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Atlas B747 > Electrical System - Question Bank > Flashcards

Electrical System - Question Bank Flashcards

1
Q

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

A

Power quality is acceptable

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2
Q

What Bus is powered on the ground when APU GEN 1 or EXT PWR 1 is available?

A

Ground Handling Bus
+
Ground Service Bus (if Ground Service Switch “ON” L1 door)

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3
Q

When is the Main Deck Cargo Handling Bus powered?

A

-Ext Power 2 “AVAIL”
or
-APU Gen 2 “AVAIL”

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4
Q

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

A 
Ext Power 1 or APU Gen 1
(Ground Handling Bus) 
and 
Ext Power 2 or APU Gen 2 
(Main Deck Cargo Handling Bus)
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5
Q

When is Ground Service Bus powered?

A

Ext Power 1, APU Gen 1 or AC Bus 1

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6
Q

What is the function of the Standby Power Switch in the auto position?

A

Allows 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

FCOM Vol 1 - Supplementary Procedures

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8
Q

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

A
  • Bus Tie Breaker (BTB) open

- AC bus isolated from Sync Bus

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9
Q

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

A
  • Disconnects IDG from engine

- Opens related GCB

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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

Irreversible action that must be mechanically reconnected by MX on the ground.

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12
Q

What does a Generator DRIVE light indicate?

A
  • IDG oil px low
  • IDG temp high
  • GCB open due to uncontrollable gen frequency fault
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13
Q

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

A
  • FWD Main Fuel Pumps 2&3
  • FWD OVRD Pumps 2&3
  • CTR OVRD Pump L
  • Galley Equip
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14
Q

Describe the electrical load shedding process.

A
  • If electrical loads exceed power avail - the load management system sheds AC loads by priority until within limits.
  • Utility busses are shed one at a time by ELCUs.
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15
Q

What is the purpose of the electrical system overload protection?

A

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

Yes.

Through load shedding priority ELCUs will shed AC utility busses until power demands are within limits.

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17
Q

What are the main AC electrical power sources?

A
  • 2x Ext Pwr Sources
  • 2x APU Gens
  • 4x IDGs
18
Q

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

A

Divides the sync bus allowing each side of the AC electrical system to be powered by Aux (APU Gen) or External sources (Ext1 or Ext2)

19
Q

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

EXT PWR 1 - ON
EXT PWR 2 - ON

A

1- IDG powers it’s side of the sync bus when voltage and frequency are acceptable.

2- Previous Power source is disconnected from sync bus

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

1- IDG online after engine start
2- SSB closes
3- IDG powers entire sync bus when volt and freq are acceptable

21
Q

Which bus powers the Captain’s transfer bus and the main standby bus?

A

AC Bus 3

22
Q

Which bus powers the First Officer’s transfer bus?

A

AC Bus 2

23
Q

Which bus provides backup power for both transfer buses?

A

AC Bus 1

24
Q

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

A
  • Fuel pumps for APU start
  • Main Batt charger
  • APU Batt charger
25
Q

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

A

Ext Pwr 1
or
APU Gen 1

26
Q

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

A
  • Fueling System
  • Aux Hyd Pump 4
  • All Lower lobe doors, lights, and handling equipment
27
Q

What bus powers the APU standby bus?

A

1- AC Bus 3 through the Capt XFer Bus
or
2- APU STBY INV

28
Q

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

A

AC Busses 1,2 & 3 are isolated from the sync bus to provide independent power sources for the 3 autopilots

29
Q

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

A

Everything the CA needs to fly the aircraft

L PFD, L ND, EFIS control, STBY Ins lights, Upper Display, L CDU, L VOR, L RTP, L VHF, L FMC

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

Main STBY Inverter

32
Q

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

A
  • Main STBY Inverter (powered by the Main Battery through the Main Battery Bus and Main Hot Battery Bus)
  • Minimum 30 mins
33
Q

What are some of the equipment items on the main standby bus?

A

Everything the CA needs to fly the A/C except the APU STBY Bus components (L PFD, L ND, L FMC)

34
Q

What are the equipment items on the APU standby bus?

A
  • L PFD
  • L ND
  • L FMC
35
Q

How is DC power provided by the electrical system?

A
  • Four TRUs

- Battery Busses (APU and Main)

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

By its related hot battery bus

38
Q

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

A
  • Fuel valves (all engines)
  • All X-FEED valves
  • APU controller
  • TE Flap Control
39
Q

How is each hot battery bus normally powered?

A

Ground Service Bus through its related battery charger (acts as a TRU)

40
Q

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

A
  • APU fuel SOV
  • Spar valves (all engines)
  • Engine fire extinguishers
  • APU & lower cargo fire extinguishers
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
42
Q

What does the battery “ON” switch do?

A

Connects hot battery busses to the main battery busses

Atlas B747 (31 decks)

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