Fillform Corrosion on an Archer

[BoeingBoy]

Sorry Guys. Me again!

My 77 Archer II has been well looked after and has a paint finish that whilst applied in 2003 looks like it was done last week. The aircraft has been hangared for the last year of my ownership and is regularly cleaned with a waterless wash/wax product made primarily for cars but formulated without salt or ammonia.

However it's previous history was to be based at Goodwood for many years and now Liverpool so plenty of salt air in its history.

All has been well until the last month when the right side of the aircraft has decided to self destruct with fillform corrosion. I have three patches on the airframe, two on the stabilator and one on the rudder. All the underwing inspection hatches have fronds coming from various screws. The right fuel tank screws are showing the start of activity and also the screws down the windscreen centre post. There is also one small area on the right side fuselage inspection hatch forward of the stabilator. However there is nothing on the left side except one long known patch on the stabilator.

What is surprising me is the speed at which all these have appeared. Put simply there was nothing visible a month ago apart from the left stabilator patch.

Obviously I want to get on top of the problem ASAP but being new to aircraft ownership I am unsure as to the viablilty of 'patching in' against simply giving the aircraft to a specialist paint company and letting them go around the whole aircraft and sort all areas out in one go.

Whilst my maintenance company are happy to start patching, to me it's probably going to be the more expensive and the least efficient option in the long term. However, if this is now something that I am going to see continually then is spending a large sum at a sprayer simply going to be eroded by having to revert to patching anyway.

Can I ask for advice on the best way to deal with this. I am happy to spend what is required as the aircraft is a true gem and I don't want to see it deteriorate in both condition or value, but at the same time I don't want to spend good money on something that will need doing again in a couple of months.

As always, thanks for any help.

[SeldomFixit]

https://www.faa.gov/regulations_policies/handbooks_manuals/aircraft/amt_handbook/media/FAA-8083-30_Ch06.pdf

Start here BB. Filiform is probably the easiest form to remove but will most likely involve fastener replacement, as you'll need to remove any in affected areas, in order to remove the worms. Patching is a bit extreme as Filiform is surface corrosion, by nature and would only require skin replacement in extreme cases.
Cheers
SF

[Bushfiva]

Has anything changed in the past few months to increase the humidity in the hangar above 72% or so?

[BoeingBoy]

Nothing has changed other than sitting in a hangar next to the Mersey during one of the wettest winters on record.

A new Concorde battery was fitted on the annual in March but other than that I am out of ideas.

Sorry for any confusion, when referring to patching I was talking about patching the paint work, not cutting out patches of metal.

I spoke to a couple of spray companies yesterday who were most helpful. One idea that did come up was to use a mobile car repair company to simply address the areas affected whilst using the maintenance company to oversee and ensure safety when removing wing tips or inspection panels. This idea appeals as it's the least inconvenient for all concerned but speaking to a classic car painter that I use he did warn that a lot of such sprayers use a single cellulose based coat that is quick to apply and easy to dry rather than the more time consuming two pack that is already on there.

Also, the company that applied the paint did warn that the Alumigrip that's on there will not readily rub down to a smooth finish as car paint does. That said, as far as I know the only difference between what's on the aircraft now and standard car two pack is that the UV resistance is higher, so again I am unsure which way to go.

If I can find a dedicated aircraft sprayer able to take the job on then it's probably the best policy.

Thanks again for all your help.

(After all, if engineers didn't exist. Pilot's wouldn't have heros)

[ferrydude]

What type of screws are installed, stainless, or cad plated?

[BoeingBoy]

Stainless as far as I know.

Sadly I have just returned from looking at the aircraft again and there are a few areas under the cabin floor and the inspection panels on the left are starting to show some activity from the screw heads.

Apart from having an annual in March (nothing done bar the new 33AH battery) I am at a loss to know why this has all come out in recent weeks.

