Electrical System - Question Bank Flashcards
What does “AVAIL” light indicate on the External and APU PWR switches?
Power quality is acceptable
What Bus is powered on the ground when APU GEN 1 or EXT PWR 1 is available?
Ground Handling Bus
+
Ground Service Bus (if Ground Service Switch “ON” L1 door)
When is the Main Deck Cargo Handling Bus powered?
-Ext Power 2 “AVAIL”
or
-APU Gen 2 “AVAIL”
What electrical power source would you select if cargo handling is required?
Ext Power 1 or APU Gen 1 (Ground Handling Bus) and Ext Power 2 or APU Gen 2 (Main Deck Cargo Handling Bus)
When is Ground Service Bus powered?
Ext Power 1, APU Gen 1 or AC Bus 1
What is the function of the Standby Power Switch in the auto position?
Allows main and APU standby busses to be powered from available sources
Where would you find the Electrical Power-up procedure?
FCOM Vol 1 - Supplementary Procedures
What does a Bus Isolation (ISLN) light illuminated indicate?
- Bus Tie Breaker (BTB) open
- AC bus isolated from Sync Bus
What happens when you push a Generator Drive Disconnect (DRIVE DISC) switch?
- Disconnects IDG from engine
- Opens related GCB
What condition would automatically disconnect the IDG if not manually disconnected by the flight crew?
Excessively high drive oil temperature
How do you reconnect an IDG that has been disconnected?
Irreversible action that must be mechanically reconnected by MX on the ground.
What does a Generator DRIVE light indicate?
- IDG oil px low
- IDG temp high
- GCB open due to uncontrollable gen frequency fault
What are some of the equipment items powered by the Utility busses?
- FWD Main Fuel Pumps 2&3
- FWD OVRD Pumps 2&3
- CTR OVRD Pump L
- Galley Equip
Describe the electrical load shedding process.
- If electrical loads exceed power avail - the load management system sheds AC loads by priority until within limits.
- Utility busses are shed one at a time by ELCUs.
What is the purpose of the electrical system overload protection?
Ensure power is available to critical and essential equipment.
During load shedding, would you expect to see an EICAS Advisory message ELEC UTIL BUS L, R?
Yes.
Through load shedding priority ELCUs will shed AC utility busses until power demands are within limits.
What are the main AC electrical power sources?
- 2x Ext Pwr Sources
- 2x APU Gens
- 4x IDGs
Describe the function of the Split System Breaker (SSB)?
Divides the sync bus allowing each side of the AC electrical system to be powered by Aux (APU Gen) or External sources (Ext1 or Ext2)
Describe the electrical system sequence of events during engine start with the SSB open.
EXT PWR 1 - ON
EXT PWR 2 - ON
1- IDG powers it’s side of the sync bus when voltage and frequency are acceptable.
2- Previous Power source is disconnected from sync bus
Describe the electrical system sequence of events with a single power source powering the synchronous bus, when an
engine is starting, SSB closed.
1- IDG online after engine start
2- SSB closes
3- IDG powers entire sync bus when volt and freq are acceptable
Which bus powers the Captain’s transfer bus and the main standby bus?
AC Bus 3
Which bus powers the First Officer’s transfer bus?
AC Bus 2
Which bus provides backup power for both transfer buses?
AC Bus 1
What are some of the equipment items powered by the ground service bus?
- Fuel pumps for APU start
- Main Batt charger
- APU Batt charger
How can the ground service bus be powered when AC bus 1 is not powered, while on the ground?
Ext Pwr 1
or
APU Gen 1
What are some of the equipment items powered by the ground handling bus?
- Fueling System
- Aux Hyd Pump 4
- All Lower lobe doors, lights, and handling equipment
What bus powers the APU standby bus?
1- AC Bus 3 through the Capt XFer Bus
or
2- APU STBY INV
How is the electrical system configured during an automatic ILS approach (auto-land)?
AC Busses 1,2 & 3 are isolated from the sync bus to provide independent power sources for the 3 autopilots
What are some of the major components of the AC standby power system?
Everything the CA needs to fly the aircraft
L PFD, L ND, EFIS control, STBY Ins lights, Upper Display, L CDU, L VOR, L RTP, L VHF, L FMC
What is the normal source of power for the main standby bus?
AC Bus 3
How does the main standby bus get power if AC bus 3 becomes unpowered in flight, all other conditions normal?
Main STBY Inverter
If both AC bus 3 and AC bus 1 are not powered, all other conditions normal, how is the main standby bus powered, and
for how long can it be powered?
- Main STBY Inverter (powered by the Main Battery through the Main Battery Bus and Main Hot Battery Bus)
- Minimum 30 mins
What are some of the equipment items on the main standby bus?
Everything the CA needs to fly the A/C except the APU STBY Bus components (L PFD, L ND, L FMC)
What are the equipment items on the APU standby bus?
- L PFD
- L ND
- L FMC
How is DC power provided by the electrical system?
- Four TRUs
- Battery Busses (APU and Main)
What is the normal power source for the main and APU battery busses?
DC Bus 3
If either AC bus 3 or DC bus 3 is unpowered, how is each battery bus powered?
By its related hot battery bus
What are some examples of individual equipment items on the main battery bus?
- Fuel valves (all engines)
- All X-FEED valves
- APU controller
- TE Flap Control
How is each hot battery bus normally powered?
Ground Service Bus through its related battery charger (acts as a TRU)
What are some examples of equipment items on the main hot battery bus?
- APU fuel SOV
- Spar valves (all engines)
- Engine fire extinguishers
- APU & lower cargo fire extinguishers
What are some examples of equipment items on the APU hot battery bus?
- IRU - L/C/R DC Power
- L/R Outflow valves
- APU inlet door, APU controller
What does the battery “ON” switch do?
Connects hot battery busses to the main battery busses
