SIT 1 Flashcards
What does “AVAIL” light indicate on the external APU PWR switches?
The related power source (APU or EXT) is plugged in and available and the power quality is acceptable.
What bus is powered on the ground when the APU GEN 1 or EXT PWR 1 is available?
Ground handling bus.
(Note: if both AVAIL, EXT PWR 1 is automatically used)
When is the Main Deck Cargo Handling bus powered?
Automatically powered on the ground with APU GEN 2 or EXT PWR 2 AVAIL.
Note: if both AVAIL, EXT PWR 2 is automatically used
Note: if APU GEN 2 or EXT PWR 2 is only available source and is selected on the main deck cargo handling bus is de powered.
Note: if both APU GEN 2 and EXT PWR 2 are AVAIL and EXT PWR 2 is selected on then APU GEN 2 will show AVAIL and power the main deck cargo handling bus
What electrical power source would you select if cargo handling is required
Select only APU GEN 1 or EXT PWR 1
APU GEN 2 or EXT PWR 2 AVAIL powers the main deck cargo handling bus (ext PWR 2 used over APU)
When is the ground service bus powered?
Whenever ac bus 1 is powered.
(Note: on the ground when ac bus 1 is not powered the ground service bus can be connected to the same source that is powering the ground handling bus by pushing the ground service switch on the cabin panel close to door 1L
What is the function of the standby power switch in the auto position
Allows the main and APU standby busses to be powered from available sources.
Where do you find the electrical power-up procedure
FCOM Vol 1, supplemental procedures, chapter SP section 6 - electrical, pg SP.6.1
What does a Bus ISLN light indicate?
BTB open - AC bus isolated from the Synchronous Bus
What happens when you push a Gen DRIVE DISC switch
Mechanically disconnects the IDG from the engine accessory drive (when above idle speed)
Opens the generator Control Breaker (GCB)
What condition would automatically disconnect the IDG if not manually disconnected by the flight crew?
Excessively high drive oil temp
How do you reconnect and IDG that’s been disconnected?
IDG can only be reset on the ground by maintenance.
What does a generator drive light indicate?
IDG oil temp high
IDG oil pressure low
Generator control breaker (GCB) open due to uncontrollable frequency fault (HOTLOP/ FREQ FAULT)
What are some of the equipment items powered by the utility busses?
Five fuel pumps: fwd main 2&3, fwd override/jettison pumps 2&3, center override/jettison pump
Galley equipment
APU T/R
Describe the electrical load shedding process
Freighter: the load management system sheds AC loads by priority until the loads are within the capacity of airplane or ground power generators
- utility bus loads are shed one at a time through ELCU’s in a programmed sequence until the overload condition is relieved
- when an additional ac power source is available loads are restored in reverse order
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 at see an EICAS advisory message UTIL Bus L, R
No. During load shedding this and the UTILITY OFF lights are inhibited
What are the Main AC electrical power sources?
4 IDG’s, 2 APU generators, 2 EXT PWR sources
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 a separate auxiliary or external power sources.
Describe the electrical system sequence of events during engine start with the SSB open.
When an engine is started with APU GEN or EXT PWR connected to each side of the electrical system (SSB open) the IDG powers its side of the sync bus when volts and freqs are acceptable. The previous power source is disconnected. SSB remains open.
Describe the electrical system sequence of events with a single power source powering the synchronous bus, when an engine is starting, SSB closed
With a single source powering the entire sync bus (SSB closed) when the first engine is started its IDG powers the entire sync bus as soon as volts and freqs are acceptable. 5)3 SSB remains closed and the operating IDG powers the entire aircraft and the APU or EXT power source is automatically disconnected.
Which bus powers the captains transfer bus and the main standby bus?
AC bus 3 (backed up by AC bus 1)
Which bus powers the first officers transfer bus?
AC bus 2 (backed up by ac bus 1)
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?
Main & APU battery chargers
fuel pumps for APU start
Flight deck flood lights
Navigation lights
Service lights
Misc. service and equipment
How can the ground service bus be powered when AC bus 1 is not powered while on the ground.
Can be connected to the same source powering the ground handling bus (ext PWR 1 or APU gen 1) by pushing the ground service switch on cabin panel door 1L
What are some equipment items powered by the ground handling bus
Lower cargo doors,
lower cargo handling equipment
Lower cargo lights
Fueling system
Aux hyd pump 4
27 what bus powers the APU standby bus?
Captain transfer bus (on freight)
Backed up by APU standby inverter
How is the electrical system configured during and automatic ILS approach (auto land)
Ac bussses 1,2&3 are isolated from the sync bus to provide independent power sources for the three autopilots
Ac bus 4 continues to power the sync bus
(1,2&3 isolated from DC tie bus. DC bus 4 powers the dc tie bus)
What are some of the major components of the AC standby power system?
Main standby bus
APU standby bus
Main battery
APU battery
Main standby inverter
APU standby inverter
Standby power selector
What is the normal source of power for the main standby bus?
AC bus 3 (backed up by the main standby inverter - powered by the main hot battery bus through the battery switch with the battery relay closed
How does the main standby bus get power if the AC bus 3 becomes unpowered in flight, all other conditions normal?
From the main stby inverter
(Normally unpowered, activated and powered by the main battery charger through the main hot battery bus. Main battery charger norm powered by AC bus 1 through ground service bus
If both the AC bus 3 and ac bus 1 are not powered all other conditions normal how is the main standby bus powered and how long
Main standby inverter. Main battery can provide 30 minutes of power to the main standby inverter
What are some of the equipment items on the main stby bus?
L EIU, L CDU, L ILS, L VOR, L ADC, L EFIS control panel, L XPNDR, Stby ignition for all engines, Primary EICAS Display, RMI, Stby inst lights, various flight control components
What are the equipment items on the APU Stby bus
L FMC, L ND, L PFD
How is DC power provided by the electrical system
Through 4 TRU’s
- powered by an AC bus
- provides DC power to a DC bus
- 4 DC busses are connected through DCIR’s to the DC tie bus
- allows each DC bus to remain powered if it’s related AC bus is unpowered or TRU fails
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 hot battery bus
What are some examples of individual equipment items on the main battery bus?
Alternate APU controller, engine fuel valves (all), crossfeed valves (all), dome light, storm light, selected interior lights, IDG disconnect, manual pressurization controller, trailing edge flap control, Capt interphone, L radio tuning panel, L VHF.
How is each hot battery bus normally powered?
Directly from the respective battery
What are some examples of equipment items on the main hot battery bus?
APU Fuel SOV, spar Fuel Valves (all), APU fire extinguisher, lower cargo fire extinguishers, engine fire extinguishers (all) fire switch unlock (all engines)
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, Pirmary APU Controller
