WAKE ENCOUNTER -- A COMMUTER ACR GETS INTO THE WAKE OF A WDB ACR 7 PT 5 NM IN FRONT.

Narrative

TCASII WAS AT 10 NM LEVEL AT 8000 FT. CLRED TO 4000 FT. ON TCASII AT APPROX 7 1/2 NM WAS AN ACFT DSNDING THROUGH 7000 FT. AT APPROX 7500 FT ENCOUNTERED WAKE (A SEVERE JOLT DOWN). ACFT WAS LEVELED AND TURNED UPWIND. SEVERAL SECONDS LATER ENCOUNTERED A MINIMAL ROLL WAKE; I BELIEVE I WAS ABOVE VORTEX. ADVISED ATC OF ENCOUNTER; AND TO DETERMINE TYPE OF ACFT FOLLOWING. AFTER 3RD CALL WAS TOLD IT WAS A B747. THE JOLT FROM THE VORTEX WAS EQUAL TO RUNNING INTO A CURB AT APPROX 20 MPH WITH A CAR. NO ROLL WAS NOTICED. THE FLT ATTENDANT WAS STANDING AT THE TIME AND WAS UNINJURED. THE B747 WAS NEVER SEEN VISUALLY. THIS OCCURRENCE IS ONE OF SEVERAL I HAVE HAD WHILE WITH MIA APCH CTL. IT APPEARS THE CTLRS ARE ONLY CONCERNED WITH 5 NM SEPARATION. (SEVERAL YRS AGO FLYING THE SF340 I WAS 6- 7 NM BEHIND A 757 AND HAD AN INDUCED ROLL OF APPROX 30 DEGS FROM WAKE). THE APCH FROM SE TO MIA WE ARE PUT AT 8000 FT. JET ACFT ARE FLOWN OVER AT 9000 FT OR 10000 FT THEN GIVEN A DSCNT FOR APCH USUALLY 3000 FT OR 4000 FT. WE ARE FLOWN TO A POINT GENERALLY 1-2 NM FROM OTHER ACFT PATH OR LESS (IF CTLR BUSY WITH OTHER ACFT) THEN GIVEN OUR DSCNT CLRNC TO 3000-4000 FT. SINCE WE ARE FLYING ON RADIALS; DEPENDING ON WINDS IT COULD BE A HIT OR MISS ENCOUNTER. MY RULE FOR WAKE IS TO BE AT LEAST 7 OR MORE NM'S BEHIND AND ALWAYS ABOVE THE FLT PATH OF THE ACFT; OR TO STAY UPWIND. SOMETIMES ATC IS MORE CONCERNED WITH THE FLOW OF TFC. THEY SEEM TO FORGET THAT AT LOWER ALTS WE CAN MAINTAIN AT LEAST 240 KTS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING: THE RPTR WAS FLYING A SAAB SF340B AND THE PRECEDING ACFT WAS A BOEING 747-200 OPERATED BY A FOREIGN ACR. THE RPTR DID NOT DISCOVER THE TYPE UNTIL AFTER THE WAKE ENCOUNTER WHEN HE QUERIED THE APCH CTLR. THE MIA CTLRS DO NOT SEEM TO UNDERSTAND THE PROBS CAUSED BY WAKES ACCORDING TO THIS CAPT. HE HAS COMPLAINED ABOUT THE SEPARATION TECHNIQUES USED HERE BEFORE HE SAID; BUT NOTHING CHANGES. THIS TIME HIS UNION SAFETY CHAIRMAN WAS GOING TO MEET WITH THE TRACON REPRESENTATIVES; BUT HE HAS NOT HEARD OF THE OUTCOME FROM THAT MEETING.