TM  1-1520-240-10 2-5-4            (7) Three control position transducers. e. Attitude changes sensed by the attitude gyros, a yaw rate gyro in each AFCS computer, and the direction- al gyro are processed by the AFCS computers and ap- plied  to  the  ILCA’s.  The  ILCA’s  extend  or  retract  and move the upper flight controls. This control input is not apparent to the pilot because AFCS control inputs do not move the cockpit controls. The pitch, roll, and yaw axis all operate in fundamentally the same manner. Should a hardover occur, the pilot can easily override AFCS. f. Pitch attitude stability, airspeed hold, and a posi- tive  stick  gradient  from  hover  to  Vmax  are  provided through the DASH actuator. The DASH actuator extends or retracts to maintain airspeed for a given stick posi- tion. 2-5-8.  Bank Angle Hold. Bank angle trim without cyclic stick movement is pro- vided through left or right position of the cyclic stick AFCS trim switch. Bank angle hold is disengaged anytime a CENTERING DEVICE RELEASE switch is pressed, a cyclic stick is moved laterally, or the HDG switch is EN- GAGED. Bank angle hold cannot be reengaged until the roll is less than 1.5_ per second. 2-5-9.  Heading Hold. The  directional  gyro  provides  an  input  to  each  AFCS which signals the yaw ILCA to maintained heading within 5  degrees.  Heading  hold  is  disengaged  if  the  swivel switch is set to STEER or UNLOCK, a CENTERING DE- VICE RELEASE switch is pressed, or the directional ped- als are moved. Also, heading hold will be disengaged at airspeed above 40 knots anytime lateral trim is used, the stick is moved laterally, or HDG switch is ENGAGED. Heading hold will not resume until yaw rate is less than 1.5_ per second at an airspeed above 40 knots with a bank angle of less than 1.5_. 2-5-10.  Airspeed Hold. The airspeed hold feature provides a constant airspeed and pitch attitude relative to cyclic stick position at air- speeds above 40 knots. Airspeed and pitch can be set with the AFCS trim switch on the cyclic stick or by displac- ing the cyclic stick until the desired airspeed is achieved then   pressing   the   CENTERING   DEVICE   RELEASE switch. Refer to Chapter 8 AFCS Off Flight Characteris- tics. 2-5-11.  Altitude Hold. Two methods of altitude hold can be selected. They are radar altitude hold or barometric altitude hold. a. Radar   Altitude   Hold.  Radar   altitude   hold   will maintain a more precise altitude in hover or over water flight than barometric altitude hold. Maximum altitude for the use of radar altitude hold is 1,500 feet AGL. An error signal, caused by radar altitude deviations, is de- rived from the pilot radar altimeter receiver-transmitter and is processed by the No. 1 AFCS computer. The processed error signal is applied to the THRUST CONT LEVER CCDA which  drives  the  THRUST  CONT  levers  in  the  direction necessary to null the error signal. b. Barometric   Altitude   Hold.  Barometric   altitude hold is used in forward flight over terrain. It uses error signals produced within the No. 1 AFCS computer. These  error  signals  are  in  response  to  static  pressure changes and are proportional to altitude changes. The sig- nal is processed by the AFCS computer and applied to the THRUST CONT LEVER CCDA which drives the THRUST CONT levers in the direction necessary to null the error signal. 2-5-12.  Heading Select. Heading select is engaged when the HDG switch on the AFCS panel (fig. 2-5-3) is pressed and the ENGAGED light illuminates. The heading bug on the selected HSI is the referenced heading. Rotating the HDG knob of the HSI to set the bug at a new referenced heading produces an error signal which is processed by the AFCS comput- ers and applied to the roll ILCA. The roll ILCA than moves to produce a standard rate turn up to a maximum bank angle  of  20_  until  the  selected  heading  is  captured. Heading select can only be selected at airspeed above 40 knots. Heading select is disengaged anytime a CEN- TERING DEVICE RELEASE switch is pressed, the HDG switch on the AFCS panel is disengaged, or when the opposite CMD SEL switch on the HSI MODE SELECT panel is pressed. 2-5-13.  Longitudinal Cyclic Trim System. Longitudinal cyclic trim (LCT) control is part of AFCS. LCT  reduces  fuselage  nose  down  attitude  as  forward airspeed is increased, thus reducing fuselage drag. The system also reduces rotor blade flapping which results in lower stresses on the rotor shafts. The LCT actuators are installed under the swashplates. Signals are transmitted to  these  actuators  either  automatically  by  AFCS  or manually by CYCLIC TRIM switches drive the actuators to GND (ground) operating position on ground contact. 2-5-14.  Controls and Indicators. 2-5-15.  AFCS CONTROL Panel. The  AFCS  control  panel  (fig.  2-5-3)  is  on  the  canted console. It consists of the heading and altitude select, SYSTEM SEL (select), and CYCLIC TRIM sections. a. Heading and Altitude Select Switches.  The leg- end on these switches will dim when the PLT INST rotary control switch is placed out of the OFF detent.