WAKE TURB ENCOUNTER.

Narrative

CCC FLT X SCHEDULED ATR-42 SVC FROM ORF TO JFK. JFK ARR ATIS WAS: INFO TANGO AT KK50Z 1400 FT BROKEN 3500 FT OVCST VISIBILITY 7 MI LIGHT RAIN WIND 110 DEGS AT 12 KTS; ALTIMETER 29.90; LNDG ILS RWY 04R AND ILS RWY 04L. NEW YORK APCH INITIALLY ASSIGNED US THE ILS RWY 04R AND THEN CHANGED IT TO ILS RWY 04L WHEN WE WERE ABOUT 10 MI OUT. ESTABLISHED ON THE RWY 04L ILS AT APPROX 1000 FT WE ENCOUNTERED WAKE TURB WHICH ROLLED THE ACFT 45 DEG R. I TOOK CTL OF THE ACFT AND EXITED THE VORTEX. WE LANDED WITHOUT FURTHER INCIDENT. A QUESTION TO THE TWR CONFIRMED WHAT WE ALREADY KNEW -- OUR PRECEDING TFC TO RWY 04L WAS A SHORTS COMMUTER. NEITHER APCH NOR TWR MENTIONED A PRECEDING HVY 747 UNTIL I SPECIFICALLY ASKED WHAT TYPE WAS PRECEDING US ON THE RWY 04R ILS. IT WAS THEN REVEALED THAT AN ACR B747 (FLT Y) HAD PRECEDED US BY 4-5 MI ON THE ILS RWY 04R. THE E WIND HAD DRIFTED HIS L WING VORTICE DIRECTLY INTO OUR FLT PATH. TO MAKE MATTERS WORSE; RWYS 04L AND 04R ARE STAGGERED WITH THE TOUCHDOWN ZONE ON RWY 04R APPROX 3200 FT FURTHER DOWN FIELD THAN THAT OF RWY 04L. THIS PLACES THE RWY 04R GLIDEPATH ABOVE THE RWY 04L GLIDEPATH AND WITH AN EASTERLY WIND HVY ACFT WAKE VORTICES DSND INTO THE RWY 04L APCH ZONE AND AS DEMONSTRATED ARE A DISTINCT THREAT TO ACFT ON ILS RWY 04L. ADDITIONALLY; THE PLTS OF CCC FLT Z; ALSO AN ATR; TOLD ME THEY ENCOUNTERED WAKE TURB DURING THEIR ARR ON THE RWY 04L ILS ABOUT 15 MINS EARLIER. UPON HEARING THIS I CALLED KENNEDY TWR AND ADVISED THEM OF THE ENCOUNTERS AND OUR ASSESSMENT OF THE WIND/RWY SIT. THEY SAID THEY WOULD 'LOOK INTO IT.' CALLBACK CONVERSATION WITH REPORTER REVEALED THE FOLLOWING: RPTR STATED THE MAGNITUDE OF THE WAKE TURB AT 1000 FT; BUT ADDED THAT THE TURB WAS BEING FELT ALL THE WAY DOWN FINAL DSCNT. IT WAS THE SUDDEN CHANGE OF TURB AT 1000 FT THAT BOTHERED THEIR FLT PATH. AS THE ACFT ROLLED TO THE R IN A 45 DEG BANK; THE CAPT TOOK OVER AS PF. CAPT STATED THAT HE WOULD NOT LET THE SAME SIT OCCUR AGAIN. HE WOULD AVOID THE SIT BY REFUSING AN ILS TO RWY 04L WHEN A HVY ACFT IS FLYING ILS TO RWY 04R WITH AN E WIND. TURB CAUSED 45 DEG BANK; PARTIAL CTL LOSS FOR A PERIOD OF 5 SECONDS; CAUSING TEMPORARY EMOTIONAL STRESS. RPTR'S ACFT WAS AN ATR 42 WHILE THE WAKE GENERATING ACFT WAS A B-747.