Given that I am now well beyond simply using car repair companies the choice is simply to start cleaning the areas myself and use an aerosol of matched paint or give the aircraft to a sprayer for hopefully a fuller and more long lasting job.

[ferrydude]

Stainless, this is more likely the root for your problem, dissimilar metal corrosion expanding into filiform. Stainless screws cause more problems than they solve. Your best bet is to use teflon, or other type non-metallic washers on the non structural panels and use only cad plated,carbon steel screws in structural application like the tanks and windshield.

[BoeingBoy]

Thanks FD. I will look into getting that done.

[wrench1]

BB.


I would attempt to determine the cause of this "sudden" emergence of corrosion before repaint. Normally this is not a quick event given the aircraft history.


Since you mention there was no evidence prior to last annual, a couple additional items.
1) Was the aircraft exterior cleaned/"revitalized" with a different product after the annual in March?
2) Why was battery changed, and was the aircraft battery ground reworked during replacement?
3) As FD mentioned, was the stainless hardware added during annual, or was this existing hardware?
4) Was there additional work performed other than the normal annual items?

I'll ask around as this seems a bit odd. I've seen a lot of corrosion working helicopters along the GOM on my side of the pond. When corrosion pops up this fast there is usually a reason.


W1

[BoeingBoy]

W1.

To answer your questions.

1. The aircraft was painted with a UV resistant two pack in 2003. It was touched up by the previous owner using the same company that did the respray in 2014. They tell me it was mostly cosmetic and not extensive.

It had a valet by a well respected aircraft detailer in June last year. They applied an acrylic paint sealant. Brand unknown.

I have kept that shine going using Triple Wax 'Shake and Shine'. Tetrosyl who make it tell me there is no salt or ammonia in it and the contents are mostly inert. I doubt this is the problem as I have applied it over stone chips for a year without problem.

Contents are listed as:

15 - < 30% Aliphatic hydrocarbons
< 5% non-ionic surfactants
perfumes
Contains Benzisothiazolinone,Methylisothiazolinone

2. The battery was changed due to age. The previous one was dated 2005 and had reached 83% capacity. It was replaced with a Concord RG35AXC 33AH 12v battery at my request.

3. I think the stainless steel screws would have been original as they still have paint on them around the inspection panels. The end caps are possibly held in by cad plated screws with metal washers. I am ashamed to be a bit of a luddite on this so will check.

4. The only work carried out on the annual was internal to the cabin with new door seals and a new throttle quadrant decal, otherwise it had no issues.

Reading through the FAA document kindly supplied by Seldom Fixit I noticed two items of interest.

Apart from Filiform corrosion being prevalent in aircraft that have been poorly prepared for painting (which I would discount as the finish has lasted well for thirteen years) there is mention of the fact that this corrosion (like all) is very prevalent in salt atmospheres and can be accelerated by the onset of warmer temperatures.

Given that it's spent most of its life in salt air and that it's sat in the hangar most of the year next to the Mersey I wonder if the recent bout of hot weather at the start of May was the trigger point to set the reaction off. The timing would be right as I last cleaned the aircraft in April and whilst I probably didn't notice the underside panels going I certainly did not have the two patches on the elevator and rudder that have now appeared in the space of a month.

I am off to see an aircraft paint company tomorrow so hopefully we can make some progress. Otherwise I will have to start rubbing back and repainting with aerosols.

[ferrydude]

Stainless screws would not be original, Piper used cad plated carbon steel screws

[BoeingBoy]

OK. I may well be mistaken then but will check with my maintenance company.

Thanks for the heads up. (No pun intended)

[wrench1]

BB

A couple more questions:
1) Is the corrosion only at the "paint patches" and various screw holes, but not evident under areas of the original paint covering in 2003?
2) Would you say the location where you keep the aircraft versus the previous owners location is closer or farther away from salt water?
3) Did you have the acrylic paint sealant applied, or the previous owner?
4) Did your maintenance company wash the aircraft with water/soap, or other cleaner after annual inspection complied with?

