INS Mode Selector
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 (NJ).
Cages the inertial reference unit (IRU) to the
orientation of the aircraft
Starts the gyro wheels spinning.
Activates the computer so information can be
When STBY is selected from any other position,
the IRU is not caged but operates the same as during
the attitude mode of operation.
position is used only during ground operation while the
aircraft is parked Setting the mode selector to ALIGN
from STBY will start automatic INS alignment, providing
that the fast warm-up heaters have shut off. Fine
alignment will not be started until present position has
been inserted. The computer automatically cycles
through leveling alignment. The ALIGN position can be
selected from the OFF position, but leveling will not be
started until the fast warm-up heaters have shut off.
Moving the mode selector from NAV will not downmode
the INS but will allow automatic shutdown if an
overtemperature is detected.
NAV. The navigation (NAV) position is
used to command entry into the navigation mode after
automatic alignment is completed. The NAV position
must be selected before moving the aircraft. The INS
will automatically sequence through standby and
alignment operation to the navigation mode when the
NAV position is selected from the STBY position,
providing that present position is inserted and the
aircraft is parked.
This position is also used to shorten the time in
STBY if stored heading is valid and to bypass the
battery test in state 8.
ATT. The attitude (ATT) position is
used to provide only INS attitude signals. This position
shuts down the computer so that navigation and steering
signals are not provided. The ATT position can be
selected from any other position. Once the ATT position
is selected, INS alignment is lost and the INS must be
realigned before the navigation mode of operation can
again be used.