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Up/Down Arrows Scroll through the waypoint dictionary pages, one page per keystroke. When constantly pressed,
will scroll through all dictionary pages at about one page per second.
BRT Control Adjust display brightness.
CLR If pressed in response to an ERROR prompt in the scratchpad, will clear the error prompt and
position the cursor at the first detected data entry error. If pressed a second time, will clear the
entire scratchpad. If no ERROR prompt is present when CLR is pressed, it will clear the entire
scratchpad.
SPC Enters a blank space character.
STR Stores DNS present position in storage locations 16 through 19 in circular rotation.
Change 3 3-47
TM 1-1520-23810
Table 3-14. AN/ASN-137 Control and Display Functions - continued
Control/Display Function
FLPPN Displays the first (H-1-2) of 7 waypoint dictionary pages Dictionary pages may then be scrolled
using the UP/DOWN ARROW keys.
NAV Displays NAV top level page. Pressing the NAV FAB will override all other display pages and
return the CDU display to the NAV top level page.
FDLS Used to access the FDLS Test page. DNS and CDU FDLS tests are initiated from this page.
COM Not active.
IFF Not active.
ATHS Not active.
TGT Not active.
CODE Not active.
DATA Not active.
3.15.1 Modes of Operation. There are four modes c
operation: Navigation, backup, hover bias calibration
(HBCM), and test (On Command and Continuous).When
electrical power is first applied to the helicopter, the CD1
is powered and the NAV top level page is displayed a
shown in paragraph a. The DNS is not powered at this
time.
NOTE
All data and messages shown in displays are typical
representations.
a. Navigation Mode. This is the initial powerup mode of
the DNS. In navigation mode, power is applied to all
DNS components. Computed present position data
is derived by the DNs computer from doppler radar
data. This is the most accurate navigation mode.
b. Backup Mode. The backup mode is manually
selected by the CPG. Backup mode is usually
selected for only one of two reasons: DNS FDLS has
detected a failure of the doppler radar ground speed
for navigation calculations. Dynamic doppler radar
velocities will not be
available. The (HARS) will go into free inertial when
the DNS is in backup mode. The CPG can change
the ground speed used by entering the computed or
best estimation of ground speed on the NAV top
level page. Ground speed can only be entered by
the CPG when the DNS is in backup mode.
c. HBCM. The HBCM calibrates the DSN system for
small velocity errors that may be present in the
doppler/transmitter subsystem. The velocity bias
corrections are computed by DNS computer, and are
applied to all subsequent doppler radar velocities.
The velocity bias (error), when present, will be most
noticeable when the helicopter is at a hover or slow
speeds. The reason is that at a hover the velocity
error, although small, is about the same amount as
the actual helicopter velocity. When HCBM is
selected, the CPG can manually start and stop the
calibration. If a calibration NO-GO status is
displayed at the conclusion, a recalibration may be
restarted by the CPG. If a GO calibration is
computed, the bias velocities will automatically be
stored and applied continuously to all subsequent
navigtion computations.
3-48 Change 3
TM 1-1520-238-10
d. Test Mode. The DNS and CDU have both
Continuous and On Command FDLS tests.
The DNS continuous test checks the
doppler antenna (RTA), and doppler signal
data converter computer (SDCC). The
CDU monitors its own internal functions and
the dedicated 1553B mux bus between the
CDU and DNS SDCC. If a failure is
detected by the Continuous test, the CDU
will display the prompt v FDLS on line 6 of
the NAV top level page. The CPG can then
display system status by pressing the FDLS
fixed action button (FAB). The CPG can
initiate the ON Command test from the
FDLS page. The On Command test
initiates a full DNS subsystem component
test. If no failures are detected, the CDU
will display the pitch, roll, and inertial
heading, in degrees, currently being used
by the DNS. The pitch and roll angles will
reflect the actual orientation of the
helicopter on level ground, pitch will be
approximately 4.5 to 5.5°, and roll should
be about 0.0. If the helicopter has a lean
due to cyclic or pedal inputs, this will be
reflected in the roll angle displayed. The
heading value displayed is the inertial
heading of the helicopter; HSI/RMI heading
中国航空网 www.aero.cn
航空翻译 www.aviation.cn
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