SECTION 3
CESSNA
EMERGENCY PROCEDURES
MODEL 172S NAV III
EMERGENCY OPERATION IN CLOUDS
(Continued)
EMERGENCY DESCENT THROUGH CLOUDS (AHRS FAILED)
When returning to VFR flight after a 180° turn is not practical, a
descent through the clouds to VFR conditions below may be
appropriate. If possible, obtain an ATC clearance for an emergency
descent through the clouds.
AHRS Failure
Choose an easterly or westerly heading to minimize non-stabilized
magnetic compass card sensitivity. Occasionally check the
compass heading and make minor corrections to hold an
approximate course. The autopilot may be engaged in ROL mode
to keep the wings level and VS mode to control rate-of-descent.
Before descending into the clouds, prepare for a stabilized descent
as follows:
1. Apply full rich mixture.
2. Turn pitot heat on.
3. Set power for a 500 to 800 feet per minute rate-of-descent.
4. Set the elevator trim for a stabilized descent at 80 KIAS.
5. Use the standby attitude indicator roll pointer and index to
keep wings level.
6. Check trend of compass card movement and make cautious
corrections with rudder to stop the turn.
7. Upon breaking out of clouds, resume normal cruising flight.
(Continued Next Page)
3-28 U.S.
172SPHAUS-03