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time-honored solution to lots of problems. Customers don’t want to hear that their expensive aircraft was whacked with a hammer, hence the term “malletization” was born. What was once an inside joke among mechanics, is now listed in the “Urban Dictionary” on the internet. Solenoids, valves, certain switches, etc., respond beautifully to malletization, provided you know what you’re doing, and it beats the heck out of replacement pricing (pun intended).
The E90 Conundrum
You E90 drivers have two torque limits on your torque gauges – one for 2,200 rpm (TQ value of 1315) and one for 1900 rpm (TQ value 1520). I ran into a puzzling situation with the owner of an E90 with Raisbeck four- blade props who complained that his OSGs had never tested in the time he owned the airplane. Of course, the first place I went was the solenoids. I verified that both had power, I removed them for bench check and they both passed with flying colors ... hmmm.
I was beginning to suspect bad OSGs when I had an “Aha!” moment. The takeoff rpm on an E90 with three- blade props is 2200, so the normal setting for the OSG is about 150 rpm below that (1950-2050 rpm is typical). But on an E90 such as this one, with four-blade props, the takeoff rpm is 1900, so the corresponding OSG setting would need to be around 1750 rpm. I found the prop
A pen pointing to the test solenoid of a King Air 200, with the overspeed governor directly to its right.
governors on this E90 were correctly set for takeoff rpm at 1900, but the OSGs were still set at 2050 to align with a takeoff rpm of 2200. Bingo! The OSGs will never test at that setting. Once both OSGs were properly adjusted to 1750 rpm, everything worked as advertised and the OSGs tested every time.
In Conclusion
If skipping that OSG test altogether sounds a tad radical to you, let me tell you where I’m coming from: The overspeed governor is a backup to the prop governor. And in the 40-plus years I’ve been working on King Airs, I have yet to hear of one with a prop governor failure. I’m not saying they have never failed on a King Air; I’m just saying I’ve never experienced it.
Therefore, based on my experience, the OSG test is an unreliable and/or misleading test of a secondary system which is backing up a very reliable primary system.
The other point I want to make is this: You could perform the overspeed governor test and get a failure – i.e., you pull the switch, but the prop rpm doesn’t stop and goes all the way to takeoff rpm. So you have the overspeed governor removed, you pay $3,500 for an exchange unit with a $15,000 core deposit
10 • KING AIR MAGAZINE
JUNE 2016