Corrosion inspection

[rudyhiller]

So I saw a youtube video about a Cessna 140 that underwent the SIDS inspection program in Australia, and one of the surprises that was found was corrosion around the wing attach blocks and aft carry through spar.
Has anyone else had this? Is this pretty common to have corrosion in this area?

[8342]

I don't know how common it is but I found the aft spar carry through on my 140 with severe inter granular corrosion which tirggered the complete overhaul of the airplane.

Rick

[V529]

Acutally, while not "common" it's not "un-common" if that makes sense.

Cessna used Zero corrosion protection inside their aircraft when built. So some, we have no idea how many, aircraft will show corrosion inside the wings, horizontals and yes, the carry through spars.

Typically, the corrosion is "light" and like most aluminum on Cessna products you will get the light white haze that aluminum shows and it goes no further.

I would look at the spar caps of your two wings, as the material there is very similar to the carry through spar material. If you have concerning corrosion on the spar caps (the "I" beam) then you may want to pull a wing, remove the blocks and shine a light inside each carry through. (this makes a massive assumption that the wings are original to the aircraft......many are not!)

Another issue that has crept up is cracking inside the carry throughs just inboard of the wing spar blocks, The cracks start at the bolt holes. This is not very common, but it does happen.

Usually from the small sampling I've seen........maybe 20-30 aircraft the corrosion is present, but pretty light. Every once in a while a "WHOA" shows up. Probably due to the climate the airplane was stored in.

As has been repeated many times, Cessna didn't think to design these aircraft to last this long, ..........

[6643]

I would point out that the surface corrosion Victor is referring to is very common and not generally an issue. I ran a plastic brush through my carry-through spars when I had the wings off and then treated the insides with Boeshield T-9.

Intergranular corrosion is caused by flaws in the metallurgy of the spar. Think lumps of sugar in cookie batter. It is not related to environmental conditions, and there is no way to avoid it other than to use materials that are free of (invisible) flaws.