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  • Question 220797

    I am an instructor working with a student who came across this question. It assumes that an overspeed of the free power turbine is caused by a broken shaft in the output. However in my training it was always assumed that a runaway up in the governor/fuel computer causing an increase of gas generator output was a more likely cause, and in fact the response would be to increase collective to avoid excess NR then take into manual throttle to land as soon as practicable. Indeed an output shaft breaking might have no indication of overspeed, depending on where it broke with respect to the NR tacho position. How confident are you of that being the correct answer to the question?

  • #2
    Hi, Could you get your student to give you the QID? I am struggling to find it in the bank and I need the detail of the question. You are correct that one cause of an NF overspeed is a failure of the FCU in some form but a break in the FP output shaft would effectively remove the drag of the rotor system and the FPT would therefore overspeed. To get to the specifics required for the answer I need to see the question so if you could get that QID that would certainly speed up the response.

    Pending............

    Andy
    Last edited by Andy Bancroft; 11-01-2019, 10:48.

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    • #3
      The QID is 220797.

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      • #4
        Having given this a lot of thought I think the question is OK. What you talk about is a governor or FCU/ECU failure leading to an engine overspeed and would be worded as such. The IA's you stated for this failure are correct, to contain NR and manually control the governor (if able). All of this however is controlling NR and engine limits rather than specifically NF. Input clutch failures or a severance of the shaft from the FPT removes the drag (causing the NF to increase) and provides no drive to the main rotor. Therefore the most correct answer in a SE Helicopter is to enter autorotation and probably (AC Dependent) shut the engine down to prevent flailing of the drive shaft. To avoid further confusion the question will be amended to specify the cause of the failure.

        Hope that helps and thanks for highlighting it.

        Andy

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