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5 Answers

Multi engine Question

Asked by: 3136 views Aerodynamics

If you were to have one engine fail in a Multi Engine aircraft of course you would feather the propeller of the failed engine. My question is, if you were to have the other engine fail after the first one (so a dual engine failure) would you also feather that propeller as well or should only one propeller be feathered in the event of dual engine failure? I believe I heard that in this situation that if you were to have a second engine failure that you should not feather the propeller and that only one propeller should be feathered. Can anyone explain why and aerodynamically what would happen if you experienced a dual engine failure and feathered both propellers?


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5 Answers

  1. John D Collins on Jan 19, 2014

    A windmilling propeller generates a lot of drag. If you want to glide the furthest distance and both engines have failed, feather both engines. A twin is often an excellent glider when both engines are feathered. For example a Bonanza has a book glide ratio of about 10 to 1. Its bigger brother, the Baron has the same basic wing and fuselage. With both engines feathered, the glide ratio is listed as 12 to 1. With one engine feathered, the glide ratio would drop substantially and with neither feathered, it would drop like a rock.

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  2. Jim F. on Jan 19, 2014

    I’m absolutely with John that you want to reduce drag as much as possible by feathering both.. Do you remember the reasons you were told not to feather the second dead engine?

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  3. DS on Jan 19, 2014

    I wasn’t given any reasons as to why not feather the second dead engine. A King Air pilot told me this and I didn’t have a chance to ask any questions. I looked up a King Air Emergency checklist and sure enough it says for a second engine flame out to not feather the propeller.

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  4. Kris Kortokrax on Jan 19, 2014

    You didn’t look far enough through the King Air checklist. It states to not feather the second propeller when you are contemplating a restart.

    In the checklist for Gliding (no successful restart), the checklist states to feather both propellers.

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  5. Brian on Jan 25, 2014

    Agree with all that is here, only one thing to add. Piston twins will auto feather once oil pressure is gone. Their constant speed system is effectively opposite that of a piston single. Turbo props have auto feather unless disabled by the pilot. I believe it is disabled at cruise, but I’m not certain; perhaps someone else here can comment to that.

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