tered in any of the 100 fly-to destinations. The landing
approach is determined by present position and the en-
tered touch down altitude, glideslope and inbound ap-
3-3-46. CDU Operation.
Various required operating data, such an initial present
position (if GPS is not valid or Doppler mode is selected).
destination coordinates with or without GPS landing
data, and magnetic variation can at any time be entered
into the CDU via its keyboard, or the dataloader via the
preprogrammed dataloader cartridge. In most cases,
these data will be entered before the aircraft takes off.
The GPS provides present positions to AN/
ASN-128B. If GPS is not available or Doppler is selected
present position can be initialized as follows:
The MODE switch should be set to MGRS or
LAT/LONG, the WT/TGT display position of the DISPLAY
switch is selected, the destination number is set to P and
KYBD key is pressed. The coordinates of the initial posi-
tion is overflown, the ENT key is pressed. The computer
then determines changes from the initial position contin-
uously, and the coordinates of the current present posi-
tion can be read either by remaining in this configuration
or by setting the DISPLAY switch to PP (present position)
and the MODE switch to MGRS or LAT/LONG.
To update present position over a stored
destination, KYBD key is depressed and released when
the aircraft overflies this destination. If an update is de-
sired, the ENT key is depressed and released and the
update is completed. The DISPLAY switch is in the DIST/
BRG/TIME position and the FLY-TO-DEST is set to this
destination during this process. The distance-to-go, dis-
played while over the stored destination, is the position
error of the system at that moment.
To update present position over fixed point
not previously stored in the computer, the DISPLAY
switch is placed PP and KYBD key is depressed and
released as the fix point is overflown. This freezes the
display while allowing computation of changes in present
position to continue within the computer. If an update is
required, the coordinates of the fix point are entered via
the keyboard, and ENT key is pressed. The position
change which occurred since over-flying the fix point
automatically added to the fix point coordinates to com-
plete the position update.
Magnetic variation can be entered for each
destination, and the system will compute present posi-
tion magnetic variation. If operation is to occur in a region
with relatively constant magnetic variation, the operator
enters magnetic variation only for present position and
the computer will use this value throughout the flight. If
MGRS data are to be entered or displayed, the MGRS
datum of operation is also entered.
Target-of-opportunity can be stored by pressing
TGT STR (target store) key when the target is overflown.
This operation stores the coordinates of the target in one
of ten destination locations in the computer; locations 90
through 99 sequentially incrementing each time the TGT
STR key is depressed. The location is displayed in the
appropriate display field. The computer can keep track of
individual target positions which may include speeds and
directions input by the operator.
Self test of the AN/ASN-128B is accomplished
using built-in-test-equipment (BITE) with the RTA, SDC,
and CDU units connected an energized for normal op-
eration. Self test enables the unit to isolate failures to one
of the four main functions (RTA, SDC, CDU or EGR) or
to one of the circuit cards in the SDC or CDU. Self test is
accomplished as follows: Self test of the AN/ASN-128B
is accomplished using built-in-test-equipment (BITE)
with the RTA, SDC, and CDU units connected an ener-
gized for normal operation. Self test enables the unit to
isolate failures to one of the four main functions (RTA,
SDC, CDU or EGR) or to one of the circuit cards in the
SDC or CDU. Self test is accomplished as follows:
The CDU (except for the keyboard and dis-
play) is checked on a continuous basis, and any failure
is displayed by illumination of the MAL indicator lamp on
the CDU. If the MODE switch on the CDU is set to the
TEST position, identification of the failed circuit card in
the CDU is indicated by a code on the display panel.
The DRVS and EGR are tested by setting
the MODE switch on the CDU to the TEST position.
Failure of the DRVS or EGR are displayed on the CDU
by illumination of the MAL indicator lamp, and identifica-
tion of the failed unit or circuit card is indicated by a code
on the display panel of the CDU.
Continuous monitoring of the Signal Digital
Data Converter and Receiver Transmitter Antenna is
provided by the system status indication. The system will
not use Doppler velocities in normal operation when fly-
ing over glassy smooth water. However, if the system
continues to not use Doppler (e.g., using GPS only when
combined has been selected) for excessive periods of
time (e.g. more than10 minutes) over land or rough wa-
ter, then a malfunction may exist in the navigation set and
the operator should set the MODE switch to TEST to
determine the nature of failure.
The display portion of the CDU is tested by
illuminating all the lamp segments in each alphanumeric
characters in the LAMP TEST mode.
Keyboard operation is verified by observing
the alphanumeric characters as the keyboard is exer-
3-3-47. Route Sequencing Modes.
The system has the ability to fly a preprogrammed se-
quence of waypoints. This sequence can be either con-
secutively numbered in which case a start and end way-
point are entered or randomly numbered in which case