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had the not-uncommon situation of some malfunction taking place in our SLPS system that locked off the oil and caused the propeller to slowly start feathering. Well-trained instructor that I was, I pulled the CB and all returned to normal as we headed back to Beech field to have the malfunction addressed and remedied.
The airplane got pulled into the delivery center hangar and one of the senior Beechcraft A&Ps was assigned to cure the problem. This great gentleman – Red Martin – had probably been a Beechcrafter since Staggerwings were the product. He and I had developed a liking for each other. As he worked on the short-circuited SLPS solenoid, he opined to me that it was stupid why this solenoid was still installed. “Why?” I asked, in my ignorance.
“Because if anything causes the PLPS to fail, the prop will immediately feather” was Mr. Martin’s response.
After the conclusion of that flight training session, I rushed back to the Training Center to verify that what Red had stated was correct ... and it was! I became an evangelist! I went to the other instructors, to Don Cary, my boss at the Beechcraft Training Center, and with his blessing, I contacted the head of the engine engineering department. To my amazement, this gentleman said “Tom, you’re right, we know this. But the Federal Aviation Administration (FAA) won’t allow use to remove the SLPS system.”
My blood began to boil! It had to be mere ignorance on the FAA’s part that keeping this unneeded and problem- prone system was necessary. I asked the head of engine engineering about this and his response was “We’ve explained it until we’re blue in the face, but they just don’t buy it.”
“Wait!” I said, “you guys are the engineers. We are the training experts. Let us have a crack at convincing the FAA.”
And so, a month or so later, I was in front of a “class” of maybe five FAA engineering employees and described to them the working of the beta valve and why the SLPS was unneeded and undesirable. Well, bless their souls! Within a few weeks the SLPS requirement on beta valve type governors was removed and Beech issued a Service Bulletin to direct its removal.
Hence, all 100s, E90s, and 200s that had this unnecessary system installed as factory standard, were allowed to remove it entirely. That explains why these airplanes have switches that are spring-loaded to the center position but have no label nor action when pressed down. Only, the top, OSG Test position, is still hooked up.
Before we end our story, there is one more fact to mention. The A100 model that replaced the straight 100 model in 1971, was the very first King Air to have four-blade propellers as factory-standard equipment. Because of the potential for “reactionless vibration” when idling at too low a speed on the ground, Beech solved this challenge by (1) increasing Idle N1 speed from about 50% to about 60%, and (2) flattening the LPS setting to
JUNE 2022
provide less rotational resistance and thus an elevated propeller speed. But now – wow! – that flatter propeller provided too much drag in the landing flare. The fix? Install anther Low Pitch Stop at a larger blade angle but have it only operate in flight, not on the ground. This was the origination of the Flight Low Pitch Stop (FLPS) and the Ground Low Pitch Stop (GLPS). And to create the FLPS? Why the bad old, unreliable, electric lock pitch solenoid was reintroduced! This system was installed on both the A100 and the earlier F90s but, thank goodness, it was replaced with a simpler and less malfunction-prone system on later F90s and all members of the 300-series.
I hope you now see why I said that you pilots flying later King Airs without the lock-pitch propeller solenoids are so lucky! KA
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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