TM 55-1510-222-10 (d)   CDU BAT annunciator is illuminated. Operation on battery is an indication that there may be no aircraft power to blower motor with resultant loss of  cooling.    The  INS  can  operate  only  a  limited  time (normally  15  minutes)  on  battery  power  before  a  low voltage shutdown will occur. Then, immediate corrective action must be taken. NOTE • CDU  BAT  indicator  will  illuminate for 12 seconds in alignment State 8 (about    5    minutes    after    turn-on). This    is    normal    and    indicates    a battery   test   is   in   progress.      No corrective action is required. • During    ground    operation,    it    is recommended    that    operation    on battery power not exceed 5 minutes. 1. To determine corrective action: (Monitor    CDU    displays    while    rotating    the    CDU selector switch.) a. If     displays     are     frozen     (do     not change  while  data  selector  is  being rotated),  problem  is  normally  in  the navigation unit. b.    If  displays  respond  normally  to  the data selector, the problem is normally    absence    of    11    5V    AC power to INS. (e)  For  corrective  action:    Check  to  assure  proper settings  of  the  following  switches  and  circuit  breakers essential to INS operation: 1. Overhead circuit breaker panel (fig.  2-6) - Circuit breakers in: (1)   AVIONICS MASTER CONTR (2)   INS CONTROL (3)   AVIONICS MASTER PWR No. 1 (4)   AVIONICS MASTER PWR No. 2 2. Overhead control panel (fig.  2-13): INVERTER  No.  1  or  INVERTER  No    2  switch  -  ON (either). 3. Mission control panel (fig.  4-1): (1)   #1 INV or #2 INV switch - ON. (2)   Bus cross tie switch - ON/AUTO. 4. Mission  AC/DC  Power  Cabinet  (fig.    2- 29):  INS AC PWR circuit breaker - In. NOTE CDU BAT indicator should extinguish     after     above     corrective action.  If it remains illuminated, INS will     eventually     shut     down     when batter), voltage drops below approximately   19VDC.      Flight   crew should prepare for shutdown. (3)   Malfunction     indications     and     procedures: Table 3-3 details the procedure for a Malfunction Code Check.        Table    3-4    lists    a    number    of    malfunction indications which occur under given modes of operation. Table    3-5    details,    action    codes    and    recommended action.    Follow  procedure  given.    Table  3-6  lists  failed test symptoms by malfunction codes and lists codes for recommended actions. 3-28. GLOBAL   POSITIONING   SYSTEM   (AN/ASN- 149 (B)3). a. Description.    Complete  provisions  are  installed for a global positioning system (GPS).  The GPS is used to  provide  updated  position  information  to  the  inertial navigation   system.      The   GPS   system   consists   of   a control/display    unit,    receiver,    observer    headset    and GPS    key    panel,    antenna    electronics    unit,    and    an antenna. (1)   Control/display unit (CDU). The control/display    unit    (fig.        3-23A),    located    on    the electronics  rack  located  in  the  cabin,  accomplishes  all display and control functions necessary for the operation of the GPS receiver. (2)   Observer   Headset   and   GPS   Key   Panel. The observer headset and GPS key panel (fig.  3-23B), located  on  the  electronics  rack  in  the  cabin,  contains  a headset connector and GPS key and loading controls. 3-68