Electrical Flashcards
What two conditions cause the BUS TIE ISLN light to illuminate?
Bus tie breaker is open because BUS TIE switch is OFF, or switch is in AUTO and fault has occurred
In the Generator Control (GEN CTRL) switch, what does the amber OFF light indicate?
The generator breaker is open
What condition illuminates the generator DRIVE light?
Low IDG oil pressure
Which system provides load management and protection to ensure critical systems are powered?
Electrical Load Management System (ELMS)
What condition might shed the galleys/utility buses in flight or on the ground?
When electrical loads exceed the power available
List the main AC electrical sources
- Left and Right IDGs
- APU generator
- Primary and Secondary external power
If an IDG fails in flight, is there sufficient power available to prevent load shedding?
No, two main AC power sources are required to supply the entire AC electrical load
Other than the IDGs, what other aircraft power source for the main AC buses is available in flight?
The APU generator
In the external power switches what does the AVAIL light indicate?
Power supply is plugged in and the voltage and frequency are within limits
In the external power switches what does the ON light indicate?
External power is supplying the bus(es)
After landing if an external power AVAIL light is in, will it take over from a main generator when the power is selected on?
Yes
When the APU is started, how is power transferred from external to the APU generator?
Automatically (replaces SEC EXT PWR on the left AC bus)
After landing with the APU generator switch ON will the APU generator take over automatically from the main generators when the engines are shut down?
Yes
With the Bus Tie switches latched in AUTO what is the position of the bus tie breakers with ground power removed, the APU operating normally and the first engine (right) just started?
Right BTB open, left BTB closed
With the Bus Tie switches latched in AUTO what is the position of the bus tie breakers When both engines are running?
Both BTBs open
Which main bus normally powers the Ground Service Bus?
The right main AC bus
Is the Ground Service Bus normally live during flight?
Yes
If the right generator fails, and the right Bus Tie ISLN light is illuminated, will the right AC bus be powered?
No, the Bus Tue Breaker is locked open
If the right generator fails, and the right Bus Tie ISLN light is illuminated, will the batteries continue to charge?
No, the Ground Service Bus will also fail
When will the Backup Electrical System automatically power one or both Transfer Busses?
- Only one main AC generator (includes APU) is available
- Power to one or both of the main AC busses is lost
- Approach (APP) mode is selected for autoland
- The system is automatically tested after engine starts
What is the power source for the Backup AC Electrical system?
One Backup Generator mounted on each engine
How many Backup Generators can connect to the electrical system at one time?
One
What normally powers the captain’s flight instruments?
C1 TRU
What powers the captain’s flight instruments if the C1 TRU fails?
C2 TRU through FO FLT INST bus
What powers the captain’s flight instruments if both C1 and C2 TRUs fail?
Battery Bus
Which units normally power the left and right main DC buses?
The L TRU and R TRU
Which buses power the L and R TRUs?
The L and R Transfer buses respectively
During normal conditions what powers the Hot Battery Bus?
The main battery charger
During normal conditions what powers the Battery Bus?
Captain’s Flt Inst Bus (C1 TRU)
During normal conditions what powers the Standby AC Bus?
L Transfer Bus
If the left TRU fails what powers the left main DC bus?
The right Main DC bus
Where are the battery chargers powered from?
The ground service bus
What are the primary electrical sources for the flight control DC electrical systems?
Engine driven Permanent Magnetic Generators (PMGs)
If PMG AC power is not available, what secondary source of power supplies which DC Flight Control Buses?
Main DC busses supply L and R Flight Control DC busses; Captain’s Flight Instrument bus supplies the C Flight Control DC bus
When operating on the Standby Electrical System, which DC Flight Control Buses will be powered from the Hot Battery Bus?
L and C Flight Control DC busses only
If primary power is lost, what does the Standby Electrical System supply power to?
AC and DC power to selected flight instruments, communications and navigation systems, and the flight control system
The Main battery can provide standby power to which busses?
- Hot Battery bus
- Battery Bus
- Captain’s Flight Instrument bus
- L and C flight control PSAs
- Standby Inverter
For how long can the Main battery provide standby power?
Minimum 10 minutes
In flight, when would the RAT deploy automatically?
When both AC transfer busses lose power
The RAT generator provides standby power to what?
To the C1 and C2 TRUs
What supplies power until RAT deployment?
The Main battery
