Powerplant

Question 1

The N2 section consists of a ___ stage axial flow compressor connected to a ___ stage high pressure turbine.

Answer 1

10 stage
2 stage

Question 2

FADEC stands for:

Answer 2

Full authority Digital Engine Control

Question 3

What is the maximum normal takeoff thrust rating for CRJ 900?

Answer 3

13,600

Question 4

Describe how the engine operates through the stages:

Answer 4

Suck, Squeeze, Bang, Blow

Question 5

What percentage of air is bypass and what percent is core air?

Answer 5

80% bypass, 20 % core (5:1 ratio)

Question 6

What is different about the first four stages of N2 compressor section?

Answer 6

VG system regulates inlet guide vanes and starter vanes for first four stages.

(SYS 22-3)

Question 7

Describe function and actuation of variable geometry system:

Answer 7

Uses high pressure fuel to actuate stator vanes guide vanes through mechanical linkages.

Maintains compressor aerodynamic performance and stall margin by changing path of air to simulate lowering AoA.

(SYS 22-3)

Question 8

How is the position of the variable geometry system controlled?

Answer 8

Programmed by FADEC.

Question 9

Describe the function of the operability valve:

Answer 9

Additional compressor airflow control. Extracts bleed air to offload compressor during engine starts and high aerodynamic load. Also relieves pressure during surges.

Question 10

How is the operability valve controlled?

Answer 10

FADEC uses high pressure fuel from the FMU (Fuel metering unit) to hydraulically activate it.

Question 11

What components are on the accessory gearbox?

Answer 11

3-2-1
3 Pumps:
1. Engine Lubrication
2. Engine Fuel
3. Hydrualic

2 Electric:
4. FADEC alternator
5. IDG

1 ATS:
6. Air Turbine Starter

Question 12

From which compressor stages do we receive bleed air and what is the purpose of the bleed air?

Answer 12

6th or 10th.

1. Air conditioning / pressurization
2. Engine Starting
3. Wing/cowl anti ice

Question 13

How many igniters are in the combustion section and what are their power sources?

Answer 13

2 Igniters:

Ignition A = AC ESS Bus
Ignition B = BATT Bus through Inverter

Question 14

How can Battery Bus be the power source of Ignition B when both igniters use AC power?

Answer 14

Static inverter converts DC to AC

Question 15

During a battery start, Ignition A is the active ignition. How will you be able to start the engine?

Answer 15

FADEC transfers to Ignition B after 15 seconds

Question 16

What happens when Continuous Ignition is selected? When is it required?

Answer 16

Both A and B Igniters are energized.

1. Contaminated RWYs
2. Moderate/Heavy Turbulence
3. Moderate/Heavy Rain
4. Vicinity of thunderstorms

Question 17

When will FADEC automatically engage continuous ignition?

Answer 17

1. Engine flame out
2. Turbulent airflow detected when close to a stall at high AoA

Question 18

Where is the probe located that gives us ITT information (Inter turbine temperature)?

Answer 18

Between high and low pressure turbines

Question 19

When will the FADEC receive power from its own alternator and when will it rely on aircraft electrical power?

Answer 19

N2 above 50% = FADEC Alt
N2 below 50% = Aircraft

Question 20

How many channels does the FADEC computer have? What happens if one channel fails?

Answer 20

2 Channels.

Status message for loss of redundancy shows up.

Question 21

When does the FADEC automatically switch channels during normal operations?

Answer 21

Every second engine start at 7% N2.

Both channels activate during overspeed to actuate the SOV in attempt to reduce RPM.

Question 22

When will FADEC command a shutdown of the engines?

Answer 22

1. Thrust lever placed at shutoff position
2. Overspeed
3. Hung or Hot start

Question 23

How are the thrust levers connected to the FMU (Fuel metering unit)

Answer 23

Wired electrically

Question 24

What would occur if the L or R FADEC failed completely?

Answer 24

Unsure what will happen since “brain” is lost

Question 25

What is APR and when would the FADEC command it?

Answer 25

Automatic Performance Reserve.

1. Max power detent
2. Mismatch of %15 N1 on takeoff, initial climb, or go around (Engine fail)

Question 26

When will engine operative system ARM making APR available in TOGA during takeoff?

Answer 26

Engines within 8% of scheduled takeoff thrust

Question 27

How is APR mode indicated?

Answer 27

Green “APR” on center of N1 circle

Question 28

Is APR available on go around?

Answer 28

Yes when gear down or flaps > 20

Question 29

Describe normal start sequence (CFM 3-55):

Answer 29

Engine start switchlight on and status message appears (Start timer). N2 increases with oil pressure and verify ITT below 120 C. 20% thrust lever moved to idle, fuel increases and L/R auto ignition advisory appears. Switchlight turns off and at 50% N2 Starter message disappears and auto ignition turns off. Verify max ITT is less than 815 C and stable engine indications.

Question 30

Would should you do if the starter doesn’t cut out automatically at 50% N2?

Answer 30

Press stop switchlight, starter air is cut off.

Question 31

You receive a HOT indication on ITT during start. What does this mean and what should you do?

Answer 31

ITT to high on startup. FADEC should automatically shut down engine. If it doesn’t bring throttle to shut off position.

Question 32

How would FADEC respond to a HOT or HUNG start?

Answer 32

Abort start.

Question 33

Describe FADEC auto relight function:

Answer 33

When flame out is detected it engages Igniters A and B automatically. Sprag clutch allows starting at N2 up to 45%.

Question 34

What thrust setting would you receive with thrust levers in the CLB detent when an engine fails?

Answer 34

APR

Question 35

What thrust setting would you receive with an engine loss in the CRZ range?

Answer 35

Proportional increase.