pitot/static instruments 1/8" pipe and 1/4" tube or hose?

[n2582d]

If you're flying IFR in your 170 you might be interested in adding an alternate static source to your system while you're switching to nylon tubing. I've added AK210-48L to the maintenance library for reference.

[lowNslow]

Your instruments should be 1/4" pipe threads all the fittings can be bought at Aircraft Spruce. the line size is 1/4"

Vaccum instruments might be 1/4" pipe with 3/8" hose, but aren't pitot/static instruments 1/8" pipe and 1/4" tube or hose?

That's what I'm trying to determine, but I guess I'll find out when I start digging in.

[lowNslow]

If you're flying IFR in your 170 you might be interested in adding an alternate static source to your system while you're switching to nylon tubing. I've added SK210-48L to the maintenance library for reference.

Thanks Gary, good idea.

[T. C. Downey]

Your instruments should be 1/4" pipe threads all the fittings can be bought at Aircraft Spruce. the line size is 1/4"

Vaccum instruments might be 1/4" pipe with 3/8" hose, but aren't pitot/static instruments 1/8" pipe and 1/4" tube or hose?
That's what I'm trying to determine, but I guess I'll find out when I start digging in.

Yes, My Bad, the instrument openings are 1/8" pipe not 1/4" as I said before.

[interstellardust]

I need to replace the rubber hose that connects my venturi as it comes through the right side wall under the instrument panel to the pressure releif valve. I cant see the fitting on the sidewall yet, but the one on the pressure releif valve looks like an 90 degree elbow AN fitting. I've read through the rest of this thread and noted the 1/8" 1/4" inch discussion but the outside diameter of this particular hose is 5/8"

I suppose I could cut the old hose off and measure but I was hoping to have the new hose on hand before I do that. I'm still pulling 4.5" of vacumm. I can just tell this hose isn't long for this world.

I don't think I still have the "original" gyro installed. The one in the panel is a newer model, probably only 40 years old. However, I think the venturi (single) is original. Part of the run between the relief valve and the gyro looks like 1/4" tubing connected at each end with the same rubber hose. It looks like replacement hose would be 306 but what size?

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