A PA32; DEPARTING FROM HPN; ENCOUNTERS WAKE TURB FROM PRECEDING DHC8.

Narrative

I FILED AN IFR FLT PLAN FOR DEP AT XA30Z FOR OUR TRIP FROM HPN TO MTN. AFTER RECEIVING CLRNC FROM GND CTL AT HPN TO TAXI TO RWY 16; WE WERE #3 FOR DEP. THE ACFT IMMEDIATELY PRECEDING US; A DH8 COMMUTER; WAS CLRED FOR TKOF; ANOTHER ACFT WAS A 3 MI FINAL; AND WE WERE CLRED FOR IMMEDIATE TKOF. WITH A NO WIND SIT; I ATTEMPTED TO SIDESTEP POSSIBLE WAKE TURB AFTER ROTATION; BUT WAS UNSUCCESSFUL. THE VORTEX CAUSED OUR ACFT TO MAKE AN ABRUPT ROLL TO THE L WITH L WING ROLL. POSITIVE RECOVERY WAS MADE AND MY COPLT ADVISED THE TWR THAT WE ENCOUNTERED THE WAKE TURB. NO WAKE TURB CAUTION WAS GIVEN BY THE TWR; NOR WAS ANY 3 MIN WAIT PUT INTO EFFECT AT THAT TIME. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR PARTICIPATED IN STRUCTURED WAKE TURB CALLBACK STUDY. RPTR STATED THAT THERE WAS NO MORE THAN 1 MIN BTWN CLRNC FOR TKOF FROM PRECEDING ACFT. THERE WAS A LONG LINE OF ACFT FOR DEP AND TWR WAS MOVING ALL ACFT AS RAPIDLY AS POSSIBLE TO GET EACH ACFT AIRBORNE WITH MINIMUM DELAY. RPTR STATED THAT SHE WOULD GO TO THE END OF THE TAXI LINE AND WAIT 30 MINS IF NECESSARY; RATHER THAN HAVE SUCH AN ENCOUNTER AGAIN. RPTR HAD PLANNED TO DEVIATE TO THE SIDE OF THE RWY TO AVOID ANY POSSIBLE WAKE. THE WINDS WERE RPTED TO BE LIGHT; AT 6 KTS; DOWN THE RWY. SHE FEELS THAT THE WINDS WERE NOT QUITE DOWN THE RWY; THERE MUST HAVE BEEN A SLIGHT XWIND THAT MOVED THE WAKE TO THE SIDE OF THE RWY; WHICH IS WHY THE ENCOUNTER HAPPENED. CTL AT THE TIME OF THE ENCOUNTER WAS RATED AS PARTIAL CTL. THERE WAS NO SIGNIFICANT DEV FROM FLT PATH. JUST 40 DEGS OF ROLL; CLOSE TO THE GND.