Aero-Tips!

A good pilot is always learning -- how many times have you heard this old standard throughout your flying career? There is no truer statement in all of flying (well, with the possible exception of "there are no old, bold pilots.")

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Aero-Tips 08.29.06

Corrosion in a metal aircraft structure can significantly reduce that structure's ability to carry flight loads. In not-too-extreme cases of corrosion control difficulty or even in-flight structural failure can result from corrosion. Corroded materials fatigue at a much faster rate than normal, further reducing stress-carrying capability. So what should we look for when preflighting an airplane?

Surface corrosion comes in several forms:

• Surface corrosion. This is corrosion that covers a wide area of unprotected metal. If paint is old and cracked, admitting moisture to metal and trapping moisture against the metal under loose flaps of old paint, the metal can corrode dangerously. Look for any discoloration, dullness or "dustiness" of metal around scratches or gaps in aircraft paint.
• Filiform corrosion. This is an elongated area of corrosion along an imperfection in metal. It is sometimes called "worm" corrosion because the tracks of corroded material look like worms under the paint surface. Sometimes it forms complete circles, or rings.
• Dissimilar metals corrosion. Different types of metals exchange electrons at different rates, leading to impurities in the metal joints that is a form of corrosion. Look for brittle-looking lines or dustiness in areas where metals come together. This sometimes results in "smoky", or black-dusted rivets in a metal structure.

If corrosion is forming pits, or noticeable breaks or holes in the metal, the airplane should not be flown until it can be addressed and repaired by a mechanic. If smokiness or discoloration is present, but there is no pitting, ask a mechanic to take a look unless you're very familiar with the symptoms and effects of corrosion. All surface corrosion should be treated as soon as its discovered to prevent spreading. A trained mechanic should inspect adjacent areas for corrosion that may be less visible.

Aero-tip of the day: Watch for corrosion during your preflight inspections.

FMI: Aero-Tips