B757 FLC CHALLENGE N90 HVY JET SPACING WHEN FOLLOWING A B747 INTO JFK.

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WE SUSPECTED THAT WE WERE FOLLOWING A B747 COMING INTO JFK AS WE WERE BEING VECTORED FOR THE VOR RWY 13L APCH. WE SUSPECTED THIS BECAUSE OF THE CALL SIGN OF THE ACFT WHICH USUALLY FLIES B747'S INTO JFK. NOTICING ON THE TCASII THAT THIS ACFT WAS LESS THAN 10 MI AHEAD OF US; AND WE WERE GAINING ON HIM; I ASKED ATC WHAT KIND OF ACFT WE WERE FOLLOWING. HE HEMMED AND HAWED A BIT; AND FINALLY SAID THAT WE WERE NOT FOLLOWING ANYONE. THIS DID NOT FIT WITH WHAT WE WERE SEEING ON THE TCASII AND WHAT WE WERE HEARING ON THE RADIO. OF COURSE; SINCE ATC WOULD NOT ACKNOWLEDGED THAT WE WERE INDEED FOLLOWING A B747; HE DID NOT GIVE A WAKE TURB WARNING EITHER. LATER IN THE APCH; WHEN WE SWITCHED TO TWR FREQ; THE TWR CTLR IMMEDIATELY INFORMED US -- WITHOUT ANY QUERY OR PROMPTING FROM US -- THAT WE WERE BEHIND A B747; ISSUED A CAUTION WAKE TURB; AND TOLD US TO LAND ON RWY 13R TO KEEP US AWAY FROM HIM. I WAS VERY ANGRY THAT THE APCH CTLR HAD ESSENTIALLY LIED TO US ABOUT THE B747 AHEAD OF US; AND DIDN'T BOTHER TO WARN US ABOUT WAKE TURB EITHER. I GOT THE IMPRESSION THAT THE REASON HE DID NOT WANT US TO KNOW WHAT WE WERE FOLLOWING IS BECAUSE HE DIDN'T WANT US TO SLOW DOWN ANY MORE. HE HAD JUST PREVIOUSLY TOLD US TO NOT SLOW ANY MORE UNTIL CRI. HE WAS MORE CONCERNED ABOUT KEEPING HIS TFC MOVING ACCORDING TO HIS PLAN THAN FOR THE SAFETY OF OUR AIRPLANE. I WOULD THINK THAT AFTER WHAT HAPPENED WITH A RECENT ACR WAKE TURB INCIDENT; CTLRS WOULD HAVE A BIT MORE RESPECT AND CONCERN FOR JUST HOW SERIOUS WAKE TURB CAN BE; BUT SADLY THAT DOES NOT SEEM TO BE THE CASE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR ADVISED THAT SHE RECOGNIZED THE CALL SIGN OF THE JET IN FRONT; AND KNEW IT WAS A B747. SHE THEN ASKED THE CTLR FOR 10 MI SPACING BEHIND THE B747; AND BEGAN A SPD RESTR BACK TO 180 KTS. THE RPTR STATED THAT THIS WAS THE POINT IN WHICH THE APCH CTLR'S COMPLAINT WITH THE FLC BEGAN. THE RPTR STATED THAT SHE ALWAYS ASKS FOR MORE THAN 'MINIMUM' SPACING; DEPENDING ON WHAT ACFT TYPE SHE IS FOLLOWING.