Leaning Using Exhaust Gas Temperature (Egt) - Cessna 172S NAV III Pilot Operating Handbook

CESSNA
MODEL 172S NAV III
CRUISE
(Continued)
SECTION 4
NORMAL PROCEDURES
LEANING USING EXHAUST GAS TEMPERATURE (EGT)
(Continued)
To aid in leaning the mixture, push the ENGINE, LEAN and ASSIST
softkeys,
~PEAK
of will display below the EGT of numerical value.
Lean the mixture by slowly turning the Mixture Control knob in the
counterclockwise direction while monitoring EGTs. As EGTs
increase, continue to lean the mixture until the hottest (cyan)
cylinder reaches Peak EGT. This is identified by the EGT bar graph
for that cylinder changing to cyan with a hollow bar at the top. Note
the
~PEAK
OF and FFLOW GPH values for the first peaked
cylinder. Peak EGT is represented by
~PEAK
O°F, if
~PEAK
OF
value is negative (-) the mixture can be on the lean side of peak.
Enrichen the mixture by slowly turning the mixture control clockwise
and monitor both fuel flow and EGTs until the leanest cylinder
returns to peak EGT
(~PEAK
0° F) or desired setting based on the
EGT Table, Figure 4-4.
~PEAK
of values rich of peak will also be a negative (-) value
(-50°). The lean assist system calculation is defined such that the
peak EGT is the highest value and any lesser value is represented
with a negative (-) value, whether on the lean or rich side of the
peak.
NOTE
The 172S engine manufacturer, Textron Lycoming,
has not approved operation of the engine at fuel flow
rates (mixture settings) less than necessary to reach
Peak EGT in the leanest cylinder (the first cylinder to
reach peak EGT). Use FULL RICH mixture when
operating the engine above 75% power.
(Continued Next Page)
I
172SPHAUS-03
U.S. 4-35