Electrical Flashcards
Load Shedding can be cause by five reasons:
- Single Source of Aircraft power
- Generator Overload
- Advancing the throttles prior to engine start
- Commanded by start switch during Engine start
- Fuel Jettison (767)
Bus Tie system
Need One for-
Need two for-
One- Flight Instrument Transfer
Two- DC Bus Tie Transfer
Bus Tie Switch functions- (4)
Auto closure of the DC bus tie breaker
Auto Flight Instrument transfer
Fault Isolation
Bus Priority System )onside, APU, other side)
If there is a fault on a bus but hasn’t tripped the bus tie yet, what will the tie indicate?
Auto AND Fault
If there is a fault on a bus but hasn’t tripped but the bus tie indicates Auto and Fault why is this good?
Why wouldn’t you select the Bus Tie to open?
It will allow the flight instrument transfer to happen when it finally trips
If you preemptively selected the Tie to off you wouldn’t get the transfer
What can power the Ground Handling Bus?
Only the APU or GPU
Which busses will shed during an Engine start using the APU
First Engine- both sides shed
Second Engine- Associated side sheds
Normal Electric Power priority
On-side
APU
other side
Powered by the HMG (Lucky Seven)
Batt Bus Hot Batt Bus Standby A/C+DC Left and Right Transfer Bus Captain's Flight Instruments
HMG
- When does it come on?
- Is it Time Limited?
- With loss of both aircraft power sources
- No, can run indefinitely
Why might you get a Batt Discharge initially when the HMG comes on?
It puts out less DC Power than the Battery so the battery will discharge for a bit until it’s below the level of the HMG output
If you are down to main battery power how long do you have?
30 minutes on most Aircraft
90 on the 753 because it has an APU battery
If you are down to main battery power what might you consider before running out of batt power?
Lowering the gear, it can not be lowered without electrical power
