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Boeing 757 Technical > Electrical > Flashcards

Electrical Flashcards

1
Q

Does the IDG automatically take over the respective AC bus during start if on?

A

Yes

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2
Q

Does the IDG get automatically (electrically) disconnected from the bus when external power is put on prior to engine shutdown?

A

Yes

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3
Q

What does the generator DRIVE light and EICAS message mean? (2)

A

Either low oil pressure or high oil temperature detected in the IDG

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4
Q

What does DRIVE DISC switch do if pushed?

A

Disconnects the IDG from the engine

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5
Q

Once an IDG is disconnected can it be reconnected by the flight crew?

A

No

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6
Q

Can the APU be used in flight to replace an IDG as a power source?

A

Yes

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7
Q

Does external power have priority over APU power?

A

Yes

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8
Q

What does APU GEN OFF mean on EICAS (APU running)? (2)

A

APU generator control breaker is open because of a fault or the APU GEN switch is selected off

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9
Q

Can External power, APU, or single IDG power both main AC buses?

A

Yes

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10
Q

What side buses do the left and right IDGs supply power to?

A 
Left = Left
Right = Right
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11
Q

What do the BUS TIE switches control and why?

A

They control the bus tie breakers to isolate or parallel the main buses

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12
Q

What do BUS TIE switches do when set to AUTO?

A

Bus Tie system operates automatically to maintain power to both main buses

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13
Q

What does AC bus ISLN light mean? (2)

A

Bus tie breaker is open because of a fault or the BUS TIE switch is off

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14
Q

What is indicated if a AC bus is off? (2)

A

EICAS message L or R AC BUS OFF and applicable BUS OFF light

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15
Q

What is the order for powering the left and right main AC buses? (no external power)

A
  1. Respective IDG
  2. APU
  3. Other IDG
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16
Q

How many utility buses?

A

2 - Left and Right

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17
Q

Where do the left and right galley buses get their power from?

A

Left and right utility buses

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18
Q

Main and alternate sources of power for the Ground Service Bus?

A 
Main = Right main AC bus
Alternate = APU or Ext power
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19
Q

What does the Ground Service Bus power? (3)

A
  1. Main Battery Charger
  2. APU Battery Charger
  3. Miscellaneous cabin and system loads
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20
Q

How/when is the Ground Handling Bus powered?

A

Only powered on the ground and only from APU gen or external power

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21
Q

What powers each autopilot and instrument transfer buses during autoland (bus isolation)?

A
  1. Left main AC for left A/P and Capt’s INST XFR BUS
  2. Right main AC for right A/P and Copilots INST XFR BUS
  3. Battery/standby system for centre A/P
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22
Q

What happens to electrical system above 200ft with a loss of a generator? (3)

A
  1. Both bus tie breakers close and operating generator powers both main buses
  2. Left main system powers the centre autopilot
  3. No LAND 3 appears
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23
Q

Below 200ft what happens to the electrical system with a loss of a generator? (4)

A
  1. Both bus tie breakers remain open
  2. Autopilot associated with the failed generator remains unpowered
  3. The flight instruments remain powered through the FLT INST XFR buses
  4. The autoland continues using the remaining two autopilots
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24
Q

During an autoland when does the electrical system revert back to normal, non-isolated?

A

When autopilot is disconnected or a G/A is initiated

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25
Q

When the bus tie breakers are in AUTO what happens to the pilots instruments when there is a loss to their respective main AC bus?

A

Transfers to opposite main AC bus through the INST XFR BUS

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26
Q

If both main AC buses are lost how are the Captain’s flight instruments powered?

A

Through the Hydraulic Motor Generator (HMG)

27
Q

What is electrical load shedding?

A

Occurs automatically to ensure power is available to critical and essential equipment once electrical load exceeds power available

28
Q

Which buses load shed first?

A

Galley buses then utility buses

29
Q

Examples of normal operations load shedding?

A

An electric hydraulic pump, centre tank fuel pump, or utility buses prior to start

30
Q

Examples of load shedding during non-normal operation?

A

Utility buses after a generator failure, centre tank fuel pump or cabin ceiling lights after an engine failure

31
Q

What inadvertent action on the ground may cause the Utility Buses to trip?

A

Moving the throttles take off range with engines shutdown. To recover, move throttles to idle and cycle the utility bus switches

32
Q

Three main sources of AC power?

A
  1. Left and right Integrated Drive Generators (IDGs)
  2. APU
  3. External AC power
33
Q

How do the Main DC buses get their power?

