Systems - Electrical

Question 1

What is APU’s primary purpose?

Answer 1

Supply electrical. Secondary is pneumatics.

Question 2

What do you see on APU start?

Answer 2

Door Open
APU in bite
APU gauges
APU SOV open
(DIGS)

Question 3

What is the function of the APU ECU (engine control unit)?

Answer 3

Generates overspeed signal to cause fuel solenoid SOV to close

Question 4

Difference in AC and DC electrics

Answer 4

AC - primary
DC - generated off AC

Question 5

What is function of TRUs?

Answer 5

Converts AC to DC. 4 located in nose.

Question 6

What does DC Service Switch do?

Answer 6

Connects DC service bus to APU battery direct bus

Question 7

What are the “hot busses” (always powered by battery)?

Answer 7

APU Battery Bus
Main Battery Bus
DC Emer Bus

Question 8

What will occur if DC Service Switch is left in the ON position?

Answer 8

Discharge APU battery :(

Question 9

When will the DC Emer bus appear?

Answer 9

Only if it loses 1 of its 2 sources of power (APU and Batt Bus) or a fault on bus itself

Question 10

What bus offers fire protection?

Answer 10

DC Emer Bus

Question 11

What does Battery Master switch connect?

Answer 11

Connects to APU Bat Direct Bus and Main Bat Direct Bus

Question 12

What are the 2 batteries used for?

Answer 12

(APU battery and Main battery)
Provides DC power for starting APU and in the event of power loss in flight, provides emergency DC power

Question 13

What are IDGs and where are they located?

Answer 13

Integrated Engine Driven Generator and on accessory gearbox

Question 14

When do you see IDG disconnect light?

Answer 14

If oil temp is too high or oil pressure is too low - get caution message
(HOTLOP)

Question 15

What is AC Ess Bus normally powered by?

Answer 15

AC BUS 1

If AC BUS 1 fails, auto switch to BUS 2 (“AC Ess Xfer”)

Question 16

When will the GCUs trip offline?

Answer 16

Overloaded (KVA too high), over/under voltage, over/under frequency.
If overloaded bus trips gen, it won’t feed same bus to other gens.

Question 17

Anytime the main tie closes, what is shed?

Answer 17

Utility bus (lightbulbs)

Question 18

When will ADG deploy?

Answer 18

Loss of power to AC BUS 1 and 2

Question 19

What do we gain when ADG deploys?

Answer 19

Essential BUS, Hydraulic pump 3B regardless of switch position, slats and flaps operate at 1/2 speed, stab channel 2

Question 20

Even if ADG auto deploys, why must I pull handle?

Answer 20

ADG handle is the DC handle. It closes the tie so won’t lose DC ESS BUS when WOW or <135 kts

Question 21

What occurs if ADG fails?

Answer 21

Have ~30 mins on DC power only. Each APU start attempt takes ~6 mins of power.

Question 22

What 2 parts do the IDGs consist of?

Answer 22

Constant speed drive, and generator

Question 23

What do the DCPCs do? (DC power centers)

Answer 23

Automatically control DC ties

Question 24

ADG powers __

Answer 24

Hyd 3 B
AC ESS BUS
Flaps/Slats 1/2 speed
ADG BUS
Stab trim Ch 2

Question 25

DC Emer BUS powers __

Answer 25

Engine fire extinguishers
APU fire extinguishers
Fuel SOVs
Hydraulic SOVs

Question 26

What is DC Emer BUS powered by?

Answer 26

APU BAT Direct BUS and DC BAT BUS

Question 27

When is the DC BATT BUS displayed on synoptic?

Answer 27

When power is lost from 1 or both busses

Question 28

Amps and volts of APU BATT

Answer 28

24 volt, 43 amp hr

Question 29

Amp and volts of Main BATT

Answer 29

24 volt, 17 amp hr

Question 30

When will ADG auto deploy?

Answer 30

AC BUS 1 and 2 are unpowered
No WOW
Generator was last power source online

Question 31

Battery Master is used to connect APU and Main Batter Direct busses (APU BATT DIR BUS and MAIN BATT DIR BUS) to the

Answer 31

Battery Bus

Question 32

Why would the Auto Transfer switch be selected thus inhibiting the auto transfer feature of the IDGs?

Answer 32

To prevent a good gen from attempting to power a bad bus

Question 33

AC Essential Bus is normally powered by:

Answer 33

AC Bus 1

Question 34

With all other sources of electricity not working (both IDGs, APU gen, and ADG), you have how long of DC emergency power from the batteries?

Answer 34

30 minutes