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Atlas Air B747 April 2022 > Electrical System *** > Flashcards

Electrical System *** Flashcards

1
Q

What does the “AVAIL” light indicate on the External and APU PWR switches?

A

• The related power source (APU or EXT) is plugged in and the power quality is acceptable and available.

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2
Q

What bus is powered on the ground when the APU generator 1 or external power 1 is available?

A

• Ground handling bus

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3
Q

When is the main deck cargo handling bus powered?

A

• When the “AVAIL” light is displayed on the APU 2 or EXT 2 switches.

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4
Q

What electrical power source would you select if ground handling is required?

A

• The number one auxiliary or external power

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5
Q

When is the ground service bus powered?

A

• When A/C bus 1 is powered, either on the ground or in flightWhen the Ground Service Switch is on and Ext or APU power is Avail

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6
Q

What is the function of the Standby Power Switch in the Auto Position?

A

• Allows the main and APU standby busses to be powered from available sources.

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7
Q

Where would you find the Electrical Power-up procedure?

A

Note:Refer to the FCOM, Vol. 1, Supplemental Procedures

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8
Q

What does a Bus Isolation (ISLN) light illuminated indicate?

A
  • BTB open

* AC bus isolated from synchronous bus

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9
Q

What happens when you push a Generator Drive Disconnect (DRIVE DISC) switch?

A
  • Disconnects IDG from engine when above idle speed

* Open related Generator Control Breaker

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10
Q

What condition would automatically disconnect the IDG if not manually disconnected by the flight crew?

A

• Excessively high drive oil temperature

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11
Q

How do you reconnect an IDG that has been disconnected?

A
  • Maintenance action is required

* The IDG cannot be restored by flight crew action

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12
Q

What does a Generator DRIVE light indicate?

A
  • IDG oil pressure low, or
  • IDG oil temperature high, or
  • GCB open due to uncorrectable generator frequency fault
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13
Q

What are some of the equipment items powered by the Utility busses?

A
  • APU T/R
  • Forward main pumps 2 and 3
  • Forward override/jettison pumps 2 and 3
  • Center override/jettison pump
  • Galley equipment (freighter)
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14
Q

Describe the electrical load shedding process.

A

• Utility bus loads are shed one at a time through the electrical load control unit (ELCUs) in a programmed sequence until the overload condition is relieved.

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15
Q

What is the purpose of the electrical system overload protection?

A

• To ensure power is available to critical and essential equipment.

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16
Q

During load shedding, would you expect to see an EICAS Advisory message ELEC UTIL BUS L, R?

A

• No, this message is inhibited during load shedding

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17
Q

What are the main AC electrical power sources?

A
  • Four IDGs
  • Two auxiliary power sources (APU generators)
  • Two external power sources
18
Q

Describe the function of the Split System Breaker (SSB).

A

• Divides the synchronous bus, allowing each side of the AC electrical system to be powered by separate auxiliary or external power sources.

19
Q

Describe the electrical system sequence of events during engine start with the SSB open.

A
  • The IDG powers its side of the synchronous bus when voltage and frequency are acceptable.
  • The previous power source is disconnected.
20
Q

Describe the electrical system sequence of events with a single power source powering the synchronous bus, when an engine is starting, SSB closed.

A
  • The IDG powers the entire synchronous bus when voltage and frequency are acceptable.
  • The SSB remains closed and the original power source is disconnected
21
Q

Which bus powers the Captain’s transfer bus?

A
  • AC bus 3

* If AC bus 3 is unpowered, AC bus 1 powers the Captain’s Transfer bus

22
Q

Which bus powers the First Officer’s transfer bus?

A
  • AC bus 2

* If AC bus 2 is unpowered, AC bus 1 powers the First Officers transfer bus.

23
Q

Which bus provides backup power for both transfer busses captain and FO transfer ?

A

1 is all you need

• AC bus 1

24
Q

What are some of the equipment items powered by the ground service bus?

A
  • Main and APU battery chargers
  • Fuel pumps for APU start
  • Flight deck flood, navigation, and service lights
  • Miscellaneous service outlets a
25
Q

How can the ground service bus be powered when AC bus 1 is not powered, while on the ground?

A

• 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.

26
Q

What are some of the equipment items powered by the ground handling bus?

A
  • Lower cargo doors , handling equipment and compartment lights
  • Fueling system
  • Auxiliary hydraulic pump 4
27
Q

What bus powers the APU standby bus?

A

• The Captain’s transfer bus

28
Q

How is the electrical system configured during an automatic ILS approach(auto-land)?

A
  • AC and DC busses 1,2, and 3 are isolated from the sync bus

* AC bus 4 continues to power the synchronous bus

29
Q

What are some of the major COMPONENTS of the AC standby power system?

A
  • Main and APU standby busses
  • Main and APU batteries
  • Main and APU standby inverters

• Standby Power selector

30
Q

What is the normal source of power for the main standby bus?

A

• AC bus 3

31
Q

How does the main STANDBY bus get power if AC bus 3 becomes unpowered in flight, all other conditions normal?

A

The Main Stby bus get power started from Main hot battery ( powered by battery than the main battery is normally powered by AC bus 1 through the ground service bus.) and through the Main stby TRU (INVR) power the main stby bus

32
Q

If both AC bus 3 and AC bus 1 are not powered, all other conditions are normal, how is the main STANDBY bus powered, and for how long can it be powered?

A

• 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).

33
Q

What are some of the equipment items on the MAIN STANDBY bus?

A
  • EFIS Control
  • L EIU, CDU, ILS, VOR, ADC, Xponder,
  • Primary EICAS, RMI, STBY Instrument Lights
  • STBY Ignition for all Engines
  • Various Flight Control Components
34
Q

What are the equipment items on the APU standby bus?

A
  • Left FMC
  • Left ND
  • Left PFD
35
Q

How is DC power provided by the electrical system?

A
  • Four transformer-rectifier units (TRUs) produce DC power, each TRU powered by its related AC bus.
  • Four DC busses are connected through DC isolation relays to the DC tie bus.
  • Battery busses distribute DC power in addition to the four main DC busses
36
Q

What is the normal power source for the main and APU battery busses?

A

• DC bus 3

37
Q

If either AC bus 3 or DC bus 3 is unpowered, how is each battery bus powered?

A

• Its related hot battery bus

38
Q

What are some examples of individual equipment items on the main battery bus?

A
  • APU Controller (alternate),
  • IDG Disconnect
  • Trailing-Edge Flap Control
  • Dome, Storm, & selected Interior Lights
  • Fuel Valves (all Engines),
  • All Crossfeed Valves
  • Manual Pressurization Controller,
  • CA’s Interphone,
  • Left Radio Tuning Panel,
  • Left VHF
39
Q

How is each hot battery bus normally powered?

A
  • The ground service bus
  • Through its related battery charger
  • Each battery is connected directly to its related hot battery bus
40
Q

What are some examples of equipment items on the main hot battery bus?

A
  • APU Fuel SOV,
  • APU & Lwr Cargo Fire Extinguishers
  • Spar Valves (All Engs)
  • Engine Fire Extinguishers (All Engs),
  • Fire Sw Unlock (All Engs)
41
Q

What are some examples of equipment items on the APU hot battery bus?

A
  • IRU L, C, R DC Power
  • L & R Outflow Valves
  • APU Inlet Door
  • APU Controller (primary)
42
Q

Where is the only place you can see DC power

A

Only on status secondary EICAS with batteries charging or discharging voltage

Atlas Air B747 April 2022 (41 decks)

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