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to crank the opposite engine. For a crossbleed start, the ENG CRANK switch opens the ECS air
isolation valve and the ATSCV, allowing compressor bleed air pressure to turn the ATS, AMAD, and
engine core. If one engine fails inflight and the engine core is rotating freely, crossbleed air may be used
to rotate the AMAD and retain some fuel, electrical, and hydraulic system output.
ATS exhaust may blister paint and cause possible door damage on the aft
underside of the fuselage during extended crossbleed operation of a failed
engine.
An external air source may also be used to start one or both engines. External air is applied to the
aircraft through a connection in the right main wheelwell. Both engine bleed air valves must be closed
(BLEED AIR knob OFF) to make sure that external air is the sole air source for engine start. For an
external air start, the ENG CRANK switch opens the ATSCV, allowing external air pressure to turn
the ATS, AMAD, and engine core.
2.3.4.1 ATS Protection. Each ATS has two sources of overspeed cutout protection. The primary
source is the corresponding generator, and the backup source is the frequency sensing relay (FSR). The
FSR monitors ATS speed and provides the signal which electrically holds the ENG CRANK switch.
When the generator comes on the line at 60% N2 rpm, it removes power from the ATSCV and the FSR,
which releases the ENG CRANK switch. If the primary cutout does not function (GEN switch OFF or
major generator malfunction), the FSR releases the ENG CRANK switch when it senses 63% ATS
rpm.
Regardless of the engine start air source utilized, the corresponding GEN
switch should be ON, as the generator provides primary overspeed cutout
protection for the ATS.
2.3.4.2 ENG CRANK Switch. The ENG CRANK switch, located on the left console, is spring loaded
to the OFF position and is electrically held in the L or R position.
A1-F18EA-NFM-000
I-2-25 ORIGINAL
L Opens the left ATSCV and/or the ECS air isolation valve to direct pneumatic pressure
to the ATS for left engine crank.
OFF Closes both ATSCVs and the ECS air isolation valve. When the left or right generator
comes online following engine start, the switch automatically returns from L or R to the
OFF position.
R Opens the right ATSCV and/or the ECS air isolation valve to direct pneumatic pressure
to the ATS for right engine crank.
2.3.5 AUG PULL. During extended ground operations, APU compressor air may be used instead of
engine bleed air to run the ECS and cool the avionics (BLEED AIR knob in AUG PULL). AUG PULL
operation is discussed in the ECS section.
2.3.6 AMAD Related Cautions. The following AMAD related cautions are described in the Warning/
Caution/Advisory Displays in Part V:
· L or R OIL HOT · L or R AMAD PR · L or R ATS
2.4 ELECTRICAL POWER SUPPLY SYSTEM
The electrical power supply system consists of two generators, two transformer-rectifiers (TR), one
battery with dedicated battery charger, and a power distribution (bus) system (figure 2-9). Each
generator provides a primary ac source and three isolated dc sources from a permanent magnet
generator (PMG). During normal operation, the left generator powers only the left buses while the
right generator powers only the right buses. If one generator fails, the other generator is capable of
carrying the entire electrical load of the aircraft. Battery power is provided for normal engine start.
External electrical power can be applied to power the entire system on the ground. The bus system
consists of the left and right 115 vac buses, right 26 vac bus, left and right 28 vdc buses, 28 vdc essential
bus and a 28 vdc maintenance bus. See figure 2-9 for a simplified schematic and Electrical System,
foldout section, for the specific systems powered by each bus.
2.4.1 Electrical RESET Button. The electrical system RESET button is located on the electrical
power panel on the right console. This button provides master reset capability for any failed generator
or electrical system relay without interrupting operational circuits.
2.4.2 AC Electrical Power. The two generators are the primary source of ac electrical power. With the
GEN switch in NORM, each generator comes online at approximately 60%N2 rpm as long as voltage
and frequency are within limits. Each generator supplies ac power to an independent 115 vac bus. In
addition, the right 115 vac bus powers a 26 vac bus through a dedicated transformer.
2.4.2.1 GEN Switches. Two generator control switches, labeled L GEN and R GEN, are located on
the electrical power panel on the right console.
NORM Provides normal generator operation.
OFF Removes the generator ac source from the bus system.
2.4.2.2 Electrical Fault Protection Circuitry. The electrical system provides fault protection with
　
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