TM 55-1510-221-10
3-30A. GLOBAL POSITIONING SYSTEM
(AN/ASN-149, (B)3).
a .
Description. Complete provisions are in-
stalled for a global positioning system (GPS). The
GPS is used to provide updated position informa-
tion to the inertial navigation system. The GPS sys-
tem consists of a control/display unit, receiver, ob-
server headset and GPS key panel, antenna
electronics unit, and an antenna.
ed by the data select switch. If more than one page
is available a double arrow is displayed in the lower
right comer of the display. Pressing the slew key will
access the next page. Repeated pressing of the slew
key will return the display to the first page after the
last page has been accessed.
(1.) Control/display unit (CDU). The con-
trol/display unit (fig. 3-25A), located on the elec-
tronics rack in the cabin, accomplishes all display
and control functions necessary for the operation of
the GPS receiver.
(i.)
Data selector switch. For all data
selector switch positions there are two modes of dis-
played data:
1.
Destination mode (active waypoint as
destination)
2. Waypoint (WP) examine mode (any
waypoint)
(2.)
Observer Headset and GPS Key Panel.
The observer headset and GPS key panel (fig. 3-
25B), located on the electronics rack in the cabin,
contains a headset connector and GPS key and load-
ing controls.
Pressing the WP key switches the CDU between
the two modes.
The 10 position data select switch is used to se-
lect the type of information to be displayed on the
b.
GPS Controls, Indicators, and Functions.
(1.) GPS control/display unit (fig. 3-25A).
(a.)
Line selection keys. Four line se-
lection keys, located to the left of the CDU display
screen, are used to initiate and terminate data en-
tries, and to select various system options.
CDU:
POS.
MSN.
OPT.
(b.) Display screen. System informa-
tion is shown on the cathode ray tube display screen.
The display screen can show four lines of text with
13 alphanumeric characters on each.
STAT.
VAR-DTM.
(c.) Mode selector switch. The four-
position mode selector switch, placarded PULL
OFF, INIT, NAV, and PULL TEST, is used to select
the operating mode of the GPS system.
ERR.
WIND.
DIS-TG.
Position data is displayed.
Mission data is displayed.
Option data is displayed. Six pages
of information pertaining to the
GPS receiver are made available
when the OPT position is selected.
Status data is displayed.
Magnetic variation and map datum
data is displayed.
Error data is displayed.
Wind data is displayed.
Distance and time to go data is dis-
p l a y e d .
(d.) Display brightness control. A
control knob placarded BRT is provided to control
the brightness of the cathode ray tube display screen.
Clockwise rotation of the control increases bright-
ness.
TRK-GS.
Track and ground speed data is dis-
played.
DTK-VA.
Desired track and vertical angle
data is displayed.
(e.) Data entry keys (0 through 9).
(j.) Waypoint key. The waypoint
The data entry keys are used to enter alphanumeric
key, placarded WP, is used to enter and examine
data.
waypoint data.
(f.) USE LTR key. The use letter
key, placarded USE LTR, is used to select alphabet-
ic prompt in free format data entry. The USE LTR
key terminates alphabetic entry when pressed.
(k.) Mark key. The MARK key is
used for MARK and FREEZE functions.
(2.)
Observer Headset and GPS Key Panel
Controls, Indicators, and Functions fig. 3-25B).
(g.) Clear key. The clear key, plac-
arded CLR, is used to clear erroneous data entry
and message displays.
(h.)
Slew key. The slew key is used to
access additional pages within a data display select-
(a.) Interphone hot microphone, nor-
mal, key radio switch. This switch, placarded INT-
PH HOT MIC-NORM-KEY RADIO allows selec-
tion of hot microphone intercom, normal, and key
radio positions.
Change 2
3-76A
