Airframe Concerns

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By Richard Zephro

Most Mooney’s have had the 208 S.B.’s done, but there are a few out there that haven’t. Currently, we are readying a nice M20-F model for the market which has not had the insulation change as yet. We are going to do this, but after taking the interior all apart for new leather, we determined the tubes to be in excellent condition in and out. It will get the new style insulation before putting it back together.

Seemingly, pre-201 Mooney’s don’t get the corrosion as much since Mooney changed the way they installed the side glass. On the earlier models, the glass was held in by screws about every 1-1/2″, so water was not as likely to enter the tubes as when they switch to pressure plates to hold the glass in.

Corrosion has been found in all models from time to time however, so an inspection is proper. If a Mooney Service Center, or a knowledgeable A&P did the 208′s, then chances of getting the problem are greatly reduced. When properly done, all tube predrilled holes are sealed, and the tubes are shot with a corrosion preventative. Additionally, the outer tubes are prepped and painted or zinc-chromated. If an aircraft owner couples this with the new water resistant insulation you really don’t have to inspect it every year. My suggestion would be to have ACF-50 or the like, treatment about every 3 years. However, if you are in a highly corrosive environment (living by the beach and/or not hangared, for example) be sure to inspect each year at your annual. This treatment usually runs $2-300, and will cost little more than simply inspecting what you have periodically.

When you use ACF-50, virtually every part of the plane gets protected from the elements. The downside to anti-corrosion treatment is weeping rivets for a time after the treatment. Never fear, the treatment washes right off, but looks ugly for the first few months if you don’t clean your plane regularly. The worst case I’ve ever seen is where the plane needed about $10K in repairs. It is not likely to equal the value of the plane, but can be expensive, especially in the few circumstances that require de-mating the plane from the wing.

Often however, serious corrosion requires only to de-rivet the pilot’s side aircraft skins to allow the re-welding of tubes to be accomplished. I know of no accidents that were caused by a rusted super structure on a Mooney, so safety is not the issue as much as financial concerns.

It is always a good idea to have a good mechanic do your annuals. If it isn’t practical to use an authorized service center, begin a budget to allow a service center annual at least every 3-4 years. In the meantime, be certain your regular mechanic fully understands what to look for on these “different animals” we fly.

We are indeed fortunate to own and operate an airplane that can have really poor airframe maintenance for years, and still be reasonably safe when we fly them. Still…remember there are a lot of mechanics out there who don’t really understand, nor enjoy working on Mooney’s. Those who understand why they are tight to work on, will usually appreciate the fine engineering that went in to this product. The one’s who prefer to work on other manufacturers are demonstrating to you the need to find another mechanic!

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