B777 fuel totalizer discrepancies
All these posts are pretty interesting. I believe Boeing had a bulletin dealing with B777 fuel totalizer discrepancies.
All is well and dandy when you do not have other problems like fuel leak. Several years ago a colleague in a major Pacific Rim carrier had this fuel totalizer discrepancy together with a small fuel leak. Sometime after departure from Seoul he had noticed that the fuel totalizer was reading about 1000-2000 lbs more than calculated and then fluctuated to slightly less than calculated. The fluctuation of the totalizer from several hundreds of lbs more and then to several hundreds less than calculated continued for sometime; this was consistent with the contents of the Boeing bulletin. A couple of hours after that, he began noticing a persistent reading less than calculated only to be followed by an increase to more than calculated as they entered turbulence. Once he climbed above the turbulent layer in smooth air, the totalizer versus FMC calculated reading gradually decreased at a small rate of 200 to 300lbs an hour. He began to think he had a fuel leak problem! He tried visual inspection but since it was dark and the fuel leak rate was pretty small, he could not visually ascertain it was fuel leak. He accomplished the fuel leak checklist and indeed, it showed a leak rate fluctuating between 200-800lbs per hour........however he could not ascertain the source of the leak.
Being an ETOPS flight and not wanting to shutdown any engine unnecessarily, he opted to make a precautionary landing. However the airline dispatch and maintenance DID NOT concur with his decision. According to the company maintenance and dispatch, the totalizer discrepancy was within limits as made out in the Boeing bulletin and real time maitenance datalink from the aircraft revealed no problems! They demanded that he continued the flight to the destination.
Nevertheless, he countermanded company directive to continue and diverted to Anchorage where upon landing it was indeed found that he had a small engine fuel leak. Of course he was exonerated but the company officials did gave him a hard time for countermanding their directive twice; once for deciding to divert and secondly, diverting to an enroute alternate despite their later stated preference he return to Seoul in case he really insisted on diverting.
All this grief came because of assumptions made because of the B777 fuel totalizer discrepancies which we see everyday so much so that any fuel discrepancy betweeen calculated and totalizer are just glossed over and ignored. Be careful here!