787 Flight Crew Operations Manual
DO NOT USE FOR FLIGHT
Electrical -
System Description
Copyright © The Boeing Company. See title page for details.
D615Z003-TBC 6.20.3
External Power
The 115 Vac external power system consists of both a forward and aft system, with
their corresponding receptacles, controls, and indications.
The forward system provides the power for general ground operations. It has two
(L, R) power receptacles located on the left forward fuselage of the airplane.
Connecting one or both power sources to the receptacles illuminates the AVAIL
light(s) in the power switch(es), and energizes “Ground Handling” mode. Only
one connection is required to power this mode. If two sources are connected, the
first source connected is the one that is used. (Refer to Modes of Operation
in
Chapter 6, Section 20, for additional information.)
Selecting the external power switch(es) to ON energizes the “External Power On”
mode and extinguishes the AVAIL light(s). Two connections are recommended in
this mode to power the maximum number of electrical loads and minimize load
shedding.
If the APU is not available, engine start may be accomplished using external
power. Connecting the two forward and one aft receptacles results in optimal start
performance. At a minimum, two forward external power sources are required. In
this configuration, either engine may be started first, however significant load
shedding occurs, and engine start time increases.
The aft external power system can assist the forward system when starting the
right engine first. The aft receptacle is located on the airplane fuselage aft of the
left wing. To receive the benefit of the aft power source, both forward power
sources must also be connected, and the right engine must be started first. (Refer
to Ground Power Engine Start
in Chapter SP, Section 7, for additional
information.)
Ram Air Turbine (RAT) Generator
A Ram Air Turbine (RAT) serves as an emergency source of electrical and
hydraulic power. It has no operating time limits, airspeeds, or altitudes.
In flight, the RAT deploys automatically if any of the following occur:
• both engines have failed
• all three hydraulic system pressures are low
• loss of all electrical power to captain’s and first officer’s flight instruments
• loss of all four EMPs and faults in the flight control system occur on
approach
• loss of all four EMPs and an engine fails on takeoff or landing
The RAT can be deployed manually if necessary by pushing the RAM AIR
TURBINE switch on the hydraulic panel.
February 15, 2010
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