1. Radome area
2. Rudder petal
3. Cockpit floor
4. Battery compartment
5. Piano hinges
6. Flight control cables
7. Exhaust areas
8. Missile rocket blast area
9. Flap carriage area
10. Magnesium wheels
11. Exposed rigid tubing
12. Main wheel well
13. Air inlet ducts and engine frontal areas
14. Nose wheel well
Figure 4-16.—Typical corrosion-prone areas on jet engine aircraft.
Active metals and dissimilar metals in contact
are often unprotected.
Closed boxes can produce condensation during
normal temperature changes during flight.
Avionic systems have many areas to trap
moisture.
Hidden corrosion is difficult to detect in many
avionic systems.
Many materials used in avionic systems are
subject to attack by bacteria and fungi.
Organic materials are often used that, when
overheated or improperly or incompletely cured, can
produce vapors. These vapors are corrosive to electronic
components and damaging to coatings and insulators.
The only requirements for a corrosion cell are a
cathode, an anode, and an electrolyte. The size of a cell
depends upon the size of its components. A cell can
form where a resistor lead is soldered to a terminal, or
where two sheets of metal join. It can also form around
a rivet head and the adjacent metal. (See figure 4-17,
views A and B.) Even two metallic crystals in the same
alloy can form a cell. All that is needed is for crystals
to be of different composition and in electrical contact
with each other in the presence of an electrolyte (fig.
4-17, view C).
Battery Compartments and Battery Vent
Openings. Fumes from battery electrolyte are difficult
to contain. They will spread throughout the battery
compartment, vents, and even adjacent internal
cavities. Battery electrolyte fumes cause rapid
corrosive attack on unprotected surfaces. Maintenance
personnel should check the external skin area around
the vent openings regularly for this type of corrosion.
Corrosion from this source is a serious problem
4-27
