B777 Electrical

Boeing 777 Electrics

Boeing 777 Electrics

1 / 15

What does the green EXTERNAL POWER AVAIL light indicate?

External power is connected to the airplane, correct and ready to power the electrical busses.

Electrical power is available to the electrical busses but may not be correct.

External power is disconnected from the airplane.

External power is connected to all the airplane's electrical busses.

2 / 15

During autoland, the busses isolate to allow three independent sources to power the three autopilots.

True.

False.

The left IDG powers the left AC transfer bus, the left main DC bus, and the captain’s flight instrument bus The right IDG powers the battery bus and AC standby bus through the main battery charger The backup system powers the right AC transfer bus, the right DC bus, and the first officer’s flight instrument bus.

3 / 15

What is the primary source of power for the transfer busses?

Engine generators.

Ram Air Turbine.

Main DC busses.

Backup generators.

4 / 15

The standby inverter converts DC power to AC power. The inverter powers the AC standby bus if the right transfer bus is not powered.

False.

True.

The standby inverter converts DC power to AC power. The inverter powers the AC standby bus if the left transfer bus is not powered.

5 / 15

Which one of the following is not a reason for the backup electrical system to automatically power one or both transfer busses?

Power to one or both of the main AC busses is lost.

Approach (APP) mode is selected for autoland.

Only one main AC generator (includes APU) is available.

One engine shutdown.

6 / 15

Which one of the following is not true about the APU generator?

In flight, when both transfer busses are unpowered, the APU starts automatically, regardless of APU selector position.

The APU generator is electrically identical to the IDG generators.

If no other power source is available when the APU generator becomes available, the APU generator automatically connects to both main AC busses.

The APU generator cannot power both main busses at the same time.

7 / 15

Backup power is provided by one variable speed, variable frequency generator mounted on each engine. A frequency converter converts the generator frequency to a constant 400 Hz. Only one backup generator can power the converter at a time.

True.

False.

8 / 15

What is the correct source order for powering left and right main busses in flight?

Respective backup generator - APU generator - opposite backup generator.

Opposite IDG - APU generator - respective IDG.

APU generator - respective IDG - opposite IDG.

Respective IDG - APU generator - opposite IDG.

9 / 15

What is the primary source of DC power during normal flight?

DC generators.

Transformer rectifier units.

Main battery.

APU battery.

10 / 15

How many total AC sources of power does the B777 accommodate?

6

7

5

4

Seven (2 IDG, APU, PRI and SEC external power, 2 BUG).

11 / 15

Which items below are de-powered if you position the BATTERY switch to OFF during power down?

The APU battery and the hot battery bus.

The engine fire extinguisher bottles and APU fire extinguisher bottle.

The battery bus, Fırst Offıcer’s dısplay and the rıght AIMS.

The standby bus, Captain's displays and left AIMS.

12 / 15

Which bus powers the main battery charger and the APU battery charger?

Ground service bus.

Left main bus.

Right main bus.

Standby bus.

13 / 15

Will the IDG disconnect automatically for high temperature?

yes

no

14 / 15

You have a cold airplane (no power connected). Which items will be powered if you push the BATTERY switch ON?

Only the main battery bus will be powered.

The APU controller and the DC fuel pump will be powered.

The hot battery bus will be powered.

15 / 15

Which one of the following is not true about Electrical Load Management System (ELMS)?

When an additional power source becomes available or the loads decrease, ELMS restores power to shed systems in the same order of shedding(First shed system restored first).

Priority for shedding is galleys first, then utility busses. Utility busses are followed by individual equipment items powered by the main AC busses.

If the electrical loads exceed the power available (airplane or external), ELMS automatically sheds AC loads by priority until the loads are within the capacity of the airplane or ground power generators.

The ELMS provides load management and protection to ensure power is available to critical and essential equipment.

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