TM 1-1510-225-10
3B-177
the radio altimeter to go into test mode. While the
radio altimeter is in test, the digital readout remains
displayed, even when the radio altimeter validity is
flagged.
(2) Decision Height (DH) Knob. The DH SET
knob is used to set the decision height. Clockwise
rotation increases the decision height. The decision
height is displayed in green following the letters DH in
the lower right corner of the EADI. When the radio
altitude is at or below the DH setting, the yellow letters
DH display in the right center portion of the EADI or
PFD display and a "Minimum" aural annunciation is
sounded. Once the DH annunciation displays, it is
removed from the display when the radio altitude
climbs at least 25 feet above the decision height. If
the radio altimeter system fails, the decision height
enunciator is removed and the radio altitude flag
appears.
3B-30. VERTICAL GYRO SYSTEM.
The pilot's and copilot's vertical gyro systems are
independent and powered by the ac power bus located
in the nose avionics compartment. The purpos e of the
vertical gyro systems is to provide the pilots with visual
indications of aircraft pitch and roll attitudes on the
flight director indicators.
The gyroscope develops through synchros,
pitch, and roll signals representative of the aircraft
attitude. Vertical reference is established by two
gravity sensitive switches that control a torque motor
for each gyro axis. High or low erection rate of the
gyro is accomplished by applying high or low voltage
to the respective torque motor. Panel mounted
switches, placarded NO. 1 (pilot) and NO. 2 (copilot),
V GYRO FAST ERECT, provide the means for fast
erection of the gyros. Pressing the FAST ERECT
switch will erect the gyro to within 1.0° of pitch and roll
within 60 seconds of power application, and erect
within 0.5° within 2 minutes.
3B-31. GYRO MAGNETIC COMPASS SYSTEM.
a. Description.
Two
identical
compass
systems provide accurate directional information for
the aircraft at all latitudes of the earth. For heading
reference,
two
modes
of
operation
are
used:
directional gyro (FREE) mode, or slaved (SLAVE)
mode.
In areas where magnetic references are reliable,
the system is operated in the SLAVE mode. In this
mode, the directional gyro is slaved to the magnetic
flux valve that supplies magnetic reference for
correction of the apparent drift of the gyro. In FREE
mode, the system is operated as a free gyro. In this
mode latitude corrections are manually introduced
using the INCREASE / DECREASE switches. The
slave/free mode is selected as desired using the
SLAVE / FREE switches.
Gyro compass 1 provides heading information
for the pilot's HSI and copilot's RMI. Gyro compass 2
serves the copilot's HSI and the pilot's RMI.
b. Power. Both compass systems (No. 1 and
No. 2) are ac power dependent, and are powered by
the selected inverter.
c. Controls.
(1) Compass 1 SLAVE / FREE Switch.
Located below the Turn and Slip indicator. Allows pilot
to switch between SLAVE and FREE mode.
(2) Compass 1 INCREASE / DECREASE.
Located next to the SLAVE / FREE Switch. Allows
manual correction to heading while in the FREE mode.
(3) Compass 2 SLAVE / FREE Switch.
Located below the Turn and Slip indicator. Allow pilot
to switch between SLAVE and FREE mode.
(4) Compass 2 INCREASE / DECREASE.
Located next to the SLAVE / FREE switch. Allows
manual correction to heading while in the FREE mode.
Section IV. RADAR AND TRANSPONDER
3B-32. WEATHER RADAR SYSTEM.
a. Description. The Honeywell Primus 300 SL
Color Radar System is a lightweight, X-band digital
radar with alphanumerics designed for weather
detection and analysis and ground mapping.
The primary purpose of the system is to detect
storms along the flight path and give the pilot a visual
indication in color of the rainfall intensity. After proper
evaluation, the pilot can chart a course to avoid these
storm areas.