787 Flight Crew Operations Manual
DO NOT USE FOR FLIGHT
Electrical -
System Description
Copyright © The Boeing Company. See title page for details.
6.20.2 D615Z003-TBC
Each generator has a drive disconnect mechanism that allows the generator to be
mechanically disengaged from the engine. Depending on the fault condition, the
generator drive is either automatically disconnected, or requires crew action to be
disconnected. The generator DRIVE light, generator DRIVE synoptic indication,
and EICAS advisory message ELEC GEN DRIVE shows when a condition is
detected that requires the flight crew to disconnect the generator drive. The
generator can then be disconnected from the engine by pushing the respective
generator drive disconnect (DRIVE DISC) switch. The drive cannot be
reconnected by the flight crew.
APU Starter/Generators
Auxiliary Power Unit (APU) starter/generators function as electrically powered
starter motors for APU start, and as generators once the APU is running. The APU
generators can provide electrical power for ground operations and supplemental
power during flight. Additionally, normal engine start is accomplished using
electrical power supplied by the APU.
The APU has two 235 Vac variable frequency starter/generators, designated left
(L) and right (R). The generators are directly connected to the APU gearbox,
producing variable frequency power proportional to APU speed.
Electrical power for APU start can be provided by forward external power, APU
battery, or engine generated power. The electrical system automatically selects a
single starter/generator to provide sufficient torque for APU start. For APU starts
with the APU battery as the power source (no engine running and forward external
power not ON), the right starter/generator is always used. Either the left or right
starter/generator is used for APU start if an engine is running or forward external
power is selected ON.
On the ground, both APU generators are available to energize the airplane’s 235
Vac electrical buses; L1, L2, R1, and R2. In flight, one or both APU generators
provide power depending on the electrical load requirements of the airplane.
Generator status is shown by generator switch indications, MFD electrical
synoptic, and the EICAS message system.
February 15, 2010
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