A B757-200 ON APCH AT 162 KTS FLAPS SELECTED TO 30 UNITS; THEN BACK TO 25 UNITS; GOT 'FLAP LOAD RELIEF' EICAS WARNING. FLAPS THEN RETRACTED 20 UNITS.

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DURING INITIAL APCH TO JFK FLT PASSED NEAR VFR TFC THAT CAUSED A TCAS RESOLUTION ALERT (RA). WE HAD BEEN ADVISED OF THE TFC BY APCH; HAD ACQUIRED THE TFC VISUALLY; AND COMPLIED WITH THE RA (A NO CLB ARC ON THE VSI). NO EVASIVE ACTION WAS REQUIRED. SOME THREE OR FOUR MINUTES LATER WE WERE COMPLETING THE VOR/GPS RWY 13L APCH TO JFK. WE WERE IN VISUAL CONDITIONS AND HAD BEEN CLEARED TO LAND BY TWR. WE APCHED THE CANARSIE VOR AT 1500 FT MSL; GEAR DOWN; FLAPS 20 AND AT ATC ASSIGNED SPD OF 180 KTS. THE PF BUGGED BACK TO VREF PLUS 5 KTS (APPROX 135 KTS); CALLED FOR FLAPS 25 THEN 30 AND AT CANARSIE VOR BEGAN A VERT SPD DSCNT. HE THEN DISCONNECTED THE AUTOPLT. I SELECTED 25 THEN 30 WITH THE AIRSPD ABOVE THE FLAPS 30 LIMIT SPD OF 162 KTS. SHORTLY THEREAFTER I HEARD AN AURAL WARNING AND NOTED A 'FLAP LOAD RELIEF' EICAS MESSAGE. I IMMEDIATELY BROUGHT THE FLAP LEVER UP TO THE 25 POSITION. THE FLAPS RETRACTED TO 20 DESPITE THE FLAP LEVER BEING AT 25. PERHAPS FIVE SECONDS LATER THE 'FLAP LOAD RELIEF' EICAS MESSAGE EXTINGUISHED AND BOTH 'LEADING EDGE SLAT DISAGREE' AND 'TRAILING EDGE FLAP DISAGREE' EICAS MESSAGES CAME ON; AS DID THE 'LEADING EDGE' AND 'TRAILING EDGE' FORWARD PANEL CAUTION LIGHTS. WE DISCONTINUED THE APCH; RETRACTED THE GEAR AND COMPLIED WITH HDG AND ALT INSTRUCTIONS FROM TWR. I REQUESTED VECTORS AWAY FROM JFK TO AN AREA WHERE WE COULD TROUBLESHOOT THE FLAP MALFUNCTION. THE FO CONTINUED TO FLY AND TALK WITH ATC WHILE I GOT OUT THE QRH; BRIEFED THE PAX AND CONTACTED BOTH DISPATCH AND MAINT THROUGH RADIO. AFTER DISCUSSION WITH MAINT; WE COMPLETED THE 'LEADING EDGE SLAT DISAGREE' QRH PROC. ALL EICAS MESSAGES AND CAUTION LIGHTS EXTINGUISHED. I ELECTED TO LEAVE THE FLAP LEVER AT 25 WITH THE FLAPS AT 20. I BRIEFED THE FA'S AND PAX; WE RETURNED TO JFK AND LANDED UNEVENTFULLY ON RWY 22R. FLAPS WERE LEFT DOWN AFTER LNDG. THE CHIEF PLT AND MAINT MET THE ACFT AT THE GATE. A LOGBOOK ENTRY DETAILING THE EVENT WAS MADE AND THE FLT RECORDER WAS REMOVED AND SENT TO ZZZ1. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE FLAP HANDLE WAS SELECTED TO 30 UNITS AT 162 KTS WHICH WAS CORRECTED IMMEDIATELY AND SELECTED TO 25 UNITS. THE RPTR SAID THE 'FLAP LOAD RELIEF' EICAS WARNING ACTIVATED AND THE FLAPS RETRACTED NOT TO 25 UNITS AS SELECTED BUT TO 20 UNITS. THE RPTR STATED THE FLAPS SHOULD HAVE RETRACTED TO 25 UNITS PER FLT OPS MANUAL. THE RPTR SAID WHEN THE FLT DATA RECORDER WAS REMOVED AND READ IT SHOWED THE FLAPS DID IN FACT GO TO 20 UNITS. THE RPTR STATED THE FLT OPS MGRS AND THE ACFT MANUFACTURERS ARE SEEKING A RESOLUTION TO THIS MALFUNCTION. THE RPTR STATED MAINT MADE A GND OP CHK OF THE FLAP SYSTEM AND LOAD RELIEF SYSTEM AND FOUND NO FAULT.