M15.13 Start and Ignition

Question 1

What is essential for starting a gas turbine engine?

Answer 1

Two separate systems:
* Compressor and turbine rotation
* Ignition of the air/fuel mixture

These systems must operate simultaneously during the starting cycle.

Question 2

What must occur before the ignition is turned on during engine starting?

Answer 2

The starter must accelerate the compressor sufficiently to establish airflow through the engine

This airflow is necessary to support combustion.

Question 3

What is the consequence of cutting off starter assistance below self-accelerating speed?

Answer 3

The engine may fail to accelerate to idle speed or decelerate

This could lead to a hot or hung false start.

Question 4

What is a cartridge starter?

Answer 4

A starter that uses high velocity gases from a burning cartridge to rotate the engine

It is an independent method of starting gas turbine engines.

Question 5

What initiates the burning of the cartridge in a cartridge starter?

Answer 5

An electrically fired detonator

This ignites the cartridge charge to generate gas for starting.

Question 6

What is the typical air supply pressure required for air starters?

Answer 6

Around 30–50 pounds per square inch (psi)

This pressure is necessary for a complete start.

Question 7

What controls the air supply to the starter in an air turbine starter?

Answer 7

An electrically operated control and pressure reducing valve

The valve opens when an engine start is selected.

Question 8

What happens when the starter reaches cutout speed?

Answer 8

The turbine switch opens, interrupting the electrical signal to the start valve

This closes the valve and shuts off the air supply to the starter.

Question 9

What are the typical maintenance tasks for air turbine starters?

Answer 9

Checking the oil level, inspecting the magnetic chip detector, and checking for leaks

Oil can be added through a port in the starter.

Question 10

What is the function of the pressure regulating and shutoff valve in the starter system?

Answer 10

To regulate air pressure and control the starter operation

It consists of a valve housing containing a butterfly-type valve.

Question 11

What are the two types of electric starting systems used on gas turbine engine aircraft?

Answer 11

1. Direct cranking electrical systems
2. Starter-generator systems

Each type has different operational characteristics.

Question 12

What is a starter-generator system?

Answer 12

A system that functions as both a starter and generator after the engine reaches self-sustaining speed

It contains additional windings for generator function.

Question 13

What is the typical voltage and current required for starting with a starter-generator?

Answer 13

A source of 24 volts and 1500 peak amperes

This is necessary for effective starting.

Question 14

What is the role of the undercurrent controller in a starter-generator?

Answer 14

To assure positive action of the starter and keep it operating until sufficient engine speed is achieved

It contains relays for controlling the starter input.

Question 15

Fill in the blank: The starter must continue to assist the engine until it reaches _______.

Answer 15

self-sustaining speed

This ensures the engine can sustain its own rotation.

Question 16

True or False: The air starter valve has a manual valve override for emergencies.

Answer 16

True

This allows for engine start even if the valve fails to open automatically.

Question 17

What is the function of the undercurrent controller in a starter-generator?

Answer 17

To assure positive action of the starter and keep it operating until the engine is rotating at a speed sufficient to sustain combustion.

Question 18

What components are controlled by the control block of the undercurrent controller?

Answer 18

• Motor relay
• Undercurrent relay

Question 19

What is the first step to start an engine equipped with an undercurrent relay?

Answer 19

Close the engine master switch.

Question 20

What relays close when the battery and start switch are turned on?

Answer 20

• Motor relay
• Ignition relay
• Battery cut-out relay

Question 21

Why is it necessary to open the battery circuit during starter operation?

Answer 21

To prevent the heavy drain of the starter motor from damaging the battery.

Question 22

What happens when the current draw of the motor decreases to less than 200 amps?

Answer 22

The undercurrent relay opens, breaking the circuit to the motor, ignition, and battery cut-out relays.

Question 23

What is a probable cause if the engine does not rotate during start attempt?

Answer 23

Low supply voltage to the starter.

Question 24

What should be checked if the power switch is suspected to be defective?

Answer 24

Check the switch for continuity.

Question 25

What is the function of the ignition system in turbine engines?

Answer 25

To ignite the fuel in the combustion chamber.

Question 26

When is continuous ignition used in turbine engines?

Answer 26

During take-off, landing, and abnormal situations like flying through hailstorms.

Question 27

What type of ignition system do most turbine engines use?

Answer 27

High-energy, capacitor-type ignition system.

Question 28

What is the primary function of the exciter box in the ignition system?

Answer 28

To supply high voltage to the igniter plugs.

Question 29

What is the purpose of the storage capacitor in the ignition system?

Answer 29

To store energy for ignition discharge.

Question 30

What is the maximum voltage the storage capacitor can charge to?

Answer 30

Approximately 4 joules.

Question 31

What distinguishes the igniter plug of a turbine engine from a conventional spark plug?

Answer 31

It must withstand a much higher energy current and has a larger electrode gap.

Question 32

What is the typical design of an igniter plug in a turbine engine?

Answer 32

Annular gap igniter plug or constrained gap plug.

Question 33

What should be done if there is no igniter spark when the system is turned ON?

Answer 33

Check the ignition relay and transformer unit.

Question 34

What is the recommended action after shutting down the ignition system before removing components?

Answer 34

Wait at least 20 minutes to allow residual charge to dissipate.

Question 35

What is a safety precaution when performing maintenance on the starting system?

Answer 35

Ensure relevant circuit breaker switches are open/off and tagged.

Question 36

What should be used when handling components of a turbine ignition system?

Answer 36

Insulated tools.

Question 37

What is the role of the transformer in the ignition system?

Answer 37

To step up the voltage for igniter spark generation.

Question 38

What indicates that the igniter is functioning correctly during a test?

Answer 38

Listening for a clicking noise as the engine begins to turn.

Question 39

What should be followed when working on engine ignition systems?

Answer 39

All manufacturer's instructions ## Footnote This is crucial for safety and to prevent accidents.

Question 40

What can be present in the ignition exciter that poses a risk?

Answer 40

Residual high voltage and current ## Footnote These can lead to injury or death if released.

Question 41

What is the most likely way for an accidental discharge to occur?

Answer 41

By touching the igniter ## Footnote This emphasizes the need for caution during maintenance.

Question 42

What is the standard procedure for igniter maintenance?

Answer 42

Disconnect the igniter lead coupling nuts at the exciter end first ## Footnote This helps ensure safety during maintenance.

Question 43

What type of tools must be used when working on ignition systems?

Answer 43

Insulated tools ## Footnote This reduces the risk of electric shock.

Question 44

What should not be touched with bare hands in ignition maintenance?

Answer 44

Coupling nuts or connectors ## Footnote This is to prevent accidental discharges.

Question 45

What is the voltage level in the engine ignition system?

Answer 45

Very high voltages ## Footnote This is a significant safety concern.

Question 46

What could happen if ignition units are touched without precautions?

Answer 46

Serious injury or death ## Footnote This underscores the importance of safety measures.

Question 47

What should be ensured before touching ignition units?

Answer 47

No electricity left in the ignition units ## Footnote This is crucial for safety.

Question 48

How long should one wait after opening circuit breakers before touching ignition units?

Answer 48

At least three minutes ## Footnote This allows any residual charge to dissipate.