Page 28 - Volume 13 Number 6

rotation creates the oil pressure that flattens the passenger rushing to get to the meeting ... there is a
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, halfway 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 metal­to­metal 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 l­o­n­g 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 not­yet­feathered 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
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 second? Believe it or not that was how the checklist procedure was written for many years in the early days of King Airs. Back then, the Environmental Protection Agency (EPA) was not yet in existence and there were no restrictions on turbine airplanes dumping a little fuel out at shutdown. As fuel pressure decreased, a dump valve would return to its spring­loaded open position and allow residual fuel to dump onto the ramp instead of into the hot combustion chamber liner – “burner can” – where it caused smoking and coking problems. (“Coking” refers to leaving deposits of carbon in the fuel nozzles.)
In King Airs, this fuel dumped out of the oil breather tube that terminated just behind the oil cooler ... and directly in front of the main tire(s). Prop wash tended to blow this kerosene back onto the tires, leading to their decreased service life. Around 1974 was when King Airs began being manufactured and retrofitted with fuel drain collector systems – usually referred to as “EPA kits” – to prevent fuel from dumping onto the ramp at shutdown. Shortly thereafter checklists were revised to feather after the fuel is cut off.
There is certainly no harm done by doing it the old way. In fact, feathering while taxiing at idle is a great way to keep the airplane quiet and avoid brake usage, especially when on a long, straight taxiway with a strong tailwind. However, there is a very definite momentary increase in thrust as the blades move through the big bite position on their way to feather. You can feel the acceleration for a moment while rolling down the taxiway.
Likewise, if we feather before – or too soon after – we have cut off the fuel at shutdown, there is enough airflow through the
26 • KING AIR MAGAZINE
JUNE 2019