Cessna Skyhawk 172N Pilot Operating Handbook page 43

CESSNA SECTION 3
MODEL 172N
EMERGENCY PROCEDURES
EMERGENCY OPERATION IN CLOUDS
(Vacuum System Failure)
In the event of a vacuum system failure during flight. the directional
indicator and attitude indicator will be disabled. and the pilot will have to
rely on the turn coordinator
if
he inadvertently flies into clouds. The
following instructions assume that only the electrically-powered turn
coordinator is operative. and that the pilot is not completely proficient in
instrument flying.
EXECUTING A 180 0 TURN IN CLOUDS
Upon inadvertently entering the clouds. an immediate plan should be
made to turn back as follows:
1. Note the compass heading.
2. Note the time of the minute hand and observe the position of the
sweep second hand on the clock.
3. When the sweep second hand indicates the nearest half-minute,
initiate a standard rate left turn. holding the turn coordinator
symbolic airplane wing opposite the lower left index mark for 60
seconds. Then roll back to level flight by leveling the miniature
airplane.
4. Check accuracy of the turn by observing the compass heading
which should be the reciprocal of the original heading.
5. If necessary. adjust heading primarily with skidding motions
rather than rolling motions so that the compass will read more
accurately.
6. Maintain altitude and airspeed by cautious application of elevator
control. Avoid overcontrolling by keeping the hands off the control
wheel as much as possible 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
compass 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 July 1978
3-13