Emergency Operation In Clouds (Vacuum System Failure); Executing A 180 Turn In Clouds; Emergency Descent Through Clouds - Cessna SKYHAWK 1976 Pilot Operating Handbook

CESSNA
SECTION 3
MODEL 172M
EMERGENCY PROCEDURES
EMERGENCY OPERATION IN CLOUDS
(Vacuum System Failure)
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 instructions
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 instrument flying.
EXECUTING A 180° TURN IN CLOUDS
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 seconds.
Then roll back to level flight by leveling the miniature airplane.
(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 ac­
curately.
(5) Maintain altitude and airspeed by cautious application
of
elevator
control.
A
void overcontrolling by keeping the hands off the control
wheel and steering only with rudder.
EMERGENCY DESCENT THROUGH CLOUDS
If conditions preclude reestablishment of VFR flight by a 180
0
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 rudder
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:
(1) Apply full rich mixture.
(2) Use full carburetor heat.
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