Lycoming O-320 76 Series Operator's Manual page 23

LYCOMING SERIES OPERATOR'S MANUAL
O-320
During let-down and reduced power flight operations it may be necessary to manually lean
or leave mixture setting at cruise position prior to landing. During the landing sequence set
the mixture control in the full rich position, unless landing at high elevation fields where
leaning may be necessary.
a. LEANING WITH EXHAUST GAS TEMPERATURE GAUGE.
(1) Maximum Power Cruise (approximately 75% power) – It is permissible to lean to
100°-150°F on rich side of peak EGT unless aircraft operator's manual shows
otherwise. Monitor cylinder head temperatures.
(2) Best Economy Cruise (approximately 75% power and below) – Operate at peak
EGT.
b. LEANING WITH FLOWMETER.
Lean to applicable fuel flow tables or lean to indicator marked for correct fuel flow
for each power setting.
c. LEANING WITH MANUAL MIXTURE CONTROL (Economy Cruise, 75% power or
less without flowmeter or EGT gauge).
(1) Slowly move mixture control from "Full Rich" position toward lean position.
(2) Continue leaning until engine roughness is noted.
(3) Enrich until engine runs smoothly and power is regained.
As shown in Figure 3-1, if engine speed and throttle setting are kept constant at normal cruise conditions,
the effect of leaning on engine power and engine temperatures will be as shown. Power drops rapidly when
the engine is leaned beyond peak exhaust gas temperature; also, best power is attained at 100°-150°F on the
rich side of peak exhaust gas temperature.
REFER TO
MANUFACTURER'S MANUAL FOR ADDITIONAL INSTRUCTIONS ON THE USE OF
CARBURETOR HEAT CONTROL. INSTRUCTIONS FOUND IN EITHER PUBLICATION
SUPERSEDE THE FOLLOWING INFORMATION.
8. USE OF CARBURETOR HEAT CONTROL. Under certain moist atmospheric conditions (generally at a
relative humidity of 50% or greater) and at temperatures of 20° to 90°F it is possible for ice to form in the
induction system. Even in summer weather ice may form. This is due to the high air velocity through the
carburetor venturi and the absorption of heat from this air by vaporization of the fuel. The temperature in the
mixture chamber may drop as much as 70°F below the temperature of the incoming air. If this air contains a
large amount of moisture, the cooling process can cause precipitation in the form of ice. Ice formation
generally begins in the vicinity of the butterfly and may build up to such an extent that a drop in power
output could result. In installations equipped with fixed pitch propellers, a loss of power is reflected by a
drop in manifold pressure and RPM. In installations equipped with constant speed propellers, a loss of
power is reflected by a drop in manifold pressure. If not corrected, this condition may cause complete
engine stoppage.
Revised September 2008
GENERAL RULES (CONT.)
THE PILOT'S OPERATING
OPERATING INSTRUCTIONS
WARNING
HANDBOOK
SECTION 3
OR AIRFRAME
3-5