MIDTERM

Question 1

What should be done when removing a turbine engine igniter plug to prevent lethal shock?

Answer 1

The ignition switch is turned off and disconnected from the power supply circuit.

This is to ensure safety during maintenance.

Question 2

What is a primary safety concern when handling damaged hermetically sealed turbine engine igniter transformer units?

Answer 2

Compounds in the unit may become a fire or explosion hazard when exposed to the air.

Some units also contain radioactive material or toxic chemicals.

Question 3

Which malfunctions can allow igniters to operate when tested but be inoperative during a start attempt?

Answer 3

1 or 4.

This indicates potential issues in the igniter circuit.

Question 4

What is the primary advantage of pneumatic (air turbine) starters over electric starters for turbine engines?

Answer 4

High power-to-weight ratio.

This is coupled with a decreased fire hazard and reduction gearing not required.

Question 5

What happens if wire No. 8 is broken or disconnected after starter rotation is initiated?

Answer 5

The starter will shut down, but the igniters will continue to fire.

This indicates a fault in the starter system.

Question 6

How does the ignition system of a gas turbine engine differ from that of a reciprocating engine?

Answer 6

One igniter plug is used in each combustion chamber.

Magneto-to-engine timing is also not critical.

Question 7

What occurs when an external power source is connected to the aircraft?

Answer 7

Both battery power and external power are available to the bus.

The battery cannot be connected to the bus.

Question 8

How is airflow to the pneumatic starter controlled to prevent overspeed during engine start?

Answer 8

Stator nozzle design that chokes airflow and stabilizes turbine wheel speed.

This is essential for controlled engine start.

Question 9

Why do turbine engine ignition systems require high energy?

Answer 9

To ignite the fuel under conditions of high altitude and high temperatures.

Question 10

What is a safety feature usually employed in direct-cranking starters?

Answer 10

Drive shaft shear point.

This prevents the starter from reaching burst speed.

Question 11

What is the purpose of an under current relay in a starter-generator system?

Answer 11

Disconnect power from the starter-generator and ignition when sufficient engine speed is reached.

Question 12

Which components are included in a typical turbine engine ignition system?

Answer 12

• Two igniter plugs
• Two transformers
• One exciter unit
• Two intermediate ignition leads
• Two low-tension igniter leads
• Two high-tension igniter leads.

Question 13

When using an electric starter motor, when is current flow highest?

Answer 13

Is highest just before starter cutoff (at highest RPM).

Question 14

Which statement is correct regarding the ignition system of a turbine engine?

Answer 14

The system is normally de-energized as soon as the engine starts.

Question 15

Why should sharp bends be avoided in ignition leads?

Answer 15

Weak points may develop in the insulation through which high tension current can leak.

Question 16

What happens if the manual override is used for a pneumatic start valve?

Answer 16

The starter T-handle must be closed at scheduled starter drop out because the starter will overspeed at a given N^2.

Question 17

Why do turbine engine igniters have a long service life despite high intensity spark discharges?

Answer 17

They do not require continuous operation.

Question 18

How do turbine engine igniters compare to reciprocating engine spark plugs in terms of fouling susceptibility?

Answer 18

The high-intensity spark cleans the igniter.

Question 19

What allows the constrained-gap igniter plug to operate at a cooler temperature?

Answer 19

The construction is such that the spark occurs beyond the face of the combustion chamber liner.

Question 20

Where are high-voltage pulses formed in a turbine engine DC capacitor discharge ignition system?

Answer 20

At the triggering transformer.

Question 21

What type of airflow impingement systems are pneumatic starters usually designed with?

Answer 21

Radial inward flow turbine and axial-flow turbine.

Question 22

What is the purpose of the flow divider in a turbine engine duplex fuel nozzle?

Answer 22

Allows an alternate flow of fuel if the primary flow clogs or is restricted.

Question 23

Why is kerosene used as turbine engine fuel?

Answer 23

Kerosene has more heat energy per gallon and lubricates fuel system components.

Question 24

What primary conditions allow microorganisms to grow in aircraft fuel tanks?

Answer 24

The presence of water.

Question 25

What is the function of boost pumps in a fuel system?

Answer 25

Provide a positive flow of fuel to the engine pump.

Question 26

Where should the main fuel strainer be located in the aircraft fuel system?

Answer 26

At the lowest point in the fuel system.

Question 27

What is a characteristic of a centrifugal-type fuel boost pump?

Answer 27

It requires a relief valve.

Question 28

What is a principal advantage of the duplex fuel nozzle used in many turbine engines?

Answer 28

Provides better atomization and uniform flow pattern.

Question 29

What is NOT a true statement about a centrifugal-type fuel boost pump?

Answer 29

The centrifugal-type pump is classified as a positive displacement pump.

Question 30

What should be checked or changed when using an alternate fuel in a turbine engine?

Answer 30

Fuel specific gravity setting.

Question 31

How is the fuel control adjusted when trimming a turbine engine?

Answer 31

Set idle RPM and maximum speed or EPR.

Question 32

What is the effect of high atmospheric humidity on jet engine operation?

Answer 32

Has little or no effect.

Question 33

What is the position of the pressurization valve when the engine is shut down?