Several points/possibilities: (some of these are out of my skill set but thought I'd pass them to you)
A) Several people mentioned filliform is very specialized and while poor preparation for paint is one cause, a more common cause is a thin coating of paint. Less than 1 mil. This may account for the "patches" and other thin paint areas corroding first.
B) Filliform needs a chloride (salt water vapor, etc) to initiate, but can be sustained by sulfides and nitrates (air pollution/rain, etc.)
C) It's possible when the paint sealant was applied it may have started the process. Porous paints are less susceptible to filliform than non-porous paints like Poly-Urethane. It has something to do with O2 absorption from air. Add in the average life of an acrylic sealer of 10 to 12 months, higher humidity, warm temps, and maybe a good washing after the annual, or rain storm.... This might be the reason for the rapid growth.
D) Unfortunately, you'll have to chase all the corrosion and repaint as you mentioned. Just be sure to prep per the available info and use products formulated for aluminum.

If I get anymore feedback will post here or PM you.

Good Luck.

W1

[BoeingBoy]

Hi Wrench,

Here goes:

1. Apart from some corrosion on the underside of the fuselage at the end of the ribs under the cabin floor which I suspect has been there a while everything showing is next to a screw head. There are no paint patches at present as this will be the first time any have needed to be applied.

2. Probably closer to the sea as the aircraft was based at Goodwood, then a farm strip in Essex and now at Liverpool adjacent the Mersey so right next to salt water. Just for good measure there are some refineries and chemical factories on the south bank to ensure lots of pollutants are added to the salt with southerly winds.

3. I had the sealant applied last June. I am told it is a product called 'Aeroglade' and it was wiped on.

4. The aircraft was not washed to my knowledge. The only water it's seen in a year is the odd shower that I've flown through or brief periods outside the hangar to allow other aircraft to be brought out.

To clarify an earlier point the maintenance company tell me that all screws and fasteners are stainless steel. Is it worth changing them all to Nickel Coated?
Also, at present all the paint is in good condition with no patches or dull sections. That said, I don't know how absorbant it is.

I flew down to a paint company today who are happy to treat the areas involved (without guarantee of course since the cause is unknown) but given the rapidity at which this is appearing (another two patches next to the screws on the port side stabilator noted today) they suggest treating areas locally and seeing how the summer develops before painting larger areas.

One possible explanation is that if the aircraft was prepared for sale in the latter half of 2014, then sealed by me in June 2015, it is possible that taking the end caps off the rudder and stabilator along with the inspection patches has broken the sealant when the screws were removed allowing built up salt deposits and moisture in. That would explain the rapid appearance of the corrosion since the annual was done in March and especially since the temperatures increased in April.

Thanks once again for all your help everyone. After all, this is a forty year old aircraft and I don't expect it not to corrode but I am perplexed why, after twelve months of nothing the aircraft has now decided to produce these symptoms so rapidly.

Best Regards. BB

[wrench1]

BB.

Looks like you have a good plan. I forwarded your other posts to several knowledgeable paint people. They agree with the local touch up and possible cause.

They mentioned filliform requires a break/fault in paint surface and salt to start. You might discuss types of sealers with your paint people. Especially one that may work better with the paint on the aircraft. Also, you may want to reseal after each annual or minor paint damage.

The addition of an aluminum or nylon washer (see link) under the screw head as FD mentioned would provide a dual purpose: reduce dissimilar metal issue and protect your new paint from damage by screws during install.

NYLON WASHERS from Aircraft Spruce (http://www.aircraftspruce.com/catalog/hapages/hanylonwashers.php)

W1

[BoeingBoy]

Thanks W1. I will get onto it this week.

Thanks to you all for your help.

BB

[RayBanJockey]

Never use stainless fasteners into aluminium.

That turtlewax you been using is suspect also, I used some for a while on some fibreglass cowlings and the plated fastners and washers holding them corroded rather quickly after using the stuff.