Electrical Flashcards
What are the sources of main AC power?
- external power
- APU generator
- engine driven generators
Where is the GROUND SERVICE bus switch located?
In the cabin on the forward flight attendant panel.
On Hydraulic Driven Generator equipped aircraft, when does the HDG activate?
Activates automatically when both the left and right main AC busses are unpowered.
When equipped, what powers the Hydraulic Driven Generator on a 767?
Center hydraulic system.
When equipped, what powers the Hydraulic Driven Generator on a 757?
Left hydraulic system.
What components are powered by the ground service bus?
- main battery charger
- APU battery charger
- miscellaneous cabin and system loads
How can the ground handling bus be powered?
- Can be powered only on the ground, and only from the APU generator or from the external power source. (AVAIL light illuminated)
- To accept late bags after pushback, a 757 must have APU power to operate cargo doors. A 767 can use the manual bulk cargo door, or if electric door operation is desired, a 767 also requires APU power.
What is the function of the Battery (BAT) switch?
In an unpowered airplane on the ground, a few annunciator lights illuminate and allows the APU to be started
In a powered airplane in flight or on the ground, when AC power is removed or lost, the standby and battery busses are powered
How long will the battery last on standby power?
30 minutes minimum, powering standby AC and DC busses.
On a 767 without an operating hydraulic driven generator, how are gear extension and flap operation affected if battery power is lost?
The flaps and gear CANNOT be extended.
Where can you find which major systems are NOT available when operating on HDG power?
In the QRH.
What does an amber utility bus OFF light mean?
The utility and galley busses are unpowered.
What are the conditions that cause the utility busses to load shed?
- both thrust levers advanced on the ground with a single power source
- system overload
- single generator operation in-flight
- starting engines with the APU providing electrical power
When galley power sheds, is there any indication?
No. Galley busses can shed without illumination of the utility bus lights.
What do external power AVAIL and ON lights indicate?
AVAIL (white)- external power is plugged in and power quality is acceptable.
ON (white)- external power is powering the bus or busses.
What is indicated by an amber AC BUS OFF light?
The associated AC bus is unpowered.
What causes an amber illuminated generator DRIVE light?
HOT-LOP in the generator drive
- High Oil Temperature
- Low Oil Pressure
Explain the meaning of an illuminated APU generator OFF light on the overhead electrical control panel.
The APU generator breaker is open because of a fault with the APU running or the APU generator control switch is selected OFF.
What does an amber battery discharge DISCH light mean?
The main battery is discharging.
What does an amber illuminated standby power bus OFF light mean?
Standby AC and/or DC bus not powered.
How does the Standby Power Selector work?
- OFF- standby busses are unpowered
- AUTO- standby busses transfer to battery power if normal AC power is lost
- BAT- the standby busses are powered from the main battery
Explain the function of the generator control switch.
ON (bar in view)- arms the generator control breaker to close automatically when generator power is available.
OFF (bar not visible)- opens generator control breaker and resets fault trip circuitry.
Explain the function of the bus tie switches.
Provides power to both main AC and DC busses, and isolates faults.
On the 767, what does the FLT INSTR BUS PWR switch do?
ALTN- allows hydraulic driven generator to power FO’s flight instruments
OFF (ALTN not visible)- allows hydraulic driven generator to power captain’s flight instruments