Answer 33

Pressurization valve closed, dump valve open.

Question 34

What factor is not used in the operation of a turbine engine fuel control unit?

Answer 34

Ambient humidity.

Question 35

What is the desirable slope for fuel lines in a turbine engine fuel system?

Answer 35

Gentle slope upward or downward without sharp curves.

Question 36

What is a characteristic of a centrifugal-type fuel boost pump?

Answer 36

It separates air and vapor from the fuel ## Footnote Additional features include having positive displacement and requiring a relief valve.

Question 37

What is the purpose of having fuel lines with a gentle slope?

Answer 37

To prevent vapor lock, prevent stagnation or 'pooling' of fuel, minimize the generation of static electricity ## Footnote Gentle slopes help decrease fluid friction in the lines.

Question 38

What is the purpose of the fuel transfer ejectors?

Answer 38

To assist in the transfer of fuel from the main tank to the boost pump sump ## Footnote They can also supply fuel under pressure to the engine-driven pump.

Question 39

Where is the engine fuel shutoff valve usually located?

Answer 39

Aft of the firewall ## Footnote It is also sometimes adjacent to the fuel pump or downstream of the engine-driven fuel pump.

Question 40

What causes the fuel divider valve to open in a turbine engine duplex fuel nozzle?

Answer 40

Fuel pressure ## Footnote It may also involve bleed air after the engine reaches idle RPM or an electrically operated solenoid.

Question 41

Where should the fuel line be located when physical separation from electrical wiring is impracticable?

Answer 41

Below the wiring and clamp the line securely to the airframe structure ## Footnote It can also be located inboard of the wiring and clamped both securely to the airframe structure.

Question 42

Why is it necessary to control acceleration and deceleration rates in turbine engines?

Answer 42

To prevent blowout or die-out, prevent overtemperature, prevent friction between turbine wheels and the case due to expansion and contraction

Question 43

What are fuel pump relief valves designed to compensate for?

Answer 43

Atmospheric pressure variations ## Footnote These are known as compensated-flow valves, pressurized-relief valves, or balanced-type relief valves.

Question 44

What are fuel crossfeed systems used for in aircraft?

Answer 44

To purge the fuel tanks, jettison fuel in an emergency, maintain aircraft stability

Question 45

Where does the fuel pump relief valve direct excess fuel?

Answer 45

Fuel tank return line ## Footnote It may also direct to the inlet side of the fuel pump or the inlet side of the fuel strainer.

Question 46

Engines using cold stream, or both cold and hot stream reversing include?

Answer 46

High bypass turbofans ## Footnote Turbojets and turbojets with afterburner may also be relevant.

Question 47

What is generally true regarding thrust reverser systems?

Answer 47

It is possible to move some aircraft backward on the ground using reverse thrust ## Footnote Engine thrust reversers on the same aircraft usually operate simultaneously.

Question 48

What is a common cause of exhaust system failures?

Answer 48

Thermal fatigue cracking in areas of stress concentration ## Footnote This condition is usually caused by drastic temperature changes at altitude.

Question 49

The hot section of a turbine engine is particularly susceptible to which kind of damage?

Answer 49

Cracking ## Footnote It may also experience galling and pitting.

Question 50

What is the purpose of cascade vanes in a thrust reversing system?

Answer 50

To turn the exhaust gases forward just after exiting the exhaust nozzle ## Footnote They help redirect fan and/or hot exhaust gases that have been blocked.

Question 51

What is the rearward thrust capability of an engine with the thrust reverser system deployed?

Answer 51

Equal to or less than its forward capability, depending on ambient conditions and system design ## Footnote It is less than its forward capability.

Question 52

What can operating thrust reversers at low ground speeds sometimes cause?

Answer 52

Sand or other foreign object ingestion, hot gas re-ingestion, compressor stalls ## Footnote Options include combinations of these issues.

Question 53

How are combustion liner walls cooled in a gas turbine engine?

Answer 53

By secondary air flowing through the combustion chamber ## Footnote This includes the pattern of holes and louvers cut in the diffuser section.

Question 54

What indicates that a combustion chamber of a jet engine is not operating properly?

Answer 54

Hot spots on the tail cone, warping of the exhaust duct liner ## Footnote Clam shells sticking in thrust reverse position is another indicator.

Question 55

On turbojet powered airplanes, thrust reversers are capable of producing between what percentage of rated thrust in the reverse direction?

Answer 55

35 and 75 percent of the rated thrust in the reverse direction ## Footnote This range can vary based on specific engine designs.

Question 56

Thrust reversers utilizing a pneumatic actuating system usually receive operating pressure from?

Answer 56

The engine bleed air system ## Footnote Other sources may include high pressure air reservoirs.

Question 57

What is the proper operating sequence when using thrust reversers to slow an aircraft after landing?

Answer 57

Advance thrust levers up to takeoff position as conditions require, select thrust reverse, de-select thrust reverser, retard thrust levers to ground idle ## Footnote Other sequences may involve different lever positions.

Question 58

Turbojet and turbofan thrust reverser systems are generally powered by?

Answer 58

Hydraulic pressure, pneumatic pressure, electricity ## Footnote Fuel pressure is also a potential power source.