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M20J Pre-buy - Questions on some squawks


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Hey everyone. I just got the pre-buy info back on a 1981 M20K I'm under contract for. There are some items which are concerning to me and I'd like to get perspective from everyone's experience.

1. Corrosion - the mechanic found some minor (his words) corrosion inside the wing. I'm attaching a picture. As far as I understand it's not anything structural, just the underside of the top of the wing (photo was taken looking up into the inspection panel). Both wings looked similar, so I'm only including one photo.

1a. However, while the inspection did include looking for corrosion in the belly inspection panels, it did not include lifting the rear carpet to look at the top of the spar cap. I am unclear on if this should've been done, if if it's a very time consuming step. For what it's worth, the plane had an SB 208 tubular frame inspection in 2007, but that's probably too old to mean anything.

2. Tank reseal - The tanks have been resealed, but with no entry in the logs. The mechanic said the most recent annual inspector take responsibility for them being airworthy, but I don't really get a warm fuzzy feeling from that. Should I be suspicious of the reseal work, and if so, how suspicious?

 

Thanks for the help!

IMG_0849.jpg

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Find what caused the corrosion to occur…

That’s not normal, expect to see more in other places…. Possibly more expensive places…

Looks like lots of sanding marks as well… do you see them?

Looks like the sanding marks are deeper than the newer corrosion?

The Alclad has a limited depth to its protection… deep sanding would be bad for the Alclad…

 

Tank re-sealing can easily change the WnB for the plane… look in the airframe logs to see where the work got documented…

If the work didn’t get documented…. Ask more questions….  Sounds like the owner may have said something different than what you understood…

 

You have identified great questions… they are serious issues…

PP thoughts only, not a mechanic…

Good luck with the hunt!

Best regards,

-a-

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Thanks for the feedback. 
 

Just to clarify, the inspector said the tanks were resealed, not the owner. He could tell visually. However, neither of us could find a logbook entry for the work. 
 

Have not sent my list of questions/repairs to the owner yet. 

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It is really helpful if you have the opportunity to discuss the plane with the owner…

Not everyone gets that opportunity… 

 

Where has the plane been living through the years?

Best regards,

-a-

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If I were doing the PPI, I’d be tell the buyer to keep looking.  The skin is part of the structure of the airframe, it’s just as important as the spars.

Clarence

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Always ask to have the fuel tanks filled for the prebuy, you can’t tell by just looking if the tanks will leak. It’s possible it was just patched, this is pretty common and since you cannot visually see where it is leaking it’s best to just do reseal it all.
Look in the logs if it has had corrosion sealant applied, generally it’s done at annual.
I can’t tell, is that bare aluminum? I think all Js had corrosion inhibitor applied from the factory (it’s green).
You need to pull carpets and lower trim pieces to check spar and steel cage for corrosion.

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Next step: going to have a complete 208B inspection done and signed in the logbooks. We'll see what that turns up.

It will be fairly obvious if the 208 was done. The front (under the windows) fiberglass insulation would have been removed and replaced with foil backed insulation.

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As for the tanks, I would be suspicious if there was no logbook entry. If there is no current entry, you need to assume that the last reseal (if there was one) was the last logbook entry or that it was never done.

Corrosion of any kind isn’t good. I think you will be hard pressed to find a 40 or 50 year old plane without some level of corrosion. That said, when I look at the level of corrosion in this plane, it sure looks like it spent a part of it’s life as a saltine cracker.


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Posted (edited)

Can you please expand on the saltine cracker comment? I'm not sure how bad you're saying it is.

 

And there have been two 208B inspections done in the past, but the last one in 2007 so I want a new one.

Edited by Jesse Cohen
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Can you please expand on the saltine cracker comment? I'm not sure how bad you're saying it is.
 
And there have been two 208B inspections done in the past, but the last one in 2007 so I want a new one.

Service bulletin 208 came out when it was discovered that water was seeping down from the Windows into the fiberglass surrounding the roll cage underneath them. Part of the SB is a visual inspection of the tubular structure. My shop pulls the panels and inspects them at the annual. My point was that if you don’t see the foil backed insulation, there is a good chance that the SB was never done (or at least correctly).

