6 - Electrical Flashcards
What does the APU Generator (APU GEN) Control Switch do?
- arms APU generator breaker to automatically close
- opens APU generator breaker
- resets fault trip circuitry
What do the BUS TIE Switches do?
- arms/opens automatic AC bus tie circuits
- arms/opens automatic DC bus tie circuits
- arms/opens automatic flight instrument transfer bus circuits
- resets fault trip circuitry
(Flight instrument transfer bus auto transfer for BUS OFF only if BUS TIE switch is in AUTO)
(Both BUS TIE breakers must be in AUTO for DC bus tie breaker to work)
What do the Generator Control (GEN CONT) Switches do?
- arms the generator breaker to close automatically when generator power is available
- opens generator breaker
- resets fault trip circuitry
External Power Available (AVAIL) Light
Illuminated (white) –
external power is plugged in and power quality is acceptable
What do the UTILITY BUS Switches do?
- connects/disconnects utility and galley busses to main AC bus
- resets overload/load shed circuitry
What happens when you push a GEN DRIVE DISC Switch?
- disconnects generator drive from the engine
* requires maintenance action on the ground to reconnect the generator drive.
What does a Generator DRIVE light indicate?
- the generator drive oil temperature is high
* the generator drive oil pressure is low
What happens with the BAT switch ON:
- Unpowered airplane
- Powered airplane (when AC power is lost/removed)
- a few annunciator lights illuminate
- allows the APU to be started
• the standby and battery busses are powered (with STBY POWER in AUTO)
What happens if AC power is lost with Standby (STBY) POWER Selector in AUTO?
How long will it last?
the standby busses transfer to battery power (Main and APU)
90 min
A hydraulic driven generator operates _____ as a backup source of power in the event _____
automatically (no time limit)
both main AC busses lose power
(less than 1/10 the power of an engine driven generator)
(may have BAT DISCH light because HDG DC output low)
The source order for powering left/right main busses is:
- respective IDG
- APU generator
- opposite IDG
The ground service bus is normally powered by _____
Alternate sources of power for the ground service bus are _____
right main bus
- the APU generator
- external power
The ground service bus powers:
- the main battery charger
- the APU battery charger
- miscellaneous cabin and system loads
The ground handling bus is powered (only on the ground) by _____ , and powers ______
APU generator or external power source
cargo handling and equipment
During autoland, the busses isolate to allow three independent sources to power the three autopilots:
• the left main system powers _____
• the right main system powers _____
• _____ powers the center autopilot
- the left autopilot and the captain’s flight instrument transfer bus
- the right autopilot and the first officer’s flight instrument transfer bus
- the battery/standby system
(Reverts to normal for autopilot GA or disengage)
Normally, the captain’s flight instruments are powered by _____ and the first officer’s flight instruments are powered by _____
If the bus tie breakers are in AUTO, the flight instrument transfer busses transfer to _____
If power is lost to both main AC busses, the captain’s flight instruments are powered by _____
left main AC Bus
right main AC Bus
opposite main AC bus
hydraulic driven generator.
Left and right AC transfer busses power items considered necessary for ETOPS (which are not powered by the battery/standby system)
Transfer busses are normally powered by _____ ,
but also can be powered by _____ when both AC busses are unpowered
associated main AC busses
Hydraulic Driven Generator
The main DC electrical system uses _____ to produce DC power, which are powered by _____
transformer-rectifier units (TRUs)
main AC busses
The TRUs operate isolated from one another
If one TRU fails, the ______ closes to keep both DC busses powered
Both _____ switches must be in AUTO for the _____ to close
DC bus tie breaker
BUS TIE
DC bus tie breaker
Where are the flight deck controls for the main DC electrical system located?
There are no flight deck controls for the main DC electrical system
The Battery/Standby Power System consists of the following busses:
- the hot battery bus
- the battery bus
- the standby AC bus
- the standby DC bus
What is the power source for the hot battery bus?
