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position. Then its rotation creates the oil pressure that flattens the blades. As the blades flatten, the lesser air bite means less rotational resistance so the propeller speed rises until normal idle conditions are met with the propeller now on its Low Pitch Stop (LPS).
As long as the propeller is rotating then the pump inside the PPG keeps supplying the necessary oil to the dome to prevent the blades from
feathering. To demonstrate this, I often have a new King Air pilot not pull the propeller levers into feather after we pull the condition levers into fuel cutoff as we shut down. Usually it is well over one minute before the propeller finally stops turning. At this point we can observe that the blade angle is quite large, in the order of 45 degrees, half-way to feather. As we watch, we can actually see the blade angle slowly becoming
larger as the feathering springs force the remaining oil out of the dome and back into the engine’s nose case. Often I will then ask the pilot to pull only one propeller lever all the way back into the feather position. When this is done – opening the passage in the PPG to allow oil to return freely into the nose case – the blade angle moves rapidly the rest of the way and the blades stop moving when they reach the metal-to-metal stop at feather. It takes in the order of two seconds for this to happen. The other side may take another five minutes or more to leak into the fully feathered position.
Try it yourself. Pick a deadhead leg and make sure the ramp is empty of nearby people when you shutdown. Leave the propeller levers alone and watch what happens. It takes a l-o-n-g time for the propeller to stop, eh? In fact, I have done this facing into a strong Kansas “breeze” and the propeller never stopped rotating! There was sufficient windmill effect to keep the not-yet-feathered propeller turning indefinitely.
Do you see why I stated the reason for feathering is “safety”? The lineperson waiting to install your nose chocks, a curious bystander or the poorly briefed passenger rushing to get to the meeting ... there is a lot more chance of someone getting hurt by a rotating propeller than by one that has stopped. When we make the propeller blade angle go to its maximum bite position immediately at shutdown – yielding the maximum amount of rotational resistance – it lessens the dangerous rotating time immensely.
Can you think of a situation in which feathering manually at shutdown is not a good idea? Yes! You are correct: When parked on a very slippery, icy ramp, the thrust that the propellers provide as the blade angle suddenly increases can cause the airplane to slide forward with no control whatsoever. It’s best here to let them coast to a gentle stop on their own.
By the way, do any of you feather first and pull the condition levers
22 • KING AIR MAGAZINE
MAY 2024