As for the saltine cracker comment. Planes that spend time near the ocean are more likely to be exposed to sea spray. Unfortunately the inspection panels are not airtight and salt can enter the plane this way. I think you indicated this plane spent a good portion of its life near the ocean. If they didn’t treat it with Corrosion X, Boeshield or some other anti-corrosion treatment, what you are seeing is probably an indicator of other corrosion that you can’t see.

I know you have a financial commitment (if not already an emotion one) to this plane. That’s a fair amount of corrosion in an area where you shouldn’t see much. As the Doc said, the skin is structural and I would be weary of assuming that it isn’t.

I would be looking deeper into the fuselage and wings for further evidence of the extent of corrosion.

Not trying tear down your enthusiasm. Rather just trying to avoid what we have seen here numerous times before. An owner posting on the site their plane is trash due to corrosion.

Good luck with the decision.


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Posted (edited)

I hear you guys and I do appreciate the advice. We checked the tailcone, no corrosion visible at all. Same thing with the other areas in the wing. This plane had two separate pre-buys, one of which ripped out all the interior panels, and the wing corrosion is all that was found so far.

I am just trying to take a balanced view from everything I am hearing. Some A&P's say the corrosion in the picture is significant. Others say it's relatively minor and just treat it. My thought on the 208B was that if there were other corrosion, say on the spar or the frame, we would find it and I would walk away.

I have heard from multiple people that a plane of this age will have some level of corrosion on it, but surface corrosion can just be treated. 

I guess if the 208B isn't any more assurance that the plane is safe, then I don't know what one can do besides pass on every plane that isn't perfect. That's kind of what I am hearing.

I also don't know how much maintenance history matters. This plane has had annuals from MSCs, like Cole and LASAR. For most of the past decade the annuals were at Sarasota Avionics, also an MSC. 

Edited by Jesse Cohen
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For what it is worth, my wings have a similar appearance in the wing compartment just outside of the landing gear.   I treat it at annual and it doesn’t seem to be deteriorating….I’ve owned the plane for 4 full years now.

I wish I didn’t have it…if I would have had a pre buy, perhaps I wouldn’t have bought the plane.  

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16 minutes ago, Jesse Cohen said:

I hear you guys and I do appreciate the advice. We checked the tailcone, no corrosion visible at all. Same thing with the other areas in the wing.

I am just trying to take a balanced view from everything I am hearing. Some A&P's say the corrosion in the picture is significant. Others say it's relatively minor and just treat it. My thought on the 208B was that if there were other corrosion, say on the spar or the frame, we would find it and I would walk away.

I have heard from multiple people that a plane of this age will have some level of corrosion on it, but surface corrosion can just be treated. 

I guess if the 208B isn't any more assurance that the plane is safe, then I don't know what one can do besides pass on every plane that isn't perfect. That's kind of what I am hearing.

SB 208 was issued to address a specific problem. If you didn't find corrosion there, it doesn't mean corrosion wouldn't be found elsewhere. What we are advocating is that due to what you showed us, I would proceed cautiously. The areas you need to be concerned with are not the easily accessible areas. It is in areas like the rear spar and other locations that you need to work to get a better view of. M20Doc and other IAs can give you an idea of where to look.

As for IA opinions, I think IAs are like any other professions, you can ask 3 of them and get 3 different opinions. The one I trust is the one who understands the limits of when something is considered a problem.

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I'm starting my annual next week.  My plane has been near the ocean for 20+ years.  My plane has been treated with ACF-50; it bleeds ACF-50.  I'm not an expert; I'm not a mechanic; I'm not a materials engineer; but I wouldn't be surprised if the aluminum sheeting doesn't look similar on a lot of these airplanes.  I have no idea what aged ALCLAD sheeting is expected to look like after decades.  I'm going to look closely at mine soon though and discuss findings with my mechanic.  

Edited by DCarlton
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1 hour ago, larrynimmo said:

Mine doesn’t look that much different

4A9AAC77-9004-4CB4-8DF0-838119C5253E.jpeg

I can report back my findings end of next week.  Like I said above, I'm not an expert, mechanic or a materials engineer but if they didn't zinc prime the skin and they depended on the ALCLAD for corrosion resistance, I wouldn't be surprised if many many planes look just like that after 30-40 years.  Seems like condensation is very likely to form and hang around under the wing skins.  Hopefully my skins are well lubricated with ACF-50 at this point....  

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