Our 1986 aircraft has some corrosion on it but not a huge amount. I'm trying to find out if there is somewhere in the uk which can do an independent assessment of the paintwork, or whether it is simply down to other paint shops to "assess" and give their recommendations? Or for a true assessment, would we need a boroscope inspection to look inside for the extent of the corrosion?
thanks.
A bit more information would help to enable a more applicable answer. Is there bubbling corrosion under the exterior paint? That should be fixed.
Most aircraft are inspectable enough, that borescope inspections on airframe parts are generally not needed, to get a sense of corrosion. Yes, there are some parts which can be hard to see, but if there is little corrosion elsewhere on the airframe, there is a lesser chance that just the uninspectable area is corroded. Though, we did have one rather glaring exception to that logic recently!
If the aircraft has factory zinc chromate primer on the inside, you probably have less to worry about. Any corrosion should be detectable by an aircraft mechanic. I would have a mechanic inspect the aircraft, and if required, a paint shop paint it. Paint shops might employ a mechanic, and that is fine, but do not rely on a painter to assist you with airworthiness decisions.
If the aircraft is stripped for painting, the preparation of any corroded areas before repaint is pretty important, and if it was necessary to remove metal during that process, it should have been done in accordance with the structural repair manual for the aircraft, or in the absence of that, AC43.13. If you want to educate yourself, have a read through the corrosion section of that AC. It can be found on line. If metal work was done, have that work properly inspected before any paint is applied, which could conceal uncertain workmanship.
Personally, I touch up little external corroded areas by removing the bubbled-up paint, removing the corrosion from the metal, and simply brushing some white 2-pack epoxy primer onto the area.
It doesn't look brilliant, especially as the primer turns yellow under UV after some months, but it stops the corrosion.
I am trying to buy the correct MAPAERO base paint but getting the part numbers (never mind getting the paint itself) from the French company is a huge process.
There is a fair number of spots that need doing on a 11 year old plane, especially if the Socata paint shop was a bit sloppy at times... but there is also damage from e.g. fuel men bashing the pump nozzle against the paint around the filler cap.
Things like vertical or horizontal stabilisers may need an endoscope to see inside. I bought one on Ebay for about £300 - 6mm diameter x 900mm long.
Once such internal cavities are found clean then spray ACF-50 in there, to make sure it doesn't start.
Thanks. Have spoken to Mick Allen this morning and said we'll drop in for an assessment shortly.
As a matter of interest, how long would you expect a new paint job to last until the first signs of corrosion start appearing? Appreciate it depends very much on where the aircraft is kept and how often it is cleaned etc. but a broad indication?
I am no expert - but will depend on it's previous life, including how it was built. Filiform corrosion should be dealt with by the preparation after a strip. The problem is identifying exfoliation/stress/ fretting and other types of corrosion that are difficult to see.
I once had a Rallye that needed two rivets replacing, in setting the rivets six more heads jumped off from what looked sound rivets, but where nothing but powder inside. Hence when I built the RV every bit was individually Alodined, two-pack primed, THEN assembled, and wet riveted with Duralac. A system that would probably be expensive for a production aircraft.
I think a lot of cases of poor paint life are caused by cockups in the process, or preparation.
For example I know of cases of a €3M turboprop on which the paint could be peeled off in 20mm wide strips, using your fingers.
It would seem that somebody did the painting when it was too hot, too humid, etc.
Or somebody touched it with their fingers, between coats.
And this is a big problem in a commercial setup. The vast majority of GA-type paint shops don't have a temperature/humidity controlled spray setup. Commercial pressure dictates that the job must be done regardless of these things. The customer is not going to notice for years, at best - even a spray can from Halfords will last a year or two - and will have probably sold the plane before then.
Wet riveting with Duralac (or some other supposedly less carcinogenic material whose name escapes me) is great but very time consuming. I had a reinforcing plate done (for a satellite antenna) which I categorically specified to be wet riveted. Did they do it? When I asked what I am supposed to do when water gets in, they suggested I spray some ACF50 in there every so often. EASA145 FAR145 company.
Wet riveting with Duralac (or some other supposedly less carcinogenic material whose name escapes me)
Perhaps the material is JC5A ?
The trouble with JC5A and ACF50 is the aircraft is really difficult to paint after using either. They never set and keep escaping from hidden places, just what they are designed to do. I will avoid them if at all possible, but used gallons on the old Rallye!
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Sure... especially ACF50 which totally prevents any painting for at least a year afterwards.
But there is another material. It can be PR1422 (the fuel tank sealant) or there is another one, and these can be overpainted.
PR1422 comes in two grades, one of which dries slower and if you assemble the components with skin clamps only and wait for the stuff to go off and only then rivet it, it's workable (I am told).
