PART 1-DESCRIPTIVE

             	 moved towards HOT the hot air valve opens
             	 further and the cold air valve closes.

          HOT    Cold air valve 'shut, hot air valve fully open.

          REDUCE Cold air valve shut, hot air valve partially
                 open. The temperature of the incoming air
                 remains the same, but since its volume is
                 reduced the overall cockpit temperature is
                 thus reduced.

      (b) With the wheel set other than OFF pressurised air is
          admitted to the cockpit through gallery pipes round the
          lower edges of the hood and windscreen. The quantity
          of warm air entering the gallery pipes, which provide for
          windscreen and hood demisting, can be varied by altering
          the position of two ventilators (63) in the shape of rotatable
          sleeves, one on each wall of the cockpit. A valve in the
          cockpit allows a steady increase in pressure differential
          at heights above 12,000 ft., increasing with altitude until
          at 35,000 ft. the full pressure differential of 3 lb./sq. in.
          is reached. At this height the cockpit altimeter (25)
          should read 21,000 ft. A CABIN PRESS LOW
          warning light (26) comes on whenever the pressure falls
          substantially below the correct figure.

      (c) If a reduction of cockpit temperature is desired at altitude,
          MIX is to be preferred to REDUCE otherwise the
          reduced volume of air entering the cockpit may adversely
          affect the pressure differential. COLD or MIX must not
          be selected on the ground otherwise overheating of the
          cold air unit may occur with subsequent damage.

      30. Windscreen de-icing, windscreen wiper and d/v, panels

      (a) The W'SCREEN DE-ICER PUMP control (55) is
          above the Ground/Flight switch. The handle is turned
          anti-clockwise to unlock and pushed in to raise pressure.
          As the handle returns to the out position, the windscreen
          is sprayed.

      (b) Two d/v panels are fitted, one on each side of the main
A.L.1     windscreen. Each is locked shut by a sliding bolt, and
          screw clamp.

      (c) The hydraulically-operated windscreen wiper for the port
          windscreen is controlled by an ON-OFF-PARK knob
          (13) below the port instrument panel.

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