Chapter 6: Electrical

Question 1

Describe the function of the GROUND SERVICE switch on the Forward F/A panel.

Answer 1

Provides manual control of ground service busses. Enables servicing of airplane using external power without activating AC transfer busses.
ON – connects external power to ground service bus.
OFF – disconnects external power from ground service bus.

Question 2

Explain the meaning of the blue GRD POWER AVAILABLE light.

Answer 2

Illuminated (blue)- Ground power is connected and meets airplane power quality standards.

Question 3

Explain the meaning of the blue APU GEN OFF BUS light.

Answer 3

Illuminated (blue)-APU is running and not powering a bus.

Question 4

Explain the meaning of the blue GEN OFF BUS light.

Answer 4

Illuminated (blue)-IDG is not supplying power to the related transfer bus.

Question 5

Recall where to read voltage, frequency and amps.

Answer 5

AC and DC Metering panel on the Forward Overhead panel.

Question 6

Explain the meaning of the amber DRIVE light.

Answer 6

Illuminated (amber)-Integrated Drive Generator (IDG) low oil pressure.

Question 7

Explain the meaning of the amber TRANSFER BUS OFF light.

Answer 7

Illuminated (amber)-
- Related Transfer Bus is not powered.
Extinguished-
-Related Transfer Bus is powered

Question 8

Explain the meaning of the amber SOURCE OFF light.

Answer 8

Illuminated (amber)-
No source has been manually selected to power the related transfer bus, or the manually selected source has been disconnected.

Note: SOURCE OFF light triggers ELEC light and Master Caution to alert crew of change to source of power to associated Transfer Bus.

Question 9

Explain the meaning of the amber BAT DISCHARGE light.

Answer 9

Illuminated (amber)-

With BAT switch ON, excessive battery discharge detected.

Question 10

Explain the meaning of the amber TR UNIT light.

Answer 10

Illuminated (amber) – TR failure.

Question 11

Explain the meaning of the amber ELEC light.

Answer 11

Illuminated (amber)-
fault exists in DC power system or standby power system.
Note: Operates only with airplane on ground.

Question 12

Explain the meaning of the amber STANDBY PWR OFF light.

Answer 12

Illuminated (amber)-One or more of the following busses are unpowered:

• AC standby bus.
• DC standby bus.
• Battery bus.

Question 13

Recall the number of minutes available on standby power with two fully
charged batteries.

Answer 13

-60 minutes.

Question 14

Recall the function of the Ground Power (GRD PWR) switch.

Answer 14

Three position switch, spring loaded to neutral
OFF – disconnects ground power from AC transfer busses.
ON – if momentarily moved to ON position and ground power is available:
-removes previously connected power from AC transfer busses.
-connects ground power to AC transfer busses when power quality is correct.

Question 15

Recall that it is not possible to use APU power and GRD power at the same time.

Answer 15

There are two basic principles of operation for the 737 electrical system:

• No paralleling of AC sources of power.
• The source of power being connected to a transfer bus automatically disconnects the existing source.

Question 16

Recall the function of positioning the APU Generator (GEN) Switches to ON.

Answer 16

Neither AC transfer bus powered by an IDG
Moving an APU GEN switch to ON:
- Powers both AC transfer busses from the APU generator.
- Disconnects external power, if connected.
-opposite SOURCE OFF light illuminates Until the APU GEN switch is moved ON.Both AC transfer busses powered by IDGs Moving an APU GEN switch to ON:
- - Powers the related AC transfer bus from the APU generator.
- Other AC transfer bus continues to receive power from the IDG.

Question 17

Recall the components powered by the ground service bus.

Answer 17

• Utility outlets.
• Cabin lighting.
• Battery chargers.

Question 18

Recall the location of the GROUND SERVICE Switch

Answer 18

The forward flight attendant control panel.

Question 19

Recall the function of the Generator (GEN) Switches

Answer 19

Three position switch spring-loaded to neutral
OFF – disconnects IDG from related AC transfer bus by opening generator circuit breaker.
ON – connects IDG to related AC transfer bus by disconnecting previous power source and closing generator circuit breaker.

Question 20

Recall the function of the BUS TRANSFER Switch.

Answer 20

AUTO (guarded position) – bus tie breakers operate automatically to maintain power to AC transfer busses from any operating generator or external power.
OFF – isolates AC transfer bus 1 from AC transfer bus 2.

Question 21

Recall the function of the Generator Drive Disconnect (DISCONNECT) Switches. (guarded)

Answer 21

Disconnects IDG if electrical power is available and engine start lever is in IDLE. IDG cannot be reconnected in the air.

Question 22

Explain the function of the BAT (battery) switch.

Answer 22

ON –

• Provides battery power.
• Provides automatic switching of standby electrical system to battery power with loss of normal power.

OFF –
-Removes battery power.