PART 1-DESCRIPTIVE
(b) Derwent Mk.8 engines
An ignition isolating switch and a priming pump isolating
switch for each engine are fitted in the appropriate under-
carriage bay. With the priming pump isolating switch OFF.
the pump is isolated. With the ignition isolating switch
OFF, the priming pump, the torch igniters and the booster
coils are all isolated. This allows the engine to be blown
through after a false start, using the normal starting gear.
(c) Derwent Mk.9 engines
Two switches, labelled MAIN SUPPLY and HIGH
ENERGY IGNITER SUPPLY, are fitted in each under-
carriage bay. Either switch isolates the high energy igniter
unit from the electrical supply, in addition, the main
supply switch isolates the igniter line relay. With either
switch off, the engine may be blown through after a false
start, using the normal starting gear.
10. Relighting controls
A relighting pushbutton (4, 78, 88, 122) is in the top of each
H.P. cock lever. In some aircraft the pushbuttons may be
on a panel on the port side of each cockpit. The push-
buttons are used for relighting the engine during flight or
for ground testing the priming pumps and torch igniters
(Derwent Mk.8) or high energy ignition units (Derwent
Mk.9). The relight buttons must always be used for
relighting in flight and never the normal starting system
11. Engine fire extinguishers
(a) There are two engine fire extinguisher bottles in the rear
fuselage. Each bottle operates through a spray ring on the
appropriate engine, whenever the associated fire extin-
guisher pushbutton (45) in the front cockpit is pressed.
In the event of a crash landing, an inertia switch in the
starboard nacelle operates both bottles.
(b) Engine fire-warning lights (36, 43), one for each engine,
are on the port and starboard glare shields in the front
cockpit; the lights are operated by fusible flame switches
in the engine nacelles; the lights will not go out when the
fire is extinguished.14
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