APU

Question 1

What types of APUs do we have?

Answer 1

Turbomach/Sundstrand APU

Garret APU

Question 2

What does the APU do?

Answer 2

It provides pneumatic power for starting the engines and operating the Environmental Control System (ECS)

Question 3

What does the APU consist of?

Answer 3

It is a gas turbine engine with a power section, a reduction gearbox, appropriate controls, and accessories.

Question 4

Fuel consumption at rated power is ___.

Answer 4

150 lbs per hour

Question 5

Operations of the APU in flight (should/shall) be limited to ___.

Answer 5

Shall

essential operations only

Question 6

What are the acceptable in-flight uses of the APU?

Answer 6

• EPs
• Single-engine training
• practice autorotations
• powering the ECS during extreme temperature operations

Question 7

What are the APU system accessories?

Answer 7

• prime/boost pump
• hydraulic accumulator (with hand pump)
• hydraulic starter
• ac generator

Question 8

What does the prime boost pump do?

Answer 8

Used to prime the engine or APU fuel lines.

Also provides fuel under pressure to the APU during starting and operations at pressure altitudes above 8000 ft

Question 9

What does the hydraulic accumulator do?

Answer 9

provides the hydraulic pressure for driving the APU starter

Question 10

What is the minimum accumulator pressure required for starting the APU?

Answer 10

2650 psi

Question 11

With AC power available, the accumulator is charged by the ____.

Answer 11

backup hydraulic pump

Question 12

What is the APU controlled and monitored by?

Answer 12

Electronic Sequence Unit (ESU) or Digital Electronic Sequence Unit (DESU)

Will automatically shut down the APU if a start sequence fails or a monitored parameter is exceeded during operation (exception of APU OIL TEMP HI)

Question 13

The DESU for the Turbomach/Sundstrand APU has the added capability to control what?

Answer 13

APU overtemperatures by regulating the main fuel valve and start bypass valve

Question 14

What does APU FAIL mean?

Answer 14

APU has failed due to:

• High/Low Ng
• High/Low TGT
• Low Oil Pressure
• Start sequence failure

Question 15

Where is fuel supplied from for the APU?

Answer 15

The right fuel cell by the prime/boost pump

Question 16

When does the APU ACCUM LOW advisory appear?

Answer 16

when accumulator pressure drops below 2650 psi

Question 17

What happens when you place the APU GENERATOR switch to ON?

Answer 17

Makes electrical power available

Question 18

If APU does not start and the APU ACCUM LOW advisory light is not illuminated, how do you attempt a start?

What happens once you do this?

Answer 18

A start may be attempted by simultaneously moving the APU CONTR switch to ON and actuating the manual START/OVERRIDE lever located on the Accumulator Manifold.

APU accum pressure will be dumped to the starter to turn the compressor until the APU has reached a self-sustaining speed.

Question 19

If the backup pump is cycled ON then to the OFF or AUTO position, it will remain on for one cycle of __. (__ with winterization kit installed.)

Answer 19

90 seconds

180 seconds

Question 20

(From Ch. 3) What happens if you fill the Turbomach/Sundstrand APU to the full line?

Answer 20

It will cause the APU to overheat

Question 21

Why start APU on ground?

Answer 21

WARNING
APU does not incorporate compressor or turbine wheel containment device. Uncontained APU failure may result in injury to ground personnel and/or damage to flight critical components including tail rotor drive shaft