Page 29 - November 2022

which oil pressure can be created and sent into the propeller dome to drive the propeller blades to lesser angles is to use the pump inside the primary propeller governor. Since that governor is driven by the propeller shaft, no propeller rotation means no oil pressure. Only with propeller rotation can we create the oil pressure necessary for unfeathering.
I have seen situations in which the forward rotation of the propeller was just too darn slow to accomplish the unfeathering. But if you have about 10 RPM or more, it will work. Just place the propeller lever forward, be patient, and soon you will observe the propeller is starting to rotate faster. And the faster it goes, the more oil pressure is created so it speeds up even more rapidly.
If you leave the propeller lever fully forward as the propeller increases its speed, it will eventually hit the speed at which the governor is operating. With the lever fully forward that is takeoff RPM, of course. There will be quite a bit of surging as the governor takes over and a lot of drag since, with no fuel flow yet, the blade angle will be quite small in order to reach takeoff RPM.
A technique I use is to pull the propeller lever back to where it is just touching, but not into, the feather detent once I see the propeller starting to increase speed. This sets the governor at the minimum possible speed. Now when the unfeathering propeller hits the governor, it will be at a lower RPM and with a bigger blade angle ... yielding less drag and with the propeller speed never surging past redline.
With the propeller stabilized at minimum governing speed, slowly move the propeller lever fully forward to get as much airflow through the engine as possible before advancing the condition lever – the next step in the windmilling airstart checklist. As soon as N1 starts increasing and ITT starts to rise, we have verification that lightoff has occurred and it is a
good time to start leveling off from the dive we have been in to get maximum airflow.
Speaking of the checklist, I believe that the airstart procedures – both no starter-assisted and starter- assisted – contain more steps than any other abnormal procedure. Since this is something done rarely, take your time and go through the checklist slowly and methodically. A benefit of doing the windmilling (not the starter-assisted) procedure is that no large electrical demands and voltage transients are experienced so there is no need to turn off things like EFIS tubes, windshield heat, Cabin Temp Mode selector, etc. But make sure you remember to move the auto-ignition switch to “Arm” when it is specified, or the fuel and air mixture has no source of ignition!
So, Mr. Propeller-Manufacturer- Service-Tech, please realize that (1) a PT6 propeller will never feather itself in flight, it must have a pilot
or the autofeather system to do so, and (2) it will never unfeather itself in flight until propeller rotation occurs. KA
This article was republished from the August 2013 issue.
King Air expert Tom Clements has been flying and instructing in King Airs for over 50 years and is the author of “The King Air Book” and “The King Air Book II.” 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 books, contact Tom direct at twcaz@msn.com. 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 editor@blonigen.net.
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NOVEMBER 2022
KING AIR MAGAZINE • 27