Realignment INS operating. (Recommended
if sufficient time and accurate parking coordinates are
INS can be downmoded to perform a
realignment and azimuth gyro calibration.
Alignment to produce an alignment state
number of "5" can be accomplished in
approximately 17 minutes. During the 17
minute period, an automatic azimuth gyro
recalibration is determined on basis of
difference between inertial present position
before downmoding and inserted present
position. To obtain further refinement of
azimuth gyro drift rate, calculated on basis
of newly computed error data, INS can be
left in alignment mode for a longer period,
allowing the alignment state number to
attain some value lower than "5".
Data selector STBY, then to ALIGN.
Present position coordinates Insert,
according to procedure: "Geographic Present Position
Insertion" or "UTM Present Position Insertion."
complete alignment procedures.
Position update. Recommended if time is not
available for realignment.
Perform position update using parking
coordinates in accordance with procedure:
Coordinates." If parking coordinates are
not available, proceed as follows: operation
accuracy appears acceptable.
estimate of parking coordinate.
Downmoding to standby:
operation which will maintain navigation
unit at operating temperature with gyro
wheels running. INS is downmoded to
standby as follows:
Mode selector STBY.
Do not leave INS operating unless aircraft
or ground power and cooling air are
available to system.
Mode selector OFF.
INS will retain inertial present position
data computed at time INS is downmoded.
This value is compared with present
position inserted for next alignment and
difference is used to determine azimuth
gyro drift rate.
General. INS contains self-testing features
which provide one or more warning indications when a
failure occurs. The WARN annunciator on the CDU provides
a master warning for most malfunctions occurring in the
navigation unit. Malfunctions in the MSU or CDU will
normally be obvious because of abnormal indications of
displays and annunciators. A battery unit malfunction will
shut down INS when battery power is used.
Automatic INS shutdown.
Overtemperature. An overtemp-erature
in navigation unit will cause INS to shut down (indicated by
blank CDU displays) when mode selector is at STBY or
ALIGN during ground operation. The WARN annunciator
on CDU will illuminate and will not extinguish until mode
selector is rotated to OFF. The cooling system should be
checked and corrected if faulty. If cooling system is
satisfactory, navigation unit should be replaced.
Change 2 3-71