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3.6 Let-Down
The let-down should be accomplished by slightly decreasing power and
letting the airplane decelerate (to safe airspeeds). Chopping the power should
be avoided unless there is an emergency. The reason is that the cylinder
barrel walls will receive cold air cooling while the piston is still hot. This can
lead to scuffing, glazing, or even barrel deformation with a washboard pattern
matching the barrel fin spacing. Rapid cooling of the head is not the major
source of structural head failures, but rapid cooling of any reciprocating parts
can lead to problems. After the cylinder heads are below 315°F, then the
power may be reduced more for a greater descent rate. During the descent,
the mixture should be INCREMENTALLY ENRICHED, or from lower altitudes,
placed in the FULL RICH position. Occasional temporary power increases
should be made to verify the engine is ready to resume full power if required.
NOTE: Reduced throttle exposes more carburetor buttery to the airow, and the
possibility of carburetor ice is more prevalent. Accordingly, use carburetor heat
to prevent ice formation.
3.7 Landing
Landings take many forms and procedures are based on environment and
skill. However, all landings should be accomplished with the idea that a go-
around may be necessary. This means that the carburetor heat should be
off and the mixture set rich when approaching the “Over-the-Fence” position.
3.8 Stopping the Engine
The engine will normally cool sufficiently during the landing and taxi. If the
engine has operated at an extended time on the ground, open the throttle
to 900-1000 RPM for at least a minute before stopping the engine. Pull the
mixture control to idle cut-off from an idle speed to shut down the engine. Turn
off dual ignition and master power from airframe. It is good practice to close
fuel valve from airframe when leaving aircraft parked for extended lengths of
time.
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