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For single-pilot VFR operations, 14 CFR 135.105(c)(1) requires that:

The autopilot is capable of operating the aircraft controls to maintain flight and maneuver it about the three axes

Does this mean an autopilot with roll, pitch, and a yaw damper would qualify?

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  • $\begingroup$ Airplanes with yaw damper systems have 2 axis autopilots. That talks about an autopilot with control about the 3 axes, so I might interpret that as a 3 axis autopilot requirement. Yaw damper systems have very limited yaw authority (about a third of rudder travel) and perhaps that's insufficient for single pilot IFR because the rudder channel needs to be able to cope with asymmetric power/thrust, which a yaw damper doesn't have to deal with. $\endgroup$ – John K Feb 22 '19 at 4:33
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    $\begingroup$ Looking around a bit, single pilot jets like the Phenom 300 have 2 axis autopilots with yaw dampers so it would seem the answer is yes. $\endgroup$ – John K Feb 22 '19 at 4:41
  • $\begingroup$ I am ignorant of the rules for part 135. Can a Phenom 300, or any of the turbine aircraft, be flown single pilot outside of part 91? Bear in mind these aircraft fly ain the flight levels normally, thus IFR. $\endgroup$ – Mike Brass May 28 '19 at 7:27
  • $\begingroup$ The Phenom 300 is single-pilot certified so the autopilot requirement is moot. $\endgroup$ – Juan Jimenez Jun 6 '19 at 15:24
  • $\begingroup$ Your question regarding whether or not a yaw damper and 2 axis autopilot qualifies as a 3-axis autopilot is a good one. However, the setup to the question "For single pilot VFR operations, 14 CFR 135.105 (c) (1) requires that:" is incorrect. Specifically, single pilot VFR operations do not ever require an autopilot of any type. Take a look at my answer posted below for more details. $\endgroup$ – 757toga Jul 28 at 18:16
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Multi Axis Autopilot

Multi Axis Autopilot is a system which controls an aircraft about the roll and pitch axis (two axis) or roll, pitch and yaw (three axis). Sometimes the rudder has an independent yaw damper incorporated but this is not considered one of the axes in the system.

For aircraft with yaw damper - rudder displacement is provided by a command signal derived by cross feeding the roll angle signal from a vertical gyro to a turn co-ordination high pass filter.

The purpose of yaw damper is to improve the airplane's directional stability and ride quality. The yaw damper system is independent, but still part of the wider autopilot system. However, it can be operated independently in manual flight to correct Dutch Roll tendencies.

Yaw damper is not considered a full authority rudder channel in Automatic Flight Control Systems, meaning it isn't included as one of the axes when defining the type of autopilot. Both 2 and 3 axis autopilots can include a yaw damper system.

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For single pilot VFR operations, unless the aircraft is certificated as requiring 2 pilots, FAR 135.105 does not require 2 pilots OR, in the alternative, a 3 axis autopilot in lieu of 2 pilots.

Exceptions to this are shown in 135.99 (e.g., using an aircraft with 10 or more passenger seats) and 135.111 (Cat 2 operations).

135.105 must be read along with 135.101 (135.101 requires a second in command for IFR passenger carrying operations). 135.105 allows an exception/alternative to the 2 pilot requirement specified in 135.101. Specifically, unless the aircraft requires 2 pilots under VFR, a 3 axis autopilot can be used in place of the 2 pilot requirement specified in 135.101 (IFR passenger carrying operations).

Specific to the 3 axis autopilot issue, I don't think a yaw damper in every case meets the requirements to be one of the 3 axis autopilot components. The technical specifications that accompany the aircraft certification data which incorporates a 2-axis auto pilot with yaw damper should be consulted for guidance.

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