Cessna 172 firewall damage

brien23

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Cessna 172M firewall damage right side above oil cooler cowling mount to firewall tore loose pulled out, also crack in firewall. Has anyone seen this before, would not have expected damage in this area.
 
Cessna 172M firewall damage right side above oil cooler cowling mount to firewall tore loose pulled out, also crack in firewall. Has anyone seen this before, would not have expected damage in this area.
A photo would help.
 
A local FBO bought a new 182 firewall from Textron recently. $40K! Yikes.

This is where owner produced parts start looking very good. I can't imaging a firewall is *that* complicated to scratch build.
 
Cessna 172M firewall damage right side above oil cooler cowling mount to firewall tore loose pulled out, also crack in firewall. Has anyone seen this before, would not have expected damage in this area.
Did this happen in one landing? or is it accumulative?
 
Rather common, one bad landing is all it takes.
Yep, seen it on a Cardinal. Plane was a hangar queen for weeks after that. What a mess to fix. (Not that I had anything to do with breaking or fixing, btw.)
 
Can you install a stainless patch on top of the damaged area ? Sounds like there was a poor doubler on initial install.

My guess is there is underlying structural damage that goes well beyond the bent up sheet of stainless that forms the firewall.
 
Can you install a stainless patch on top of the damaged area ? Sounds like there was a poor doubler on initial install.

The damage is a major repair, no patches, the firewall has to be replaced. The damage is from the pilot driving the nose gear into to runway during landing.
 
The damage is a major repair, no patches, the firewall has to be replaced.
Why would you say that?
Here's Cessna's take on repairing a 100 Series firewall. Whether it becomes a major repair will depend if the final repair meets the requirements in 43 App A(b):
upload_2019-5-23_13-14-23.png
 
You guys should read before posting things like "nosegear damaged firewall and it must be replaced." The OP has a cowling shockmount bracket torn out just above the oil cooler. The 172M does exactly that and it just needs a stainless patch and the bracket reinstalled. I've done those.
They tear out because the bracket flexes the firewall there. It's a weak spot. The other side will be cracking too.
 
You guys should read before posting things like "nosegear damaged firewall and it must be replaced." The OP has a cowling shockmount bracket torn out just above the oil cooler. The 172M does exactly that and it just needs a stainless patch and the bracket reinstalled. I've done those.
They tear out because the bracket flexes the firewall there. It's a weak spot. The other side will be cracking too.
Firewall is structure, It will be a major repair, using the structural repair manual as data.

this area is a real PITA to work, unless you are a contortionist, it's easiest to remove the instrument panel to get to the area.
 
Why would you say that?
Here's Cessna's take on repairing a 100 Series firewall. Whether it becomes a major repair will depend if the final repair meets the requirements in 43 App A(b):
View attachment 74321
are you certain that this SRM applies to the 172 in question?
 
Firewall is structure, It will be a major repair, using the structural repair manual as data.

this area is a real PITA to work, unless you are a contortionist, it's easiest to remove the instrument panel to get to the area.

The damaged area will be at the shelf just above the oil cooler. It's easy enough to get at from both front and back. And the SRM for the 172M will cover it.
 
172 firewall.png

This is the firewall on a 172R or S. The area circled in red is the area in question. In the 172M those reinforcing doublers behind the cowl mounts weren't there, and the mounts flexed the firewall and caused cracking from the mount rivets. It was a problem on all the old 172s with shock-mounted cowls, and it's why Cessna added those doublers.

The oil cooler was immediately below that mount. In the R/S airplanes the cooler was moved to the aft engine baffle.
 
This is where owner produced parts start looking very good. I can't imaging a firewall is *that* complicated to scratch build.

Ever worked with stainless? Not much fun at all. And if the old firewall is all bent/torn/distorted, what do you use for a pattern?
 
Ever worked with stainless? Not much fun at all. And if the old firewall is all bent/torn/distorted, what do you use for a pattern?

I have worked with stainless. There are a couple of custom fabbed (by me) parts on my RV-10 that are stainless. As far as dimensions, either hammer the original flat and duplicate it or go measure another C-172. I can do a lot of fabrication for $40K. Besides, it isn't like missing a firewall dimension by 1/32" or whatever tolerance you can achieve in your garage workshop will matter.
 
I have worked with stainless. There are a couple of custom fabbed (by me) parts on my RV-10 that are stainless. As far as dimensions, either hammer the original flat and duplicate it or go measure another C-172. I can do a lot of fabrication for $40K. Besides, it isn't like missing a firewall dimension by 1/32" or whatever tolerance you can achieve in your garage workshop will matter.
The tolerances matter. Getting it a little small will result in unacceptable rivet hole edge distances. And measuring another 172 with all the stuff on the firewall would be fun indeed.

There is still the matter of which stainless. SInce I retired I can't remember if Cessna specified wich one it is in the manual, chapter 19.
 
The tolerances matter. Getting it a little small will result in unacceptable rivet hole edge distances.

You can screw it up a bunch of ways. But for $40k, I'm willing to screw it up a time or two if that's what it takes to get it right. Any decent IA, A&P, or homebuilder with sheet metal experience could do it. Honestly, I don't see fabricating a firewall as that big of a deal. Referencing the problem you threw out there, you fit the firewall with oversized flanges, drill the firewall to the fuselage, mark the flanges for trimming, pull it off and trim it. Sheet metal isn't that hard.
 
In the real world if the OEM says no or to repair it via some reciculous time consuming expense, that's when third party engineering is consulted. Just saw it today, OEM wanted the whole frame segment replaced, for some chafing damage caused by too long of screws installed in sidewall panels, third party generated a doubler drawing with 8110-3 that took way less time to install.
 
You can screw it up a bunch of ways. But for $40k, I'm willing to screw it up a time or two if that's what it takes to get it right. Any decent IA, A&P, or homebuilder with sheet metal experience could do it. Honestly, I don't see fabricating a firewall as that big of a deal. Referencing the problem you threw out there, you fit the firewall with oversized flanges, drill the firewall to the fuselage, mark the flanges for trimming, pull it off and trim it. Sheet metal isn't that hard.
It won't fit at all, even for drilling, if it's oversize. It's inset back from the edges of the fuselage skins, against formed angles riveted to the skins. You'd have to trim, fit trim some more. And you'd need to make sure that the fuselage sides haven't been distorted by whatever forces ruined the firewall in the first place, or the new one would just fix those distortions permanently in place, which would dislocate the engine mounting points and a bunch of other stuff.

Sheet metal looks easy until you get into it as a job and run into way more complexities than you expected. Been there, done that, both as a homebuilder and licensed mechanic.
 
Sheet metal looks easy until you get into it as a job and run into way more complexities than you expected. Been there, done that, both as a homebuilder and licensed mechanic.

Nobody said it was trivial or easy. But, if you're convinced you can't do it, you're probably right.
 
This is no easy repair, lots of stuff must be removed to gain access to the area.
 
Good pictures, turn it in to the insurance company, it should easy total the aircraft, then that POS 172 can go way.

:):):) Harsh man... C'mon Tom, giver her some love. That grand 'ole lady has trained quite a few PPLs in her day huh? :D:D:D
 
Has anyone seen this before,
Yes. But as mentioned above, can be a bit challenging to work the other side especially if there is additional interior damage.
 

I'm wondering if there is corrosion at the root of that fitting, between the fitting's forks and the spar, that's putting the outward pressure on it. If so, it wasn't an assembly fault by Cessna.

The prices are up to Cessna, for sure, but at the same time, we don't expect GM to provide parts at reasonable cost for the tiny number of 1970 Chevy El Caminos still running around.
 
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