BEECHCRAFT
DESCENT
SectlonX
Safety Information
In piston-powered airplanes, whether single
or
twin
engines, supercharged
or
normally aspirated,
it
is
necessary
to avoid proJonged descents with low
power,
as
this
produces
two
problems:
(
1)
E.xcessively cool cylinder head temperatures which
cause premature engine wear, and (2) e.xcessively
rich mi.xtures 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
desc~~nt.
Both
problems
are
amenabie
to
one
solution:
maintain
adequate
power to keep cylinder head
temperatures in the
"green"
range during descent,
and
lean
to
best
power
mi.xture
(that
is,
progressively enrich the mixture from cruise only
slightly
as
altitude decreases). This
pr~edure
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 Iandings, 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
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