Page 25 - March19

away the wheel will move back to where the AP wants
it. If you find your KFC-400 flying with one wing low,
an avionics technician with experience in that system
will be required. (This does not apply to the much-more-
common KFC-300 system.)
All other autopilot systems available in King Airs have
four, not five, autopilot servomotors, more commonly
called servos. One servo controls roll by moving the
ailerons, one controls pitch by moving the elevators, one
controls yaw by moving the rudder, and one adjusts the
elevator trim to lighten the load on the elevator servo.
Only the KFC-400 has the fifth one that adjusts the
rudder trim.
A single-axis autopilot controls only roll. A two-axis
autopilot controls both roll and pitch. A three-axis
autopilot (yes, you guessed it!) controls all three: roll,
pitch and yaw. To the best of my knowledge all King Air
autopilots are and always have been the three-axis type.
As you know, the only trim control that routinely
gets much use is pitch trim. Change airspeed? Trim.
Change configuration? Trim. Aileron trim hardly ever
gets touched unless a large fuel imbalance exists. Rudder
trim? Many pilots must believe it is akin to aileron trim
… hardly ever used (except for single-engine work). Yes,
a normal flight can be successfully completed with never
a tweak of the rudder trim wheel. Is that the way to go?
No! Did you hear me? NO!
The rudder (yaw) servo is there for only one purpose
… to dampen yaw. It helps in keeping the nose from
swinging side-to-side. Cruising in perfectly smooth air
with no change in power the rudder servo would never
be needed and would never activate. But since air is
rarely that smooth, imagine keeping your feet on the
floor while flying manually. What? You say you’ve ridden
with pilots who do that? Yes, I have too … and it drives
me nuts! Now every little bump usually leads to some
nose-swinging. Even in perfectly smooth air, lack of
rudder awareness and proper usage leads to what this
article is all about … correcting a wing-low situation.
Imagine this scenario, which is a very good one for
instructors to teach/demonstrate to their flying students.
In level flight, tell the student to keep both feet on the
floor, away from the rudder pedals. Now assign a heading
– let’s use an example of 270 degrees – and observe the
student doing the proper job, on the control wheel only, to
maintain altitude and heading. Now suppose the instructor
slowly put some force on the right rudder pedal. The
airplane will respond by swinging the nose slightly to the
right, making the heading change to, say, 275 degrees.
The student, following the assignment that was given,
will turn the wheel counterclockwise, dropping the left
wing, and turning back to 270. Now, to keep holding that
assigned heading while the instructor is still pressing the
right pedal, the wings cannot be brought back to level.
Instead, a slight left bank must be retained.
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MARCH 2019 KING AIR MAGAZINE •
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