- Main battery
- Battery charger powered from the ground service bus
Prior to establishing electrical power _____ powers the hot battery bus
After establishing electrical power _____ powers the hot battery bus
main battery
main battery charger (powered by the Ground Service Bus)
After establishing electrical power _____ powers the battery bus, and _____ provides a backup source of power
left DC system
main battery
What does the HDG (Hydraulic Driven Generator) power? (7, 4-AC, 3-DC)
- CA Flight Instrument Transfer bus
- L AC Transfer bus
- R AC Transfer bus
- Stby AC bus
- Stby DC bus
- Battery bus
- Hot Battery bus
(L FMC, flap posit, auto press controllers, stby engine indications, ISFD, CA pitot heat)
What happens if you get an APU FAULT light?
immediate automatic shutdown (no cool down)
How long can the Main Battery power the STBY Power system?
30 min
CBT says 90 min for Main and APU batteries
On STBY Power if battery is depleted (30 min), what is the effect on flaps and gear?
C ADP pneumatic supply valve closes with loss of DC power. No way to hydraulically operate flaps and gear.
What happens when you place BAT switch to ON?
allows battery to power Battery Bus if no other source is available
What happens with STBY POWER selector to AUTO?
the STBY busses transfer to battery power if normal AC power is lost
(AC STBY bus normally powered by L AC bus. If L AC power is lost, DC tie bus powers STBY Inverter. If both AC busses are unpowered, main BAT powers STBY Inverter)
(DC STBY bus normally powered by L DC bus)
What does a STBY POWER OFF light mean?
loss of power to STBY AC and/or STBY DC bus
What does a Bus Tie ISLN light mean? Due to _____ (2)
BTB open due to a fault or switch OFF
What does a GEN Drive Disc DRIVE light mean?
high oil temp or low oil press
What does a Gen Cont OFF light mean?
generator breaker open
When do utility busses shed? (4)
The galley bus is powered by the left utility bus, and has no direct controls or indications
BOSS
B - both T/Ls TO range on ground with engines shutdown
O - overload of available electrical power
S - starting engines
S - single GEN source
What is max altitude for APU power?
FL 431
What happens to the APU if you get an APU FAULT light?
immediate automatic shutdown with no cool down
APU Starter limit
3 attempts in 60 min
What happens if BAT Switch is turned OFF with APU running?
APU shutdown after cool down cycle without fire detection
Hot Battery Bus powers (10)
regardless of BAT switch position
- Clock time base
- IRS emergency power
- Equipment cooling ground warning
- Fire extinguisher bottles
- Fueling system
- APU fuel shutoff valve
- Wing spar fuel shutoff valve
- Alternate landing gear extension
- Parking brake valve
- RAT manual deployment
What is powered from the Battery Bus? (5)
- Fire detection
- PA system
- Fuel quantity indicating system
- Stby engine indications
- Alternate stab trim
What is powered by the STBY POWER system? (5)
- Stby instruments
- L VHF, VOR, RDMI
- C ILS
- Instrument panel flood lights
- Manual pressurization control
Normal load shedding during engine start (3)
- an electric hydraulic pump
- center tank fuel pumps
- utility buses
How is the Ground Handling Bus powered and what is on the bus?
EXT (AVAIL) or APU
- Cargo systems
- Cargo lights
- Maint access lights
- Fueling systems
How is the Ground Service Bus powered and what is on the bus?
- R main bus
- APU
- EXT
- Main/APU battery chargers
- Left forward fuel pump
- Cabin lighting and outlets
- Misc cabin and system loads
What happens with a L or R BUS OFF light illuminates?
only if BUS TIE switches in AUTO
- Flight instrumental transfer bus switches to other bus
- DC bus tie closes to keep the DC busses powered
- (L bus fail) Stby AC bus powered from the Stby Inverter
- (R bus fail) Lower EICAS screen blanks
If EXT power is powering both main busses what happens when the APU is started and APU GEN becomes available?
What happens if IDGs or APU Gen are powering both main busses and EXT is selected ON?
Nothing. EXT continues to power both busses until switched off.
EXT powers both main busses
