Cessna 1973 172 - Section III EMERGENCY PROCEDURES; Electrical Power Supply Malfunctions

Section III
EMERGENCY PROCEDURES
Emergencies caused by aircraft or engine malfunctions are extreme-
ly rare if proper pre-flight inspections and maintenance are practiced.
Enroute weather emergencies can be minimized or eliminated by careful
flight planning and good judgement when imexpected weather is encounter-
ed. However, should an emergency arise the basic guidelines described
in this section should be considered and applied as necessary to correct
the problem.
ELECTRICAL POWER SUPPLY SYSTEM MALFUNCTIONS.
Malfunctions in the electrical power supply system can be detected
by periodic monitoring of the ammeter and over-voltage warning light;
however, the cause of these malfunctions is usually difficult to determine.
A broken alternator drive belt or wiring is most likely the cause of alter-
nator failures, although other factors could cause the problem. A dam-
aged or improperly adjusted voltage regulator can also cause malfunctions.
Problems of this nature constitute an electrical emergency and should be
dealt with immediately. Electrical power malfunctions usually fall into
two categories', excessive rate of charge and insufficient rate of charge.
The paragraphs below describe the recommended remedy for each situa-
tion.
EXCESSIVE RATE OF CHARGE.
After engine starting and heavy electrical usage at low engine speeds
(such as extended taxiing) the battery condition will be low enough to ac-
cept above normal charging during the initial part of a flight. However,
after thirty minutes of cruising flight, the ammeter should be indicating
less than two needle widths of charging current. If the charging rate
were to remain above this value on a long flight, the battery would over-
heat and evaporate the electrolyte at an excessive rate. Electronic com-
ponents in the electrical system could be adversely affected by higher
than normal voltage if a faulty voltage regulator setting is causing the
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