Cessna 172N - Page 35

CESSNA
MODEL 172N
SECTION 3
EMERGENCY PR,O
CEDUR,ES
EMERGENCY
OPER,ATION IN CTOUDS
(Vocuum
System
Fqilure)
In the
event
of a
vacuum
system
failure
during
flight
in marginal
weather,
the directional
indicator
and
attitude
indicator
will be disabled,
and the
pilot
will have
to
rely on the
turn coordinator
or the
turn and
bank
indicator if
he
inadvertently
flies into
clouds. The
following instnrctions
assume that only the
electrically-powered
turn coordinator
or the
turn
and bank
indicator
is
operative, and
that the
pilot
is
not completely
pro-
ficient in instnrment flying.
EXECUTING
A
ISOO TURN
IN
CTOUDS
Upon inadvertently
entering
the
clouds,
an immediate
plan
should
be
made
to
turn back as
follows:
(1)
Note the
time
of the minute hand and observe
the
position
of the
sweep second
hand
on the clock.
(2)
When
the sweep second
hand indicates
the nearest half-minute,
initiate
a
standard rate
left turn, holding
the turn coordinator sym-
bolic airplane
wing
opposite
the
lower
left
index
mark
for
60 se-
conds.
Then
roll
back
to level flight
by
leveling the miniature air-
pIane.
(3)
Check accuracy of the
turn
by observing
the
compass heading
which
should
be
the reciprocal of the
original
heading.
(4)
If
necessary,
adjust
heading
primarily
with
skidding motions
rather
than
rolling
motions
so that the
compass
will read more
accurately.
(5)
Maintain
altitude and
airspeed
by
cautious application
of eleva-
tor
control.
Avoid
overcontrolling
by
keeping the
hands
off
the
control wheel
as
much
as
possible
and steering
only
with rudder.
E'NERGENCY
DESCENT IHROU GH
CtO
U DS
If
conditions
preclude
reestablishment
of
VFR flight
by a 180"
turn, a
descent through
a cloud
deck
to
VFR conditions
may
be appropriate,
If
possible,
obtain radio
clearance for an
emergency descent
through
clouds.
To
guard
against a
spiral dive,
choose an
easterly or
westerly
heading
to
minimize
compass card
swings
due to changing bank angles. In addition,
keep hands
off the control
wheel
and
steer
a
straight
course with nrdder
control
by monitoring
the
turn coordinator.
Occasionally check
the
com-
pass
heading
and
make
minor corrections to
hold
an
approximate
course.
Before descending
into
the
clouds, set up
a
stabilized let-down
condition
as follows:
Apply
tull
rich
mixture.
Use
full
carburetor
heat.
(1)
(2)
3-11