OPERATIONS MANUAL

Electrical
Ground Service Bus:
The ground service bus powers equipment that is used on the ground
as well as in flight. The bus is powered automatically when AC bus 1
is powered. When AC bus 1 is unpowered and the aircraft is on the
ground, the ground service bus can be reconnected to external power 1
or APU generator 1 when either of them are available. This reconnection,
however, can be controlled only manually by pushing the ground service
switch at door 2L (or 1L). The first push connects, the second push
disconnects the bus.
(In the simulator, the ground service switch is represented on Instructor >
Situation > Service under External supplies.)
Ground Handling Bus:
The ground handling bus is powered automatically whenever power is
available at the external power 1 receptacle, or when APU generator 1
power is available. External power has priority. The bus cannot be
powered in flight; it is used only for ground handling equipment.
Cargo Handling Bus:
The cargo handling bus is installed on freighter and combi aircraft. It is
used for main deck cargo equipment. The bus is powered whenever power
is available at the external power 2 receptacle, or when APU generator 2
power is available. External power has priority. When the available power
is connected to the synchronous bus, that is, when the AVAIL lights of
EXT 2 and APU 2 on the overhead panel are extinguished, and an ON
light illuminates instead, the cargo handling bus is not powered.
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