TM 55-1510-220-10 (a) Realignment  INS  operating.    (Recommended if   sufficient   time   and   accurate   parking   coordinates   are available). NOTE 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". 1. Data selector STBY, then to ALIGN. 2. Present    position    coordinates    Insert, according     to     procedure:     "Geographic     Present     Position Insertion"     or "UTM Present Position Insertion." (b) Realignment INS shutdown. Perform complete alignment procedures. (c) Position update.  Recommended if time is not available for realignment. NOTE Perform    position    update    using    parking coordinates in accordance with procedure: "Insertion of Geographic Waypoint Coordinates."  If  parking  coordinates  are not available, proceed as follows: operation in NAV, if INS accuracy appears acceptable. Continue operation in NAV, if INS accuracy appears acceptable. Perform position update using best estimate of parking coordinate. (16) Downmoding to standby: NOTE INS can be downmoded to standby operation  which  will  maintain  navigation unit   at   operating   temperature   with   gyro wheels   running.      INS   is   downmoded   to standby as follows: (a) Mode selector STBY. CAUTION Do  not  leave  INS  operating  unless  aircraft or    ground    power    and    cooling    air    are available to system. (17) Shutdown: (a) Mode selector OFF. NOTE 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. (18) Abnormal procedures: (a) 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. (b) Automatic INS shutdown. 1. 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