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747 Electrical
updated 12/5/13
46
Aviation
Professional
11/04/2012

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Cards

Term
What are the main AC electrical power sources?
Definition
Four IDGs

Two auxiliary power sources (APU generators) (except LCF)

Two external power sources
Term
How is DC power provided by the electrical system?
Definition
Four transformer-­rectifier units (TRUs)
APU and Main batteries
Term
If you lose an AC Bus, is the associated DC Bus still powered?
Definition
Yes, the DCIR remains closed and the DC Tie Bus powers the DC Bus
Term
What does the “AVAIL” light indicate on the EXT and APU PWR switches?
Definition
APU or EXT power is plugged in and available
The power quality is acceptable
Term
Which bus is powered on the ground when APU 1 or EXT 1 is available?
Definition
Ground Handling Bus
Term
What are some of the equipment items powered by the Ground Handling Bus?
Definition
Lower cargo handling equipment and compartment lights
Fueling system
Auxiliary hydraulic pump 4
Term
When is the Main Deck Cargo Handling Bus powered?
Definition
When the “AVAIL” light is displayed on the APU 2 or EXT 2 switches.
Term
What electrical power source would you select if cargo handling is required?
Definition
APU 1 or EXT 1
Term
When is the Ground Service Bus powered?
Definition
When A/C bus 1 is powered, either on the ground or in flight
Term
How can the Ground Service Bus be powered when AC bus 1 is not powered, while on the ground?
Definition
By pushing the ground service switch at door L1, ground service is then connected to the same power source as the Ground Handling Bus
Term
What is the source of power to the battery chargers?
Definition
Ground Service bus
Term
What are some of the equipment items powered by the Ground Service Bus?
Definition
Main and APU battery chargers
Fuel pumps for APU start
Flight deck flood, navigation, and service lights
Miscellaneous service outlets and equipment
Term
Which busses are powered with the Battery switch OFF?
Definition
Main and APU Battery
Main and APU Hot Battery
Term
Which busses are powered with the Battery switch ON?
Definition
Main and APU Battery
Main and APU Hot Battery
Main and APU Standby
Term
What is the function of the Standby Power Switch in the AUTO position?
Definition
Allows the Main and APU Stby busses to be powered from available sources
Term
How do you know if the Standby bus is powered?
Definition
Captain's PFD, ND, FMS-CDU
Primary EICAS
Term
Describe the function of the Split System Breaker (SSB).
Definition
Divides the synchronous bus, allowing each side of the AC electrical system to be powered by separate auxiliary or external power sources
Term
Describe the electrical system sequence of events for starting engines 4 and 1 with two sources powering the sync bus.
Definition
SSB is open
The IDG for engine 4 powers its side of the sync bus and disconnects previous power source
SSB remains open
When engine 1 is started, the previous power source is removed and the SSB closes
Term
Describe the electrical system sequence of events for starting engines 4 and 1 with a single power source powering the sync bus.
Definition
SSB is closed
The IDG for engine 4 powers the sync bus and disconnects previous power source
When engine 1 is started, SSB remains closed
Term
Describe the electrical load shedding process.
Definition
Utility busses are shed one at a time through ECLUs
They are restored in reverse order
Term
What are the indications that load shedding has occurred?
Definition
EICAS messages for fuel pumps only
ELEC UTIL BUS and utility off lights are inhibited
Term
What are some of the equipment items powered by the Utility busses?
Definition
Forward main pumps 2 and 3
Forward override/jettison pumps 2 and 3
Center override/jettison pump
Galley equipment (freighter)
Term
What happens when you push a Generator Drive Disconnect (DRIVE DISC) switch?
Definition
Disconnects IDG from engine when above idle speed
Opens related Generator Control Breaker (GCB)
Term
What condition would automatically disconnect the IDG if not manually disconnected by the flight crew?
Definition
Excessively high drive oil temperature
Term
How do you know when an IDG has been disconnected?
Definition
DRIVE DISC msg
Term
What does a Generator DRIVE light indicate?
Definition
IDG oil pressure low, or
IDG oil temperature high, or
GCB open due to uncorrectable generator frequency fault
Term
What does a Bus Isolation (ISLN) light indicate?
Definition
BTB open
AC bus isolated from sync bus
Term
What is the difference between a BTB opening automatically and pushing the BTB switch to off?
Definition
Auto: disconnects AC bus from sync bus

Manual: disconnects AC bus from sync bus and opens DCIR
Term
What are the indications that an AC Bus is not powered?
Definition
ELEC AC BUS
ISLN light in bus tie switch
OFF light in GCB
Term
What are the indications when there are OFF and ON lights in a GCB switch?
Definition
The GCB opened due to a fault
Term
What are the normal and backup power sources for the Captain and First Officer Xfer busses?
Definition
Captain - AC Bus 3
First Officer - AC Bus 2

Backup - AC Bus 1
Term
What is the normal power source for the Main and APU Batt busses?
Definition
DC Bus 3
Term
If either DC or AC Bus 3 is unpowered, how is each battery bus powered?
Definition
Its related Hot Batt Bus
Term
How is each Hot Batt Bus normally powered?
Definition
Through its related battery charger which is powered by the Ground Service Bus
Term
What are the normal power sources for the Main and APU Stby busses?
Definition
Main - AC Bus 3
APU - Captain Xfer Bus
Term
What items are powered by the APU Standby bus?
Definition
Left PFD, ND and FMC
Term
How does the Main Stby Bus get power if AC Bus 3 becomes unpowered in flight?
Definition
Through AC Bus 1
Route is AC Bus 1 - Ground Service Bus - Battery Charger - Hot Batt Bus - stby inverter - Stby Bus
Term
How does the APU Standby Bus get power if AC Bus 3 becomes unpowered in flight?
Definition
Bus is still powered through the Captain Xfer Bus, but the source is now AC Bus 1
Term
If both AC bus 3 and AC bus 1 are not powered, how is the Main Standby Bus powered and for how long?
Definition
30 minutes through the battery
Route is battery - Hot Batt Bus - stby inverter - Stby Bus
Term
If both AC bus 3 and AC bus 1 are not powered, how is the APU Standby Bus powered and for how long?
Definition
30 minutes through the battery
Route is battery - Hot Batt Bus - stby inverter - Stby Bus
Term
How is the electrical system configured during an automatic ILS approach (autoland)?
Definition
Below 1500' RA:
AC and DC Bus 1,2, and 3 are isolated from the sync bus
AC Bus 4 continues to power the synchronous bus
Term
Where are the P6 and P7 circuit breakers located?
Definition
P6 - on right sidewall
P7 - aft of the overhead panel
Term
What items are powered in flight with a loss of all normal AC power (loss of all generators)?
Definition
Left PFD, ND, FMC
Upper EICAS
Left VHF Comm
Left and right interphone panels
Captain's pitot heat
Dome light
Term
How is the trim system affected with a loss of all generators?
Definition
Control wheel trim switches are inoperative
Alternate trim is available
Term
Can an ILS be flown with a loss of all generators?
Definition
Yes, but no flight director or autopilot
Term
Which flight control and landing gear systems are not available with a loss of all generators?
Definition
Leading edge flaps cannot be extended (FLAP DRIVE msg)
Left trailing edge flap indication
Anti-skid
Auto-speedbrakes (manual okay)
Thrust reversers
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