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Quiz: 6 Questions To See How Much You Know About Turbofan Engine Start Sequences

Thanks to Republic Airways for making this story possible. Check out the full series here. And if you want to fly an E175, check out Republic Airways.
Live from the Flight Deck

It's not as simple as a quick crank of the engine to get a turbine started...


  1. 1) The first step in starting a jet engine is using a bleed source to turn an air turbine starter, which rotates the N2 shaft. Where can this bleed source come from?

    Bleed sources normally come from the APU, however, in the event the APU is inoperative, you can start the rotation of the N2 shaft using a "Huffer" or high-pressure cart and/or crossbleed from another engine.

    Bleed sources normally come from the APU, however, in the event the APU is inoperative, you can start the rotation of the N2 shaft using a "Huffer" or high-pressure cart and/or crossbleed from another engine.

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  2. 2) Bleed air is ducted to the air turbine starter, which in turn rotates the N2 shaft. Where is the air turbine starter located?

    It's attached to the accessory gearbox.

    It's attached to the accessory gearbox.

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  3. 3) When and where is fuel normally introduced during start?

    Fuel is introduced in the combustion section and is normally introduced when N2 reaches about 20%.

    Fuel is introduced in the combustion section and is normally introduced when N2 reaches about 20%.

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  4. 4) When does the starter cut-out?

    Starter cut-out occurs when the engine has reached a point at which it is self-sustaining and no longer requires the assistance of the air turbine starter. This usually occurs at 50% N2.

    Starter cut-out occurs when the engine has reached a point at which it is self-sustaining and no longer requires the assistance of the air turbine starter. This usually occurs at 50% N2.

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  5. 5) You are monitoring the engine during its start sequence and you notice that the engine isn't accelerating as it should. What is this called and what should be done?

    This is called a hung start and is indicated by a slow acceleration of the engine during startup. N1 and N2 values will lag and EGT will reach an abnormally low temperature. This is usually caused by a faulty starter which prevents the engine from reaching an appropriate rotational speed during the start sequence. Once discovered, the engine should be shut down.

    This is called a hung start and is indicated by a slow acceleration of the engine during startup. N1 and N2 values will lag and EGT will reach an abnormally low temperature. This is usually caused by a faulty starter which prevents the engine from reaching an appropriate rotational speed during the start sequence. Once discovered, the engine should be shut down.

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  6. 6) How will you know when the engine is fully started and at ground idle (approximately)?

    On most engines, the simple answer is when all engine parameters have stabilized. On turbofan engines, this will usually occur when N2 has reached 20%, inlet turbine temperature (ITT) is roughly 400 degrees Celsius and N2 has reached 60%.

    On most engines, the simple answer is when all engine parameters have stabilized. On turbofan engines, this will usually occur when N2 has reached 20%, inlet turbine temperature (ITT) is roughly 400 degrees Celsius and N2 has reached 60%.

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That was rough...

You scored %. Better luck next time.

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Better luck next time...

You scored %. Keep at it and you'll be starting turbine engines like a pro.

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Someone studies!

You scored %. Nice work.

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Ready to start your airline career? Join Republic Airways and start flying the E175. Learn more and get started here.


Corey Komarec

Corey is an Embraer 175 First Officer for a large regional airline. He graduated as an aviation major from the University of North Dakota, and he's been flying since he was 16. You can reach him at corey@boldmethod.com.

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