Page 23 - March 25

When you move the power lever on your King Air, you
are not controlling fuel. You are controlling air (Py air)
that subsequently controls fuel. When you push the
power lever forward, you increase the Py pressure in
the fuel control, which opens the metering valve and
sends more fuel to the thirsty engine. Pulling back on
the power lever means lessening Py air and decreasing
fuel flow.
If you’ve ever noticed, there’s a bit of a delay between
power lever movement and engine response. Turbine
pilots become accustomed to this delay in response.
This delay is because it takes a while for the compressor
to speed up and provide the air pressure that moves the
metering valve.
The FCU on a PT6 is a mechanical device, and
mechanical things can break. If there is a break (leak)
in the air lines bringing the Py air to the fuel control (or
forward to the prop control), then there will be no Py
pressure to move the metering valve, and the engine will
roll back to idle. The pilot can move the power lever as
MARCH 2025 much as desired, but there will be no engine response.
The engine will remain at idle.
This power rollback causes the engine to roll back to
idle, creating the question, “Did the prop feather?” If
you’re like most pilots in training, there will be some
confusion in the cockpit. The engine will still be running,
so you should have otherwise normal engine indications.
However, the torque will be near zero, and if your power
lever is forward (arming the autofeather function with
the power lever angle switch), the autofeather system
should feather the prop.
But what if the power lever isn’t set to forward arming
autofeather? What if you pulled the power lever back
in an attempt to diagnose the issue? What if your King
Air doesn’t have autofeather installed?
Your King Air emergency procedure checklist will
direct you to try to add power, check the Ng speed
(which will be at idle if you are experiencing a power
rollback), feather the propeller and eventually shut down
KING AIR MAGAZINE •
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