TM 1-1520-238-10 2-42 Change 9 Section V. FLIGHT CONTROL SYSTEM 2.37 FLIGHT CONTROL SYSTEM. The flight control system (fig 2-25) consists of hydrome- chanical flight controls, augmented by digital automatic stabilization equipment (DASE), and an automatically or manually controlled stabilator. The flight control system establishes vertical, longitudinal, lateral, and directional flight of the helicopter. The flight controls provide a cyclic stick, collective stick, and directional pedals in each crew station, connected in tandem, to provide control inputs to the main and tail rotor hydraulic servo actuators. A mixing unit combines inputs from the servoactuators, and trans- mits them to a non-rotating swashplate. The swashplate changes the linear motion from the mixer unit to rotating motion. The swashplate provides pitch changes for the four main rotor blades. Pedal inputs are transmitted in a similar manner to the tail rotor blades, except the mixer unit is not required. Description and operation of the main and tail rotor systems is in Section VIII. NOTE Helicopters with operable BUCS have shear pins installed in the SPADs in place of steel pins. They also have servos equipped for BUCS operation. Each mechanical flight control linkage has a shear pin actuated decoupler (SPAD) installed. The SPADs allow backup control system (BUCS) engagement by means of a microswitch inside each SPAD if a jam occurs in the me- chanical flight controls. The shear pins in the pilot SPADs shear at a force lower than those in the CPG SPADs. The SPADs are continuously monitored by the FD/LS. A single microswitch failure in one or more axes will cause a FD/LS message to appear. CAUTION Do not move flight controls without hydraulic power. You may damage or shear pins in the SPADs. Care shall be exercised in extending or folding down the CPG cyclic stick when the rotors are turning. Cyclic control system inputs may occur. It is recommended that the pilot hold his cyclic stick steady while the CPG is extending or folding his cyclic stick. 2.37.1 Cyclic Sticks. The cyclic sticks, one in each crew station, provide for helicopter movement about the pitch and roll axes. The CPG stick has a lockpin release mechanism at the base of the stick. This allows the CPG to fold the stick down while viewing the heads-down dis- play and provides greater ease for ingress/egress. The cyclic stick remains functional in this position and is re- turned to the extended position by pulling aft on a lever in front of the stick grip. Both cyclic stick grips (fig 2-26) have switches for weapons firing, DASE disengagement, trim feel, radio and intercommunications, and flight modes symbology. The pilot grip also has a remote transmitter selector switch for radio selection. These switches will be described in more detail with their associated systems. 2.37.2 Collective Sticks. The collective sticks in both crew stations (fig 2-26) provide the crew with a means of adjusting pitch angle of the main rotor blades and fuel flow metering requirements of the gas generator turbine. Each collective stick has an engine chop collar just aft of the col- lective stick switch box (see Section III) to permit both en- gines to be reduced to idle without moving the PWR lev- ers. A switch panel at the end of each collective stick contains a searchlight (SRCH LT) switch, an extend-re- tract (EXT-RET) momentary searchlight switch, a wing stores jettison guarded button (ST JTSN), a NVS switch, a BRSIT HMD/PLRT switch, and a radio frequency over- ride (RF OVRD) switch. The RF OVRD switch is nonfunc- tional. Both collective sticks have a BUCS select trigger switch. The switch in the Pilot station is non functional. The switch in the CPG station is utilized to select BUCS. These switches will be discussed in more detail with their respective systems. A twist-type friction adjustment is installed on the collective assembly to prevent the collec- tive stick from creeping during flight. 2.37.3 Directional Control Pedals. The directional control pedals, one set in each crew station, provide for helicopter movement about the yaw axis. Both sets of pedals are adjusted by applying foot pressure and moving a pedal adjust quick-release lever. Pressing the upper portion of either pedal actuates a master brake cylinder which delivers hydraulic power to a brake disc at the re- spective main landing gear wheel. Section I contains de- scriptions of the main landing gear and brake system.