How do you Time Wake Turb. Separations on Departure
After a recent event we have been trying to get an idea of how to correctly time the wake turbulance separations applied to departing aircraft.
For a Medium aircraft Departing behind a Heavy 2 min Wake Turb. separation is needed. From what point do you time this 2 min and how do you apply it?
We all know Wake Vortex is only generated from rotation so when do you start timing the 2 minutes?
Do you start timing from when the heavy rotates? And then at what point to you issue take off clearance to the medium behind? If you time from rotation and then wait the full 2 min then issue the 2nd acft takeoff Clearance by the time this 2nd acft rolls and rotates surely about 2min 30 sec has passed now? This obviously starts eating into an airport's efficiency.
If you time from the time you issue a take off clearance and a heavy may "road run" and only rotate towards the end of the runway however the 2nd acft may rotate at the RWY midpoint thereby having rotated 20 sec prior to the heavy. In this case however the medium should be above the heavy's wake vortex however this may not remain so if ATC impose climb restrictions on the 2nd acft. the just here is that the full 2 min may have been timed from take off roll to take off roll however between rotation points there may be less than 2 min.
Do any of your units/ANSPs have prescribed (written) procedures in your local Procedures on how to time the separation etc?
Any thoughts on how you apply the Wake Turb time separations will be valued as I would like to find out how other ATCs/ANSPs comply with this.