HEADQUARTERS OH-58A, Technical Manual

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TM 55-1520-228-10
u tility lig h t is a tta ch e d to a fle xib le g oo se n ec k ex te ns ion
mounted on the centerpost between the pilot and copi-
lot seats (figure 2-4). The flexible gooseneck holds the
u tility lig ht in the p o sitio n se le cte d b y t he pilo t or co p ilot.
An e xte n sio n c ord allo ws re m ov al o f th e u tility lig ht from
the gooseneck for manual us e.
The light is equipped
with a self-contained rheostat and has a rheostat over-
ride pushbutton that provides full lamp output regardles s
of knob setting. Power for the lig
ht is provided by the
COCKPIT LTS circuit breaker. Three NVG-compat ible
floodlights are mounted on the glareshield (figure 2-4).
F loo d ligh t inten sity is c on tro lled b y th e CO NSO L E LT
rheostat. The floodlights are powered by CSL LTS cir-
cuit breaker (
figure 2-12).
WARNING
N V G -co m p atible flip filte rs a re to re ma in in th e
open pos ition (
unfiltered) during day flight and
night flight without night vision goggles.
NVG-compatible flip filters are mounted next to the mas-
ter caution, caution advis or
y, RPM, and radar warning
indicators (figure 2-13 and figure 2-14). The filters are
positioned closed for NVG flight only.
SECTION XIII. FLIGHT INSTRUMENTS
2-61. AIRSPEED INDICATOR.
The airspeed indicator (figure 2-13 and figure 2-14) dis-
plays the air speed of the helicopter indicated in knots.
The airspeed is obtained by measuring the difference
between impact air pressure from the pitot tube and the
static air pressure from the static ports.
2-62. AAU-31/A PNEUMATIC ALTIMETER.
1. Description. The AAU-31/A pneumatic
counter-drum-pointer altimeter is a precision pressure
altimeter (figure 2-14). Pressure altitude is displayed
by a 100-foot drum and a single pointer indicating
hundreds of feet on a circular scale, with 50’ center
markings. Below an altitude of 10,000 feet, a diagonal
warning symbol will appear on the 10,000-foot counter.
A barometric pressure setting knob is provided to insert
the desired altimeter setting in inches of Hg. A DC pow-
ered vibrator operates inside the altimeter whenever air-
craft power is on.
2. Operation
a Normal Operation. The ALT VIB or
ALT AAU 31/32A circuit breaker must be in. The
altimeter indicates pneumatic altitude reference to the
barometric pressure level as selected by the pilot. A
vibrator, powered by the DC essential bus, is contained
in the altimeter and requires a minimum of one minute
warmup prior to checking or setting the altimeter.
b Abnormal Operation. If the altimeter’s in-
ternal vibrator becomes inoperative due to internal fail-
ure of DC power failure, the pointer and drum may mo-
mentarily hang up when passing from “9” through “0”
(climbing) or from “0” through “9” (descending). This
hang-up will cause lag, the magnitude of which will de-
pend on the vertical velocity of the aircraft and the fric-
tion in the altimeter. Pilots should be especially watch-
ful for this type failure when the minimum approach alti-
tude lies within the “8” — “1” part of the scale (800-100,
1800-2100, etc.).
2-62.1. ALTITUDE ENCODER/PNEUMATIC
ALTIMETER AAU-32/A
a. Description. The AAU-32/A pneumatic
counter-drum-pointer altimeter is a self-contained
unit which consists of a precision pressure altimeter
combined with an altitude encoder (figure 2-18.1). The
display indicates and the encoder transmits, simultane-
ously, pressure altitude reporting. Altitude is displayed
on the altimeter by a 10,000 foot counter, a 1,000 foot
counter and a 100 foot drum. A single pointer indicates
hundreds of feet of a circular scale, with 50 foot center
markings. Below an altitude of 10,000 foot a diagonal
warning system will appear on the 10,000 foot counter.
A barometric pressure setting knob is provided to insert
the desired altimeter setting in inches of Hg.
A DC
powered vibrator operates in-
Change 4 2-45
2-60. N VG-COMPATIBLE FILTE RS.