2 - auxiliary power unit

Question 1

What is the primary and secondary function of the APU?

Answer 1

The primary is electrical the secondary is pneumatic.

The primary function of the APU is to operate the assessory gearbox Mounted 30 kVA generator. BAP use a secondary function is to supply bleed air for air conditioning and engine starting

Question 2

What is the maximum operating altitude of the APU?

Answer 2

36,000 feet PSA

Question 3

Does the APU vary it’s RPM

Answer 3

The APU is required to run at a constant 12,000 RPM to maintain a frequency of 400 Hz

Question 4

What controls and monitors all APU operations?

Answer 4

An automatic electronic control unit (ECU) Controls all of the APU operations.

Question 5

Is the APU ECU DC or AC powered?

Answer 5

The ECU is DC powered

Question 6

What is the maximum altitude to start the APU?

Answer 6

30,000 feet

Question 7

What is the maximum altitude to use APU bleed air?

Answer 7

15,000 feet

Question 8

What is the maximum altitude to start an engine with the APU?

Answer 8

13,000 feet

Question 9

Where is the APU air intake located?

Answer 9

The intake is located on the upper left rear side of the fuselage.

Question 10

How many positions does the APU intake door have?

Answer 10

It has three positions, open, mid, or closed.

Question 11

What factors determine the position of the APU intake door?

Answer 11

The position is determined by the ECU and is based on aircraft altitude and true airspeed.

Question 12

What is a limitation if the APU intake door is failed open or if the door position is unknown?

Answer 12

The airspeed is restricted to 300 knots or the APU must remain running then there will not be a restriction.

Question 13

How many feet is the APU exhaust danger area?

Answer 13

15 feet

Question 14

How was the APU lubricated?

Answer 14

The APU has a self-contained lubrication system. There is a gearbox mounted oil pump, oil cooler assembly, and an integral oil tank.

Question 15

Where does the APU normally receive fuel?

Answer 15

The APU receives fuel from both wing tanks.

Question 16

How is the APU shut down normally?

Answer 16

By pressing the APU START/STOP switch light there is a simulated overspeed signal generated to close the fuel solenoid SOV. This will stop the flow of fuel and the APU will shutdown.

Question 17

How many pounds per hour does the APU burn?

Answer 17

Approximately 120 pounds

With electrical and bleed air loading

Question 18

What does the green AVAIL in the APU START/STOP switch light indicate?

Answer 18

The light means that the APU is ready to accept bleed air loading. The slight will come on for seconds after the RPM is at 99% or more.

Question 19

Which battery is used for starting the APU?

Answer 19

Both the main and APU batteries are required to start and operate the APU. The APU battery is used to turn on the APU starter and the main battery is used to operate the APU ECU.

Question 20

What is the minimum battery voltage to start the APU?

Answer 20

22 V on both the main and APU battery.

Question 21

Can the APU be shutdown from outside the aircraft?

Answer 21

There is a remote cut off switch located at the external services panel in the aft equipment bay on the APU.