GPS Controls, Indicators, and Functions.
(1) GPS control/display unit (fig. 3-23A).
(a) Line selection keys. Four line selection
keys, located to the left of the CDU display screen, are
used to initiate and terminate data entries, and to select
various system options.
(b) Display screen. System information is
shown on the cathode ray tube display screen. The
display screen can show four lines of text with 13
alphanumeric characters on each.
(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.
(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 brightness.
(e) Data entry keys (0 through 9). The data
entry keys are used to enter alphanumeric data.
USE LTR key. The use letter key,
placarded USE LTR, is used to select alphabetic prompt
in free format data entry. The USE LTR key terminates
alphabetic entry when pressed.
(g) Clear key. The clear key, placarded
CLR, is used to clear erroneous data entry and message
(h) Slew key. The slew key is used to
access additional pages within a data display selected
by the data select switch. If more than one page is
available a double arrow is displayed in the lower right
corner 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
Data selector switch. For all data
selector switch positions there are two modes of
Destination mode (active waypoint
Waypoint (WP) examine mode (any
Pressing the WP key switches the CDU between the
The 10 position data select switch is used to select the
type of information to be displayed on the CDU:
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
Track and ground speed data is
Desired track and vertical angle
data is displayed.
Waypoint key. The waypoint key,
placarded WP, is used to enter and examine waypoint
(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. 3-28B).
(a) Interphone hot microphone, normal, key
radio switch. This switch, placarded INTPH HOT MIC -
NORM - KEY RADIO allows selection of hot microphone
intercom, normal, and key radio positions.
(b) Observer headset connector. Allows
connection of observer headset.
(c) GPS Zeroize switch. Actuating the
declassify the GPS receiver.