Alti M Eter; Vacuu M System And Instru Ments; Attitude I Ndicator; Directional I Ndicator - Cessna 172SPHUSR05 Pilot Operating Handbook

CESSNA
MODEL 1 72S
ALT I M ETE R
Airplane altitude is depicted by a barometric type altimeter. A
knob n ear the lower left portion of the indicator provides adjustment
of th e i nstrument's barometric scale to the current alti meter setting .
VAC U U M SYSTE M A N D I NSTR U M E NTS
The vacu u m system (Refer to Figure 7-9) provides suction
necessary to operate the attitude i ndicator and the directional
indicator. The system consists of two engine-driven vacu u m pu mps,
two pressu re switches for measuri ng vacu u m available through
each pump, a vacu u m relief valve, a vacuu m system air fi lter,
vacuu m operated i nstru ments, a vacu u m gauge, low vacu u m
warni ng on t h e annunciator, and a manifold with check valves to
allow for normal vacuum system operation if one of the vacu u m
pumps should fail .
ATTITU D E I N DI CATOR
The attitude i ndicator is a vacu u m air-driven gyro that g ives a
visual i ndication of flight attitude. Bank attitude is presented by a
poi nter at the top of the indicator relative to the bank scale which
has index marks at 1 0°, 20°, 30°, 60°, and 90° either side of the
center mark. Pitch and rol l attitudes are presented by a miniature
airplane superimposed over a symbolic horizon area divided i nto
two sections by a wh ite horizon bar. The upper "bl u e sky" area and
the lower "gro u nd" area have pitch reference li nes usefu l for pitch
attitude control . A knob at the bottom of the instru ment is provided
for in-flight adj ustment of the symbolic airplane to the horizon bar
for a more accurate flight attitude indication .
D I RECTIONAL I N D I CATOR
A directional indicator is a vacuu m ai r-driven gyro that displays
airplane heading on a compass card in relation to a fixed s i m u lated
airplane i mage and index . Th e indicator will precess slightly over a
period of ti me. Therefore, the co mpass card should be set with the
magnetic compass j ust prior to takeoff, and readjusted as requ i red
th roughout the flight. A knob on the lower l eft edge of the i nstru ment
is used to adjust the compass card to correct for precession. A knob
on the lower right edge of the i nstru ment is used to move the
heading bug.

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