Electrical - Power distribution Flashcards
How many busses provide power for airplane servicing? Which busses?
2 busses.
The ground handling bus & the ground service bus
Where are the controls located for the ground handling bus?
There are no controls for the ground handling bus.
How is the Ground Handling bus powered?
Automatically when external power is plugged in or, via the APU (automatically if it’s running).
Which power source has priority (for the Ground Handling Bus)?
External power has priority over the APU
The Ground Handling Bus powers ?
- Cargo Doors
- Cargo Compartment lights
- Maintenance access lights
Is the Ground Handling Bus powered in flight?
No
Who needs the Ground Service Bus?
Cabin Service Personnel
What does the Ground Service Bus power?
- Cabin lighting & outlets
- Main & APU battery chargers
- The Left fwd fuel pump (which supplies fuel to the APU)
When is the Ground Service Bus available?
It powers loads needed both on the ground & in the air.
When external power is the only source of power, & the main busses are not powered, how can you power the Ground Service Bus?
Selecting the GROUND SERVICE switch at the attendant panel at door 1L
Whenever the right Main AC bus is powered, the Ground Service Bus is ?
Powered
Ground Service Bus Power Sources
- External Power
- Right Main bus
- APU generator
If the right Main AC is not powered, the APU is running, the Ground Service bus is powered by ?
The APU generator through the GROUND SERVICE switch
With the CABIN/UTILITY power switch ON what is powered normally?
- GND SERVICE BUS
- Utility Bus
- Galleys (via Main DC Bus)
If you select the CABIN UTILITY power switch OFF what do you lose?
Cabin lighting & outlets
When the CABIN/UTILITY switch is selected OFF, the following cabin lights are turned on:
Night lights
Supplemental night lights
Reading lights
Attendant work lights
DC electrical power operates which important items?
- PFD’s & ND’s
- GPS
- ADIRU (Air Data Inertial Reference Unit)
How many batteries does the 777 have?
2
What are the 2 batteries on the 777
- APU battery
- Main battery
What does the APU battery power?
APU starter motor & APU control circuits
What does the Main a/c battery power?
Critical airplane systems when no other power sources are available
What monitors the battery functions?
ELMS (Electrical Load Management system)
Displayed on ELEC synoptic
What is the primary source of DC power?
4 Transformer rectifier units (TRUs)
What do the TRUs do & what powers them?
Convert AC into DC
Powered from the 2 XFER busses
The TRUs supply 4 DC busses, they are ?
- Left Main DC bus
- Right Main DC bus
- Captain’s flight instrument bus
- First Officer’s flight instrument bus
If a TRU fails……
DC Tie relays connect the L & R Main DC busses & the Captain’s & First Officer’s flight instrument busses
Are there any controls for the DC system?
No, it’s fully automatic
The 777 is a Fly-by-Wire airplane, what does this mean?
Flight controls are actuated hydraulically, but controlled electrically
How many backup generators are there?
2, 1 on each engine
2 Permanent Magnet Generators (PMGs), are housed within each backup generator. What are their purpose?
They are the power source for the flight controls
The PMGs provide dedicated power to ?
L, C & R power supply assemblies & their respective flight control DC busses
(L FCDC BUS, C FCDC BUS, R FCDC - Flight Control DC Busses)
What happens if 1 or more PMGs fail in flight?
The Main DC busses or the Captain’s flight instrument bus power the flight control DC busses
If the Main DC busses become unpowered, what provides power to the L & C power supply assemblies?
The Hot Battery Bus
Should a transfer of power occur from one source to another (in the Flight Controls DC System), what insures no interruption of power during the transfer?
The 1 minute batteries provided on each power supply assembly
To allow automatic landings with the lowest possible minimums, the electrical system configured to that ?
Each of the 3 autopilots is powered by a seperate power source
Autoland Electrical Config - During approach, power to the R XFER bus switches from the R Main AC bus to ?
The backup generators (same for the L etc).
This transfer provides indeed EBT sources to each of the 3 autopilots
Elec system returns to normal when a GA is performed or APs are disengaged.
Which bus operates only on the ground?
The Ground Handling Bus
What provides DC power on this airplane?
TRUs
What is the electrical configuration during Autoland approaches?
The right transfer bus isolates from the right main bus
What is the secondary source of power for fly-by-wire if one or more PMGs are unpowered?
DC Busses
