SECTION 3
CESSNA
EMERGENCY PROCEDURES
MODEL 172RG
EXTENSION MALFUNCTIONS
Normal landing gear extension time is approximately 5 seconds. If the
landing gear will not extend normally, perform the general checks of
circuit breakers and master switch and repeat the normal extension
procedures at a reduced airspeed of 100 KIAS. The landing gear lever must
be in the down position with the detent engaged. If efforts to extend and lock
the gear through the normal landing gear system fail, the gear can be
manually extended (as long as hydraulic system fluid has not been
completely lost) by use of the emergency hand pump. The hand pump is
located between the front seats.
A checklist is provided for step-by-step instructions for a manual gear
extension.
If gear motor operation is audible after a period of one minute
following gear lever extension actuation, pull the GEAR PUMP circuit
breaker to prevent the electric motor from overheating. In this event,
remember to re-engage the circuit breaker just prior to landing.
GEAR UP LANDINGS
If the landing gear remains retracted or is only partially extended, and
all efforts to fully extend it (including manual extension) have failed, plan
a wheels-up landing. In preparation for landing, reposition the landing
gear lever to GEAR UP and push the LDG GEAR and GEAR PUMP circuit
breakers in to allow the landing gear to swing into the gear wells at
touchdown. Then proceed in accordance with the checklist.
ELECTRICAL POWER SUPPLY SYSTEM
MALFUNCTIONS
Malfunctions in the electrical power supply system can be detected by
periodic monitoring of the ammeter and low-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
alternator failures, although other factors could cause the problem. A
damaged or improperly adjusted alternator control unit 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 situation.
3-18
1 July 1979
CESSNA
SECTION 3
MODEL 172RG
EMERGENCY PROCEDURES
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
accept 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 overheat and
evaporate the electrolyte at an excessive rate.
Electronic components in the electrical system can be adversely
affected by higher than normal voltage. The alternator control unit
includes an over-voltage sensor which normally will automatically shut
down the alternator if the charge voltage reaches approximately 31.5 volts.
If the over-voltage sensor malfunctions or is improperly adjusted, as
evidenced by an excessive rate of charge shown on the ammeter, the
alternator should be turned off, alternator circuit breaker pulled, nones-
sential electrical equipment turned off and the flight terminated as soon as
practical.
INSUFFICIENT RATE OF CHARGE
NOTE
Illumination of the low-voltage light and ammeter
dischargeindications may occur during low RPM conditions
with an electrical load on the system, such as during a low
RPM taxi. Under these conditions, the light will go out at
higher RPM. The master switch need not be recycled since
an over-voltage condition has not occurred to de-activate
the alternator system.
If the over-voltage sensor should shut down the alternator or if the
alternator circuit breaker should trip, a discharge rate will be shown on the
ammeter followed by illumination of the low-voltage warning light. Since
this may be a "nuisance
"
trip-out, an attempt should be made to reactivate
the alternator system. To do this, turn the avionics power switch off, check
that the alternator circuit breaker is in, then turn both sides of the master
switch off and then on again. If the problem no longer exists, normal
alternator charging will resume and the low-voltage light will go off. The
avionics power switch may then be turned back on. If the light illuminates
again, a malfunction is confirmed. In this event, the flight should be
terminated and/ or the current drain on the battery minimized because the
battery can supply the electrical system for only a limited period of time. If
the emergency occurs at night, power must be conserved for later use of the
landing lights and flaps during landing.
1 July 1979
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