Page 24 - Volume 11 Number 6

back to Low Idle, that’s great! It confirms that your dead band is large enough to kill your residual taxi thrust without adding power.
However, if one or both N1 speeds hang up at something between Low and High Idle, then your dead band is too narrow and your props are candidates for sandblasting ... not good. I have even discovered rigging so out-of- spec that the N1 started to exceed High Idle before we found that flat pitch, peak RPM position. Yuck! This dead band is much too small!
We are not quite done yet. Presuming your N1 speeds did indeed drop to Low Idle when the condition levers were pulled back to the hooks – as they should – now take each power lever individually and pull it back further from your Flat Pitch mark until you see an N1 increase. We hope it happens almost immediately, before we move even 1/8 of an inch. If we need to move significantly more than that, then the dead band is so large that a big decrease in propeller speed will be seen, leading to sluggish reaction when Maximum Reverse is reached.
There is one last check to make and record: What is the stabilized N1, Np, and Torque in Max Reverse? Make sure the run-up surface is very, very clean before selecting full Reverse while stopped. Do this with one engine at a time, since there is a possibility of rocking back onto the ventral fin if both propellers are in Maximum
Reverse at the same time. If no such ultra clean run- up pad exists, then record the values after you have selected Max Reverse while rolling down the runway soon after touchdown, before beginning to ease out of Max Reverse when 60 KIAS shows up. We hope the N1s come out near 85 percent and that Np is within 100 to 200 RPM of takeoff redline.
It takes an experienced and dedicated PT6 mechanic to make the proper rigging adjustments in a timely and accurate manner. If you have access to such an individual, I am happy for you. If you don’t, then it will be a time-consuming and frustrating endeavor. The description of the work in the Maintenance Manual leaves much to be desired. Having access to an old-timer with lots of experience is invaluable!
Poor Beta and Reverse range rigging is common to find and, in truth, has little impact on safety. But when the rigging is correct, the pilot’s job is easier and more enjoyable, and the propeller blades will fare much better! 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 www.flightreview.net. 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 kblonigen@cox.net.
22 • KING AIR MAGAZINE
JUNE 2017