I hope I'm missing something here - but I fear not...
I have an object which is not aligned to any ortho plane. I have a construction plane aligned to a primitive of that object.
In most 3D DCC's there is an option to now use the construction plane as the basis for the ortho views, eg: the top / front / right views to be aligned relative to the construction plane rather than world. This is rather important for modelling work.

In Houdini?

do you mean this?
the construction plane can align to a primitive, and the primitive can snap to the c-plane. but I don't find how to align a primitive to the c-plane.

Thanks luoqiulin - that's pretty much what I want. I wasn't expecting it to be at the bottom of the 'Home' menu : )
It would be better IMHO if there was a global view option for 'construction plane orientation' so when a cp was active the user could choose that option and all views would switch to the cp alignment, ie: top, right, left views in a 4 view set would now be top right and left relative to the cp - rather than world. Neverthless - this will get me by.

Thank you!

Regarding aligning objects to the active cp:
The only way I know:
Create a new box on the construction plane - this will auto align to the plane.
Select the object to be aligned.
Enter the 'Align state' with the semi-colon key (
Shift click the new box your made in step 1.
Delete the reference box.

Shift clicking in the align state will rotate align without moving.