Lowkoon,
Departures paths use criteria based on minimum values to determine terrain clearance. These are based on the minimum rate of climb required as is stated as "standard" with either PANOPS or TERPS etc. My memory fails me but I believe it's about 200'/nm on departure. Any departure which requires a higher ROC will have the minimum ROC required posted on the departure sheet.
Based on the minimum ROC the turn at PORPA allows for only a turn radius associated with a speed of 220kts. Not being an ATC type, I'm not sure what formulas are programmed into their computers but I'm sure they can automatically calculate your current altitude, ROC and speed and make the calculation seamlessly and automatically for the controller to then clear you unrestricted or high speed.
White None,
You are correct once cleared for high speed.
Last edited by cpdude; 17th Apr 2013 at 12:53.