INFLT WAKE TURB ENCOUNTER.

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ENRTE FROM DALLAS TO PHX; ZAB HAD OUR G-4 AND A B-757; BOTH ENRTE TO PHX. WE WERE APPROX 4000 FT ABOVE THE B-757 JET AT THE TIME WE WOULD NORMALLY BEGIN DSCNT. ZAB HI SECTOR ANTICIPATED THE SIT WELL AND SENT THE B-757 ON DIRECT ROUTING TOWARD THE TONTO INTXN AND STARTED US BOTH DSNDING INCREMENTALLY. WHEN WE HAD SEPARATION; WE WERE GIVEN A NOTICE TO 'EXPECT TONTO AT 12000 FT AND A 280 KT SPD RESTR.' THE B-757 WAS GIVEN THE 'EXPECT...' NOTICE AS WELL; AND WE WERE BOTH SWITCHED TO THE LOWER ALT SECTOR CTLR; WHO CLRED US BOTH TO CROSS TONTO AT 12000 FT. A THIRD ACFT; A KING AIR; WAS BTWN OURSELVES AND THE B-757 AT A LOWER ALT; DSNDING TO 11000 FT; PER THE STAR. I AM CERTAIN WE HAD 7-8 MI IN-TRAIL SEPARATION FROM THE B-757; AND SINCE SEPARATION CRITERIA WERE MET; WE WERE NOT TOLD THE TYPE ACFT. IT ALSO APPEARED WE WERE ABOVE THE B-757 IN OUR DSCNT ANGLE. WE HIT THE WAKE TURB AT ABOUT 13800 FT; ROLLING THE G-4 VIOLENTLY THROUGH APPROX 60 DEGS OF BANK. I IMMEDIATELY PULLED UP ELEVATOR AND POPPED RIGHT OUT OF THE VORTEX; BUT WAS IN NO HURRY TO DSND AGAIN. WE CROSSED TONTO INTXN AT ABOUT 14000 FT. I BELIEVE THIS WAS A FLUKE OCCURRENCE. WINDS WERE NOT PARTICULARLY STRONG OUT OF THE W. THERE IS A TOPOGRAPHIC UPSLOPE IN THAT AREA WHICH MIGHT ACCOUNT FOR THE VORTEX NOT SETTLING AS USUAL AND THE POSSIBILITY THAT THE B-757 MAY HAVE HAD TO SHALLOW ITS DSCNT ANGLE TO MEET THE 250 KT RESTR AT TONTO INTXN; BUT ENOUGH TO CONTRIBUTE TO THE VORTEX BEING AT A HIGHER ALT THAN ANTICIPATED. BELIEVE ME; I WILL GIVE THOSE GUYS ALL THE ROOM THEY NEED AND TAKE ALL FACTORS INTO CONSIDERATION FOR WAKE TURB AVOIDANCE. RECOMMEND B- 757 BE CLASSED FORMALLY AS A 'HVY.' CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR PARTICIPATED IN WAKE TURB STRUCTURED CALLBACK STUDY. RPTR WAS HURRIED DUE TO IMPENDING FLT AND ONLY ADDED THAT HE BELIEVES MORE SPACING IS REQUIRED BTWN B-757 ACFT AND THEY SHOULD BE RECLASSIFIED AS A HVY.