AC3D's coordinate system is the same as X-Plane i.e. Y is up.
https://developer.x-plane.com/articl...ft_Coordinates
Your diagram shows a coordinate system where Z is up i.e. like Blender and some other 3D packages - mostly CAD.
It could be that Planemaker is transforming the coordinates to another coordinate system on saving?
in AC3D, use menu Views->Configure-views to choose the individual view angles but note that you can't change the coordinate system used e.g. from right-handed to left.