Is there a knack to using the AP?

[Aedui]

I have no issues with the lateral aspects of the AP, but the vertical functionality is all over the place. Selecting an altitude and VS then arming produces random VS (sometimes climbing when it should be descending and vice versa).  AP often busts through an altitude (again both climbing and descending). Seems to be totally erratic. The strange thing is that occasionally it behaves itself and works as it should.  Am I alone with this? 

[Coop]

There could be two different things at play:

1) The altitude preselect must be "armed" by clicking the ARM button. If not it will continue at the selected VS and just keep going. The knob is used to select the altitude preselect, the Up/Down buttons are used to select the VS.

2) The Turbine Islander is especially tail heavy. If the weight/balance is too far aft or too light, the aircraft can run out of trim authority at higher cruising speeds. Running out of trim can cause oscillations and climbing through a selected altitude.

[Aedui]

Thanks Coop, I'll look at the W/B aspect.  As stated above I am arming the altitude.  It's the erratic behaviour that's throwing me. i.e. sometimes it works perfectly, others not. Will report back later once I've had a chance to experiment further. 

[Aedui]

Ok - tested in various load configurations (front heavy, full load etc) and no change. So far, I've noticed that the AP behaves perfectly the first time it is engaged.  If it is disconnected then re-engaged that's when the vertical control goes to pot. No idea why that should be the case.  Going to try a reinstall to see if that helps.