A

From their respective main AC buses through individual TRUs

34
Q

How does the TRU isolation system work?

A

Both TRUs work in isolation and if the bus tie switch is set to auto if one TRU fails the bus tie switch closes so the other TRU powers the DC bus.

35
Q

Do both BUS TIE switches need to be in AUTO for the DC bus tie breaker to close?

A

Yes

36
Q

Are there any flight deck controls for the main DC electrical system?

A

No

37
Q

What are the four buses of the Battery/Standby power system?

A
  1. Hot Battery Bus
  2. Battery Bus
  3. Standby DC Bus
  4. Standby AC Bus
38
Q

What powers the hot battery bus before, and the after electrical power is established?

A

Main battery then the main battery charger once electrical power is established

39
Q

What powers the battery bus before, and then after electrical power is established?

A

The main battery powers the battery bus then after electrical power is established the left DC system

40
Q

What provides electrical power backup to the battery bus once normal power is established?

A

Main battery

41
Q

What does the battery DISCH light mean?

A

The main battery is discharging

42
Q

What does the battery OFF light and BATTERY OFF on EICAS mean?

A

Battery switch is off after electrical power has been established

43
Q

What can power the standby buses? (Off/Auto/BATT)

A
  1. Off - The standby busses are unpowered
  2. Auto - the standby busses transfer to battery power if normal power is lost
  3. Batt - the standby busses are powered from the battery
44
Q

What powers the standby AC bus normally and without normal AC power?

A

Normally powered by the left AC system

When no left AC system or when switch is in BAT then it is powered by the main battery through the standby inverter

45
Q

When does the HMG activate?

A

Automatically when both the left and right main AC busses are unpowered

46
Q

Which hydraulic system powers the HMG?

A

Left

47
Q

What electrical systems does the HMG provide AC power to? (4)

A
  1. Left AC transfer bus
  2. Right AC transfer bus
  3. Standby AC bus (through the left AC transfer bus)
  4. Captain’s flight instrument transfer bus
48
Q

What DC electrical systems does the HMG provide power to? (3)

A
  1. Hot battery bus
  2. Battery Bus
  3. Standby DC bus
49
Q

Does the HMG produce more or less DC power than a fully charged battery?

A

Less

50
Q

Why can the Batt DISC light come on during HMG operation?

A

Because the HMG can produce less power than a fully charged battery so it can drain the battery for a period of time before the battery level gets as low as the HMG

51
Q

What are the three circuits that the bus tie switches affect?

A
  1. Auto AC bus tie circuits
  2. Auto DC bus tie circuits
  3. Auto flight instrument transfer bus circuits
52
Q

Rating of the electrical generators?

A

90Kva

53
Q

What systems powered by the Hot Battery Bus?

A 
RAFFIP
R-Rat Manual Deploy
A-APU Fuel Valve
F-Fueling System
F-Fire Protection (Bottles)
I-IRS Emerg Power
P-Parking Brake Valve
54
Q

What is powered from the Battery Bus?

A 
FDRGAS
F-Fire Detection (Eng, APU, Cargo)
D-DC Fuel Pump
R-Rat Auto Deployment
G-Gear Alt Ext
A-Alt Stab Trim
S-Standby Engine Indications
55
Q

What are the power source priorities for the left and right buses? (3)

A
  1. Engine IDG
  2. APU
  3. Other engine’s IDG
56
Q

Does any one generator have sufficient capacity to supply all flight loads?

A

Yes

57
Q

3 things main battery also powers?

A
  1. Standby power system
  2. Passenger address and interphone system
  3. Fuel Quantity system
58
Q

What powers the battery charger? (Bus and power source)

A

Ground service bus - normally powered by right main bus but also either Ext Pwr or APU

59
Q

When is ground handling bus powered? (2 sources - which has priority?)

A
  1. APU

2. Ext Power (priority)

60
Q

What does the ground handling bus power? (4)

A
  1. Cargo comp systems
  2. Cargo comp lights
  3. Main access lights
  4. Fueling systems
61
Q

What does the ground service bus power?

A

Cabin lights and outlets,
Main and APU battery chargers
Left fwd fuel pump
Miscellaneous cabin loads

62
Q

With no main power or HMG how long does battery last powering standby buses?

A

30min

63
Q

Do both bus tie switches need to be in auto for the DC transfer bus tie to work?

A

Yes, both must be

64
Q

What powered off APU Battery? (3)

A

APU door
Starter
APU ctl circuits

Boeing 757 Technical (16 decks)

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