"In theory it should be possible to compile the HIL version of the code outside of the arduino and run it on a desktop interfaced with Xplane. In practice, it is much easier to just plug in APM and use the hardware, unless you're a C++ programmer."

"1) There is a variable called airspeed_enabled in the code that can now be directly controlled. The one place I remember seeing it used is to control whether nav_pitch is used for airspeed control or altitude control.
2) This sounds like a rate…"

"Regarding the airspeed_enabled issue, I believe that
controls whether the energy/altitude loop for the throttle control is
being used for the altitude or the nav_pitch. The altitude is still being controlled, but the tolerance is within 20 meters. I…"