Corrosion Prone Areas - Piper Malibu Meridian PA-46-500TP Airplane Maintenance Manual

E.

Corrosion Prone Areas

Certain areas are more prone to corrosion than others. The following list is intended to be a general
guide to areas where corrosion is frequently found.
(1) Areas around steel fasteners are susceptible to corrosion. The paint on these areas cracks
which allows moisture to seep in and corrode the underlying metal. Each time the fastener is
removed, it should be coated with zinc chromate before reinstallation. The paint should be wet
when the fastener is installed.
(2) Fluids tend to seep into faying surfaces, seams and joints due to capillary action. The effect of
this type of intrusion is usually detectable by irregularities in the skin's surface.
(3) Spot welded assemblies are particularly prone to corrosion. The only means to prevent this
type of corrosion is by keeping potential moisture entry points in the spot weld filled with a
sealant or preservative compound. On an aluminum spot welded assembly, a chromate
conversion coating before paint is applied will help prevent corrosion.
(4) Areas which are exposed to exhaust gases may have their finish damaged by deposits. These
deposits may result in an aggressive attack on the metal by corrosion. Heat from the exhaust
may also blister or otherwise damage the paint. Gaps, seams, hinges and fairings are some
places where exhaust gas deposits may be trapped and not reached by normal cleaning
methods.
(5) The wheel well and landing gear are the most exposed parts of the aircraft. Due to the
complexity of its shape, assemblies and fittings, maintaining a protective coverage is difficult.
The especially troublesome areas are:
(a) Magnesium wheels: around bolt heads, lugs and wheel well areas:
(b) Exposed rigid tubing, B-nuts, ferrules, under clamps and tubing identification tape:
(c) Exposed position indicator switches and other electrical equipment:
(d) Crevices between stiffeners, ribs and lower skin surfaces.
(6) Flaps, flight control slots and equipment installed in these areas may corrode unnoticed unless
a careful surveillance is maintained.
(7) Engine frontal areas, air inlet ducts and the leading edge of wings, because they are constantly
exposed to abrasion by dirt, dust, gravel and rain, should be checked frequently for the
beginning of corrosion.
(8) Hinges (piano hinges especially) are extremely vulnerable to corrosion due to the wearing
away of their protective coating and their being a natural trap for dirt, salt and moisture.
(9) Control cables may have bare spots in their preservative coating which could lead to corrosion.
Cables having external corrosion should be checked for internal corrosion. If internal corrosion
is present, replace the cable. If only external corrosion is present, remove corrosion with a wire
brush and recoat cable with preservative.
(10) Any area where water may be trapped is a trouble spot for corrosion. Drain holes should be
checked and cleaned regularly.
(11) Battery compartment and vent openings are particularly prone to corrosion due to spilled
electrolyte. Fumes from overheated battery electrolyte will spread to adjacent areas and cause
rapid corrosion of unprotected surfaces. Frequent cleaning and neutralization of deposits will
minimize corrosion from this cause.
(12) Due to magnesium parts being prone to corrosion, special attention should be given to their
surface treatment, proper insulation (due to dissimilar metal corrosion) and paint coatings.
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Apr 15/07
PIPER AIRCRAFT, INC.
PA-46-500TP, MALIBU MERIDIAN
MAINTENANCE MANUAL
6F14