APU

Question 1

What kind of APU do we have and describe it?

Answer 1

What kind of APU do we have and describe it?

• Sundstrand APS 2300
• Single-stage impeller with 2 stage axial-flow turbine
• Independent oil system
• Independent AC Generator
• APU bleeds can run AirCon, Water pressurization, cabin pressurization (primarily on ground)

Question 2

What controls the APU?

What battery is used for APU Start?

Answer 2

What controls the APU?

Its dedicated dual channel FADEC

What battery is used for APU Start?

BATTs 1 (FADEC & EICAS) and 2 (APU Start Bus)
or
BATTs 1 and DC GPU

Question 3

What is the fuel source for the APU?

Answer 3

What is the fuel source for the APU?

1. Right fuel tank
2. X-feed (Low 2)

Question 4

What fuel pump is used to start the APU?

Answer 4

What fuel pump is used to start the APU?

1. If no engines on and AC power is avail then ACMP2
2. No AC power then DCMP
3. Right Eng ON then right Eng 2 primary ejector pump

Question 5

Will the APU shutdown automatically if speed and

acceleration rate isn’t reached in starting cycle time?

Answer 5

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

Yes

Question 6

How many different ways can fuel be supplied to the APU?

Answer 6

How many different ways can fuel be supplied to the APU?
• DC Fuel Pump (tank 2)
• AC Fuel Pump (tank 2)
• Tank 2 ejector pump
• Tank 1 ejector pump via X-Feed
• Tank 1 AC Fuel Pump via X-Feed

Question 7

When does the APU auto shutdown in flight?

Answer 7

When does the APU auto shutdown in flight?

1. Overspeed
2. Underspeed
3. FADEC Critical Fault

Question 8

When does the APU auto shutdown on the ground?

Answer 8

When does the APU auto shutdown on the ground?

1. Overspeed
2. Underspeed
3. FADEC Critical fault
4. High oil temp
5. Low oil pressure
6. Fire
7. Overheat
8. Sensor Failure

Question 9

What does selecting the OFF position on the APU selector

do?

Answer 9

What does selecting the OFF position on the APU selector
do?

1. removes pneumatics only (only electrics for 1 min)
2. Starts 1 min cooldown period

Question 10

When is electrical and pneumatics available from the APU

after APU start?

Answer 10

When is electrical and pneumatics available from the APU
after APU start?
95% plus 3 seconds

Question 11

Can APU shutdown be canceled?

Answer 11

Can APU shutdown be canceled?
Yes, moving the APU start switch back to ON before 1 min
cooldown period is over

Question 12

How can the APU be shutdown immediately?

Yes

Answer 12

How can the APU be shutdown immediately?
Yes
1. APU EMER STOP is pressed
2. BATTs are turned OFF during 1 min cooldown

Question 13

What will happen if batteries are turned OFF during the 1-minute cool down period?

Answer 13

What will happen if batteries are turned OFF during the 1-minute cool down period?
The APU will shut down immediately

Question 14

Can the APU be started after a critical fault?

Max start EGT for APU Start?

Max EGT for continuous operation?

Max Rotor Speed of the APU?

Max continuous and transient oil temps for the APU?

Answer 14

Can the APU be started after a critical fault?
No

Max start EGT for APU Start?
1032 ̊ C

Max EGT for continuous operation?
717 ̊ C is start of the Red; amber is permitted 662 ̊ - 717 ̊

Max Rotor Speed of the APU?
108%

Max continuous and transient oil temps for the APU?
155 ̊ C and 163 ̊ C (up to 15 mins)

Question 15

What are the electrical numbers associated with the APU AC

Generator?

Answer 15

What are the electrical numbers associated with the APU AC
Generator?
115 VAC, 400 Hz, 3-Phase, 40 KVA

Question 16

Which fuel pump provides fuel supply to APU during engine

start with AC GPU avail, unavail, and after engine start?

Answer 16

AC Avail for start = ACMP2
AC Unavail = DCMP
After Engine #2 Start = primary ejector in right integral tank

Question 17

Can you restart the APU after receiving a APU Fail EICAS

Message?

Answer 17

Can you restart the APU after receiving a APU Fail EICAS
Message?
No; automatic shutdown has occurred;

Question 18

APU Bleed Priority

Answer 18

APU Bleed Priority

1. A/C on Ground
2. GS below 50 kts for more than 30 secs after touchdown
3. Packs off AND A/I not ALL or Single-Engine Taxi
4. APU normal, APU bleed & x-bleed buttons pushed in (auto)

Question 19

What 3 things open or are energized when you move APU

Start Knob to ON?

Answer 19

What 3 things open or are energized when you move APU
Start Knob to ON?
1. APU FADEC is energized
2. APU EICAS messages are displayed
3. APU Fuel SOV opens

Question 20

What is closed when the APU Emer. Stop Button is pressed?

Answer 20

What is closed when the APU Emer. Stop Button is pressed?

1. Denergizes APU FADEC
2. Closed APU Fuel SOV
3. Overrides APU Master Switch

Question 21

What powers APU Start Sequence?

Answer 21

What powers APU Start Sequence?

Batt 1 FADEC, Batt 2 APU Start Bus which powers Electronic
Starter Controller –> Brushless Starter Generator (attached to
rotor shaft for APU Start, basically electronic version of Air
Turbine Starter)

Question 22

What provides the EICAS with APU temp information?

Answer 22

What provides the EICAS with APU temp information?

2 thermocouples located in the exhaust section of the APU that
are dangling in front of outgoing exhaust air