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3 Answers

Governor/Propeller Check

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Aircraft Systems

How to perform the propeller governor check of an engine, properly?

According to the engine operator´s manual, I have to move propellers control toward low RPM position and observe tachometer. Engine speed should decrease to minimum governing speed (200-300 RPM drop).

It also says that to test the ¨feather¨ observe a 300 RPM drop below minimum governing RPM.

What does mean ¨Minimum Governing Speed¨? or wich is this minimun governing speed in RPM?

Best Regards


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3 Answers

  1. Best Answer

    John D. Collins on Aug 23, 2011

    From your question, I assume you are talking about a twin engine aircraft with fully feathering propellers. You should follow the “Before Takeoff” checklist in the POH.  I previously owned a 55 Baron. Its check list included bringing the power up to 2200 RPM and retard the prop control to the minimum governable value, which for my aircraft was between 2000 and 2100 RPM. Below that value, the prop would start to feather, which was not desirable.  After the RPM governor check, the prop was returned to full RPM.  Then the throttles were used to reduce the RPM to 1700 and the Magneto’s were checked. Finally the throttles were used to lower the RPM to 1500 and the feather check was performed by retarding the prop past the feather detent and as the prop started to feather, the props were advanced back to full RPM with the warning that the RPM was not to be allowed to fall below 1000 RPM.
    Regardless, follow the POH instructions for your aircraft when performing this check as it can be very hard on the prop and engine if you don’t follow the procedure.  You should have an instructor with you to show you how to accomplish it before you do it yourself.

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  2. Emiliano on Aug 24, 2011

    Thank you very much for your reply.
    Yes, I forgot to clarify that I meant a twin-engine aircraft.
    Why below that value between 2000 and 2100 RPM like your example in the B-55 (minimum governing speed) the prop would start to feather? and why is this not desirable?  
    And why reason can be very hard to the prop and engine if don’t follow the procedure?
    Best Regards

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  3. John D. Collins on Aug 24, 2011

    In the case of my Baron, the minimum cruise RPM that is listed in the POH is 2100 RPM and the green arc runs from 2000 to 2625 RPM.  At some point below this value, the prop control can allow the propeller to drop into feather and the engine will quit due the high air loads on the propeller.  When you shut down the engine, the propeller will not go into feather because at about 1000 RPM, a mechanical lockout  prevents it, but at higher RPM’s if the prop control is below the normal governing range, the lockout won’t happen and the propeller will drop into feather.  If the engine is developing any significant power, dropping into feather can cause bad vibration as it feathers.


    When the prop shop wanted to check the feathering action of the propeller on the ground, they would set the power to 1500 RPM and then retard the prop control to the rear stop. As the propeller dropped into feather, the RPM would fall off rapidly and to keep the vibration down, the mixture would be pulled to idle cutoff as the RPM hit 1000 RPM.  Then they could measure the angle of the blades while the engine was stopped to verify the correct values.  On my airplane, we had unfeathering accumulators, so after they made the measurements, all that had to be done to get the propeller out of feather was to advance the prop lever to maximum RPM while the engine was still stopped. Then a normal start could take place.  Without the accumulators, starting an engine with a feathered propeller is very hard on the systems, again due to the excess vibration.


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