Engine, Prop and Associated Systems

Question 1

How much shaft horsepower does the Pratt+Whitney PT6A-68 free turbine turboprop engine produce at sea level?

Answer 1

1100 shaft horsepower.

Question 2

Where are the Interstage Turbine Temperature (ITT) probes located?

Answer 2

Between the compressor turbine and the power turbines.

Question 3

What does N1 represent?

Answer 3

The speed of the compressor.

Question 4

What does Np represent?

Answer 4

The speed of the propeller.

Question 5

Where is the Chip Detector located?

Answer 5

In the reduction gearbox.

Question 6

What speed does the propeller typically turn at?

Answer 6

2000RPM

Question 7

Describe the two ways that the throttle controls fuel flow to the engine.

Answer 7

A mechanical linkage directly from the throttle to the Fuel Management Unit, and an electrical unit to the FMU via the Power Managment Unit.

Question 8

What advantage does the PMU give to throttle response.

Answer 8

The PMU provides a more linear throttle response.

Question 9

How is the PMU powered?

Answer 9

By a Permanent Magnetic Alternator. If this fails, or Np is less than 40-50%, the PMU will revert to the Bat Bus for power.

Question 10

Describe the operation of the Engine Data Manager (EDM).

Answer 10

The EDM receives and processes information from the aircraft systems. It then sends this information to the two Integrated Avionics Computers. This IACs turns this information into graphics to display on the EICAS.

Question 11

How is the EDM powered?

Answer 11

Via the FWD Gen Bus. If that fails, it switches to the Fwd Bat Bus.

Question 12

What controls the propeller variable pitch?

Answer 12

The Propeller Interface Unit.

Question 13

Describe the operation of the PIU.

Answer 13

The PIU supplies the propeller with high pressure oil. This high pressure oil counters forces in the propeller generated by a spring and counterweight system. To make the propeller pitch finer, it adds more oil. To make pitch coarser, it reduces the amount of oil.

Question 14

Give the range of Np within which sustained operation on the ground is prohibited due to ground resonance.

Answer 14

62% to 80% Np.

Question 15

What is the absolute upper limit for Np?

Answer 15

110%

Question 16

For how long is it acceptable for Np to be between 100% and 110%?

Answer 16

20 seconds (transient).

Question 17

Above what value will Np turn red at when in the air?

Answer 17

102%

Question 18

Under what circumstances will Np display XXX?

Answer 18

When the EDM or IACs receive an invalid signal.

Question 19

If there is an oil leak or oil pressure loss, what should happen to the propeller pitch automatically?

Answer 19

It should feather (i.e. coarsen). Note that if the engine fails, the prop may not be able to feather fully or quickly enough on its own.

Question 20

Name the two mechanisms controlled with the PIU that can dump residual oil pressure, causing the prop to feather quickly and smoothly.

Answer 20

The Prop Servo Valve and the Feather Dump Solenoid.

Question 21

How are the Prop Servo Valve and Feather Dump Solenoid activated?

Answer 21

When the throttle is put in the Cut Off position.

Question 22

Which of the following requires an active PMU in order to dump residual oil pressure when the throttle is set to Off?
A) The Prop Servo Valve
B) The Feather Dump Solenoid
C) Both of the above
D) None of the above

Answer 22

A) The Prop Servo Valve

Question 23

List the reasons why you or the PMU may abort a start.

Answer 23

1) The ITT is likely to rise to above 1000 degrees C.
2) The ITT is likely to remain between 871 and 1000 degrees C for >5 seconds.
3) There is no ITT rise within 10 seconds of fuel flow starting.
4) The N1 rise is halted (hung start).
5) The BAT BUS caption illuminates.
6) The ST READY Caption goes out or the throttle is moved from the start position.
7) The Hyd pressure does not immediately jump into the green after start.
8) The oil pressure does not start rising after start.