Electrical

Question 1

(ALL) Identify the location of the GROUND SERVICE bus switch

Answer 1

In the cabin on the forward flight attendant panel.

Question 2

(756) Recall the main AC power sources.

Answer 2

• The Left and Right Engine Integrated Drive Generators (Engines
  Operating)
• The APU Generator
• External Power

Question 3

(756) Recall when the hydraulic driven generator activates (HDG
equipped aircraft only).

Answer 3

The Hydraulic Driven Generator (HDG) activates automatically when both the Left and Right main AC busses are unpowered.
- The HDG is powered by the Left hydraulic system on the
757 if installed.
- The HDG is powered by the Center hydraulic system on the
767-300 and ER if installed.

Question 4

(ALL) List the components powered by the ground service bus.

Answer 4

 The main battery charger.
 The APU battery charger.
 Miscellaneous cabin and system loads.

Question 5

(756) Identify how the ground handling bus can be powered.

Answer 5

The ground handling bus can be powered only on the ground and
only from the APU generator or from the external power source
(AVAIL light illuminated)

Question 6

Identify what power sources are required to operate cargo doors

Answer 6

Note:
To accept late bags after pushback, the 757 must have APU power to operate the cargo doors.

To accept late bags after pushback, the 767 must have APU power to operate the right side cargo doors.

The manual bulk cargo door on the 767 can be used with no power requirements.

Question 7

(ALL) Explain the function of the battery (BAT) switch

Answer 7

BAT switch off (ON not visible)
 Turns battery power off.

BAT switch ON
 Turns battery power on.
 Allows the APU to be started
 A few annunciator lights illuminate

Powered airplane on the ground or in flight, and AC power is removed or lost:
 The battery bus and standby busses are powered.

Question 8

(756) Recall how long the battery will last on standby power

Answer 8

 30 minutes minimum powering standby AC and DC busses.

Note: The 757-300, the MAIN and APU batteries are paralleled for a
standby power operation of 90 minutes.

Question 9

(756) Recall how landing gear extension and flap operation are affected
if battery power is lost on a 767 without an operating HDG.

Answer 9

 The flaps and gear CANNOT be extended.

Note:
- The normal landing gear and flap extension methods require
Center hydraulic pressure. Pressure will not be available.
- The alternate landing gear and flap extension methods require
electrical power. Power will not be available.

Question 10

(756) Identify where to find the major systems NOT available when
operating on HDG power.

Answer 10

 The QRH identifies the major systems NOT available when operating on HDG power.

Question 11

(756) Recall the meaning of an illuminated L/R UTILITY BUS OFF light and the conditions that cause the utility busses to load shed.

Answer 11

 Illuminated (amber) – the utility and galley busses are
unpowered.

Utility Bus load shedding
 Both thrust levers advanced on the ground with a single power
source.
 Overload.
 Single generator operation in-flight.
 Starting engines with the APU providing electrical power

Question 12

(756) Recall that galley power can shed without illumination of the L / R
UTILITY BUS OFF lights. (Utility busses are still powered)

Answer 12

No indication

Question 13

(756) Recall what an EXT PWR AVAIL light indicates.

Answer 13

Illuminated (white) – external power is plugged in and the power quality is acceptable.

Question 14

(756) Recall what an EXT PWR ON light indicates.

Answer 14

External Power ON light

 Illuminated (white) – external power is powering the busses.

Question 15

(756) Recall what is indicated by an AC BUS OFF light.

Answer 15

Illuminated (amber) – the respective AC bus is unpowered.

Question 16

6 (756) Explain the meaning of a generator DRIVE light.

Answer 16

 Illuminated (amber) –

• The generator drive oil temperature is high
• The generator drive oil pressure is low.

Question 17

(756) Explain the meaning of an illuminated APU GEN (generator) OFF light on the overhead electrical panel. (Switch ON)

Answer 17

 The APU generator breaker is open because of a fault with the
APU running.
 The APU GEN switch is selected OFF.

Question 18

(756) Recall the meaning of a BAT discharge (DISCH) light.

Answer 18

Illuminated (amber) – the main battery is discharging.

Question 19

(756) Explain the meaning of an illuminated STBY POWER bus OFF
light.

Answer 19

Illuminated (amber) – standby AC and /or DC bus not powered.

Question 20

(756) Explain the operation of the STBY POWER selector.

Answer 20

 OFF – the standby busses are unpowered.
 AUTO – the standby busses transfer to battery power if normal
AC power is lost.
 BAT – the standby busses are powered from the main battery

Question 21

(756) Explain the function of the L/R GEN CONT (generator control)
switch.

Answer 21

 ON (bar in view) –
- Arms the generator control breaker to close automatically when
generator power is available.

 OFF (bar not visible):

• Opens the generator control breaker.
• Resets the fault trip circuitry.

Question 22

(756) Explain the function of the BUS TIE switches.

Answer 22

 Provides power to both the main AC and DC Busses

 Isolates faults

Question 23

(756) Recall the function of the FLT INSTR BUS PWR switch (767 ER only).

Answer 23

 Off (ALTN not visible) – allows the hydraulic driven generator to
power the Captain’s flight instruments
 ALTN – allows the hydraulic driven generator to power the First
Officer’s flight instruments