Cessna 17273274 Pilot Operating Handbook page 149

SECTION 7
AIRPLANE & SYSTEMS DESCRIPTIONS
indicator, first rotate the ring until pressure altitude is aligned with
outside air temperature in degrees Fahrenheit. Pressure altitude should
not be confused with indicated altitude. To obtain pressure altitude,
momentarily set the barometric scale on the altimeter to 29.92 a.nd read
pressure altitude on the altimeter. Be sure to return the altimeter baromet­
ric scale to the original barometric setting after pressure altitude has been
obtained. Having set the ring to correct for altitude and temperature, read
the true airspeed shown on the rotatable ring by the indicator pointer. For
best accuracy, the indicated airspeed should be corrected to calibrated
airspeed by referring to the Airspeed Calibration chart in Section 5.
Knowing the calibrated airspeed, read true airspeed on the ring opposite
the calibrated airspeed.
VERTICAL SPEED INDICATOR
The vertical speed indicator depicts airplane rate of climb or descent in
feet per minute. The pointer is actuated by atmospheric pressure changes
resulting from changes of altitude as supplied by the static source.
ALTIMETER
Airplane altitude is depicted by a barometric type altimeter. A knob
near the lower left portion of the indicator provides adjustment of the
instrument's barometric scale to the current altimeter setting.
VACUUM SYSTEM AND INSTRUMENTS
An engine-driven vacuum system (see figure 7-9) provides the suction
necessary to operate the attitude indicator and directional indicator. The
system consists of a vacuum pump mounted on the engine, a vacuum relief
valve and vacuum system air filter on the aft side of the firewall below the
instrument panel, and instruments (including a suction gage) on the left
side of the instrument panel.
ATTITUDE INDICATOR
The attitude indicator gives a visual indication of flight attitude. Bank
attitude is presented by a pointer at the top of the indicator relative to the
bank scale which has index marks at 10
the center mark. Pitch and roll attitudes are presented by a miniature
airplane superimposed over a symbolic horizon area divided into two
sections by a white horizon bar. The upper "blue sky" area and the lower
"ground" area have arbitrary pitch reference lines useful for pitch attitude
control. A knob at the bottom of the instrument is provided for in-flight
adjustment of the miniature airplane to the horizon bar for a more accurate
flight attitude indication.
7-32
° ° ° ° °
, 20 , 30 , 60 , and 90
CESSNA
MODEL 172N
either side of
1 July 1979