Understanding Aircraft Corrosion

[XX621]

I am in the process of purchasing a share in an aeroplane. The aircraft is 28yrs old and has been parked outside most of its life.

The pre-buy inspection has thrown-up ~6 areas of corrosion. Some of it regarded as "exfoliation" corrosion. Non of the areas are particularly big, but I am told that exfolition is the worst type and starts within the metal and works out.

So I am concerned, naturally.

Should I give this aircraft a wide berth?

One area of corrosion is, for example, one of the wing attachment bolts which is displaying a patch of corrosion on the surface.

I got the impression from the engineer that the presence of any exfolition is a deal-breaker?

Opinions greatly received.

[SeldomFixit]

Exfoliation is certainly nasty but relative to the area in which it is found. Is it structural ? Ask your inspecting LAME to classify the damage for you with an eye to repair costs. That will give you a starting point to either move forward or an end point at which you can make an informed decision to exit the deal.

[Avtrician]

Corrosion on the bolt is not so much of a problem, as it can be replaced. Exfoliation corrosion in the skin can possibly be repaired, but if it has got in to the spars or structural attachment points then that is bad as it will continue to spread like a cancer thru bone. effect is not unlike the effect of rust in a chasis rail.

[XX621]

Thanks guys

[stevef]

If the corrosion is only evident on the skin, it may be a bargaining point rather than a purchase refusal. As others have mentioned, the problems are when extruded or worked materials, such as spars or stringers are affected by intergranular corrosion. That could well turn out to be expensive. What type of aircraft are we talking about and where is the corrosion located.
Please don't say it's a Rallye...

[XX621]

Its a 1980 TB10.

[mavrik1]

It depends on which parts of the aircraft it is in! If it light surface corrosion it can be blended out to a certain degree specified by the manufacture.
If its exfoliation in primary structures that will need to be replaced that can not be removed or dismantled easily it can cost a fortune due to labor and parts!
Some aircraft metal types are much worse than others and some batches of spec metals that aircraft have be made from also worse than others. If it is exfoliation or intergranuler due to metal type or bad batch the aircraft could riddled with corrosion.
When the aircraft starts being striped down you will find it around fasteners, between skins and all the little hiding places. Your hangar visit could be become very expense.
Unlike general corrosion caused by environment, ie surface.
Exfoliation can be fatal due to corroding from the inside out being unnoticed until it lets go!
Not trying to scare you from the purchase just educating.
If its all secondary structures,ie eng cowls, wing to body fairing, easy to replace. No problems

[XX621]

Ok thanks for the comments!
The main corrosion in question, from what I have seen, is located on the underside of the wing in a small area around the front attachment bolts, and some on a flap bracket and a bit more on one of the fuselage strakes. Interestingly on the other wing a new plate had been affixed in the same area (around the attachement bolts).

Regarding structural corrosion, to be 100% sure there isn't any - this would require a full survey I assume, as the inspection I had done only highlighted the surface occurances?

Should a CoFA pickup any structural corrosion?

Thanks again.

[smarthawke]

Fuselage strakes....? Must be a TBxx then! I'd have a very close look at the spars then as well, not unknown for them to need new wings. PM me with a reg and more details if you want a few pointers.

[Beeline]

May be worth an NDT inspection of the local areas of the corrosion no detailed surveillance can pick up, assess the depth of the problem if on primary/secondary stucture. SRM surface repairs can be acheived but what lies beneath wilthin the material could manifest itself into a problem!!
No idea on pricing sorry, I just raise a card and its done ....

[ivor toolbox]

Here you go, easy to understand,courtesy of Mr Boeing

http://www.boeing.com/commercial/aer...7/corrosn.html

and a picture too

http://www.boeing.com/commercial/aer...osn_fig05.html

Corrosion is difficult to treat, the best method being complete replacement of affected parts; any metal repairs, (cutting out bad and joining in good) will have to be done iaw manufacturer or type cert holders recommendation as listed in the Structural Repair Manual or by a one-off request.

The pre-buy surveyor is probably giving you the best advice, shop elsewhere unless you want to end up paying more than originally budgeted.

ttfn

[FIMbar the Furious]

Guys can we please refer to corrosion by its proper name















Overtime Dust

[Engineer_aus]

To be honest, I have written off a few aircraft due to corrosion. The more you look the more you find. It starts off as a little spot, so you fix that, and then you see another spot etc etc. How deep are your pockets? Honestly you better off getting a better aircraft, or dig a hole in the backyard and throw your cash into it and burn it all.

[WOTME?]

Overtime Dust?

CONNIE GOLD!