Page 28 - June 2022

“ ... the SLPS works in a small range of blade angles varying from, maybe, 11° to 13°.”
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we could more-accurately say that the SLPS works in a small range of blade angles varying from, maybe, 11° to 13°.
Why is this important? You would expect the SLPS annunciator to cycle on and off as the solenoid did its cycling. Starting with serial number LJ-572, when an electro- optic SLPS trigger replaced the mechanical switch, this cycling of the annunciator indeed occurs. Earlier airplanes, however, include a latching circuit and once the SLPS annunciator illuminates it remains on even as the valve loses and then receives power again. This is not good!
Why? First, there must be a method that allows the pilot to finally extinguish the annunciator after the SLPS is no longer working and yet the annunciator is still locked in its illuminated condition. Second, it makes the recognition of a SLPS malfunction more difficult to detect.
Let’s talk about this SLPS malfunction. If you fly these airplanes long enough, I predict that you WILL experience the malfunction at least once! Here’s what happens: The SLPS electrical circuit activates (shorts out) when it shouldn’t, when the blade angle is in cruise well above the 12° triggering angle. Because this is a switch malfunction, there is an excellent chance that the malfunction will remain until an A & P does some work.
With the SLPS solenoid now powered, the oil to the propeller is blocked but the transfer gland leakage slowly but surely sends the propeller blade angle to larger and larger values. Given enough time (maybe 30 seconds or so) the prop will be totally feathered. Of course, unless the power lever was retarded, there is an excellent chance that redline torque will be exceeded.
The indications of this malfunc- tion are (1) the SLPS annunciator il- luminates, and (2) RPM starts slowly decreasing and torque starts slowing increasing. What should the pilot do
26 • KING AIR MAGAZINE
JUNE 2022