AN ACR LTT EXPERIENCED WAKE TURB BEHIND A B-757.

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4 MI BEHIND A BOEING 757 AT 3000 FT AND JUST CLRED TO 2700 FT AND CLRED FOR THE APCH. THE BOEING INTERCEPTED THE GS ABOVE US AT ABOUT 4000 FT. SUDDENLY WE HIT HIS WAKE TURB AND BEGAN RAPIDLY ROLLING TO THE L. AT ABOUT 30 DEG BANK; BOTH I AND MY FO WERE APPLYING MAXIMUM EFFORT TO ROLL TO THE R. THE ROLL STOPPED AT ABOUT 45 DEGS AND THE SUBSEQUENT ROLLOUT WAS VERY RAPID BECAUSE OF THE MAXIMUM EFFORT APPLIED IN THE WAKE. THE INCIDENT WAS RPTED TO ATC AND THEY REALLY DID NOT KNOW WHAT TO SAY (THEY WERE FOLLOWING ACCEPTED PROCS). IT IS COMMON PRACTICE FOR TURBOPROPS TO INTERCEPT THE GS AT A LOWER ALT THAN HVY JETS. EVEN WITH MINIMUM SEPARATION BEHIND THESE HEAVIES; SOONER OR LATER YOU ARE GOING TO FLY INTO THE DSNDING WAKE WHEN INTERCEPTING THE GS. SOLUTION: 1) DOUBLE THE SEPARATION FOR TURBOPROPS BEHIND THESE HEAVIES (NOT ALWAYS PRACTICAL FOR THE CTLR AND TURBOPROP PLTS). 2) WHEN A TURBOPROP IS FOLLOWING A HVY; HAVE BOTH INTERCEPT AT THE SAME ALT SO THAT THE DSNDING WAKE IS ALWAYS BELOW THE TURBOPROP RECIPROCATING ENG AIRPLANE AND THE SMALLER CORPORATE JETS. NOTE: THIS WAS MY SECOND ENCOUNTER WITH WAKE BEHIND A B757. THE FIRST WAS IN THE CLB (2000 FT PLUS AGL) AND I DON'T REALLY KNOW HOW THAT COULD BE AVOIDED IN THE REAL WORLD.