Page 22 - February 2022

In the old days, those solenoids failed so frequently that we kept them in stock. I don’t know if it was a vendor problem or a change in design, but the tendency for stuck solenoids on the overspeed governors seemed to lessen over time. It still happens, however, and always at an inopportune time. Being able to identify and fix the problem is very handy.
Malletization Beats Beaucoup Bucks
So why didn’t I replace the solenoid in that B200 or tell the E90 pilot to have his replaced? Once you look up the price, you’ll see why. They have become absurdly expensive. Five years ago the price at Beech (Textron) was close to $7,000.
Malletization, or hitting something with a soft- blow hammer, is a time-honored solution to lots of mechanical hangups. Years ago, the term “malletization” was an inside joke among savvy mechanics. It was a sophisticated way to say they fixed it with a couple whacks of a mallet. I was amused to find “malletization” 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 sure beats (pun intended) the heck out of the exorbitant cost of replacement.
The E90 Conundrum
Years ago, I ran into a puzzling situation with the owner of an E90 who complained that his OSGs had never been tested in the time he owned the airplane. It’s important to know that E90s are the only King Air model with two torque limits marked on the torque gauges: 2200 RPM (TQ value of 1315) and 1900 (TQ value 1520).
As soon as this E90 showed up at my shop, I went straight to those pesky OSG test solenoids. I verified they both had power, I removed them for bench check and they both passed with flying colors. That wasn’t what I expected. My lead mechanic was convinced the OSGs were bad, but I was doubtful. It was highly unlikely that both would fail. Then I had my “Aha” moment – this E90 had 4-blade Raisbeck props!
The takeoff RPM on an E90 with 3-blade props is 2200, so the OSG setting should be 150 RPM below that (1950- 2050 RPM is typical). But the takeoff RPM for 4-blade props is 1900, and the corresponding OSG setting should be around 1750 RPM. I checked the prop governors first and found them set correctly for takeoff RPM at 1900. But the overspeed governors had not been adjusted. Bingo! They were still set at 2050 to align with the 3-blade takeoff RPM of 2200. Those OSGs would never test at that setting. We adjusted them properly to 1750 RPM, aligning with a takeoff RPM of 1900. Finally, the OSGs tested properly and everything worked as advertised.
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20 • KING AIR MAGAZINE
FEBRUARY 2022