TM  1-1520-240-10            2-1-5 The switch positions are arranged so the power steering system cannot be energized and used with swivel locks engaged. The aft right landing gear is hydraulically steer- able and electrically controlled by the steering control knob. The PWR STEER caution capsule on the master caution panel indicates that power steering circuits have failed or the aft right wheel has exceeded turning limits. These limits are set at 58_ for a left turn and 82_ for a right turn. If turning limits are exceeded, an out-of-phase switch on the landing gear automatically closes the power steering solenoid valve, lights the caution capsule, and removes electrical power from the control box. To reenergize the power  steering  system,  the  landing  gear  must  be  re- turned  within  operating  limits  and  the  SWIVEL  switch must be recycled. Hydraulic power to operate the power steering actuator and the swivel locks is supplied by the utility hydraulic system through the utility system pressure control mod- ule and separate power steering and swivel lock module. Electrical power to control the steering and swivel locks system  is  supplied  by  the  No.  1  DC  bus  through  the BRAKE STEER circuit breaker on the No. 1 PDP. 2-1-6.  STEERING CONTROL Panel. The STEERING CONTROL panel (fig. 2-1-4) is on the aft end of the console. It contains the SWIVEL switch, the steering control knob, a fail-safe module and relay, and a   servoamplifier.   The   fail-safe   module   monitors   the steering  electrical  circuits.  A  malfunction  which  could cause a steering hardover will be detected by the fail- safe module and the relay which disables the system and turns on the PWR STEER caution light. a. SWIVEL switch.  A three-position switch labeled STEER,  UNLOCK,  and  LOCK.  Setting  the  switch  to STEER applies DC power to the circuits in the power steering control box and arms the power steering actua- tor. Rotating the steering control knob will activate the power steering actuator and the aft wheel will Figure  2-1-4.  Steering Control Panel swivel. Setting the SWIVEL switch to UNLOCK deener- gizes the power steering circuits in the control box and the power steering actuator. It maintains the swivel locks in the disengage position and both aft wheels are free to swivel. Setting the SWIVEL switch to LOCK energizes the swivel lock and centering cam control valve. Utility system pressure is directed to the lock port of the swivel lock cylinder and centering cam. The aft wheels will ro- tate to neutral trail position and the swivel lock will en- gage when the helicopter weight is lifted from the rear wheels. AFCS heading hold is disabled at STEER and UNLOCK. b. Steering control knob.  The steering control knob has index marks around the knob to indicate degrees of knob  rotation  LEFT  and  RIGHT  in  increments  of  30_. These index marks do not represent wheel turn angle; they are reference marks only. The knob is spring-loaded to zero turn angle. Power steering is accomplished by rotating the knob a given amount in the desired direction. When the knob is rotated, a servo valve on the power steering actuator regulates hydraulic pressure to extend or retract the actuator. A feedback variable resistor, also on  the  power  steering  actuator,  stops  actuator  travel when the selected turn radius is reached. 2-1-7.  Brake System. The four wheels of the forward landing gear, and two wheels of the aft landing gear, are equipped with self–ad- justing disk brakes. Both forward and aft brakes can be applied and brake pressure maintained by depressing the pedals. Hydraulic pressure is supplied by utility hy- draulic system. 2-1-8.  Brake Pedals. When  either  the  pilot’s  or  copilot’s  brake  pedals  are pressed, pressure from the master brake cylinders goes to a transfer valve in the brake lines. This allows indepen- dent braking by either pilot. From these transfer valves, pressure is directed through a parking brake valve to the forward and aft wheel brakes. 2-1-9.  Parking Brake Handle. A parking brake handle (4, fig. 2-1-3) is at the bottom left corner of the pilot’s section of the instrument panel. The brake handle is mechanically connected to the parking brake valve. The parking brake valve is electrically con- nected to the PARK BRAKE ON caution capsule on the master   caution   panel.   When   the   brake   pedals   are pressed  and  the  parking  brake  handle  is  pulled  OUT, pressure is trapped and maintained on forward and aft wheel brakes. At the same time, electrical power from the DC essential bus through the LIGHTING CAUTION PNL circuit breaker, lights the PARK BRAKE ON caution cap- sule. The parking brakes must be released by applying pres- sure to the brake pedals. This action automatically opens the parking brake valve, retracts the parking brake han- dle, and extinguishes the PARK BRAKE ON caution cap- sule.