Piper Cherokee Firewall Repair

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machkhatib

Pre-takeoff checklist
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Mach
Hello. I’m looking for mechanics’ opinions on this firewall repair on a Piper Cherokee. There is a logbook entry but no 337 was filed. I’m the buyer and I’m under contract but I can still back out if I’m unsatisfied.

https://imgur.com/a/EEjoRFz
 
Why would a 337 be needed for a fire wall repair? Do you know what type of damage there was and how it came to be? Get the CD from the FAA to see if there was some kind of accident or incident reported. You could maybe try to talk to the person who made the repair.

My $0.02 worh.
 
somorris said:
Why would a 337 be needed for a fire wall repair? Do you know what type of damage there was and how it came to be? Get the CD from the FAA to see if there was some kind of accident or incident reported. You could maybe try to talk to the person who made the repair.

My $0.02 worh.
Click to expand...

According to the seller, an "exhaust leak scorched the firewall over time. The firewall and exhaust were fixed."
 
Quite common on Cherokees in my world. Even w/o an exhaust leak.
If the “ tailpipe” is too close to the firewall the zinc coating is burned off.
You then have bare steel exposed and a rust-through occurs.

Mufflers and stacks generally will not come with pre-drilled holes . The clamps have pins to prevent the muffler from rotating . If the muffler is not “ clocked” properly BAD things happen.

1. Zinc burn off as mentioned.

2. Tailpipe Contacting the engine/nose gear mount can result in an $$$$ repair.
 
Magman said:
Quite common on Cherokees in my world. Even w/o an exhaust leak.
If the “ tailpipe” is too close to the firewall the zinc coating is burned off.
You then have bare steel exposed and a rust-through occurs.
Click to expand...

Thanks for sharing. Any concerns with the pictured repair to the firewall?
 
machkhatib said:
Thanks for sharing. Any concerns with the pictured repair to the firewall?
Click to expand...
This is funny, just put almost the exact same repair on my firewall. I doubt the exhaust leaked, rather the heat from the muffler burned off the zinc causing corrosion. Firewall isn't structural. Now, piper says to use stainless rivets on the firewall. If you use stainless rivets the patch should not be aluminum. Those aren't solid rivets like we used
 
It appears to me like you have at least $100 of Cherry-max rivets in the patch.
These are “ blind” aluminum rivets with a steel mandrel. I’m not sure of Piper requirements but my recall is Cessna wants Monel rivets in the Firewall.
I would have used Monel myself. If your IA feels necessary existing could be replaced with about 1 hr labor.

it would be wise to check backside of firewall during PB. A drill bit could have nicked wires or fluid lines.

If nothing has changed with the exhaust system and galvanized material is used per original this may happen again. Painting with high temp paint and assuring good
clearance from tailpipe should be considered.

My take is it’s not a show stopper on a deal.
 
Wow, thanks for the detailed feedback, guys! So maybe not the best kind of rivet but no major issues. That's good to hear.
 
The reason for stainless or Monel on the firewall is aluminum melts in a fire. You don't want stainless and aluminum touching, galvanic corrosion. So the patch should be stainless or galvanized. Can't tell what it is there. I wouldn't worry about it, but not how we did it on mine.
 
Repair was done IAW 43.13 more than 6 years ago and no issues. I would not be too concerned even with a steel core cherrymax.

@Racerx , if I'm on fire I don't care what's touching! LOL
 
Log entry says patch was galvanized.

Person to do your Annual should be in this loop.

Telling him SGOTI says good or bad is something IAs don’t want to hear.
 
FYI: there are/were OEM firewalls that were made from aluminum coated steel and installed with AD rivets. There is also a route to substitute CherryMax rivets for AD rivets. Given the log entry and finished product it would take more checking than a bad photo to confirm if it is acceptable or not.
 
I told my pre-buy mechanic to give this extra attention. But it sounds like it’s probably ok (and if rivets need to be corrected, probably inexpensive to fix).

I suspect you’re right about the heat-induced corrosion.
 
I think I would be more concerned about having zinc burned off with bare steel and just starting to rust through. Repositioning tailpipe and high temp paint may eliminate need for a patch if addressed EARLY before structural integrity is compromised.
 
Even though it's not structural....and probably a good repair....the paperwork should be fixed. According to 14CFR 43.13 appendix A the definition of a major repair - (xxii) The repair of damaged areas in metal or plywood stressed covering exceeding six inches in any direction.

So, if that patch is larger than 6" it's a major repair and needs to be recorded in a 337.
 
Doesn’t “ stressed skin” imply “structural”§?
 
Magman said:
Doesn’t “ stressed skin” imply “structural”§?
Click to expand...
FYI: not all firewalls are installed in tension or shear, i.e., stressed. You can usually tell if it is a stressed firewall by the rivet patterns which the OP's firewall does not show in the pic.
 
Meh....I'd probably do the 337 even though it's not stressed. Takes an extra 30 minutes to type it out and it's done.
 
somorris said:
Why would a 337 be needed for a fire wall repair? Do you know what type of damage there was and how it came to be? Get the CD from the FAA to see if there was some kind of accident or incident reported. You could maybe try to talk to the person who made the repair.

My $0.02 worh.
Click to expand...

They repaired the Engine mounts
 
Checkout_my_Six said:
Meh....I'd probably do the 337 even though it's not stressed. Takes an extra 30 minutes to type it out and it's done.
Click to expand...

It only takes an “ extra” 30 minutes if YOU did the repair. What if you didn’t and were doing an Annual? Would you do a 337 then?

fictitious courtroom

Insurance Co. Mr FAA ; is this ( repair or alteration) a Major( repair or alteration)?

FAA : Yes it is.

Ins Co : Does a Major Repair or Alteration require a Form 337?

FAA. : Yes it does.

Ins Co : is the aircraft Airworthy w/o the completed Form 337?

FAA : No ; it isn’t .

Ins Co. : So then w/o a Form 337 the aircraft did not meet the agreed upon
Conditions of the Policy and we deny coverage.


After actually hearing this from FAA I wound up doing over 100
“Grandfathered “337s that year.
 
Checkout_my_Six said:
Meh....I'd probably do the 337 even though it's not stressed. Takes an extra 30 minutes to type it out and it's done.
Click to expand...
So if it's not stressed... what non-approved data do you plan to use for your 337? Or do you plan to seek a field non-approval for the repair? :)
Clip4 said:
They repaired the Engine mounts
Click to expand...
Repaired what engine mounts?
 
FAA inspectors rarely testify in civil trials...
 
Anyone would or wouldn’t do a 337 if you found this at Annual? Make some changes first?

btw - The hypothetical situation was presented at an IA Meeting by the FAA’s best
that is no longer with us. There is an award named after him.
 
machkhatib said:
Hello. I’m looking for mechanics’ opinions on this firewall repair on a Piper Cherokee. There is a logbook entry but no 337 was filed. I’m the buyer and I’m under contract but I can still back out if I’m unsatisfied.

https://imgur.com/a/EEjoRFz
Click to expand...

Mind posting the picture again? I’m going through the exact same thing.
Any lessons learned?
 
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