TACAN control unit in the A/A position and tuning to
channels that are 63 channels apart from each other
(such as channel 20 and channel 83). The X/Y mode
switches will have to both be in the X or Y mode position.
3-27. INERTIAL NAVIGATION SYSTEM.
Description. The inertial navigation system (INS)
is a self-contained navigation and attitude reference
system. It is aided by (but not dependent upon) data
obtained from the global positioning system (GPS),
TACAN, encoding altimeter data, and heading information
from the gyromagnetic compass system. The position
and attitude information computed by the INS is supplied
to the automatic flight control system, the electronic flight
instrument system (EFIS), and to mission equipment.
The INS provides a visual display of present position data
in universal transverse mercator (UTM) coordinates or
conventional geographic (latitude-longitude) coordinates
during all phases of flight. When approaching the point
selected for a leg switch, a WPT will be displayed on both
EHSI's and '"waypoint alert" will be displayed on the
multifunction display (MFD) 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.
The INS consists of a navigation unit (NU), mode
selector unit (MSU), and a battery unit (BU).
The aircraft survivability equipment/avionics control
system (ASE/ACS) keyboard (fig. 4-3) provides a means
for entering data into the INS and displaying navigation
and system status information. Refer to chapter 4 for a -
complete description and operating instructions for the
The INS system receives AC power from a 10-
ampere INS PWR, a 5-ampere INS HTR POWER, and a
5-ampere INS FAN PWR circuit breaker, located on the
mission power cabinet. The INS system receives DC
power from a 5-ampere INS CONTROL circuit breaker
located on the overhead circuit breaker panel (fig. 2-9).
Navigation unit. The navigation unit (NU)
contains an inertial reference unit (IRU), a digital
computer unit (DCU), and an inertial reference unit
electronics (IRUE). All INS attitude, navigation, and
steering information is determined in the NU.
Inertial reference unit. The inertial
reference unit (IRU) is a gyro-stabilized platform and
gimbal assembly which is electronically controlled to
provide a local horizontal azimuth reference regardless of
Battery unit. The battery unit (BU)
provides auxiliary DC power to initiate INS turn-on and to
supply essential power to maintain INS operation should
115 volt primary power be interrupted after INS turn-on.
The battery unit will sustain operation of the INS for 15
Inertial reference unit electronics.
The inertial reference unit electronics (IRUE) includes
power circuits, temperature control circuits, and circuits
required for interface between the inertial reference unit
(IRU), computer, mode selector unit (MSU), aircraft
(ASE/ACS), battery unit, and for malfunction warning
Controls, Indicators, and Functions, INS Mode
Selector Unit (fig. 3-28).
READY NAV lamp. The READY NAV
(ready to navigate) lamp illuminates when high-accuracy
alignment status of the INS has been attained. When
alignment has been accomplished with the mode selector
set to ALIGN, the ready NAV lamp will remain illuminated
until NAV is selected. The READY NAV lamp will
illuminate momentarily during transition from state 9 to 8
and when alignment is accomplished with the mode
selector at the NAV position.
BAT Iamp. The battery (BAT) lamp
illuminates only when the INS has automatically shut
down due to low battery unit voltage. The INS will
automatically shut down before the battery unit is
completely discharged. A shutdown due to low battery
unit voltage can only occur while the INS is operating on
battery unit power. The INS operates on battery power
for a short period during coarse leveling (alignment state
8). If the battery unit charge is below the required
minimum level during this period, the INS will shut down
and the BAT lamp will illuminate to indicate the reason.
Mode selector knob. The mode selector
knob controls the operating modes of the INS. The knob
must be pulled out for rotation across mechanical stops
between STBY and ALIGN and between NAV and ATT.
OFF. Deactivates INS.
STBY. The standby (STBY) position
is used only during ground operation. Setting the mode
selector to STBY from OFF:
Starts fast warm-up in the navigation unit (NU).