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A.L.1                                             PART 1 - DESCRIPTIVE
Page 26

                before the controls revert automatically to Manual, but even if no
                control movement is made, accumulator pressure will not be main-
                tained for a long period due to seepage through the hydraulic com-
                ponents.  With some types of hydraulic failure immediate reversion
                to Manual will result.

          21.   Controls and Indicators
          (a)  Pre-mod. 452 aircraft
                Two ON/OFF switches (44) are on the instrument panel and control
                electrically the hydraulic cocks, one for the aileron circuit and the
                other for the elevator circuit.  When the engine is running and a switch
                is selected ON hydraulic pressure is fed to that circuit and to the pawl
                which engages in the jack piston rod.
          (b)  Post-mod. 452 aircraft
                When mod. 452 is embodied a revised wiring and switching arrange-
                ment is applied to the aileron and elevator pawl release units so that
                Manual is automatically selected if any pawl disengages even though
                momentarily.  The aircraft can therefore be flown only with Power
                correctly engaged or in Manual.  The two ON/OFF switches of pre-
                mod. 452 aircraft are replaced by two ganged MANUAL-Off-
                POWER selector switches, which are spring-loaded to the central
                (off) position.  Deflection upwards to POWER isolates the fail safe
                circuit to allow initial engagement or re-engagement.  Deflection
                downwards immediately selects Manual.
          (c)  All aircraft
                (i)   Two magnetic indicators (43), one for the aileron circuit and the
                      other for the elevator, are mounted beside the switches and show
                      black when the piston rod locking pawls are correctly engaged
                      and white when the appropriate pawl is disengaged or incorrectly
                      engaged, or alternatively when electric power to the indicator is
                      not available.
                (ii)  An audio warning over the pilot's headset warns the pilot if the
                      pump is losing pressure.  Further warning is given by the red
                      warning light and the reading of the hydraulic pressure gauge.
          (d)  Manual emergency selector buttons (Mod. 502)
                When Mod. 502 is embodied, two yellow and black striped push-
                buttons are fitted at the bottom left hand corner of the instrument
                panel to permit the emergency selection of Manual of either ailerons
                or elevators or both, should the aircraft electrical system have failed.
                When either button is pressed an electrical supply from an indepen-
                dent dry battery is connected to the appropriate selector cock and
                the associated controls then revert immediately to Manual.
                NOTE.-These buttons must not be pressed if normal electrical power
                           is available as in this event it is likely that the control circuit
                           fuse will be blown.

          22.   Elevator feel and trim
          (a)   The air loads on the elevator are resisted entirely by hydraulic jack
                 effort, no load being felt on the control column.  To provide control
                 feel, a spring is fitted in the control circuit between the control column
                 and the variable incidence tailplane.  The spring gives an artificial feel
                 to the elevator control circuit by imposing a force proportional to stick
                 deflection but not airspeed (i.e. air loads).


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