PART I-DESCRIPTIVE

          available at the wheel brakes, the operation by-passing
          the differential relay valve and reducing valve.  The
          pressure at each wheel will not in this case be shown on
          the triple pressure gauge. Use of this control enables full
          reheat power to be used without brakes slipping.
          
     (d)  If the hydraulic system has failed, the pressure in the
          wheel brakes accumulator as shown on the triple pressure
          gauge will be sufficient for landing but will leave little in
          hand for subsequent taxying. When pressure falls to
          below 1,750 lb./sq. in. no further braking will be avail-
          able, since the accumulator is then empty of hydraulic
          fluid.


     30.  Flight instruments

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A.L.4    (a)    The turn and slip indicator is operated by D.C. whenever electrical
Para. 30(a)     supply is available. If electrical supply is lacking the word OFF
Page 34         appears in the face of the instrument. When Mod. 599 is embodied
                    a TURN & SLIP NORMAL-EMERG switch on the instrument
                    panel provides a separate emergency d.c. supply when set to
                    EMERG.
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     (b)  The Mk.4 artificial horizon is operated by A.C. (see
          para. 16(b)). A power failure indicator shows the word
          OFF when electrical supply is lacking. If the fast
          erection button (51) is used before flight to erect the
          horizon it must not be kept depressed after satisfactory
          erection is achieved. In flight the button should only be
          used in unaccelerated level flight.

     (c)  The Mk.4F compass is also operated by A.C. (see para.
          16(b)).
          
     (d)  The accelerometer indicates all normal accelerations
          imposed on the aircraft by means of three concentrically
          mounted pointers. One pointer indicates instantaneous
          G, the other two register the maximum positive and
          negative G readings respectively until re-set.

     (e)  The heater element in the pressure head is controlled by
          switch (37) on the port side of the instrument panel.

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