B747-400 CAPT REPORTED POSSIBLE PARTIAL DEPLOYMENT OF ENG #4 REVERSER DURING DEP; WHICH NECESSITATED A RETURN TO LAND.

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WE FLEW ACFT INBOUND THE DAY PREVIOUS WITH #4 THRUST REVERSER MECHANICALLY INOP. ACFT WAS SVCED OVERNIGHT IN HONG KONG AND ACFT REVERSER #4 WAS RETURNED TO SVC. (PAST LOGBOOK WRITE-UPS SHOWED HISTORY OF REVERSER UNLOCKED LIGHT OVER THE PAST SEVERAL DAYS). TKOF ON RWY 13 HKG REQUIRES TRACK OUTBOUND ON THE LOC 31. WX WAS STEADY RAINSHOWERS; 1500 SCATTERED/BROKEN VISIBILITY 3000 METERS. WIND 250 DEGS AT 11 KTS. WIND DRIFT SHOULD HAVE BEEN L OF CTRLINE. ON TKOF; MAX PWR USED FOR WET RWY AND SLIGHT TAILWIND. AT ABOUT 400 FT AGL; SLIGHT VIBRATION WAS NOTED AND ACFT STARTED TO DRIFT R OF CTRLINE. I WAS FLYING AND NOTED THE DRIFT; AS DID TWR CTLR. THE AMBER REV WAS NOW ANNUNCIATED ABOVE #4 ENG DISPLAY. TKOF ROLL HAD BEEN NORMAL; ALL INDICATIONS NORMAL. I RETARDED #4 THROTTLE; WHICH INCREASED DRIFT R OF CTRLINE UNTIL RUDDER APPLIED FOR CORRECTION. THROTTLE WAS RETARDED BELOW 1.23 EPR AT WHICH POINT THE AMBER REV #4 WAS EXTINGUISHED. IT WAS DECIDED BTWN THE CAPT AND I THAT #4 SHOULD BE LEFT AT IDLE AS WE WERE IN THE WX AT THIS POINT; DODGING TSTMS/RAINSHOWERS AND THE ENG INDICATORS WERE NORMAL. I GAVE THE ACFT TO THE CAPT AT INITIAL LEVEL-OFF AND DID ALL APPROPRIATE CHKLIST PER SOP AND THE SIT WARRANTED. IT WAS DECIDED TO RETURN TO HKG. APCH WAS MADE WITH #4 ENG AT IDLE. 3 ENG APCH CHKLIST USED. COM WITH THE COMPANY; MAINT; DISPATCH; ALL VERY POOR DUE TO WX; PLUS HONG KONG DRAGON RADIO UNAVAILABLE FOR PHONE PATCH. REVERSER WAS INOP ONCE AGAIN; WE RETURNED BY HONG KONG MAINT. WE RE- DISPATCHED AND DEPARTED IN SAME ACFT FOR TOKYO ABOUT 2 HRS LATER. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: FO WAS FLYING THE ACFT. HE STATED THAT HE NOTICED THE AMBER REVERSE LIGHT ON SHORTLY AFTER TKOF. DURING THE INITIAL CLBOUT A CROSS-CTL CONDITION EXISTED WHICH HE CORRECTED WITH A SMALL APPLICATION OF L RUDDER TO STOP THE R DRIFT. A SLIGHT VIBRATION STARTED AT 400 FT AND STOPPED WHEN THE PWR WAS REDUCED TO 1.23 EPR. RUDDER APPLICATION WAS NEVER MORE THAN A SLIGHT APPLICATION. THE AMBER REVERSE LIGHT ALSO EXTINGUISHED AS THE VIBRATION STOPPED. THE ACFT WAS RETURNED TO HONG KONG WHEREIN MAINT LOCKED THE REVERSER INTO THE STOWED POS. ON THE NEXT FLT; THE REVERSER NEVER SHOWED AN AMBER REVERSE LIGHT; NO VIBRATION OCCURRED; AND ALL FLT CTL APPLICATIONS WERE NORMAL.