TM 1-1510-225-10 3A-24 (l)    Not Used. (m) Vertical Speed Hold Mode Annunciator.    Illumination  of  the  vertical  speed  hold mode, placarded  VS, indicates that the vertical speed hold mode has been selected and is engaged. (n)   Vertical    Speed    Hold    Mode    Push- Button  Selector  Switch.    Pressing  the  vertical  speed hold mode push-button selector switch, placarded  VS, selects  the  vertical  speed  hold  mode.    In  the  vertical speed    mode,    the    flight    director    commands    pitch attitudes to maintain the vertical speed selected on the altitude/vertical  speed  indicator.    In  the  absence  of  a pre-selected  vertical  speed,  engaging  the  mode  will cause   the   flight   director   to   command   a   climb   or descent at the rate current upon selection.  In addition, vertical speed commands may be modified through the use  of  the  autopilot  vertical  trim  at  the  rate  of  100  feet per minute per click during momentary trim operation or  100  feet  per  minute  per  second  during  continuous trim operation. When  vertical  speed  mode  is  engaged  or  the pre-select function of altitude/vertical speed indicator is activated,  an  orange  marker  appears  on  the  vertical speed  scale.    Using  the  vertical  trim switch or the  VS  select   knob   on   the   altitude/vertical   speed   indicator repositions  the  marker  for  reference  for  the  pilot  and autopilot. (o)   Indicated Airspeed Hold Mode Annunciator.      Illumination   of   the   indicated   airspeed hold mode annunciator, placarded  IAS, indicates that the  indicated  airspeed  hold  mode  has  been  selected and is engaged. (p)   Indicated  Airspeed  Hold  Mode  Push- Button    Selector    Switch.        Pressing    the    indicated airspeed    hold    mode    push-button    selector    switch, placarded    IAS,    will    cause    the    flight    director    to command   pitch   attitudes   to   maintain   the   indicated airspeed current upon selection.  Airspeed commands may be altered through the use of the autopilot vertical trim rocker switch at the rate of two knots per click or one knot per second. As a safety feature, the flight director automatically     reverts     to     indicated     airspeed     hold whenever     the     aircraft     exceeds     a     predetermined maximum   speed.      The   flight   director   will   command pitch attitudes to reduce indicated airspeed to V_moa and then maintain that airspeed. (q)   Descent Mode Annunciator.   Illumination of the descent mode annunciator, placarded DESC, indicates that the descent mode has been selected and is engaged. (r)    Descent  Mode  Push-Button Selector Switch.      Pressing   the   descent   mode   push-button selector switch, placarded  DESC, selects the descent mode.        In    the    descent    mode    the    flight    director commands  pitch  attitudes  to  initiate  a  descent  at  a predetermined rate of descent.  Engaging the descent mode  also  arms  the  altitude  capture  sequence  if  the selected  altitude  is  lower  than  the  aircraft's  present altitude. (s)   Climb Mode Annunciator.   Illumination of the climb mode annunciator, placarded CLB, indicates that the climb mode has been selected and is engaged. (t)    Climb    Mode    Push-Button    Selector Switch.  Pressing the climb mode push-button selector switch, placarded   CLIMB,  selects  flight  director  climb mode.        At    typical    aircraft    climb    power    settings, selecting the climb mode causes the flight director to command  pitch  attitudes  to  maintain  a  programmed climb  that  alters  airspeed  with  reference  to  altitude.   The  climb  profile  conforms  to  a  comfortable  aircraft attitude  for  use  during  en  route  climbs.    The  exact climb profile is programmed for this aircraft type. Engaging   the   climb   mode   also   activates   the altitude   select   mode   whenever   a   higher   altitude   is displayed    in    the    altitude/vertical    speed    indicator's altitude   pre-select   window.      In   that   case,   the   flight director  automatically  cancels  the  climb  mode  upon initiation  of  altitude  capture  and  transition  to  altitude hold. Selecting    the    climb    mode    with    the    aircraft operating  at  a  reduced  power  setting  may  cause  the flight  director  to  command  level  flight  until  the  aircraft accelerates  to  the  scheduled  airspeed  for  the  current altitude.    Only  upon  reaching  that  target  airspeed  will the  flight  director  command  pitch  attitudes  to  initiate the climb. (u)   Altitude     Select     Arm     Annunciator.   Illumination of the altitude select arm mode annunciator,     placarded     ARM,     indicates     that     the altitude select mode has been selected and is armed. (v)   Altitude    Select    Mode    Push-Button Selector  Switch.    Pressing  the  altitude  select  mode push-button    selector    switch,    placarded    ALT   SEL, selects  the  flight  director  altitude  select  mode.    The altitude select mode arms the flight director for capture and tracking of altitudes selected with the altitude/vertical speed indicator or the flight management system.  A separate vertical mode must be  engaged  to  provide  flight  guidance  to  the  point  of altitude  capture.    Upon  reaching  the  altitude  capture point,  the  selected  vertical  mode  will  cancel  and  the