TM 1-1510-225-10 3C-27 (7)   Vertical  Speed  Hold  Mode  Selector.    The Vertical  Speed  (VS)  is  selected  by  pressing  the    VS button on the mode selector.  When VS is selected, it overrides the APR CAP, GA, ALT, ALTSEL CAP, IAS, or  PITCH  HOLD  modes.    In  the  VS  mode,  the  pitch command  is  proportional  to  VS  error  provided  by  the air   data   computer.      Pressing   and   holding   the   TCS  button  allows  the  pilot  to  maneuver  the  aircraft  to  a new   VS   reference   without   disengaging   the   mode.   Once engaged in the VS mode, the mode will be reset if  the  air  data  computer  is  not  valid  and  the  command cue will bias out of view if the VS is not valid. (8)   Altitude  Pre-select  Mode  Selector.    The Altitude   Pre-select   (ALTSEL)   Mode   is   selected   by pressing the   ALTSEL  button  on  the  mode  selector.   The  desired  altitude  is  selected  on  the  altitude  pre- select   controller.      Pitch   hold,   VS   or   IAS   may   be selected  as  a  mode  to  fly  to  the  selected  altitude.   When   outside   the   altitude   bracket   trip   point,   the ALTSEL   ARM  annunciator,  along  with  the  selected pitch mode, is illuminated on the mode selector.  When reaching the bracket altitude, the system automatically switches to the ALTSEL CAP mode and the previously selected   pitch   mode   is   canceled.      At   bracket,   a command  is  generated  to  asymptotically  capture  the selected  altitude.    When  the  altitude  is  reached,  the ALTSEL CAP mode is automatically canceled and the FD  switches  to  the  ALT  hold  mode.    If  the  air  data computer   is   not   valid,   the   altitude   pre-select  mode cannot be selected.  The command cue will bias out of view if the VG is not valid. (9)   Altitude  Hold  Mode.    The  Altitude  Hold Mode (ALT) is selected by pressing the  ALT button on the mode selector.  When ALT is selected, it overrides the  APR  CAP,  GA,  IAS,  VS,  ALTSEL  CAP,  or  PITCH HOLD modes.  In the ALT mode, the pitch command is proportional  to  the  altitude  error  provided  by  the  air data   computer.      The   altitude   error   signal   is   gain programmed as a function of airspeed.  Pressing and holding the  TCS  button  allows  the  pilot  to  maneuver the  aircraft  to  a  new  altitude  hold  reference  without disengaging the mode.  Once engaged in the altitude hold   mode,   the   mode   will   be   reset   if   the   air   data computer  is  not  valid  and  the  command  cue  will  bias out of view if the VG is not valid. NOTE If    the    Baro    setting    on    the    altimeter    is changed,  a  command  is  generated  to  fly the   aircraft   back   to   the   original   altitude reference. e.     Other Mode Selection. NOTE The  TACAN  receiver  must  be  tuned  to  a valid TACAN frequency.  TACAN functions are identical to VOR using TACAN information  rather  than  VOR  signals.    The ARM / CAP annunciation is the same as   in VOR mode. (1)   TACAN   Mode.      The   TACAN   mode   is selected by pressing the HSl source selector   TACAN button.  TACAN navigation information is then selected and  displayed  on  the  HSl  by  pressing  the  respective HSl TACAN button. (2)   Pitch  Hold  Mode.    Whenever  a  roll  mode is  selected  without  a  pitch  mode,  the  command  cue will  display  a  pitch  attitude  hold  command.   The  pitch attitude  can  be  changed  by  pressing  the   TCS button on  the  control  wheel  and  maneuvering  the  aircraft.   The command cue will be synchronized to zero  while the button is pressed.  Upon release of the button, the pitch  command  will  be  such  as  to  maintain  the  new pitch  attitude.    In  the  pitch  hold  mode,  the  command cue will be biased out of view if the VG is not valid. (3)   Go-Around    (GA)    Mode.        The    GA    is selected   by   pressing   the   remote   go-around  switch.   When   selected,   all   other   modes   are   reset   and   the remote go-around annunciator  GA  is illuminated.  The command cue receives a wings level command, zero command  when  roll  is  zero.    The  command  cue  also receives  the  go-around  command  which  is  a  7 pitch up  attitude  command.    Selecting  GA  disconnects  the autopilot.  The yaw damper remains on. Once  go-around  is  selected,  any  roll  mode  can be   selected   and   will   cancel   the   wings   level   roll command.      The   go-around   mode   is   canceled   by selecting another pitch mode or TCS. 3C-19.  ALTITUDE SELECT CONTROLLER. a.     Description.  The Altitude Select Controller provides   a   means   for   setting   the   desired   altitude reference   for   the   altitude   alerting   and   altitude   pre- select system.  Refer to Figure 3C-13. (1)   Altitude  Alert.    As  the  aircraft  reaches  a point  1000  feet  from  the  selected  altitude,  a  signal  is generated  to  light  the  warning  light  on  the  altimeter and  sound  a  warning  horn  for  1  second.    This  light remains on until the aircraft is 300    50 feet from the selected  altitude.    If  the  aircraft  now  deviates  by  300 50 feet or more from the selected altitude, the light is again  energized  and  the  horn  is  sounded.    The  light remains on until the aircraft returns to within 300   50