Page 19 - April 23

Auto-ignition and Autofeather
Each engine has a high pressure switch on the torque manifold that actuates at approximately 400 to 500 foot-pounds of torque. These pressure switches have a dual function: they turn auto-ignition off and they arm the autofeather system (they don’t activate it, they just arm it). It is common practice to test auto-ignition and autofeather in the same power run-up. At this point in your ground run-up, you would have the auto-ignition switch in the “On” position and you’re holding the autofeather switch down in the “Test” position.
Both the autofeather and the auto-ignition annunciator lights are green. Below 400 lb-ft your auto-ignition annunciators will be on. As the power levers are advanced toward 500 lb-ft, the auto-ignition greens go out and the autofeather greens light up. Most King Air training programs use the phrase “two greens off and two greens on” as a memory technique to teach this relationship. Just don’t expect the autofeather greens to come on simultaneously. The pressure switches on the torque manifold can trigger anywhere between 400 and 500 lb-ft, and engine N1 acceleration is another variable. You want two greens off and two greens on ... eventually.
The main thing to remember about autofeather arming is that each engine arms the opposite side. This is where new King Air pilots can get easily confused. The
The torque meter in question still reads 200 lb-ft after being removed from the King Air and was clearly out of calibration. This prevented the switch from activating so the prop would not feather.
left engine arms the right side autofeather and vice versa. Imagine advancing your power levers and the left autofeather light comes on but the right light does not. You have to fight the instinct to continue advancing your right engine power lever, because at this point, the right engine just armed the left-side autofeather and gave you a green light. In this scenario, the right-side autofeather is not yet armed and the left power lever must be moved further forward. So, if your left light comes on first, continue advancing your left lever until you get the right-side autofeather light. Conversely, if you get the right light first, keep advancing the right lever until the left-side autofeather light comes on. It’s counterintuitive in the beginning, but you’ll get the hang of it.
Autofeather Test Continued
Now you have two greens on, so autofeather is armed on both sides, and it’s time to test the system. Starting with the left side, pull the left power lever back while holding the autofeather switch in the Test position. As you pull back through 400 lb-ft with your left power lever, the right light should extinguish (the right side is now unarmed and cannot go into feather).
At approximately 200 lb-ft of torque, the left prop should feather. A different pressure switch on the torque manifold triggers the feathering. It activates a solenoid
APRIL 2023
KING AIR MAGAZINE • 17