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PART I-DESCRIPTIVE
switches (45) (46) on the port quarter panel. The out-
board warning light/press switch is for zones 1 and 2,
which are the compressor and flame tube zones
respectively; the inboard switch is for zone 4. which is the
rear fuselage. The bulbs may be tested by pulling the
switches out.
(b) Zone 3 comprises the turbine and exhaust cone regions
of the engine also the interspace between the inner and
outer jet-pipe skins, via which the ventilating air for this
zone is exhausted. This zone is fire-protected by stainless
steel but should high temperatures occur due to a gas
leak or a break-down in ventilation the HOT GAS amber
warning light (48) will come on.
(c) All three warning lights are controfled by resetting flame
switches, i.e., indication that a dangerous condition no
longer exists is given by the warning light going out when
the circuit is broken as the flame switches cool.
(d) The crash-operated inertia switch automatically dis-
charges the contents of both bottles in the event of a
crash, irrespective of the position of the battery isolating
switch.
(e) To assist in cooling zone 4 on the ground, air from the
seventh stage of the engine compressor is blown through
the zone 4 extractor. The valve controlling this air is
operated by the undercarriage selector and the position
of the valve is shown by the magnetic indicator (49), on
the port quarter panel, labelled AIR EXTRACT. The
indicator will show white if the valve is in the wrong
position relative to the selected undercarriage position.
Overheating will occur if the indicator shows white on
the ground.
14. Variable pitch guide vanes and air-bleed valves
(a) The first row of stator blades in the engine compressor
consists of variable pitch inlet guide vanes which assist
in imparting swirl to the incoming air. At r.p.m. below
6,200 the first stages of the compressor deliver more air
than is acceptable to the later stages. To prevent18
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