Narrative:

Just before top of climb; 'bleed duct leak' message displayed on the EICAS for a couple of seconds then vanished. Just after top of climb; 'bleed duct leak left' displayed and stayed on the EICAS. Performed the checklist in the QRH which isolates the left side of bleed air system. Confirmed bleed valves closed using the cmc. Elected to continue for the following reasons: aircraft confign was stable for the time being; several options existed for diversion; rksi; rjaa; rjbb; etc; no adverse WX was forecast en route or at destination. Informed the company using ACARS of the situation. Maintenance requested the error codes which we provided. Arrival was uneventful. Maintenance had not been informed of the situation. Maintenance was unable to find any problem and cleared the item. We continued to ord. All parameters were normal. On arrival in ord; maintenance was well aware of the previous write-up and began working on the left wing as soon as we arrived. We were led to believe that this was an indication problem by maintenance. I briefed the outbound crew in ord of the chain of events and that I believed that maintenance control 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 aircraft 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.

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Original NASA ASRS Text

Title: 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.

Data retrieved from NASA's ASRS site as of January 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.