Ignition And Starter System; Ai R I Nduction System - Cessna 172SPHUSR05 Pilot Operating Handbook

S ECTION 7
&
AI RPLAN E SYSTEMS DESC R I PTION
I G N ITION A N D STA RTER SYSTEM
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Engine ignition is provided by two eng ine-driven magnetos , and
two spark plugs i n each cyli nder. The right mag neto fires the lower
rig ht and upper left spark plugs, and the left magneto fi res the lower
left and u pper rig ht spark plugs. Normal operation is conducted with
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both magnetos due to the more complete burning of the fuel/air
m ixtu re with d ual ignitio n .
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Ignition and starter operation is controlled b y a rotary-type switch
located on the left switch and control panel. The switch is labeled
clockwise, OFF, R, L, BOTH , and START. The eng ine should be
operated on both magnetos (BOTH position) except for magneto
checks . The R and L positions are for checki ng pu rposes and
emergency use only. Wh en the switch is rotated to the spring
loaded START position , (with the master switch in the ON position) ,
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the starter contactor is closed and the starter, now energized , will
crank the engine. When the switch is released , it will automatically
return to the BOTH position .
A I R I N D U CTION SYSTEM
The eng i ne air i nduction system receives ram air through an
i ntake on the lower front portion of the eng ine cowl ing. The i ntake is
covered by an air filter wh ich removes d ust and other foreign matter
from the i nduction air. Airflow passi ng th rough the filter enters an air
box. The air box has a spring-loaded alternate air door. If the air
i nd uction filter should become blocked , suction created by the
engine wi ll open the door and draw u nfiltered air from i nside the
lower cowl area. An open alternate air door wi ll resu lt i n an
approximate 1 0%
the air box, i nduction air enters a fuel/air control u n it u nder the
engine, and is then ducted to the eng i ne cyl i nders through i ntake
manifold tubes.
7-22
power loss at full th rottle. After passi ng th rough
CESSNA
MODEL 1 72S
May 30/00