TM 1-1510-225-10 2-117 Table 2-11.  Standby Attitude Indicator Control / Functions  T3   NO. FUNCTION 1 Moveable sphere with line between colors to indicate the earth’s horizon. 2 Rotates with aircraft to provide measurement of angular displacement by the roll pointer. 3 Indicates vertical in any roll attitude. 4 Indicates earth's horizon relative to aircraft pitch attitude. 5 Rotated to adjust the miniature aircraft. 6 Measures pitch displacement of miniature aircraft. 7 Represents  aircraft  nose  and  wings.    Indicates  roll  and  pitch  attitude  relative  to  the horizon.  Adjustable through pitch knob for varying pitch attitudes. c.   Description  F3  OSA .    The  standby  attitude reference   system,   Figure   2-40,  is  comprised  of  the attitude indicator located on the extreme left center of the  pilot's  instrument  panel  and  a  28  Vdc  emergency power  supply.    They  provide a visual indication of the aircraft flight attitude.  The attitude reference system is designed to provide a standby attitude indicator that is powered   by   a   source   independent   of   the   aircraft electrical generating system.  The system will provide reliable   attitude   information   for   at   least   30   minutes after  a  total  failure  of  the  aircraft  electrical  system.   The  power  supply  contains  sealed  lead-acid batteries with   a   rating   of   5.0   ampere   hours.      During   normal operation,  the  aircraft  28 Vdc  system  supplies  power to  the  indicator  and  power  supply  batteries.    In  the event aircraft electrical power fails, the standby power supply will take over the duties of powering the attitude indicator. The   attitude   indicator   is   a   28   Vdc   powered electrically  driven  gyro  and contains an inverter circuit board  for  converting  the  28  Vdc  input  to  22 Vac 400 Hz  for  indicator  operation.    The  power  warning  flag  is rotated out of sight by a flag motor that allows the flag to    appear    if    one    or    more    phases    of    power    are interrupted.      The  flag  motor  also  allows  the  flag  to appear if the   PULL  TO  CAGE   knob  is  in  the  caged position.  The rotor speed and the mechanical erection system enables the indicator to provide a minimum of 9 minutes of useful attitude information after complete electrical power interruption. A    three-position    switch    and    a    three    legend annunciator  unit  located  below  the  indicator  provide system control, test and visual indication of the system status.  The three position switch, placarded ON / OFF /   TEST   (normally   OFF),   provides   control   and   test capabilities  of  the  battery  powered  system.    While  in the normal  OFF  position,  the  annunciator,  placarded AUX   ARM,  will  be  illuminated  indicating  the  system batteries are being maintained in a charged condition and the system is in a standby (non-active) mode.  In the   TEST    position,    a    check    of    the    battery    pack illuminates the  AUX TEST annunciator. Placed   in   the    ON   position,   it   activates   the Standby Horizon Indicator system and illuminates the AUX   ON   annunciator,   provided   the   system   circuit breaker is set. Table    2-12    describes    the    functions    of    the controls/indicators. d.  Standby Attitude Indicator Controls, Indicators, and Functions.  (1)   Bank  Angle  Scale.    Used  in  conjunction with bank angle pointer to indicate aircraft bank angle. (2)   Bank  Angle  Index.    Rotates  with  aircraft to  provide  measurement  of  angular  displacement  by roll pointer during maneuvers. (3)   Bank Angle Pointer.  The moveable bank angle  pointer  indicates  aircraft  bank  angle  by  moving around a fixed bank angle scale. (4)   Pitch  Angle  Scale.    Aircraft  pitch  angle may be read under the symbolic miniature aircraft on a vertical pitch angle scale located on the attitude drum. (5)   Horizon  Line.    The  horizon  line  displays aircraft pitch and roll attitude with respect to the earth's horizon. (6)   Caging  and Pitch Trim Adjustment Knob.   This   knob,   placarded   PULL   TO   CAGE,  is  used  to vertically   adjust   the   symbolic   miniature   aircraft   for changes in the aircraft's level flight pitch attitude and to cage the instrument.