B757 Review Questions

Electrical

• You select the battery switch to ON and place the standby switch in AUTO, what

busses are available?

• Hot battery bus, battery bus, standby AC and DC.

Electrical

• What is the normal source of power for the standby AC and standby DC busses?

• Left AC transfer bus, and left DC bus respectively.

Electrical

• What are the three types of load shedding?

• Engine start, overload, and generator loss load shedding.

Electrical

• For the electric system to automatically maintain power to both main busses, which

electrical switches must be in AUTO position for this to happen?

• The bus tie breakers must be in AUTO.

Electrical

• What is the only way to have STBY bus power?

• STBY power switch in either AUTO or BATT

Electrical

• What is the normal power for ground service bus?

• Right Main AC bus

Electrical

• What does the OFF light in a generator mean?

• A fault or the switch is OFF

Electrical

• TRUE / FALSE: With a loss of a generator in flight, do both utility busses shed?

• TRUE

Electrical

• With external power ON, BATT switch On and STBY power switch OFF, are the

STBY busses powered?

• No.

Electrical

• What bus is only powered on the ground?

• Ground handling bus.

Electrical

• What does the bus tie system do in AUTO?

• It operates automatically to prevent paralleling and keep the main AC busses

powered.

Electrical

• If you manually isolate the left bus tie and lose the left generator will the captain’s flight instrument transfer bus, or left DC

BUS be powered?

• No.

Electrical

• If you have a left AC bus fault, how many autopilots will be available?

• One, right autopilot.

Electrical

• If you have a right AC bus fault, what are the primary things you will lose?

• Right autopilot, both battery chargers, both utility busses.

Electrical

• What would cause the HDG to start? What power source must be available for it to

work?

• Loss of both the AC busses. There must be hydraulic pressure in the left hydraulic

system for the HDG to operate.

Electrical

• How many electric generators are there on the airplane?

• Four. 2 IDG’s, the APU, and the HDG

Electrical

• Is there a bus tie breaker system for DC power?

• Yes, if there is a loss of DC power on one of the two DC busses the DC bus tie

breaker closes automatically. AC bus tie switches must both be in AUTO for this

switching to work.

Electrical

• If the STBY POWER switch is selected to the BAT position, how are the standby

busses powered?

• Battery Bus powers standby DC, and the static inverter powers standby AC.

Electrical

• With the STBY POWER switch in BAT position, is the battery being charged.

• No. Battery chargers are cutoff.

Electrical

• What bus is powered only on the ground by the APU or external power?

• The ground handling bus.

Electrical

• Can external power be used simultaneously with the APU?

• No.

Electrical

• Will the selection of external power trip off APU or engine driven generators?

• Yes. External power has priority.

Electrical

• How is power provided to the DC busses?

• From the respective AC busses through TR’s, transformer rectifiers.

Electrical

• What busses are powered by the HDG?

• Seven busses. AC standby bus, DC standby bus, Hot battery bus, Battery bus, Left

transfer bus, Right transfer bus, and Captain's flight instrument transfer bus.

Electrical

• What is the normal power source to the ground service bus?

• Right main AC bus.

Electrical

• With no power on the airplane but external power plugged in, can you get power to the

ground service bus?

• Yes. By turning on the ground service switch located on the flight attendant panel

at L1.

Electrical

• What does the OFF light indicate on the APU generator control switch?

• It indicates a fault, or the generator control switch is OFF.

Electrical

• What is the power source for the fuel crossfeed valves?

• Both on battery bus.

Electrical

• When EXT power is plugged in, how do you know its good quality?

• The AVAIL light is ON

Electrical

• Are the First officers instruments powered on HDG?

• No.

Electrical

• With loss of one generator in flight, do both utility busses trip off?

• Yes, and cannot be reset until that generator is back on line, or the APU is started.

Electrical

• TRUE/FALSE: If external power is connected to the AC tie bus when the APU

is started, the APU will automatically supply power to the tie bus and disconnect

the external power.

• False

Electrical

• TRUE/FALSE: When the AC transfer buses switch their power source to the HDG because of loss of power to both main AC buses, the left AC transfer bus contactor not only maintains power to

its bus but also applies power to the Captains flight instrument transfer bus.

• TRUE

Electrical

• Which bus powers the battery chargers for the main aircraft battery and the APU

battery?

• Ground Service Bus

Electrical

• When a generator crossties from one side of the AC system to the other side,

the_______ are shed?

• Utility buses

Electrical

• In addition to the battery chargers, the ground service bus also powers_______ and

the left main tank forward fuel pump

• One equipment cooling fan

Electrical

• TRUE/FALSE: None of the generators can operate in parallel with one another

• True

Electrical

• When normal power is on the aircraft, the Ground Service Bus is powered by.

• The right AC bus