A B747-400 AT TOP OF CLB; FL330; HAD 'BLEED DUCT LEAK' MESSAGE ON EICAS FOR 2 SECONDS. CLOSED L BLEED VALVES. OPERATED 2 LEGS WITH NO REPEAT RPT.

Narrative

JUST BEFORE TOP OF CLB; 'BLEED DUCT LEAK' MESSAGE DISPLAYED ON THE EICAS FOR A COUPLE OF SECONDS THEN VANISHED. JUST AFTER TOP OF CLB; 'BLEED DUCT LEAK L' DISPLAYED AND STAYED ON THE EICAS. PERFORMED THE CHKLIST IN THE QRH WHICH ISOLATES THE L SIDE OF BLEED AIR SYS. CONFIRMED BLEED VALVES CLOSED USING THE CMC. ELECTED TO CONTINUE FOR THE FOLLOWING REASONS: ACFT CONFIGN WAS STABLE FOR THE TIME BEING; SEVERAL OPTIONS EXISTED FOR DIVERSION; RKSI; RJAA; RJBB; ETC; NO ADVERSE WX WAS FORECAST ENRTE OR AT DEST. INFORMED THE COMPANY USING ACARS OF THE SITUATION. MAINT REQUESTED THE ERROR CODES WHICH WE PROVIDED. ARR WAS UNEVENTFUL. MAINT HAD NOT BEEN INFORMED OF THE SITUATION. MAINT WAS UNABLE TO FIND ANY PROB AND CLRED THE ITEM. WE CONTINUED TO ORD. ALL PARAMETERS WERE NORMAL. ON ARR IN ORD; MAINT WAS WELL AWARE OF THE PREVIOUS WRITE-UP AND BEGAN WORKING ON THE L WING AS SOON AS WE ARRIVED. WE WERE LED TO BELIEVE THAT THIS WAS AN INDICATION PROB BY MAINT. I BRIEFED THE OUTBOUND CREW IN ORD OF THE CHAIN OF EVENTS AND THAT I BELIEVED THAT MAINT CTL WAS NOT TELLING US THE ENTIRE STORY. 2 DAYS LATER; I LEARNED FROM TALKING WITH THAT SAME CREW THAT I BRIEFED IN ORD; THAT A BLEED LEAK WAS IN FACT FOUND AND REPAIRED IN ORD. MY CONCERN IS THIS: IN AN EFFORT TO MAKE SCHEDULE WE WERE 'SOLD' THE ACFT THAT IN FACT HAD A REAL BLEED AIR LEAK; AND WE OPERATED IT TO ORD WITH THAT LEAK. THE FACT THAT NO INDICATION OCCURRED DURING THE LAST LEG IS AT BEST SURPRISING AND LEADS ME TO BELIEVE THAT SOME SENSORS WERE DISABLED BY AN UNDISCLOSED METHOD.