TM 1-1510-225-10 3A-25 flight   director   will   engage   altitude   capture   and   then altitude hold. During  transitions  to  armed  altitudes  the  flight control system will briefly sound an alert tone when the aircraft    passes    within    1000    feet    of    the    selected altitude.    In  addition,  an  alert  annunciator  illuminates on    the    altitude/vertical    speed    indicator    when    the aircraft  is  between  1000  and  300  feet  above  or  below the   armed   altitude.      The   annunciator   will   illuminate again  briefly  when  the  aircraft  reaches  the  selected altitude.  Subsequent alerts are provided if the aircraft deviates 300 feet or more from the selected altitude. Altitude   select   will   engage   automatically   with selection  of  climb  or  descent  modes,  provided  that  a higher or lower altitude is displayed in the altitude pre- select    window    on    the    altitude    and    vertical    speed indicator. (w)  Altitude Hold Mode Annunciator.   Illumination   of   the   altitude   hold   mode   annunciator, placarded  ALT,  indicates  that  the  altitude  hold  mode has been selected and is engaged. (x)   Altitude Hold Mode Push-Button Selector   Switch.      Pressing   the   altitude   hold   push- button   selector   switch,   placarded   ALT,   selects   the flight director altitude hold mode. In    the    altitude    hold    mode    the    flight    director commands  pitch  attitudes  for  capture  and  tracking of the  barometrically  corrected  aircraft  altitude  current  at the  moment  of  mode  selection.    Altitude  hold  can  be entered   directly   or   in   conjunction   with   the   altitude select mode.  Engaging altitude hold directly during a climb or descent will allow the aircraft to fly through the desired  altitude  and  then  recover  from  the  other  side.   For this reason, altitude is most useful for engagement when vertical speed is less than 500 feet per minute. Selecting  altitude  hold  after  the  altitude  select mode  has   been  engaged  cancels  altitude  select  and causes the  ARM  annunciator  to  extinguish.    The  flight director  will  command  the  aircraft  to  hold  the  altitude present at the moment of mode selection. Altitude   hold   commands   may   be   modified   by holding  the  autopilot   vertical  trim  rocker  switch  in  the up  or  down  position  either  momentarily  or  for  several seconds   at   a   time.      Momentary   switch   activation modifies target altitudes at the rate of 20 feet per click.   Continuous   vertical   trim   operation   causes   the   flight director to command a climb or descent, as appropriate,  at  500  feet  per  minute  until  the  switch  is released. m. Autopilot Operation. (1)   Autopilot Self Test. 1.   AVIONICS MASTER PWR – ON. 2.   EFIS POWER switches – ON. 3.   AP / TRIM POWER switch – ON. 4.   Allow  3-4  minutes  for  gyros  to  erect HDG and ATTITUDE flags clear. 5.   AP    FAIL    and    AP    TRIM    FAIL    – Annunciators    illuminate    upon    initial application  of   AP/TRIM  POWER and then  extinguish  (followed  by  an  audio test  tone)  after  successful  completion of   the   self-test.      Allow   60   seconds after gyros are valid. CAUTION Taxi with caution. The autopilot temporarily  engages  the  servos  during  the automatic self-test. Be prepared to overpower the autopilot as required. NOTE Illumination   of   the   AP   FAIL   annunciator other than during initial power-up indicates a   failure.      This   failure   annunciation   will result  in  power  being  removed  from  the roll, pitch, yaw, pitch trim, and rudder trim servos.      The   flight   director   may   remain functional   depending   upon   the   nature   of the  failure.    The  continual  self-test  feature may   also   inhibit   flight   director,   autopilot and electric trim use without illumination of the AP FAIL annunciator. (2)   Flight  Control/Autopilot  System  Preflight Check. 1.   AP XFER switch – Select pilot's side. 2.   AP mode selector button (AP ) – Press to engage autopilot. 3.   Flight controls   –  Overpower  autopilot in pitch, roll, and yaw axis. If unable to overpower the autopilot in any axis, do not use. 4.   Auto trim – Check. WARNING