Page 25 - Volume 11 Number 3
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Knowing how fickle ice can be – benign one flight, scary the next – always makes me think of the classic movie line spoken by Clint Eastwood in Dirty Harry: “Are you feeling lucky, punk?”
If you choose to continue to be casual in your deployment of ice vanes, you must be feeling very lucky! I hope your luck holds out. Because if it does not, then the airplane’s owner is going to be faced with a large, wasteful, maintenance expense. Flying a few knots slower will produce a lot less lost time than having the plane be grounded for a month or so for engine repairs!
I will leave you with a positive thought: Do you realize that specific range – the nautical miles you are traveling for each pound of fuel burned, calculated by dividing ground speed by fuel flow – almost always is improved due to ice vane deployment?! Amazing, but true. Unless you are flying at a very high altitude close to the certified ceiling, or fighting an extreme headwind, or you were using a reduced power setting closer to max range than max power, then this statement is true.
You see, since the Fuel Control Unit (FCU) is a governor for compressor speed (N1), the reduction in
intake air density due to ice vane extension makes N1 want to increase due to less compressor air drag. But the FCU reacts by reducing fuel flow to keep N1 constant. The reduction in ground speed is proportionally less than the reduction in fuel flow, so the airplane actually becomes more, not less, fuel efficient. Write down your stabilized ground speed and fuel flow numbers next time, before and after ice vane deployment. Get your smartphone’s calculator and do the division. I’m right, aren’t I? Perhaps that will give you a little comfort when you observe the decrease in speed.
Bottom line? You’ve heard it before but I’ll state it again: “When in Doubt, Get ‘em Out!” KA
King Air expert Tom Clements has been flying and instructing in King Airs for over 44 years, and is the author of “The King Air Book.” He is a Gold Seal CFI and has over 23,000 total hours with more than 15,000 in King Airs. For information on ordering his book, go to Tom is actively mentoring the instructors at King Air Academy in Phoenix.
If you have a question you’d like Tom to answer, please send it to Editor Kim Blonigen at
MARCH 2017

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