777s have ultrasonic fuel qty indication system. As mentioned above there are some 20 probes in each tank (60 total) to detect qty. Few clarifications regards to above posts:
1) there is a Water detector in both tanks and if there is Water then the Maintenance Page will def show the message.
2) Was the APU running all along the transit???? and how long was the transit for?? If it was.....then it does consume a significant amout and causes lot of discrepancies.
3) the density of the uplifted fuel is another factor. What the refueller mentions might not be exactly accurate untill and unless he or she has actually checked it just before refuelling. If the uplift is quite large then theres lot of room for discrepancies.
4) Going back the fuel system on 777s.....the whole logic set-up in the FQPU computer relies on these 60 probes in the tanks ( 20 in each). Now if there is some kind of problem in the sensing of these probes then the FQPU starts showing the quantities according to the Logic status of the software.....meaning the average qty coming from the serviceable probes and then gets more complicated when the quantities start to go blank when the minimum number required to detect actual quantity goes u/s.The ones which really cause trouble is those which are intermittent.....meaning they are serviceable 1 minute and goes u/s in second minute......the computer monitors them constantly and goes mental with the calculations if it has a good number of probes which are working 1 second then not working and then start working again......
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There are lots of things that could have caused those errors.....pin-pointing it to something that actually was the cause is really difficult......anyways the fuel was enough to land safely and thats what matters most!!!!
