Is Scheduled Fire from all Air and Artillery considered contemporaneous please?

E.g. All registered targets for Air and Artillery are taken to be hit at the same time. So roll all dice together (being careful to segregate any dice that have a different attack value than others) for any units in overlapping Artillery + Air attacks?

Or ...

Does the player choose to do all Air or all Artillery attacks separately? Only rolling dice together for overlapping artillery zones ...or overlapping Air zones.

In the second example -  Could Suppress a unit with Air and then cause Fall Back with Artillery (or visa-versa). Cant do that in the first example.

Thanks!
Adam

I havw always done them separately as different entities and if suppressed by artillert and then air come down on the same hit point, then roll for fall back, if they survive. 

Separately - hit and suppress with arty, then gang up with AirPower if you fancy it on anything badly damaged and destroy it. 

Thanks both !

What's the Official rule for BKCIV please Mark?
Thanks
Adam

It is Separately AJ ... they are separate actions - so separate dice are required.