TM 1-1510-225-10 3A-114 3A-33.  GROUND PROXIMITY ALTITUDE ADVISORY SYSTEM. The ground proximity altitude advisory will provide little, it any, warning for flight into precipitous   terrain   approaching   a   sheer wall if there is little gradually rising terrain before reaching the steep terrain. a.   Description.  The Ground Proximity Altitude Advisory  System  (GPAAS)  is  provided  to  aid  the  flight crew in terrain avoidance. The  GPAAS  is  a  completely  automatic  system (requiring  no  input  from  the  crew)  which  continuously monitors    the    aircraft's    flight    path    at    altitudes    of between   100   and   2000   feet   Above   Ground   Level (AGL). The  GPAAS  computer  processes  the  data and, when    conditions    warrant,    selects    the    appropriate digitized    voice    advisory/warning    message    from    its memory.    This  message  is  then  announced  over  the pilot's and copilot's audio systems.  If the condition is not  corrected,  the  GPAAS  will  rearm,  and  will again announce   and   repeat   the   warning   if   the   condition recurs.      The   GPAAS   computer   remains   ready   to announce   a   different   message   during   the   intervals between repetitions.  All messages are disabled below 100  feet  AGL.    The  GPAAS  system  receives  28  Vdc power  through  a  1-ampere  circuit  breaker,  placarded GPAAS POWER,  located  on  the  right  sidewall  circuit breaker panel, Figure 2-6. (1)   GPAAS Switch-Indicator Lights. A switch-indicator is located on the audio control panel.   The   upper   half   of   the   switch-indicat or   (yellow)   is placarded  VOICE  OFF.  The lower half is an indicator (red) only and is placarded VA FAIL. Pressing     the     upper     (VOICE OFF)     switch- indicator disables the GPAAS advisory, and illuminates the VOICE OFF indicator light. The     VA     FAIL     annunciator     light     (red)     will illuminate when the GPAAS fails. (2)   GPAAS    Volume    Control.        A    GPAAS volume  control  placarded   VOL,  located  on  the  audio control panel, controls the audio volume of the GPAAS advisory/warning messages down to a certain minimum level. (3)   GPAAS  Aural  Warning  Indications.    The following   is   a   list   of   aural   indications.      Due   to   the possibility  of  activating  more  than  one  condition  at  a time,  a  warning  priority  has  been  established.    The highest  priority  message  will  be  announced  first.    If  a higher   priority   item   is   received   after   a   message   is started,    voice    annunciation    of    the    higher    priority message   shall   be   announced   after   a   lower   priority message   in   progress   at   the   end   of   the   message segment.  It will not stop in the middle of a word.  On messages   that   are   repeated   three   times   at   four- second  intervals,  the  priority  list  will  be  scanned  for higher  priority  messages  and  will  insert  them  in  the interval    between    the    messages.        The    messages provided by the system are listed in descending order of priority as follows: 1.   "Two Thousand" at 2000 feet AGL. 2.   "One Thousand" at 1000 feet AGL. 3.   "Nine Hundred" at 900 feet AGL. 4.   "Eight Hundred" at 800 feet AGL. 5.   "Seven Hundred" at 700 feet AGL. 6.   "Six Hundred" at 600 feet AGL. 7.   "Five Hundred" at 500 feet AGL. 8.   "Check     Gear"     will     be     announced immediately after 500 foot announcement if gear is not down. 9.   "Four Hundred" at 400 feet AGL. 10.   "Check     Gear"     will     be     announced immediately after 400 foot announcement if gear is not down. 11.   "Three Hundred" at 300 feet AGL. 12.   "Check     Gear"     will     be     announced immediately after 300 foot announcement if gear is not down. 13.   "Two Hundred" at 200 feet AGL. 14.   "Check     Gear"     will     be     announced immediately after 200 foot announcement if gear is not down. 15.   "One Hundred" at 100 feet AGL. 16.   "Check     Gear"     will     be     announced immediat ely after 100 foot announcement if gear is not down. 17.   "Minimum, Minimum" at decision height. WARNING