replace defective switches with
switches of the same type and
(1) Conduct a visual examination for
physical damage, and check to see that switches are
securely attached to the mounting panel.
(2) Check for loose or deformed electrical
connections or evidence of corrosion of the terminals,
terminal lugs or screws.
(3) Check for manual operation by actuating
toggle lever several times. This also serves to remove
any superficial contamination or foreign deposits on the
internal electrical contacts. Return toggle lever to
measured across the external terminals by means of an
ohmmeter. Electrical resistance across any set of
closed contacts should not exceed 1 ohm. Intermittent
or excessive resistance normally indicates that the
internal contacts are corroded. In the event a few
additional actuations of the switch does not clear up this
condition, replace the switch with like item. Continuity
tests of installed switches require that the switch be
electrically isolated from other circuitry to preclude
measurement of low resistance parallel systems. This
can usually be accomplished by opening the circuit
breaker or fuse on the line side of the switches.
(5) Check switches that are frequently
exposed to direct water spray, rain or heavy dust
concentration. These switches require timely checks for
manual operation, corrosion and continuity.
n. Circuit Breakers. Inspect circuit breakers using
the following procedures:
Replace breakers with breakers of
the same type and current rating
breaker is unserviceable.
(1) Determine that the breaker case and
mounting means are secure to the mounting panel and
there is no evidence of physical damage.
(2) Inspect for loose electrical termination or
evidence of corrosion of the terminals, terminal lugs or
(3) Ensure positive manual operation by
actuating push-pull button or toggle several times. This
operation also serves to remove any superficial
contaminants or foreign deposits present on the surface,
of the internal electrical contacts. Return actuator to
(4) Check for evidence that breaker had
been subjected to burning or overheating in the area
adjacent to the manual actuator. The burned area is
usually caused by electrical arcing as a result of a
combination of the presence of excessive moisture and
poor dielectric characteristics of the breaker.
Do not connect ohmmeter to a live
measured across the external breaker terminals. Use a
reliable ohmmeter capable of indicating an appropriate
dc resistance value for the purpose of determining that
the maximum overall electrical resistance does not
exceed 1 ohm. Intermittent or excessive resistance
readings normally indicate that the internal breaker
contacts are corroded. In the event a few additional
actuations of the breaker do not clear up this condition,
the breaker should be replaced. Continuity tests of
installed breakers require that the breaker be electrically
isolated from other circuitry to preclude measurement of
low resistance parallel systems. This can usually be
accomplished by opening the switch or switches on the
load side of the breaker. Circuit breakers in live circuits
can be checked by performing a voltage check.
(6) Test and physically inspect associated
wiring for short circuit condition to the aircraft structure.
Tripped circuit breakers indicate that an abnormal
electrical overload occurred and require immediate
investigation to determine the cause for the fault.
Repetitive tripping in the same circuit will require an
engineering investigation if the operating equipment or
electrical load otherwise functions properly and the
breaker replacement does not correct the fault.
frequently exposed to direct water spray, rain, snow or
heavy dust concentrations. These breakers require
continuity, evidence of burning or electrical arcing.