Hi Sheldo86
Where I work, It'd be rare that you get a clearance into class 'C' whilst still taxying. You'd be most likely to receive the clearance once airborne and identified.
If you planned IFR the controller should already be aware, through your flight plan, that you'll be requesting a clearance if your planned level has you transiting through CTA.
If planned VFR, it'll be once you are airborne and identified. Give the controller as much notice as possible, so hopefully you'd be able to avoid any delays whilst a flight plan is found/created.
Cheers
TD80
Last edited by tyler_durden_80; 15th Aug 2014 at 03:34.
Reason: I write good England