LTSS. ACR DSNDING TO A LOWER ALT RECEIVES A TCASII RA AND FOLLOWS IT. LATER THE APCH SUPVR SAID THAT THE ACR WAS CLRED TO A HIGHER ALT.

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AT FL190; ON THE LENDY ARR FOR JFK; OUR FLT WAS GIVEN A 140 DEG HDG; A DSCNT CLRNC TO 16000 FT; AND RADAR VECTORS FOR A VOR RWY 13L APCH. FURTHER DSCNT CLRNCS WERE ISSUED TO 6000 FT ON A HDG OF 180 DEGS. THE FO READ BACK 'CLRED TO 6000 FT.' HE SET 6000 FT IN THE ALT ALERT UNIT; AND I REPEATED THE HDG (180 DEGS) AND ALT (6000 FT). AS WE PASSED 9000 FT; APCH CTL ADVISED US OF CLBING TFC (LEAR JET) AT OUR 9 O'CLOCK POS. I CHKED THE TCASII AND LOCATED THE TFC; BUT I WAS NEVER ABLE TO GET A VISUAL SIGHTING OF THE ACFT. DSNDING OUT OF 7900 FT THE TCASII GAVE US A TA AND I NOTICED THE TFC WAS NOW AT OUR 6 O'CLOCK POS AND STILL CLBING. AT 7500 FT THE TCASII GAVE AN RA WITH A MANEUVER TO 'REDUCE DSCNT.' I IMMEDIATELY APPLIED PWR; STOPPED MY DSCNT AND STARTED A CLB. THE CONFLICT WAS RESOLVED IN LESS THAN 6 SECONDS 200 FT OF CLB. AS SOON AS WE GOT THE RA THE FO NOTIFIED APCH CTL OF OUR CLB AND THE REASON FOR IT. THE TFC CONTINUED TO MOVE FROM OUR 6 O'CLOCK POS TO OUR 4 O'CLOCK POS; APPROX 1 MI BEHIND US ON THE TCASII DISPLAY AND 700 FT BELOW US. WHEN THIS EVENT OCCURRED I CHKED THE ALT ALERT UNIT; 6000 FT WAS SET IN THE WINDOW; WE HAD RECEIVED NO AURAL OR VISUAL ALERTS FROM THE UNIT AND ALL 3 ALTIMETER SETTINGS WERE THE SAME. AT NO TIME DURING THIS EVENT DID APCH CTL QUESTION US AS TO OUR PASSING ALT OR OUR CLRED ALT. NORMALLY WHEN YOU DEVIATE MORE THAN 200 FT FROM AN ASSIGNED ALT; ATC CALLS TO QUESTION YOUR ALT IMMEDIATELY. AFTER THE CONFLICT WAS RESOLVED; IE; 'CLR OF TFC' WE INFORMED APCH CTL THAT WE WERE CONTINUING OUR DSCNT TO 6000 FT ON A HDG OF 180 DEGS. WE WERE THEN TOLD TO TURN TO A HDG OF 340 DEGS AND DSND TO 3000 FT. AFTER LNDG I WAS REQUESTED TO CALL NEW YORK TRACON. I SPOKE TO A SUPVR AND WAS THEN TOLD AN INVESTIGATION WOULD BE CONDUCTED BECAUSE I HAD DSNDED BELOW MY CLRED ALT OF 8000 FT. MY QUESTION IS WHY DID IT TAKE AN RA FROM MY TCASII AND OUR CALL TO APCH CTL TO ALERT THEM TO THE CONFLICT. APCH CTL NEVER ASKED WHAT ALT WE WERE DSNDING TO WHEN WE PASSED 7900 FT; 7800 FT; 7700 FT; 7600 FT OR EVEN AFTER WE TOLD THEM WE WERE IN A CLB TO SATISFY THE RA. NORMALLY THE ATC CTLRS DO AN OUTSTANDING JOB EVEN THOUGH THEY ARE OVERWORKED; UNDERSTAFFED; AND ARE OPERATING ANTIQUATED EQUIP. HOWEVER; IN REGARDS TO THIS INCIDENT I CAN ONLY SAY THANK GOODNESS FOR AN OPERATING TCASII. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THIS CAPT SAID THAT HE AND HIS FLC DEFINITELY HEARD AND READ BACK THE CLRNC TO 6000 FT. THEY THEN FOLLOWED THEIR AIRLINE'S PROCS FOR THE B727-200 AND SET AND VERIFIED THE ALT IN THEIR ALERTER AND STARTED DOWN. WHEN THE CTLR TOLD THEM OF THE TFC AND THAT IT WAS CLBING HE DID NOT SAY TO WHAT ALT IT WAS CLBING. AFTER THEY TOLD THE CTLR OF THEIR TCASII INSPIRED MANEUVER HE NEVER MENTIONED THAT THEY HAD BEEN ON THE WRONG ALT. ONLY AFTER THEY TALKED TO THE N90 SUPVR DID THEY REALIZE THAT THERE MAY BE AN ALT ASSIGNMENT ERROR. THE FAA HAS NOT CONTACTED THE CAPT OR THE COMPANY. THE CAPT RPTED THIS INCIDENT TO THE COMPANY AND THE COMPANY WAS UNABLE TO OBTAIN FURTHER INFO FROM THE TRACON WHICH AT LAST CONTACT WAS INVESTIGATING.