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ATLAS 747 Electrical
Terms in this set (41)
What does the AVAIL light indicate on the External and 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 APU generator 1 or external power 1 in available?
Ground handling bus
When is the main cargo deck handling bus powered?
When the AVAIL light is displayed on the APU 2 or EXT 2 switches
What electrical power source would you select if cargo handling is required?
The number 1 auxiliary or external power
When is the ground service bus powered?
When AC bus 1 is powered either on the ground or in flight
What is the function of the Standby Power Switch in the Auto position?
Allows the main and APU standby buses to be powered from available sources
Where would you find the Electrical Power-up procedures?
Refer to FCOM Vol. 1 Supplemental Procedures
What does a Bus Isolation (ISLN) light illuminated indicate?
AC bus isolated from synchronous bus
What happens when you push a Generator Drive Disconnect (DRIVE DISC) switch?
Disconnects IDG from engine when above idle speed
Opens related 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 an IDG that has been disconnected?
Maintenance action is required
The IDG cannot be restored by flight-crew action
What does a Generator DRIVE light indicate?
IDG oil pressure low or
IDG oil temp high or *GCB open due to uncorrectable generator frequency fault
What are some of the equipment items powered by the Utility buses?
Forward Main Pumps 2 and 3
Forward override/jettison pumps 2 and 3
Center override/jettison pump
Galley equipment (freighter)
Describe the electrical load shedding process.
Utility bus loads are shed one at a time through ELCUs in a programmed sequence until the overload condition is releived.
What is the purpose of the electrical system overload protection?
To 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?
No, this message is inhibited during load shedding
What are the main AC electrical power sources?
Two auxiliary power sources (APU generators *Two external power sources
Describe the function of the Split System Breaker (SSB)?
Divides the synchronous bus, allowing each side of the AC electrical system to be powered by separate auxiliary or external power source.
Describe the electrical system sequence of events during engine start with the SSB open.
The IDG powers its side of the synchronous bus when voltage and frequency are acceptable.
The previous power source is disconnected
Describe the electrical system sequence of events with a single power source powering the synchronous bus when an engine is starting.
The IDG powers the entire synchronous bus when the voltage and frequency are acceptable *the SSB remains closed and the original power source is disconnected
Which bus powers the Captain's transfer bus and the main standby bus?
AC BUS 3
Which bus powers the FO'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?
Main and APU battery chargers
Fuel pumps for APU start
Flight deck flood, navigation and service lights
Misc. service outlets and equipment
How can the ground service bus be powered when the AC bus 1 is not powered while on the ground?
By pushing the ground service switch on the cabin panel at door L1 the ground service is then connected to the same power source as the ground handling bus
What are some of the equipment items powered by the ground handling bus?
Lower cargo handling equipment and compartment lights
Fueling system *Aux HYD pump 4
What bus powers the APU standby bus?
The Captain's transfer bus
How is the electrical system configured during an automatic ILS approach (autoland)?
AC and DC buses 1, 2, and 3 are isolated from the synch bus
AC bus 4 continues to power the synch bus
What are some of the major components of the AC standby power system?
Main and APU standby buses
Main and APU batteries
Main and APU standby inverters
Standby power selector
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?
The main standby inverter powers the main standby bus through the main battery charger through the main hot battery bus. (The main battery normally powered by AC bus 1 through the ground service bus)
If both AC bus 3 and AC bus 1 are not powered, all other conditions normal, how is th main standby bus powered and for how long can it be powered?
The main standby inverter powers the main standby bus from the main battery through the main hot battery bus. (since the battery charger is unpowered, the main battery can provide power to the main standby bus for a minimum of 30 minutes)
What are some of the equipment items on the main standby bus?
Left EIU, CDU, ILS, VOR
Various flight control components
Standby ignition for all engines
Primary EICAS display, standby inst. lights
RMI (if installed)
Left ADC, Left EFIS control panel *Left Txpdr (some exceptions)
What are the equipment items on the APU standby bus?
Left FMC, ND and PFD
How is DC power provided by the electrical system?
Four Transformer/Rectifier Units (TRUs) produce DC power, each TRU powered by its respective AC bus
Four DC buses are connected through DC isolation relays to the DC tie bus *Batt buses distribute DC power in addition to the four main DC buses
What is the normal power source for the main and APU battery buses?
DC bus 3
If either AC bus 3 or DC bus 3 is unpowered, how is each battery bus powered?
Its related hot battery bus
What are some examples of individual equipment items on the main battery bus?
APU controller (alt)
Fuel valves (all engines)
All x-feed valves
Dome, storm and selected indicator lights
IDG disconnect (all engines)
Manual pressurization control
Trailing edge flap control
Left radio tuning panel
How is each hot battery bus normally powered?
The ground service bus
Through its related battery charger *Each battery is connected directly to its related hot battery bus
What are some examples of equipment items on the main hot battery bus?
APU fuel shutoff valve
Spar valves (all engines)
APU and lower cargo fire extinguishers
Engine fire extinguishers (all engines) *Fire switch unlock (all engines)
What are some examples of equipment items on the APU hot battery bus?
IRU left, center, and right DC power
Left and right outflow valves *APU inlet door, APU controller (primary)
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