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b. TOTAL fuel is estimated by the MC based on the last valid fuel quantity and engine fuel flow.
c. A flashing ESTIMATED cue is displayed along with a minutes and seconds (XX:XX) timer
which indicates the duration since the displayed fuel quantities were last updated.
2.2.8 Fuel Low Level Indicating System. The fuel low level indicating system is completely
independent of the fuel quantity indicating system. When the fuel level in either feed tank drops to
1,125 lb, a FUEL LO caution, caution light, and voice alert are activated. If a low level indication was
set by a transient condition, such as prolonged negative g flight, the cautions remain on for 1 minute
after the low level indication is removed.
If the FUEL LO cautions are set, assume that at least one feed tank is
below 1,125 lb regardless of displayed fuel quantity indications.
Figure 2-7. FUEL Display
A1-F18EA-NFM-000
I-2-22 ORIGINAL
2.2.9 Fuel System Related Cautions. The following fuel system related cautions are described in the
Warning/Caution/Advisory Displays in Part V:
· L or R BOOST LO
· L or R FUEL HOT
· L or R FUEL INLT
· FUEL XFER
· EXT XFER
· EXT TANK
· TK PRES LO
· TK PRES HI
· L or R THERMAL
· PROBE UNLK
· REFUEL DR
· DUMP OPEN
· FUEL LO caution, caution light, and voice
alert
· BINGO caution and voice alert
2.3 SECONDARY POWER SYSTEM
The aircraft secondary power system contains two airframe mounted accessory drives (AMAD) and
a single auxiliary power unit (APU). Figure 2-8 shows the major components of the secondary power
system.
2.3.1 AMAD - Airframe Mounted Accessory Drive. During normal operation, each AMAD is
mechanically driven by its corresponding engine through a power transmission shaft and is used to
drive a fuel boost/motive flow pump, an ac/dc electrical generator, and a 3000/5000 psi hydraulic pump.
Pneumatic pressure is used to rotate an air turbine starter (ATS) on each AMAD for engine crank/start
capability.
For ground maintenance use, either AMAD can be decoupled from its engine, allowing pneumatic
pressure to drive the AMAD and its accessories.
NOTE
Failure of the power transmission shaft (PTS) results in the display of
the associated GEN, BOOST LO, and both HYD circuit cautions.
2.3.2 APU - Auxiliary Power Unit. The APU is a small gas turbine engine used to generate a source
of air to power the ATS for normal engine start or to provide an alternate air source for the
environmental control system (ECS). The APU is located between the engines, with intake and exhaust
facing downwards.
The aircraft battery provides electrical power for APU ignition and start. A hydraulic motor powered
by the APU accumulator is used to start the APU. The APU receives fuel from the left engine feed line
upstream of the left engine feed shutoff valve. During normal operation, the APU shaft turns a
separate compressor which supplies air for main engine start or alternate ECS operation.
If an APU fire or overheat condition is detected on the ground, the APU fire extinguishing system
automatically shuts the APU down and, after 10 seconds, discharges the extinguisher bottle.
2.3.3 APU Switch. The APU switch, located on the left console, is spring loaded to the OFF position
and is electrically held in the ON position.
A1-F18EA-NFM-000
I-2-23 ORIGINAL
ON Automatic start and normal APU operation. The switch returns to OFF 1 minute after
the second aircraft generator comes online (BLEED AIR knob not in AUG PULL).
OFF Manual APU shutdown
To prevent an APU running engagement and to prevent APU exhaust
torching, a minimum of two minutes must elapse between APU shutdown
and another APU start.
Figure 2-8. Secondary Power Supply
A1-F18EA-NFM-000
I-2-24 ORIGINAL
2.3.3.1 APU READY Light. The APU READY light, located on the left console adjacent to the APU
switch, comes on when the APU has completed the start cycle and is capable of supporting engine
crank.
2.3.4 ATS Air Sources. Pneumatic pressure from one of three sources can be used to power the ATS
for engine crank/start: APU compressor air, opposite engine bleed air (crossbleed), or external air.
The APU compressor is the primary engine crank air source. With the APU online, the ECS air
isolation valve is closed and the ENG CRANK switch opens the desired air turbine starter control valve
(ATSCV), allowing APU compressor output to turn the ATS, AMAD, and engine core.
A crossbleed start can be utilized when one engine is operating and the APU is shutdown. The
operating engine should be set to a minimum of 80% N2 rpm to make sure bleed air output is sufficient
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本文链接地址：
NATOPS Flight Manual 飞行手册 1(41)
