Corrosion on aircraft is nothing more than rust of the metal parts, although aluminum corrosion doesn’t produce the reddish color most people think of as rust. Rather, it usually first shows as a whitish or gray “dulling” of the aluminum surface, then progresses to more and more severe pitting and eventual destruction of the metal. Left untreated, corrosion can make an aircraft unairworthy in just a few years.

Types of corrosion normally found on aircraft include:

⤞ Corrosion Uniform surface attack. This is the most common type and is caused simply by exposing the metal to oxygen in the air, such as when the paint is worn off wing skin or the fuselage. Poor pre-paint preparation at the factory, fumes, acid, pollutants or high humidity accelerates the decay.

⤞ Intergranular corrosion. Normally worst on 7000-series alloys (those with an appreciable amount of zinc, like wing spars, stringers, and other high-strength aircraft parts), this is not frequently found but is a particularly nasty type of corrosion. It can be difficult to detect, and once you see it, it’s too late: that piece of metal is toast.

⤞ Stress corrosion. In highly stressed parts like landing gear or engine crankshafts, this type may develop from a scratch or surface corrosion. Crankshaft failures are often due to undetected corrosion of this type.

⤞ Crevice or deposit corrosion. This can occur anywhere there is an area where moisture or other pollutants are trapped. Lapped skin joints or rivets on an oil-stained belly are examples of prime corrosion spots.

⤞ Filiform corrosion. Particularly on aluminum surfaces poorly prepared for polyurethane paints, this type of corrosion will show up as fine, worm-like lines of corrosion under the paint that will eventually lead to bubbling and flaking.