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The Test position of the autofeather switch is spring- loaded for a good reason. It makes it impossible to accidentally leave the system in Test mode and risk unintentional arming of the autofeather system at an insufficient power level.
The King Air automatic feathering system allows only one prop to feather at a time; they will never go together. You will recall the left engine arms the right side auto feather (between 400-500 lb-ft in Test and above 92% N1 in Arm) and vice versa. Imagine this: Your left engine fails on takeoff and the left prop goes into feather; it is now physically impossible for your right prop to feather, because the left engine, being well below 400 lb-ft, has unarmed the right side autofeather.
Leaving the Switch in Arm
In my opinion, autofeather is most crucial during takeoff. Some leave the switch armed in cruise, but at FL 250, if you had an engine failure and the switch was off, you’d still have plenty of time to cage the problem engine. On approach, even if the switch is in the Arm position, the system is unarmed as long as you are below the 92% N1. However, if you need to make a go-around and your switch is in Arm, the system will arm as soon as you push the power up high enough.
Maintenance
Where’s the maintenance tip in all of this? How you squawk an autofeather problem can make your mechanic’s job simple or complex. Many a pilot has dropped the aircraft off for maintenance on a Sunday night and realized they forgot to write up their squawks, so they leave a hastily scribbled list in the cockpit that includes “Autofeather inop.” Of course I can troubleshoot from square one and work my way to the root of the problem. But if I get more precise information from the start, the job goes faster and that saves you money.
How about this squawk? “Autofeather tests good on ground but L/H annunciator fails to illuminate on takeoff.” Aha! That sends me straight to the righthand power lever switch in the pedestal. Or this: “Autofeather will not test.” Great! I can verify that the greens are not coming on at 400-500 lb-ft torque, and then I know to zero in on those torque switches. The more specific the information you give to your mechanic, the faster the problem will be diagnosed and fixed. I hope this helps. KA
Dean Benedict is a certified A&P, AI with over 45 years of maintaining King Airs. He owned and ran Honest Air Inc., a maintenance shop
that specialized in Beechcrafts with an emphasis on King Airs. Currently, with BeechMedic LLC, Dean consults with King Air owners, operators and maintenance shops on all things pertaining to King Air maintenance. This includes troubleshooting, pre-buys and maintenance management. He can be reached at dr.dean@beechmedic.com or 702- 524-4378.
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APRIL 2023
KING AIR MAGAZINE • 19