Electrical System Flashcards
What powers the Ground Handling Bus?
What does it power?
Can only be powered by the APU generator or primary external power.
Powers ground cargo handling, fueling/defueling, and other equipment required for ground operations.
The Ground Service Bus powers:
- The main battery charger
- The APU battery charger
- Miscellaneous cabin and system loads
What happens if the ADIRU is switched off in flight?
System logic prevents the ADIRU from becoming un-powered in flight.
What does the RAT supply power to?
What are it’s operating limitations?
Supplies power to C1 and C2 TRUs.
No operating time limits, and operates at all airspeeds and altitudes
What is the ELMS?
Electrical load management system
Manages load of the electrical system and automatically sheds loads when demand exceeds power available.
As power becomes available it will bring systems back online.
When does the backup power system automatically power one or both main transfer buses?
- Only one main AC power source (including APU) is available.
- Power to one or both AC power sources is lost.
- Approach (APP) mode is selected for autoland.
How many TRUs are there?
4 - L, R, C1, and C2
What constituted the standby electrical system?
- the main battery
- the standby inverter
- the RAT generator and its associated generator control unit
- the C1 and C2 TRUs.
When does the RAT deploy?
HEED
Hydraulics - all 3 hyd systems pressure is low
Electrical - both AC transfer buses fail
Engines - both fail
Deployed manually
What do the PMGs do?
Each backup generator contains two permanent magnet generators (PMGs) that supply power to the flight control DC electrical system.
What things are powered by the hot battery bus with all electrical power off (batt off)?
ADIRU and APU/engine fire bottles
Flight Control DC electrical system power sources
Primary - PMGs
Secondary - Related main DC bus (for L/R only)
Secondary for center PSA is provided by the captain’s flight instrument bus.
HOT Battery Bus provides additional backup power for L and center only
What happens if the ADIRU fails in flight?
If the ADIRU fails, the SAARU automatically supplies attitude, heading, and air data. SAARU heading must be manually set to the standby compass magnetic heading periodically.
If ADIRU inertial data fails, the EICAS caution message NAV ADIRU INERTIAL displays. The SAARU supplies attitude data to the PFD and three minutes of backup heading. The heading is based on ADIRU heading prior to failure. The CDU POS INIT page displays the SET HDG prompt three minutes after ADIRU failure. Use the SET HDG prompt to periodically set the SAARU heading to the standby compass magnetic heading. There are no other prompts to remind the crew to enter or to update the SAARU heading.
During preflight of the overhead panel you notice that the ADIRU ON BAT light is Illuminated. What is happening?
If electrical power is subsequently removed from the airplane and the Battery switch is switched OFF, the hot battery bus continues to supply electrical power to the ADIRU. The ON BAT light illuminates, and the horn in the landing gear wheel well sounds to alert maintenance personnel the ADIRU is on battery power.
How long can the main battery provide power to the standby system?
At least 10 minutes
What does the Standby inverter do?
Converts DC to AC power and powers the standby AC bus
What bus does the APU automatically connect to when started on the ground?
Left main AC bus.
Can you turn the main battery off in flight?
No, system logic prevents it.
What should you check before disconnecting external power?
APU RUNNING in white letters on EICAS.
What will cause an automatic shutdown of the APU (unattended)?
In the unattended mode, any of the following faults cause the APU to shut down immediately: • APU fire/inlet overtemperature • overspeed/loss of overspeed protection • high EGT • low oil pressure • high oil temperature • generator oil filter approaching bypass • intake door failure • APU controller failure • speed droop • no combustion on start • no acceleration on start.
What will cause an automatic shutdown of the APU in flight (attended)?
In the attended mode, any of the following faults cause the APU to shut down immediately: • APU fire/inlet over temperature • overspeed/loss of overspeed protection • APU controller failure • speed droop.
If the APU shuts down automatically in flight because of a fire warning will the bottle discharge automatically?
No, it will only automatically discharge the bottles in unattended mode
What happens when you pull the APU fire switch?
Six things: BBFAGS
- arms the APU fire extinguisher bottle
- closes the APU fuel valve (at the wing and APU)
- closes the APU bleed air valves
- closes the APU air inlet door
- trips the APU generator field and generator breaker
- shuts down the APU (if automatic shutdown does not occur).
When is the APU fire switch lock automatically released?
unlocks automatically for a fire warning.
What does the APU FAULT light mean?
- APU fault and/or fire is detected
- APU shutdown due to fault and/or fire
- momentarily during APU controller self–test
What causes the generator drives to disconnect automatically?
High oil temperature
What is the priority sequence for AC power (controlled by the bus tie)?
RAO
The source order for powering left and right main busses in flight is the:
• respective IDG
• APU generator
• opposite IDG.
What does the PRESS green light mean once the RAT is deployed?
Center system primary flight control hydraulic pressure is greater than 1500 psi
With the RAT as the only source of power, other than batteries, what is powered?
The RAT generator provides standby power to the C1 and C2 TRUs for emergency DC power
It will provide power to the CA and FO Flight Inst Bus
Power for standby electrical loads is provided by the main battery during deployment of the RAT and when RAT generator loads are shed.
With only battery power, what is powered?
- Hot Battery Bus
- Battery Bus
- left and center flight control buses
- CA Flight Instrument Bus
- Standby Inverter
What will cause the emergency lights to illuminate automatically when armed?
If airplane electrical power fails or is turned off with the switch in the armed position.
What powers the Ground Service Bus?
The ground service bus is normally powered by the right main bus. Alternate sources of power for the ground service bus are:
• the APU generator
• primary external power.
Can one back up generator power both transfer busses?
Yes
How long will the emergency lights last?
A fully charged battery provides at least 15 minutes of operation.
The main battery provides standby power to the:
- hot battery bus
- battery bus
- captain’s flight instrument bus
- left and center flight control PSAs
- standby inverter.
