Electrical System

Question 1

What are the sources of electrical power?

Answer 1

Battery, 2 Generators, and the ground power unit.

Question 2

What are the two functions of the battery and/or the generator?

Answer 2

Start the engines, provide electrical power.

Question 3

What are the functions of the GCU?

Answer 3

voltage regulation, differential voltage, reverse current protection, paralleling, cross start current limiting, and over voltage protection.

Question 4

How many BUS BAR’s are there?

Answer 4

7, Battery, L Gen, R Gen, Center, Triple Fed, Dual Fed and ESIS Battery Bus.

There are 4 Mission Gear related buses too.

Question 5

What is the significance of the colored circles around each circuit breaker?

Answer 5

It designates which BUS is the source of power for that circuit.

Question 6

What is the significance of the white circle around individual switches?

Answer 6

Equipment with a WHITE CIRCLE around the control switch remains operable during dual generator failure and automatic load shed conditions.

Question 7

What are the recommended amperage requirements of an external power source?

Answer 7

The external power unit should be capable of producing

1000 amperes for 5 seconds,

500 amperes for 2 minutes and

300 amperes continuously.

Question 8

What does a flashing EXT PWR caution annunciator indicate?

Answer 8

Voltage is low or electrically disconnected

Question 9

What is the fail safe feature of the AVIONICS MASTER Circuit Breaker?

Answer 9

If the avionics buses become disconnected as a result of a control circuit fault, the AVIONICS MASTER circuit breaker can be pulled to restore power.

Question 10

At FL240 what is the maximum authorized generator load?

Answer 10

90%

Question 11

What is the CAUTION associated with the use of Ground Power for engine start?

Answer 11

Any current in excess of 1000 amperes may overtorque the drive shaft of the starter-generator or produce heat sufficient to shorten the life of the unit.

Question 12

What are the volts and amperage of each source of power?

Answer 12

Battery = 24VDC / 42 amps.

Generators = 28VDC / 400 amps (300 amps W-model).

GPU = 28VDC,
1000 amps for 5 seconds, 500 amps for 2 minutes
300 amps continuously.

Question 13

External Power Limitations

Answer 13

External power carts will be set to: 28.0 – 28.4 volts
and must be capable of generating 1000 amps momentarily, 500 amp for 2 min., and 300 amps continuously.

A maximum continuous load of 350 amperes will damage the external power relay and power cables of the airplane.

Note: Ensure the GPU provided no more than 1000 amps. Aircraft damage may occur from applying greater than 1000 amperes.

Question 14

Can the pilot takeoff with more than 10 amps on the battery charge?

Answer 14

The battery charge current should be 10 amps or less prior to takeoff

Takeoff with a battery charge current above 10 amps is permitted at the discretion of the pilot

Question 15

Starter Limitations

Answer 15

Starter, 30 seconds on – 
5 Min off, 
30 seconds on – 
5 Min off,  
30 seconds on – 
30 Min off.

Question 16

What does a flashing EXT PWR caution annunciator indicate?

Answer 16

Voltage is low or electrically disconnected

Question 17

Generator Load Limitations at altitudes?

Maximum sustained load surface to 21,000 = 
21,000 – 26,000 = 
26,000 – 30,000 = 
30,000 – 32,000 = 
32,000 – 35,000 = 

Single engine operation at all altitudes –

Answer 17

Maximum sustained load surface to 21,000 = 100%
21,000 – 26,000 = 90%
26,000 – 30,000 = 80%
30,000 – 32,000 = 75%
32,000 – 35,000 = 70%

Single engine operation at all altitudes – 90%