Waypoint key. The waypoint key.
placarded WP, is used to enter and examine waypoint data.
Mark key. The MARK key is used for
MARKand FREEZE functions.
GPS key, load, and zeroize panel controls.
indicators, and functions (fig. 3-25B).
GPS zeroize switch. Actuating the
guarded switch. placarded ZEROIZE GPS, will declassify the
GPS key connector. Connects GPS
Load switch. This pushbutton switch
initiates loading process.
Load status indicator light. Illuminates
to indicate load status.
Dust cap. Covers GPS key connector
when not in use.
GPS System Modes of Operation.
Off mode. When the PULL OFF mode has
been selected. power is removed from the system. except
Critical memory and other circuits which
cannot be turned off remain powered by
batteries in the receiver.
Initialize mode. When the INIT (initialize)
mode has been selected, position and time estimates can be
entered via the keypad. Waypoint data may be entered and
examined. and option selections made. No navigation
functions can be performed. If the INS is in NAV mode. the
INS position from the INS and altitude from the pilot's
encoding altimeter will be displayed on the CDI. This data
will be used by the GPS for initial position and altitude.
Navigation mode. Selection of the NAV
(navigation) mode enables normal GPS functions (satellite
tracking and navigation). including data transfer to and from
Test mode. Selection of the PULL TEST
mode initiates a full command test of GPS user equipment for
line replaceable unit (LRU) fault identification and isolation.
GP.S Normal Operation.
GPS start procedures. The GPS must be
initialized prior to being used for navigation. There are three
types of start: normal, quick, and cold. A position estimate,
time estimate, and almanac (or ephemeris) data are required
for a normal start. A quick start uses stored position, time,
and recent ephemeris information. A cold start is used only
when the GPS is unable to perform a normal startup.
GPS normal start.
Mode selector switch INIT. When
built-in-test is complete the display will
show data corresponding to the data
selector switch position.
Data display will not be illuminated for
about 30 seconds after GPS has been
turned on. Ensure that the display
brightness control has been set to the full
clockwise position to receive the INIT
display, then adjust as desired.
If the GPS has been OFF for more than 30
seconds when INIT mode was selected. the
set will perform the initial built-in-test
which takes approximately 30 seconds.
Data selector switch POS. If
ENTER POS message is displayed
press line select key 3 next to message.
Position must be entered.
Displayed position Check. Verify
or enter new updated position and
altitude as required .
Verify correct track and groundspeed
are displayed. If not valid, enter correct
Slew key Press. Check, verify, or
enter current time, year, and day of
year on page 2.
Change 5 3-76C