Areas Prone To Corrosion - Piper Dakota Maintenance Manual

* Red rust generally shows on bolts, nuts, and other aircraft hardware. Rust in these areas is generally not
dangerous. It is indicative of a need for maintenance and also of possibility of corrosive attack in more critical
areas.
Any surface corrosion on highly stressed steel parts is potentially dangerous. A careful removal of
corrosion using mild abrasives (rouge or fine grit aluminum oxide paper) is necessary. Be careful not to
overheat metal when removing corrosion.
** For abrasion, do not use dissimilar material (ex. steel wool on aluminum). Remove only material
required to clean up affected area.

AREAS PRONE TO CORROSION

Certain areas are more prone to corrosion than others. The following list is a general guide to areas where
corrosion is frequently found.
1. Areas around steel fasteners are susceptible to corrosion. Each time the fastener is removed, it should
be coated with zinc chromate before reinstallation.
2. Fluids tend to seep into faying surfaces, seams, and joints. This type of corrosion is usually detected by
irregularities in skin's surface.
3. Spot welded assemblies are prone to corrosion. On an aluminum spot welded assembly a chromate
conversion coating before paint is applied will help prevent corrosion.
4. Areas exposed to exhaust gases may have their finish damaged by deposits. Heat from the exhaust
may also damage paint. Gaps, seams, hinges, and fairings are some places where exhaust gas deposits
may be trapped.
5. The landing gear are the most exposed parts of the aircraft. The especially troublesome areas are:
a. Magnesium wheels; around boltheads, lugs, and wheel well areas.
b. Exposed rigid tubing, B-nuts, ferrules; under clamps, and tubing identification tape.
6. Areas around flaps, flight control slots and equipment installed in these areas may corrode due to
erosive conditions.
7. Check frequently engine frontal areas, air inlet ducts, and wing leading edges, because they are
constantly exposed to abrasion by dirt, dust, gravel, and rain.
8. Hinges (piano hinges especially) are vulnerable to corrosion.
9. Control cables may have bare spots in their preservative coating which could lead to corrosion. Cables
having external corrosion must be checked for internal corrosion. Replace the cable if internal
corrosion is present. If only external corrosion is present, remove corrosion with a wire brush and
recoat cable with preservative.
10. Check and clean drain holes regularly.
11. Battery compartment and vent openings are 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.
12. Magnesium parts are prone to corrosion. Special attention must be given to their surface treatment,
proper insulation (due to dissimilar metal corrosion), and paint coatings.
13. Electrical components and connectors must be checked. Inspection frequency is based on operational
environment and past trouble.
14. Skin joints and lap-overs are areas which may contain moisture. Corrosion in these areas may go
unnoticed unless checked during inspection.
15. Hoses having an internal wire braid located in a position where they are frequently water soaked need
a protective treatment.
16. Drilled holes and trimmed ends of sandwich panels must be protected. Use an inhibitor solution or
sealant application. Any gaps or cavities which allow dirt or moisture to enter must be filled with a
sealant.
PIPER AIRCRAFT
PA-28-236
MAINTENANCE MANUAL
1E16
21 - 24 - 00
Page - 20 - 13
Reissued: August 1, 1986