resynchronize to the vertical mode. Example: with
IAS mode selected, the pilot may depress the CWS
pushbutton and manually change airspeed. Once
trimmed at the new airspeed the CWS pushbutton is
released, and the autopilot will hold this airspeed. If
a large pitch attitude change is made, the pilot
should trim the aircraft normally before releasing
the CWS button.
and by the 20-ampere circuit breaker on the front of
the INS battery unit.
6. Controls/Indicators and Functions (INS
Mode Selector Unit, fig. 3-24).
N O T E
Either pilots CWS button will permit
changing of the autopilot regardless of
which pilot has control of the autopilot.
However, use of the CWS will cancel the
other pilots flight director GA mode.
(1.) READY NAV lamp. Illuminates to
indicate INS high accuracy alignment has been
attained. If attained during ALIGN mode, light
remains illuminated until NAV mode is selected.
Light illuminates momentarily during alignment, if
alignment is accomplished while in NAV mode.
(2.) BAT lamp. Illuminates to indicate
INS shutdown due to low battery unit voltage.
(3.) Mode select knob. Controls INS acti-
vation and selects operating modes.
3-30. INERTIAL NAVIGATION SYSTEM.
(a.) OFF. Deactivates INS.
Description. The Inertial Navigation Sys-
tem (INS) is a self-contained navigation and attitude
reference system. It is aided by (but not dependent
upon) data obtained from its own TACAN system,
the GPS, the aircraft encoding altimeter and the
gyromagnetic compass system. The position and
attitude information computed by the INS is sup-
plied to the automatic flight control system, weather
radar system, horizontal situation indicator, and
radio magnetic indicators. In conjunction with other
aircraft equipment, the INS permits operation under
Instrument meteorological Conditions (IMC). The
INS provides a visual display of present position
data in Universal Transverse Mercator (UTM) coor-
dinates or conventional geographic (latitude-
longitude) coordinates during all phases of flight.
When approaching the point selected for a leg
switch, an ALERT light will illuminate informing
the pilot of an imminent automatic leg switch or the
need to manually insert course change data. The
INS may be manually updated for precise aircraft
present position accuracy by flying over a reference
point of known coordinates. The INS may be
updated automatically by the TACAN system or the
GPS. Altitude information is automatically inserted
into the INS computer by an encoding altimeter
whenever the INS is operational.
(b.) STBY. Moving to STBY from
OFF mode: Starts fast warmup of system to operat-
ing conditions; activates computer so information
may be inserted; all INS controlled warning flags
will indicate warning. Moving to STBY from any
other mode: INS operates as if in attitude reference
(c.) ALIGN (ground use only,
parked). Moving to ALIGN from OFF mode: Level-
ing starts after fast warmup heaters are off. Moving
to ALIGN from STBY: Alignment starts if fast war-
mup heaters are off. Moving to ALIGN from NAV
mode: INS is not downmoded, but will allow auto-
matic shutdown if overtemperature is detected.
(d.) NAV. Activates normal naviga-
tion mode after automatic alignment is completed;
must be selected before moving aircraft. Moving to
NAV from STBY mode causes INS to automatically
sequence through STBY and ALIGN to NAV mode,
if present position is inserted and aircraft is parked.
NAV mode is used to shorten time in STBY and to
bypass battery test, if stored heading is valid.
The Mode Selector Unit (MSU) (fig. 3-24) con-
trols system activation and selects operating modes.
The Control Display Unit (CDU) (fig. 3-25) pro-
vides controls and indicators for entering data into
the INS and displaying navigation and system status
(e.) ATT. Activates attitude refer-
ence mode. Used to provide only INS attitude sig-
nals. Shuts down computer and CDU leaving only
BAT and WARN lights operative. Once selected,
INS alignment is lost.
c. Controls/Indicators and Functions, (INS
Control Display Unit, fig. 3-25).
The INS system is protected by the 10-ampere
INS AC POWER and the 5-ampere INS HTR AC
POWER circuit breakers on the mission AC/DC
power cabinet, by the 5-ampere INS CONTROL cir-
cuit breaker on the overhead circuit breaker panel
(1.) HOLD key. Used with other CDU
controls to stop present position display from chang-
ing, in order to update position and to display
recorded malfunction codes. Lights when pressed
first time; goes out when pressed second time or
when inserted data is accepted by computer. When