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which causes the shutoff valve to close, terminating fuel flow. Fuel flow
should stop within 20 seconds.
FUEL ADDITIVES
Refer to Airplane Flight Manual Addendum I Fuel Servicing for recommended
concentrations and the proper blending methods of approved
fuel additives.
REFUELING
The aircraft is refueled through a gravity filler cap located on the right
side of the fuselage above the engine pylon or through the single-point
pressure refueling (SPPR) adapter located on the right side of the fuselage
below the engine pylon. A refueling panel access door is located
next to the SPPR adapter access door. Refer to Airplane Flight Manual
Addendum I Fuel Servicing for a list of approved fuels and refueling
procedures.
Pilot’s Manual
PM-126A 2-39
FUEL DRAINS
Figure 2-8
RIGHT DRAIN MAST
RIGHT WING ACCESS DOOR
LEFT DRAIN MAST
RIGHT WING SUMP LEFT WING SUMP
• FUEL VENT/EXPANSION
• FUEL TRANSFER
• ENGINE SUPPLY
• FUEL FILTER
LEFT WING ACCESS DOOR
• FUEL CROSSFLOW
• FUEL VENT/EXPANSION
• FUEL TRANSFER
• ENGINE SUPPLY
• FUEL FILTER
•
•
•
•
A28-5001
Pilot’s Manual
2-40 PM-126A
AUXILIARY POWER UNIT (APU)
The Auxiliary Power Unit (APU), located in a special enclosure above
the baggage compartment and tailcone equipment bay, is a self-contained,
single-stage gas turbine unit that can be operated continuously
up to an ambient temperature of 125° F (52° C). The APU provides
pneumatic and electric power for ground operations of the aircraft Environmental
Control System and aircraft electrical systems, independent
of the aircraft main engines. It is restricted to ground operations
only. The starting, acceleration and operation of the engine is controlled
by an integral system of automatic and coordinated pneumatic and
electromechanical controls.
The APU engine is comprised of three major sections: the accessory section,
compressor section and turbine section. Engine power for the auxiliary
power unit is developed through compression of ambient air by
a single entry, radial, outward-flow, centrifugal compressor. The compressed
air, when mixed with fuel and ignited, drives a radial inwardflow
turbine rotor.
The APU control panel (located on the center pedestal) contains all of
the primary controls to operate the APU. There is also a Maintenance
Control Panel in the tailcone equipment bay (primarily for maintenance
use). There is an EMER SHUTDOWN switch on this panel.
The engine is controlled and serviced by four systems: the engine fuel
system, lubrication system, electrical system and indicating system.
Fuel for the APU flows from the right wing fuel tank through the right
standby pump and shutoff valve prior to reaching the APU. The APU
uses approximately 150 pounds of fuel per hour. The APU should not
be started and run in excess of 1 hour with less than 200 pounds in the
right wing tank. Running out of fuel in the right wing tank will introduce
air in the APU fuel lines which will cavitate the APU and prevent
it from restarting immediately. The APU gearbox serves as an oil sump
for the APU self-contained lubrication system. The APU Electronic
Control Unit (ECU) is a fully automatic system that directs delivery of
the correct amount of fuel regardless of ambient conditions and load requirements,
as well as properly sequencing control of fuel and ignition
during starting. The ECU is also used for trend monitoring (in lieu of a
start counter or hour meter, etc.), which is accessed through the RS 232
maintenance port on the Maintenance Control Panel.
A warning horn is installed in the nose avionics bay. The audible alert
can be heard out of the nose gear wheel well to alert personnel outside
of the aircraft of an APU fire.
Pilot’s Manual
PM-126A 2-41
There are cooling fans installed in the tailcone equipment bay — one on
the tailcone access door, the other on the opposite side of the fuselage.
These fans are installed to improve cooling in the tailcone when the
APU is operating. They are controlled by a 60° C thermostat located in
the area of the tailcone most likely to exceed 70° C. If the temperature
falls below 55° C the fans go off. Power for the fans is provided through
the APU CMPTR circuit breaker.
If the temperature in the tailcone reaches 70° C, the APU FAN FAIL indicator,
in the tailcone, will activate (amber). The indicator is magnetically
latched and will remain in the amber position until manually reset
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