Cessna 172SPHUSR05 Pilot Operating Handbook page 121

CESSNA
MODEL 1 72S
BEFORE TAKEOFF
WAR M U P
If the engi n e i d les (approximatley
smoothly, the airplane i s ready for takeoff. Since the engine i s
cl o sely cowl e d for effi c i e nt in-flight engine cooling, precauti o ns
should be taken to avoid overheating duri n g prolonged engine
operati o n on the ground. Al s o, long peri o ds of idling may cause
foul e d spark plugs.
MAGN ETO C H EC K
The magneto check shoul d be made at
Move igni t i o n swi t ch first to R posi t i o n and note RPM. Next move
swi t ch back to BOTH to cl e ar the other set of plugs. Then move
swi t ch to the L posi t ion, note RPM and return the swi t ch to the
BOTH posi t i o n. RPM drop shoul d not exceed
magneto or show greater than
magnetos. If there is a doubt concerning operati o n of the igni t i o n
system, RPM checks at hi g her engi n e speeds will usually confirm
whether a defi c iency exi s ts.
An absence of RPM drop may be an i n dicati o n of faul t y
grounding of one si d e of the igni t i o n system or shoul d be cause for
suspi c i o n that the magneto timing i s set in advance of the setti n g
speci f i e d .
CHECK
Prior to flights where veri f i c ati o n of proper al t ernator and
al t ernator control uni t operati o n i s essenti a l (such as ni g ht or
instrument flights), a posi t i v e veri f i c ati o n can be made by loading
the electri c al system momentaril y
light or by operati n g the wi n g flaps during the engine runup
RPM). The ammeter will remai n wi t hin a needl e wi d th of i t s ini t i a l
reading i f the al t ernator and al t ernator control uni t are operati n g
properl y .
Revi s i o n
4
NORMAL PROCEDURES
RPM) and accelerates
600
1 800
RPM di f ferenti a l between
1 50
50
to seconds) wi t h the landing
(3 5
SECTION
RPM as foll o ws.
RPM on ei t her
( 1 800
4-23
4
1