1. B757 Review Questions

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

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

4. Electrical What are the three types of load shedding?
Engine start, overload, and generator loss load shedding.

5. The bus tie breakers must be in AUTO.
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.

6. Electrical What is the only way to have STBY bus power?
STBY power switch in either AUTO or BATT

7. What is the normal power for ground service bus?
Electrical
What is the normal power for ground service bus?
Right Main AC bus

8. Electrical What does the OFF light in a generator mean?
A fault or the switch is OFF

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

10. Electrical
With external power ON, BATT switch On and STBY power switch OFF, are the STBY busses powered?
No.

11. What bus is only powered on the ground?
Electrical
What bus is only powered on the ground?
Ground handling bus.

12. What does the bus tie system do in AUTO?
Electrical
What does the bus tie system do in AUTO?
It operates automatically to prevent paralleling and keep the main AC busses powered.

13. 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.

14. Electrical
If you have a left AC bus fault, how many autopilots will be available?
One, right autopilot.

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

16. 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.

17. Electrical How many electric generators are there on the airplane?
Four. 2 IDG’s, the APU, and the HDG

18. Is there a bus tie breaker system for DC power?
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.

19. 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.

20. No. Battery chargers are cutoff.
Electrical
With the STBY POWER switch in BAT position, is the battery being charged.
No. Battery chargers are cutoff.

21. Electrical
What bus is powered only on the ground by the APU or external power?
The ground handling bus.

22. Can external power be used simultaneously with the APU?
Electrical
Can external power be used simultaneously with the APU?
No.

23. Yes. External power has priority.
Electrical
Will the selection of external power trip off APU or engine driven generators?
Yes. External power has priority.

24. Electrical How is power provided to the DC busses?
From the respective AC busses through TR’s, transformer rectifiers.

25. What busses are powered by the HDG?
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.

26. What is the normal power source to the ground service bus?
Electrical
What is the normal power source to the ground service bus?
Right main AC bus.

27. 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.

28. Electrical
What does the OFF light indicate on the APU generator control switch?
It indicates a fault, or the generator control switch is OFF.

29. What is the power source for the fuel crossfeed valves?
Electrical
What is the power source for the fuel crossfeed valves?
Both on battery bus.

30. When EXT power is plugged in, how do you know its good quality?
Electrical
When EXT power is plugged in, how do you know its good quality?
The AVAIL light is ON

31. Are the First officers instruments powered on HDG?
Electrical
Are the First officers instruments powered on HDG?
No.

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

33. 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

34. 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

35. Electrical
Which bus powers the battery chargers for the main aircraft battery and the APU battery?
Ground Service Bus

36. Electrical
When a generator crossties from one side of the AC system to the other side, the_______ are shed?
Utility buses

37. One equipment cooling fan
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

38. Electrical
TRUE/FALSE: None of the generators can operate in parallel with one another
True

39. Electrical
When normal power is on the aircraft, the Ground Service Bus is powered by.
The right AC bus