AN ACR LGT SUFFERED THROUGH WAKE TURB FOLLOWING A WDB. THE ACFT WERE ON STAGGERED APCHS; IN THE WX; TO RWYS 4L AND 4R AT JFK.

Narrative

THE SYS ALLOWS STAGGERED (LESS THAN 2 MI) APCHS TO RWYS 4L AND 4F AT JFK. ALTHOUGH THIS RPT IS NOT ABOUT ANY RULE INFRACTION; IT DOES ILLUSTRATE A DEFECT IN THE SYS OF ACFT SEPARATION BTWN HVY'S AND OTHERS. I HAVE WRITTEN A LETTER TO THE 'AIR TFC MGR; NY TRACON' IN HOPES THAT THIS DEFECT CAN BE CORRECTED. THE TWR SUPVR SUGGESTED THAT I WRITE YOU AND RELATE THIS INCIDENT TO YOU. HE SAID MOST OF HIS TWR PEOPLE READ YOUR RPTS; SO IT WOULD BE A GOOD WAY TO GET THE WORD OUT. I WAS THE CAPT OF AN ACR LGT AS IT APCHED JFK FOR LNDG. THERE WAS A RAGGED CEILING AT ABOUT 1000 FT; GOOD VISIBILITY; LIGHT SNOW; SEVERE ICING IN THE CLOUDS AND A WIND OUT OF THE SE AT ABOUT 15 KTS. THE ATIS RPTED AN ILS TO 4R AND TKOFS ON 4L. WE WERE INITIALLY TOLD WE WERE TO MAKE AN APCH TO 4R. BEFORE WE INTERCEPTED THE LOC OF 4R; WE WERE TOLD TO CHANGE TO 4L. MY FO REQUESTED OUR DISTANCE FROM THE HVY AHEAD AND THE TWR TOLD US '6 MI.' AT ABOUT THE SAME TIME; THE ACFT SUDDENLY ROLLED UNCTLABLY AND THE AUTOPLT WAS DISCONNECTED EITHER BY THE VIOLENT MANEUVER OR BY THE AUTOPLT YOKE DISCONNECT SWITCH HITTING MY HAND AS THE YOKE TURNED RAPIDLY. MY FIRST REACTION WAS THAT WE ENCOUNTERED A WINDSHEAR PROB; BUT THE WIND READOUT DID NOT INDICATE A CHANGE IN THE WIND DIRECTION OR VELOCITY. IT WAS ILLOGICAL THAT WAKE TURB FROM A HVY ACFT 6 MI AHEAD WITH SUCH A XWIND WOULD AFFECT US; SO THAT WAS DISCOUNTED. SHORTLY THEREAFTER; WE RECEIVED ANOTHER SUDDEN ROLL AND THEN A THIRD ONE A FEW SECONDS LATER. AT THIS POINT; I DECIDED TO GAR WITHOUT REALLY KNOWING WHAT WAS CAUSING THE VIOLENT MOVEMENTS TO THE ACFT. THE FO AT THIS TIME SUGGESTED THAT THERE MIGHT BE A HVY MAKING AN APCH TO 4R THAT WAS A LOT CLOSER THAN 6 MI. WE WENT AROUND AT ABOUT 800-1000 FT STILL IN THE CLOUDS AND NOT AWARE OF ANY OTHER ACFT EXCEPT THE HVY RPTED AT 6 MI AHEAD (PROBABLY ON THE GND AT THIS POINT). ANOTHER APCH WAS MADE AND AN UNEVENTFUL XWIND LNDG. THE FO CALLED THE TWR TO DISCUSS THE INCIDENT. AT THIS TIME WE FOUND OUT THAT THERE WAS A HVY; UNRPTED TO US; MAKING AN APCH TO 4R AT THE SAME TIME WE WERE ON 4L ILS AND THAT HE WAS AT THE LEGAL MINIMUM SEPARATION OF 2 MI. SINCE WE WERE DOWNWIND FROM THE 4R LOC; THE WIND APPARENTLY WAS CARRYING THE WAKE TURB OF THE HVY MAKING THE APCH TO 4R OVER TO THE LOC OF 4L AND RIGHT IN OUR PATH. THIS IS THE SAME AS BEING 2 MI BEHIND A HVY FOR THE SAME RWY IF THE WIND WERE RIGHT DOWN THE RWY.