APU

Question 1

What brand APU do we have?

Answer 1

Hamilton Sundstrand APS 2300

Question 2

What type of engine is the APU?

Answer 2

Single-stage gas turbine engine

Question 3

What is the purpose of the APU?

Answer 3

To provide pneumatic air pressure and AC power

Question 4

Which fuel tank is the APU normally supplied from?

Answer 4

Normally fed from the right wing tank

Question 5

How can the APU receive fuel in abnormal operations?

Answer 5

Fed from the left tank via the crossfeed valve (XFEED LOW 2)

Question 6

If there is a complete loss of AC power (electrical emergency), how will the APU operate?

Answer 6

The ejector pumps should provide fuel to the APU with the engines running. The DC fuel pump will supply fuel pressure from the right wing if the engines have failed.

Question 7

If the engines are not running, what will normally provide fuel to the APU?

Answer 7

The AC power will provide fuel via the AC fuel pump

Question 8

When does the APU’s FADEC shutdown the APU on the ground automatically?

Answer 8

Overspeed/underspeed, high oil temp/low oil pressure, overheat, fire, FADEC critical fault, sensor failure

Question 9

When does the APU’s FADEC shutdown the APU in flight automatically?

Answer 9

Overspeed/underspeed, FADEC critical fault

Question 10

How is normal APU start/shutdown controlled?

Answer 10

By the APU selector knob

Question 11

What happens when the APU selector knob is turned OFF?

Answer 11

Removes pneumatics only, placing the APU into a 1-minute cool down period before shutting it down (to cancel the shutdown, deselect ON within 1 minute)

Question 12

What is the APU EMER STOP button used for?

Answer 12

An abnormal shutdown without a 1-minute cool down period, closed both bleed air SOV and illuminates white

Question 13

After the APU is started, when are electric power and pneumatic pressure available?

Answer 13

Electrics and pneumatics will be available via system logic (usually around 95% plus 3 seconds)

Question 14

Describe the APU

Answer 14

Constant speed, single-stage impeller (impeller pump) with a 2-stage axial-flow turbine, with an independent oil system

Question 15

What controls the APU?

Answer 15

A dedicated FADEC

Question 16

What battery is used for the APU start?

Answer 16

BATT 1 powers the FADEC and EICAS for monitoring, BATT 2 powers the starter

Question 17

What fuel pump is used for APU start?

Answer 17

Batteries ON only DC fuel pump in right tank; AC powered airplane ACMP 2; Right engine running Ejector fuel pump

Question 18

Will the APU shutdown automatically if speed and acceleration rate isn’t reached in starting cycle time?

Answer 18

Yes. The limitation is 1min ON.

Question 19

Can the APU shutdown be cancelled?

Answer 19

Yes, by moving the START switch back to ON before the 1-minute cool down is over

Question 20

What will happen if batteries are turned OFF during the 1-minute cool-down period? (Pilot wants to leave the airplane early)

Answer 20

APU will shut down immediately

Question 21

Can the APU be started after a critical fault?

Answer 21

No

Question 22

When will automatic shutdown of the APU occur on the ground and in flight?

Answer 22

Ground - overspeed/underspeed, high oil temp/low oil pressure, overheat, fire, FADEC critical fault, sensor failure; In Flight - overspeed/underspeed, FADEC critical fault

Question 23

Normal operating range for APU?

Answer 23

100%

Question 24

What altitude is APU start limited to?

Answer 24

30,000’

Question 25

What altitude is APU operation limited to?

Answer 25

33,000’ which includes electrical generation

Question 26

What is the max altitude for APU-assisted engine start?

Answer 26

FL210

Question 27

What is the max altitude for APU to supply bleed air to the AMS?

Answer 27

15,000’

Question 28

Where is the air inlet for the APU?

Answer 28

The bottom of the tailcone with a mesh screen to minimize ingestion of FOD

Question 29

What are the mechanical components of the APU?

Answer 29

FADEC
Compresser impeller
2-stage axial turbine mounted on a rotor shaft
gearbox assembly driven by the engine rotor shaft reduces the engine rotor speed to drive the:
40KVA oil cooled AC generator
oil pump assembly

Question 30

Describe the APU start sequence

Answer 30

APU ON - powers APU FADEC and opens APU Fuel SOV
APU START - FADEC energizes the starter controller
APU speed 7%, FADEC commands fuel module to open and energize the exciter
50%RPM - ignition exciter and starter are de-energized
95%RPM +3sec - electric and pneumatic becomes available

Question 31

When are APU electirc and pneumatic power available after APU start?

Answer 31

95%RPM + 3sec

Question 32

Describe the APU normal shutdown sequence

Answer 32

APU OFF - pneumatic is immediately removed
If APU GEN is not the onlu source of AC power, then the APU GEN will be taken offline as soon as the switch is OFF
If the APU GEN is the only source of AC power, then the APU GEN will remain on the entire shutdown process
1min cooldown - then Fuel Module Closes
spooldown period
(APU SHUTTING DOWN dissapears at the end of spooldown period)