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engine and aircraft not directly related to thrust production. An internal gearbox
between the LP and HP compressors acts as a power takeoff to drive the external
low-speed (LP) and high-speed (HP) gearboxes. The gearbox drive housing
contains the front and rear LP compressor shaft bearings and the HP compressor
shaft front bearing.
A series of gears within the gearbox transmit LP and HP compressor shaft torque
to a pair of driveshafts. These driveshafts extend through the engine’s immediate
compressor case to drive their respective external gearbox. The LP compressor
drives the low-speed gearbox and the HP compressor drives the high-speed
gearbox.
A. Aircraft Service Bleeds:
• Environmental Control System (ECS)
• Wing Anti-Icing
• Crossbleed Starting
• Precooling of Air for Aircraft Systems
B. Engine Handling Bleeds:
• Cowl Anti-Icing
• Engine Stability, Surge Recovery and Flameout Protection
C. Accessory Gearbox:
• Power for Gearbox-Mounted Accessories
• Power for Starting and Cranking
2. Description of Subsystems, Units and Components:
A. Aircraft Service Bleeds:
(1) General:
During normal operations, engine compressor bleed air entering
each system (left or right engine) is primarily extracted through the
mid-stage (7th stage) check valve. When required (mid-stage
pressures too low), mid-stage bleed air is assisted by high-stage
(12th stage) bleed air by either augmenting (adding to) mid-stage
airflow or by complete mid-stage to high-stage switching (12th stage
taking over all pneumatic functions).
(2) Environmental Control System (ECS):
The environmental control system provides for pressurization,
heating, cooling, ventilation and the means for reduction of humidity
in flight or on the ground. True air conditioning is classified as
heating or cooling as necessary to maintain a specific level of
temperature within the occupied areas of the aircraft, regardless of
the ambient temperatures or the operating conditions.
Pressurization is the control over the pressure within the occupied
areas.
(3) Wing Anti-Icing:
The wing anti-ice system consists of a leading edge which is fed by
OPERATING MANUAL
PRODUCTION AIRCRAFT SYSTEMS 2A-71-00
Page 13
May 31/01
Revision 4
a perforated duct called a piccolo tube. An open air space in the
leading edge forms a passage for hot bleed air. The bleed air
prevents formation of ice on the wing leading edges. Bleed air
tapped from the bleed air manifold flows to the wing leading edges,
via anti-ice valves, wing anti-ice ducts and piccolo tubes when the
system is in operation.
(4) Crossbleed Starting:
After starting one engine from either APU or an external air supply,
the other engine may be started by crossbleeding air from the
running engine. Power is advanced on the running engine to
achieve a minimum of 25 to 30 PSIG on the bleed air pressure
indicator or ENGINE START synoptic page and the remaining
normal start procedures are used. Upon completion of crossbleed
starting, the engine is returned to idle.
(5) Precooling of Air for Aircraft Systems:
From the bleed air pressure regulator and shutoff valve outlet,
regulated bleed air passes through the bleed air precooler heat
exchanger located in the pylon of the aircraft, where it is cooled by
fan air from the engine. Precooler bleed discharge temperature is
controlled to a nominal 400° F by a transfer of heat to the cooler and
lower pressure engine fan air that flows through the cooling air
passages of the precooler heat exchanger. The cooling air is ducted
overboard through the louvers in the lower surface of the engine
pylon.
Bleed air from the bleed air precooler heat exchanger outlet enters
the crossover manifold ducting in the tail compartment with its
temperature and pressure controlled to 400° F and 40 PSIG (for
most conditions). The crossover manifold is tapped to distribute
bleed air to the various systems.
B. Engine Handling Bleeds:
(1) Cowl Anti-Icing:
The nose cowl assembly mounted on the engine air intake consists
of a piccolo tube mounted inside where air is admitted directly from
a tap off of the engine bleed air manifold. For anti-icing purposes,
hot air is supplied to the nose cowl leading edge duct (top of cowl)
and piccolo tube by a feed pipe coming from the bleed air manifold.
A series of holes in the piccolo assembly allows hot air to flow
around the insides of the nose cowl. This air is exhausted through
holes on the inside of the cowl leading edge to the engine air intake.
The anti-icing air supply is controlled by a shutoff and pressure
　
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