Corrosion in bulkhead stiffeners

[integritywood]

Jim
Some more pics and questions. Took gear legs out to do a good inspection and redo a bunch of rivets. Found some intergranular corrosion on bottom side of RH outboard landing gear bracket.

Gear.JPG

Gear3.JPG

Gear2.JPG

Top half of bracket looks excellent. My AME suggested asking you if this is structurally okay yet if we clean the corrosion out with a die grinder and round carbide burr and the put corrosion proofing on or should we be replacing this bracket. By the way with deeper inspection the bulkhead stiffener corrosion is not near as bad as he initially thought so the game plan is clean it as best we can and give it a good inspection and shot of ACF-50 every year.
I realize the hardware in the photo's looks kinda bad and we'll pull it all and inspect yet. So far all the bolts and nuts in this area have had rusty heads but are in excellent shape otherwise.
Thanks for now
Kim

[hilltop170]

With all the other problems you have shown in the gearbox area, it looks like its time to open it up and fix it right. But that's just what I would do, others might disagree.

[lowNslow]

With all the other problems you have shown in the gearbox area, it looks like its time to open it up and fix it right. But that's just what I would do, others might disagree.

Agree! PPonk should have most of the parts you need. http://www.pponk.com/HTML%20PAGES/landi ... ducts.html

[c170b53]

The course of action...is really dependant on the risk tolerance of the individuals involved. What's right? ...well even new airplanes come out not right. If you can repair things to allow continued operation within your risk tolerance level and have a plan to address items as they accumulate, that's what I generally advocate. If you're in no-mans land then get several opinions, as generally the consensus will provide you with an idea as to the most probable solution. And it's no different here with your latest issue.
But I see there's a bit of a problem with your plan from the start with respect to the latest photo's. likely (it's my opinion) the corrosion originated when the gear leg was allowed to have relative movement within the fitting. The items in contact being dissimilar metals would begin corroding once the protective coverings were compromised by fretting. In your case the corrosion has progressed to the exfoliation stage which has removed all doubt of the severity of the inter-granular corrosion. The problem with corrosion which runs through the grain in the material (inter-granular) in your fitting is knowing where it has stopped. Some sheet metal craftsmen liken the process to mining, theres a vein running through and there's a significant amount of material to remove until the "vein" is exhausted. Even if it was a small spot located on the surface and depending on the orientation of the grain in the material, in trying to remove the corrosion your might have to remove a significant amount of sound material. Once the structural strength has been compromised you're into part replacement.
So it looks like you'll be needing some new parts. Again you'll have to evaluate as you go what is sound, what needs to be replaced and where to stop. None of this is easy but make the decisions and move on as that's the only way to keep a repair on track.

[integritywood]

Thanks for all good advice. Ive been looking on the pponk website and part numbers don't line up with what I've got here. Did Cessna make changes to landing gear support brackets for later models? As far as I can trace my part numbers being superceded they don't supercede to what pponk says their parts replace. Just made me wonder if things got changed.
Kim

[marathonrunner]

I would also put an inspection hole in the center of the panel on the belly between the landing gear. There is a Cessna SB you can reference for this for 180s on floats. I have put this in many Cessnas for the P Ponk landing gear beef up installation and, for cleaning and inspection. Cessna made this a blind area originally. In talking to Dave Swartz of the Anchorage ACO, they would never get certification by having this a blind area today. I ended up talking to them because an owner of a 180 had many loose rivets in his gear boxes that actually had the floor on one side lifted about 3/16". I had to pull it together with bolts and nuts then remove them individually and buck rivets back in. This was to replace the cherry, not cherry max rivets that someone had previously installed.
When the owner got his aircraft back he was not happy with the "illegal" cover and had several mechanics tell him it rendered his aircraft unairworthy and dangerous. I got the ACO and FSDO involved along with Cessna engineering. Even with all those organizations saying it was completely legal including a letter from Cessna engineering he still insisted it was illegal. I finally filled out a 337 which was denied because I was using approved data so no 337 was needed only a log entry and the letter could be included in the log books stating this.

Needless to say the bill did not get paid.

[GAHorn]

I would also put an inspection hole in the center of the panel on the belly between the landing gear. There is a Cessna SB you can reference for this for 180s on floats. ...Needless to say the bill did not get paid.

Did the owner continue to operate that "illegal" airplane? Did he "un-modify" it back to original?
Or did he continue to use the airplane as you modified it...??? ...in which case he clearly considered it OK and owes you.
I don't know about Alaska...but down here there's a thing called a "lien"after-which shops sometimes get paid. (Maybe in AK you just go out and beat the snot out of them. We used to do that down here in TX until we got so many immigrants from Silicon-Valley, CA we had to start letting 'em get away with "alternative behavior". Now we're just known as "Silicon-Gulch".)

[marathonrunner]

I did put a lien on the aircraft but that won't do any good until it is sold. Yes the aircraft is being flown "illegally" I did not have to do it in Kodiak but since moving to where there is a larger population base, I have now gone to not returning the aircraft until the bill is paid. This is very common in almost every other profession. Somehow some owners believe that their hobby should be your hobby as well. I really like the ones that go over the list of discrepancies and like to try to omit the ones that may be airworthy but costly. Cost has a lot to do with what owners believe needs to be done on an annual inspection. I always tell them I know they are a great super hero pilot and all but I really do not care about the person in the pilots seat since they are super human. I care about the other seats that will be occupied.

