A LNDG B747-400 BALLOONS AFTER INITIAL TOUCHDOWN DURING A XWIND LNDG. POSTFLT INSPECTION REVEALS A SCRAPED #4 ENG POD AT JFK; NY.

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I WAS CAPT/PIC AND THE PF OF FLT APR/XA/00. PREDEP; DEP; TKOF; CLB; ENRTE CRUISE WERE NORMAL. ON DSCNT TO JFK ABOUT 17000 FT; APCH CTL REQUESTED THAT WE INCREASE OUR DSCNT RATE. AS PF; I EXTENDED THE SPD BRAKES AND SHORTLY THEREAFTER; WE WERE ALERTED TO AN EICAS MESSAGE: HYD PRESSURE DEMAND (4). I RETRACTED THE SPD BRAKES AND FOLLOWED THE APPROPRIATE IRREGULAR PROC. THIS RESULTED IN THE DEMAND PUMP SELECTOR #4 BEING PLACED IN THE OFF POS. ATIS INFO AT JFK INDICATED RWY 4R IN USE FOR LNDG. APCH WAS BRIEFED; AUTOBRAKES 3 WERE SELECTED AND FLAPS 30 DEG LNDG WAS PLANNED. JFK TWR CLRED US FOR THE RWY 4R APCH AND INFORMED US THAT WINDSHEAR WAS RPTED BY A PREVIOUS B747 WITH A +/-15 KTS WITHIN 300 FT OF THE GND. OUR REF SPD WAS 135 KTS FOR FLAPS 30 DEGS. I ADDED 15 KTS FOR RPTED WIND CONDITIONS AND MADE THE TARGET SPD 150 KTS. LNDG CHKLIST WAS COMPLETED. WE WERE IN VISUAL CONDITIONS BELOW ABOUT 1400 FT AGL. I DISCONNECTED THE AUTOPLT AND AUTOTHROTTLES AND HAND FLEW THE ACFT. AT 1000 FT AGL; I NOTICED THE WIND VECTOR INDICATING 38 KTS FROM ABOUT 100 DEGS. WE WERE #2 TO LAND ABOUT 3 1/2 MI BEHIND ANOTHER ACR. AT ABOUT 800 FT; THE R SEAT FO RPTED BIRDS; WHICH I OBSERVED TO OUR FRONT L AND PASSING ABOVE OUR L WING. TWR CLRED US TO LAND WHEN WE WERE ABOUT 300 FT AGL AND AS I RECOLLECT; RPTED THE WIND 100 DEGS AT 17 KTS. APCHING 50 FT AGL; I REMOVED THE R CRAB WITH USE OF L RUDDER AND SLIGHT R AILERON DOWN. I WAS LOOKING DOWN THE END OF THE RWY CONFIRMING OUR ALT AND THAT THE PREVIOUS LANDED JET WAS CLR OF THE RWY. THE INITIAL LNDG WAS SMOOTH WITH THE UPWIND R WING LOWERED SLIGHTLY. IN THAT INSTANT AS THE R GEAR TOUCHED DOWN; THE NOSE CAME UP AND THE R WING ALSO CAME UP AS IF AFFECTED BY A STRONG WIND GUST. I LOWERED THE NOSE AND R WING AND CTLED THE ACFT TO TRACK CTRLINE. ROLLOUT; PARKING; CHKLIST AND DEBRIEFING WERE NORMAL. THERE WAS NO MENTION OR THOUGHT OF ANYTHING UNUSUAL HAPPENING DURING THE FLT OR LNDG. NO ONE MENTIONED OR HAD ANY POSSIBLE THOUGHT THAT THERE MIGHT HAVE BEEN GND CONTACT WITH AN ENG POD. ON THE FOLLOWING MORNING; I RECEIVED A TELEPHONE CALL FROM OUR JFK CHIEF PLT INFORMING ME THAT MAINT PERSONNEL RPTED FINDING A 2 INCH BY 8 INCH SCRAPE AT THE 6 O'CLOCK POS OF THE #4 ENG POD DURING THEIR OVERNIGHT MAINT CHKS. I INFORMED HIM THAT I WAS SURPRISED AND DID NOT BELIEVE THAT THE DAMAGE COULD HAVE HAPPENED DURING OUR FLT. I RECOUNTED OUR ENTIRE FLT AND LNDG SEQUENCE WITH HIM. I HAVE SINCE CONFIRMED WITH THE FO WHO CONDUCTED THE PREFLT BEFORE DEP IN NARITA THAT NO DAMAGE WAS OBSERVED REF THE #4 ENG POD. I DO NOT HAVE ANY KNOWLEDGE OR IDEA AS TO WHAT CAUSED THE 2 INCH BY 8 INCH SCRAPE IN THE #4 ENG POD. IN HINDSIGHT AND RELATIVE TO THE ACFT REACTION AT TOUCHDOWN; IT IS MY OPINION THAT IT IS POSSIBLE THAT THE ACFT ACTED DIFFERENT AT TOUCHDOWN THAN WHAT MY EXPERIENCE AND TRAINING EXPECTED. MY INITIAL THOUGHT AT THE TIME WAS THAT WE EXPERIENCED A WIND GUST AT THE INSTANT TOUCHDOWN. NOW I WONDER IF THE INOP #4 HYD DEMAND PUMP MAY HAVE PLAYED A PART IN THE WAY THE NOSE AND R WING BEHAVED AT TOUCHDOWN. THE HYD SYS #4 PROVIDES PRESSURE TO THE: 1) R OUTBOARD ELEVATOR; 2) R INBOARD ELEVATOR; 3) SPOILERS #5; #6; #7; #8; 4) R INBOARD AILERON; 5) LOWER RUDDER; 6) R OUTBOARD AILERON; 7) #4 THRUST REVERSER; 8) NORMAL BRAKES; 9) WING GEAR ACTUATION; AND 10) OUTBOARD TRAILING EDGE FLAPS. THE #4 HYD DEMAND PUMP IS PWRED BY AIR PRESSURE FROM THE AIRPLANE PNEUMATIC SYS AND OPERATES WHEN IN THE AUTO POS WHEN THE RESPECTIVE ENG DRIVEN OUTPUT PRESSURE IS LOW. THIS LNDG DID NOT HAVE THE USE OF THE #4 HYD DEMAND PUMP. AT THE INSTANT OF TOUCHDOWN ALL OF THE ABOVE ITEMS #1 THROUGH #8 NOTED CTLS CAME INTO USE SIMULTANEOUSLY. IS IT POSSIBLE THAT THE #4 HYD SYS BECAME OVERLOADED AT THAT LNDG TOUCHDOWN INSTANT AND ADVERSELY AFFECTED ONE OR SEVERAL OF THE ABOVE NOTED CTLS? I DO NOT HAVE THE NECESSARY ENGINEERING INFO AVAILABLE AND HAVE ASKED ENGINEERING TO RESEARCH THIS QUESTION FURTHER.