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.
ALIGN. The alignment (ALIGN)
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
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 ATTa position
is selected, INS alignment is lost and the INS must be
realigned before the navigation mode of operation can
again be used.
INS Modes of Operation. The INS can be
operated in four modes: Standby (STBY), Align,
navigation (NAV), attitude (ATT). When the INS is turned
on it will (under normal conditions) proceed through the
STBY and ALIGN modes and enter the NAV mode,
where it will remain until it is downmoded at the end of the
flight. The only exception will be in the event of a
malfunction, in which case the INS will be shut down or
placed in the
1. READY NAV Lamp
2. BAT Lamp
3. MODE Selector
Figure 3-28. INS Mode Selector