Textron Aviation Cessna 172S NAV III Skyhawk SP, Information Manual

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SECTION 3 CESSNA
EMERGENCY PROCEDURES MODEL 172S NAV III
KAP 140 AUTOPILOT
U.S.
ELECTRICAL POWER SUPPLY SYSTEM
MALFUNCTIONS
(Continued)
INSUFFICIENT RATE OF CHARGE
When the overvoltage sensor circuit, or other fault, opens the alternator
(ALT FIELD) circuit breaker and de-energizes the alternator, a
discharge (-) current will be shown on the main battery ammeter and
the low voltage annunciator (LOW VOLTS) will come on. The ACU can
de-energize the alternator due to minor disturbances in the electrical
system, resulting in a nuisance opening of the ALT FIELD circuit
breaker. If this happens, an attempt should be made to energize the
alternator system.
To energize the alternator system
1. MASTER Switch (ALT Only) - OFF
2. ALT FIELD Circuit Breaker - CHECK IN
3. MASTER Switch (ALT Only) - ON
If the problem was a minor ACU disturbance in the electrical system,
normal main battery charging will start. A charge (+) current will be
shown on the main battery ammeter and the LOW VOLTS annunciator
will go off.
If the LOW VOLTS annunciator comes on again, there is an alternator
system problem. Do not repeat steps to energize the alternator system.
The electrical load on the battery must be minimized (by de-energizing
nonessential electrical equipment and avionics) because the battery
can supply the electrical system for only a short time. Reduce electrical
load as soon as possible to extend the life of the battery for landing.
Land as soon as practical.
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172SPHAUS-05
3-36
For
Training
Purposes
Only