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Multi engine feather check

Asked by: 1152 views Aircraft Systems

Hello, I have a multi engine test coming up and he wants us to know some stuff about the propeller check while in the run up. When checking the propeller before takeoff on a full feather twin aircraft like a Seminole why do the following things happen?

Manifold Pressure goes up.
Oil Press goes down.
RPM drops

2 Answers

  1. Best Answer


    Bryan on Sep 22, 2023

    Look at the airplane flying handbook, Chapter 13. On page 13-5, read the last two paragraphs carefully.

    In short, oil pressure is what keeps the blades to low pitch, high RPM. So when you pull the blue lever back, the blades go high pitch which means they are grabbing more air. Unless you also increased engine power, the increased load is going to slow the engine–and that’s why you get the RPM drop. The drop in RPM means that less of the induction gas (fuel air mixture) is getting drawn into the engine but you didn’t touch the throttles so the same amount is available to the engine as before–and that’s why you get an increase in manifold pressure. Then you move the blue lever forward again (hopefully much faster than it took to read this) and the oil pump must now “refill” the pressure in the governor and until it does, the oil pressure drops.

    Once the governor is full of oil again, the blades go low pitch, high RPM, your manifold pressure goes back down, and your oil pressure stabilizes.

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  2. KDS on Sep 23, 2023

    Note that the aircraft will give the same indications if the mixture control is mistakenly used instead of the propeller control. I once saw a CFI applicant in a complex single grab the wrong control and perform the prop check using the mixture control. It would be harder to make that mistake in a twin, but the takeaway lesson is don’t just grab a critical control. Look too. I’ve seen people shut down the wrong engine in a simulator by grabbing for a control.

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