I been rather curious after flying around in the B1900D about how the AP actually works. What I found is that it needs some fine tuning and a few features introduced. I've read the 'how-to' article on AP and I understand how it works. But I was curious on a few things before I set off to see if I can improve on the AP of this aircraft or not.
The one thing that I looked at first was the 'ALT' mode of the FCP-65, it works in that it will grab the current altitude and stable the airplane in on that alt. The problem arises when AP kicks in, it jerks the plane causing it to become unstable before it settles. This is also noticeable I think when you go from one local airport to another when flying, if the baro. changes the AP will see this and immediately jerk down or up to adjust the altitude causing it to become unstable and start the process of settling again.
I am not sure if the initial KP needs to be changed or if this is one of those situations that dictates a <filter> element to slow down the immediate changes in elevator and make it more natural? I'm all in for updating this model
Also, if I can fix the altitude hold, then I believe I can easily finish creating the altset, climb, dsc features that are currently missing. I also think the AP can be tweaked a little but with such limited knowledge of flying in general, all i can offer up is my efforts fixing and tweaking code if I have ideas on how to do it.