[n2582d]

I would also put an inspection hole in the center of the panel on the belly between the landing gear. There is a Cessna SB you can reference for this for 180s on floats. I have put this in many Cessnas for the P Ponk landing gear beef up installation and, for cleaning and inspection. Cessna made this a blind area originally. In talking to Dave Swartz of the Anchorage ACO, they would never get certification by having this a blind area today.

Joel,
Thanks for bringing this SB to our attention. My project had two holes added in the plate above the landing gear box, inboard of the existing two access holes. I've made a new sheet without these additional holes but have wondered how I'll buck the rivets in the inboard section of the landing gear box. Using this documentation should help with a field approval to add an access hole underneath.

landing gear box cover.jpg

I've attached a copy of AK180-2 here. The same information is also found on fig. 13 of AK180-1B and fig. 13 of AK180-7.

[marathonrunner]

That is the bulletin. Actually the ACO guy is structures as well as metalurgical and said that putting holes in the top is a way bad idea structural wise. I did not get all the details. You do not need a 337. I referenced I believe chapter 17? which is structural repair in the Cessna 100 series maintenance manual. I am not where I can easily access this information right now. However they give you specific information on installing access holes, size of damage that is repairable for access holes etc. I think you can use a later version as well. I should probably dig up that email from Cessna engineering so that if anyone has problems with their local FSDO they will have that. Maybe a copy of the letter that denies my 337 because I was using approved data would work also.

Again this is a log book entry only not a field approval and yes that inspection hole on the belly makes installing the P Ponk kit easier as well as bucking the "hidden" rivets. Be prepared for 50 plus years of dirt and crud to come out when you make the hole in the belly as it for sure finds a way in somehow through the minor cracks in there.

Good luck on the repair

[GAHorn]

.... I really like the ones (owners) that go over the list of discrepancies and like to try to omit the ones (squawks) that may be airworthy but costly. Cost has a lot to do with what owners believe needs to be done on an annual inspection. I always tell them I know they are a great super hero pilot and all but I really do not care about the person in the pilots seat since they are super human. I care about the other seats that will be occupied.

I can appreciate your point of view on this, and I largely agree. However, I also believe it is indeed the owners money, and it's his prerogative to choose where to spend it. If it's an item that is "airworthy but costly"... then that's a subjective decision and it's their choice. (It's YOUR obligation to point out how much more expensive it will be later-on, or to convince them of the wisdom of correcting the deficiency while you have it apart in your shop...and how strongly you may feel about approving it for return to service.... but it is still their property.)

It's also their responsibility if they carry passengers in it, as long as you've approved it for RTS. Your sense of honor cannot protect all the fools.

[n2582d]

I referenced I believe chapter 17? which is structural repair in the Cessna 100 series maintenance manual. I am not where I can easily access this information right now. However they give you specific information on installing access holes, size of damage that is repairable for access holes etc. I think you can use a later version as well. I should probably dig up that email from Cessna engineering so that if anyone has problems with their local FSDO they will have that. Maybe a copy of the letter that denies my 337 because I was using approved data would work also.

I looked through Chapter 19 (Structural Repair) of the 100 Series 1962 and Prior Service Manual but didn't find anything that covered additional access holes. In the Maintenance Library I've added a page from the 1977 C-172 Service Manual that gives directions for adding inspection / access holes to the wing. Is that the document you were referring to? To me it seems limited to adding holes in the wing. It would be great if you could add the reference material you have--emails, letters from your ACO/FSDO guy, Cessna engineering, etc. -- to our Maintenance Library.

[marathonrunner]

I will add those when I return home in March. I may even have used a 180/180 manual and yes I had to go through the manual and pick paragraphs so I will do that again. George, I have no problem signing off an aircraft as unairworthy if it is due to airworthy items. I also list the items in the logbook as opposed to giving the owner a list. I had the "give the owner a list" blow up in my face decades ago when I signed one off as unairworthy and it was operating literally one day later. The A&P had signed it off "All discrepancies complied with" or something along those lines. The items in question were home made float deck fittings that still had hack saw marks in them. An FAA inspector who was doing some air taxi work saw them and investigated on his own. He called me in and luckily I had kept a copy of my list. They were so bad he did not have to paint them fire engine red to point them out and the really poor workmanship that went along with "owner produced parts" It was grounded again until he was able to buy readily available although in his opinion, expensive fittings.

You are aware that the inspection authorization has evolved from what it was originally supposed to be. When it first started, the FAA literally made a new Airworthiness Certificate. This meant what it still does, that the aircraft meets its TCDS or as approved for alterations. When they could not keep up they started using people they could trust as Authorized Inspectors and picked the people and number for a location based on need. Now anyone who can memorize test questions and meet the recordkeeping requirements and has the minimum qualifications can become an IA. We are dumbing down our system and as you have stated you and otheres who do not have a rating have far more experience and common sense then some with A&P's or IA's

[GAHorn]

I know what you mean.
Yes, I recently found a coworker who was still operating with a pre-54 airworthiness certificate,
...he has been getting mail-order annuals for decades...until his"inspector" died.
His next inspection was performed properly, and FAA discovered the matter when the obsolete
certificate was presented for replacement.
I would have liked to be a fly on the wall during that meeting.