FAA Advisory Circular 43.13-1B
Acceptable Methods, Techniques, and Practices
Aircraft Inspection and Repair
AC 43.13-1B | 8. Engines, Fuel, Exhaust, and Propellers | 1. Engines | 8-16. Operational Problems
9/27/01
AC 43.13-1B CHG 1
FIGURE 8-6b. Typical oil-fouled spark plug.
d. Metal Deposits. Whenever metal spray
is found on the electrodes of a spark plug, it is
an indication that a failure of some part of the
engine is in progress. The location of the cyl-
inder in which the spray is found is important
in diagnosing the problem, as various types of
failures will cause the metal spray to appear
differently. For example, if the metal spray is
located evenly in every cylinder, the problem
will be in the induction system, such as an im-
peller failure. If the metal spray is found only
on the spark plugs in one cylinder, the problem
is isolated to that cylinder and will generally
be a piston failure.
In view of the secondary damage which occurs
whenever an engine part fails, any preliminary
indication such as metal spray should be thor-
oughly investigated to establish and correct the
cause.
FIGURE 8-6c. Typical spark plug with cracked
core nose.
e. Flashover. It is important that spark
plug terminal contact springs and moisture
seals be checked regularly for condition and
cleanliness to prevent “flashover” in the con-
nector well. Foreign matter or moisture in the
terminal connector well can reduce the insula-
tion value of the connector to the point the ig-
nition system voltages at higher power settings
may flash over the connector well surface to
ground and cause the plug to misfire. If
moisture is the cause, hard starting can also re-
sult. The cutaway spark plug shown in fig-
ure 8-7 illustrates this malfunction. Any spark
plug found with a dirty connector well may
have this condition, and should be recondi-
tioned before reuse.
Par 8-16
Page 8-13