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MANAGEMENT OF ANCILLARY CONTROLS
55. Cowl flaps are used to modulate the flow of cooling air through the engine compartment
in flight. Opening the cowl flaps creates a low pressure area which effectively pulls air through
the engine for increased cylinder and oil cooling. Air flowing through the engine creates a
significant amount of drag which is minimized by closing the flaps when enhanced cooling
airflow is not required. Cowl flaps are used as follows:
a. Aircraft Parked – OPEN – to keep birds from nesting in the cowling;
b. Start and Ground Operations – OPEN – to ensure even airflow distribution
through engine compartment;
c. Takeoff and Climb – OPEN – to ensure maximum cooling airflow;
d. Cruise – cowl flaps will normally be CLOSED to maintain appropriate CHTs and
to minimize cooling drag. Cruise with cowl flaps open can reduce IAS by 3-5
MPH. Intermediate settings may be required at high density altitudes and / or high
power settings to prevent engine overheating; and
e. Descent and Landing – CLOSED – to minimize shock cooling of engine. When
conducting continuous circuits, the cowl flaps may be left OPEN.
56. To prevent fouled plugs, rough running and/or engine damage, correct leaning
procedures must be followed during all phases of flight. Proceed as follows:
a. Ground Handling - full rich unless operating at high density altitudes or extended
ground idling is anticipated, in which case the mixture should be leaned
aggressively. Return to full rich prior to run-up or takeoff;
b. Takeoff - mixture normally set to full rich unless taking off at high density altitude
(> 3000’ MSL). For high altitude takeoffs, hold brakes, apply full power, then lean
as necessary for smooth running / maximum power;
c. Climb - lean progressively in climbs above 3000 ft MSL. Adjust mixture as
required to maintain takeoff EGT readings (approx 1100-1300ºF);
d. Cruise - after altitude, airspeed and power settings have stabilized, lean to 50ºF
Rich of Peak in accordance with the “LeanFind” procedure in EDM-930 manual;
and
e. Descent, Circuit - mixture normally set to full rich.
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