firewall damage

firewall damage

I have a Cessna 172 on leaseback that has suffered firewall damage from a hard nose wheel landing.  Only damage appears to be a wrinkle in the left side of the lower firewall.  The maintenance manual states that a new section can be spliced in.  Need info on materials to use and where they can be found. e.g. stainless steel sheet- what thickness ?  Rivets are MS20450- what length and how do you drive them ?  How much overlap is required for the splice?

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Re: firewall damage

Seems to me like your mechanic should know these things..

       Dave

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Re: firewall damage

If there is no manufacturer repair instructions in existance, you might refer to the Advisory Circular...
AC 43.13-1B "Acceptable Methods, Techniques, and Practices/Aircraft Inspection, repair & Alterations.
You can find it online at...
<http://www.faa.gov/certification/aircraft/av-info/dst/43-13/default.htm>

Or you can order one from the Superintendent of Doccuments, U.S. Government Printing Office, Washington, D. C. 20402.
Your mechanic should have a copy or ready access to it.

I think you're going to end up with a "doubler".  Your firewall would get an equal or greater matching piece of aluminum riveted to it.  But then, I'm not a mechanic.

Michael

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Re: firewall damage

In this case,  I am the mechanic.   AC 43.13 has very little to say about stainless steel firewalls.   And I have yet to find another mechanic who has seen, much less used the steel rivets that are used to install the firewall at the factory.  I have seen firewalls repaired with cherry max blind rivets - a "no-no" according to the maintenance manual.   I have seen firewalls repaired using AD rivets - also a "no-no" due to corrosion issues -- although plenty of them are used by the factory.  I have talked to airframe "rebuilding" shops who use Monel rivets.   No one can give documentation though of what exact materials and dimensions are needed for stainless repair.   I'm trying to exhaust all possibilities of technical data before proceeding with my "educated guess" for the correct procedure.

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Re: firewall damage

I am looking at a 182 Service Manual and it says  - "Firewall sheets may be repaired by removing the damaged material (.016 - inch aluminumized iron sheet), and splicing in the new section. The new portion must be lapped over the old material, sealed with Pro-Seal No. 700 or equivalent, and secured with MS16535 (steel) or MS20613 (corrosion-resistant steel) rivets.  The heater valve assembly is attached with MS16535 and MS20613 rivets.  Carburetor heat and mixture control doubler, firewall plates, firewall doublers and nutplates are attached to the firewall with MS20470 (aluminum) rivets".

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Re: firewall damage

Thanks for the info.  That is by far the most discriptive exerpt of any of the maintenance manuals that I've seen.

Lonnie

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Re: firewall damage

Lonnie,  I have the same deal on a C-150.  Can you tell me what you found out?  Sheet thickness,  Rivets, ect.   Thanks  Mike

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Re: firewall damage

buy a complete firewall from cessna.  therefore there will be less of a devaluation of your plane due to its new "damage history" status.    sounds like something your insurance should pick up anyway.  we just got one out of the shop in july that had the nose strut shoved six inches up in the firewall.  we used all cessna parts and the repair turned out great.

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Re: firewall damage

thanks to hurricane ivan, i have a pa28-181 with lower left firewall damage.  i plan to purchase a used firewall from a salvage outfit and splice in the area that i need.  cherrymax does sell the monel type rivets as well as the aluminum type.

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Re: firewall damage

I had an issue with a 172 back in 2000. I called Cessna and got an engineer to give me the repair. I e-mailed him photos of the damage from both inside and out with the engine removed. I unfortunatly do not have his name or number any more. I would call your local dealer and ask who the area's tech rep is and give that person a call.

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Re: firewall damage

Here's the scoop on firewalls.   If you have a galvanized firewall you can use standard AD aluminum rivets.  If you have a stainless steel firewall then you require stainless steel rivets. You drive these rivets the same way as aluminum rivets but you need a good 4X gun and make sure you keep the bucking bar square on the head as far as part number for the rivets get MS20613 in 4-3.  Follow the same procedures for an overlap joint to fit a single row of rivets.  Hope this helps

Mike Block

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