Descent - Beechcraft C23 SUNDOWNER 180 Pilot Operating Handbook

BEECHCRAFT Section X
Safety
Information
DESCENT
In
piston-powered
airplanes,
whether
single or twin
engines, supercharged or normally
aspirated,
it is
necessary
to avoid
prolonged
descents
with
low
power,
as
this
produces two
problems:
(1)
Excessively
cool cylinder head temperatures
which
cause premature engine
wear,
and (2) excessively
rich mixtures due to idle enrichment (and altitude)
which
causes soot and lead deposits on the spark
plugs (fouling).
The second of these
is the
more
serious consideration; the engine may not respond to
the throttle
when
it is desired
to
discontinue the
descent.
Both problems
are
amenable
to one solution:
maintain
adequate
power
to
keep cylinder
head
temperatures in the
"green"
range
during descent,
and lean to best
power
mixture (that
is,
progressively
enrich the mixture from cruise
only
slightly as altitude decreases).
This procedure
will
lengthen the descent,
of
course, and
requires
some
advance
planning.
If it is necessary to make
a prolonged
descent
at
or
near idle,
as
in practicing forced landings,
at
least
avoid
the
problem of fouled
spark
plugs
by
frequently
advancing
the throttle
until
the engine
runs
smoothly,
and
maintain
an appropriate
mixture
March,
1981
10-55