Electrics

Question 1

If you disconnect an IDG in flight can it be reconnected?

Answer 1

• No requires maintenance action on the ground to reconnect

Question 2

Generator DRIVE light illuminates?

Answer 2

• Oil temp is high or:
• Oil press is low

Question 3

EXT PWR AVAIL light?

Answer 3

• External power is plugged in and power quality is acceptable

Question 4

ISLN light illuminates on the bus tie breaker?

Answer 4

• Fault has occurred automatically opening the AC bus tie breaker or:
• AC bus tie switch is OFF

Question 5

UTILITY BUS OFF light?

Answer 5

• Utility and galley buses are unpowered

Question 6

How can an IDG be disconnected from the buses?

Answer 6

• By pushing the GEN CONT switch to off or:
• By selecting EXT PWR prior to ENG shutdown

Question 7

What does the EICAS MSG L or R GEN DRIVE and the DRIVE light indicate and what should be done?

Answer 7

• High oil temp **or: **
• Low oil press
• The DRIVE can be disconnected but can not be deselected by flight crew

Question 8

Indication that EXT PWR is powering the main buses?

Answer 8

• ON light illuminates

Question 9

What is the source order for powering the LEFT and RIGHT main buses?

Answer 9

• Respective IDG
• APU GEN
• Opposite IDG

Question 10

How is the Battery bus powered?

Answer 10

• Main Battery: if no electrical power and BAT switch ON
• After establishing ELEC power: Left DC system, Main BAT provides a backup source of power

Question 11

During an Autoland what happens with the electrical system?

Answer 11

• Buses isolate to allow 3 independent sources to power three autopilots
• LEFT main system powers: left autopilot and captains flight instrument transfer bus
• RIGHT main system powers: Right A/P and FO’s flight instrument transfer bus
• BATERY/STANDBY system powers: Centre A/P

Question 12

Autoland ABV 200ft, loss of Generator results in?

Answer 12

• Both Tie breakers close
• Operating GEN powers L&R AC buses
• LEFT main AC system powers centre A/P
• NO LAND 3 appears on the Autoland status annunciator

Question 13

Below 200ft loss of a Generator results in?

Answer 13

• Both tie breakers remaining open
• A/P associated with a failed GEN is unpowered
• Flight instruments remain powered through the flight instrument transfer buses
• Auto-land continues using the remaining 2 A/P

Question 14

What gets shed first in Electrical load shedding

Answer 14

• Galleys then Utility buses

Question 15

AC Transfer buses?

Answer 15

• Left and right AC transfer busses power items considered necessary for ETOPS flights, which are not powered by the battery/standby system
• Transfer busses are normally powered by their associated main AC busses, but also can be powered by the Hydraulic Driven Generator when both AC busses are unpowered

Question 16

Examples of load shedding that may be observed during normal operations include:

Answer 16

• An electric hydraulic pump prior to engine start
• Center tank fuel pumps prior to engine start
• Utility busses during engine start

Question 17

Examples of load shedding that may be observed during non normal operations include?

Answer 17

• Utility busses after a generator failure
• Center tank fuel pump after an engine failure
• Cabin ceiling lights after an engine failure

Question 18

How does the system produce DC power?

Answer 18

• By TRU’s powered by the main AC buses

Question 19

The Battery/Standby Power System consists of the following busses:

Answer 19

• Hot battery bus
• Battery bus
• Standby AC bus
• Standby DC bus

Question 20

If all power is lost what powers the IRS and how long for?

Answer 20

• HDG Installed: standby power to the right IRS is limited to 5 minutes to save battery power
• HDG not installed: standby power to the LEFT and CENTER IRS is limited

Question 21

What does the Hydraulic Drive Generator do and when does it automatically activate?

Answer 21

• Activates automatically when both left & right AC buses are unpowered
• HDG is powered from the Center system and ADP runs automatically to ensure adequate pressure
• Provides AC power to:
  
  • AC transfer bus (L/R)
  • AC standby bus (through left AC transfer bus)
  • Captains flight instrument transfer bus
• Provides DC power to:
  
  • Hot battery bus
  • Battery Bus
  • Standby DC bus