Boeing 777-300ER fuel indication
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Real time datalink of onboard data?
Me thinks it's a myth like all urban legends. Been to a maintenance base in the sandpit once and we have guys yowling out bets on English soccer ; they ain't got no time for any real or pseudo time datalinks!
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Me thinks it's a myth like all urban legends. Been to a maintenance base in the sandpit once and we have guys yowling out bets on English soccer ; they ain't got no time for any real or pseudo time datalinks!
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Well, Old Smokey's trick to " soft reboot " the VNAV function of the FMC does seem to work in getting the calculated figure to reconcile with the totalizer. However, in many many flights where the flight was exactly conducted as per computer flight plan ( as far as TOWs, routes and flight levels are concerned ), the calculated figures are almost equal to the computed flight plan figures at the various check waypoints. On the other hand the totalizer figures fluctuated from plus to minus several hundreds of kgs! By " soft rebooting " the VNAV function, the calculated figure almost immediately equals the totalizer and as time goes on, the two values start to drift apart again.
I still think that the totalizer suffers from inaccuracies in the FQIS; B777 drivers should heed woody spooney's warning about the totalizer misleading the unlucky ones who get slow fuel leaks.
I still think that the totalizer suffers from inaccuracies in the FQIS; B777 drivers should heed woody spooney's warning about the totalizer misleading the unlucky ones who get slow fuel leaks.
I've noticed this happening on about one out of three flights over the last decade. It has improved since the early days with software mods but you still expect some discrepancies - it's even got a name now: "mid-Atlantic dip"!
The good thing is that the accuracy returns as the amount reduces, so the danger of running dry unexpectedly is small.
I remember being over the middle of Khazakstan about 10 years ago, looking at the scenery, when the "fuel imbalance" checklist pops up... OK, 2T difference, let's see what's in the tanks... Oh, the total seems to be going down by at least several tonnes a minute - that's not good - might have to shut one down. Got the 3rd pilot to go back and see if there was any indication of a fuel leak: no. Were just contemplating chopping the motor on the offending side when we noticed that the "leak" had stopped and we seemed to getting a bit of in-flight refuelling.
As the indicated imbalance was in the order of 15T, we took the autopilot out and let go: steady as a rock. Hmmm. Over the next 20mins or so the fuel displays returned to normal. We also checked the expanded engineering page which shows the fuel at each of the measuring stations - this was very uneven and depicted somewhat of a 'slope' on something liquid, which was rather unlikely. We were told later it was a software issue with failed sensors messing up the readings, rather than being excluded from the calculation...
The good thing is that the accuracy returns as the amount reduces, so the danger of running dry unexpectedly is small.
I remember being over the middle of Khazakstan about 10 years ago, looking at the scenery, when the "fuel imbalance" checklist pops up... OK, 2T difference, let's see what's in the tanks... Oh, the total seems to be going down by at least several tonnes a minute - that's not good - might have to shut one down. Got the 3rd pilot to go back and see if there was any indication of a fuel leak: no. Were just contemplating chopping the motor on the offending side when we noticed that the "leak" had stopped and we seemed to getting a bit of in-flight refuelling.
As the indicated imbalance was in the order of 15T, we took the autopilot out and let go: steady as a rock. Hmmm. Over the next 20mins or so the fuel displays returned to normal. We also checked the expanded engineering page which shows the fuel at each of the measuring stations - this was very uneven and depicted somewhat of a 'slope' on something liquid, which was rather unlikely. We were told later it was a software issue with failed sensors messing up the readings, rather than being excluded from the calculation...
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It's interesting to know if a similar problem existed on 767 or 744.
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Be Careful .....
In my original post, I did describe the "soft reboot" fix (which works), but don't forget that we have three possible reasons for strange B777 fuel indications, i.e.
(1) A VNAV problem being addressed by Boeing, the "soft reboot",
(2) Suspect FQI for the centre tank in some instances,
(3) The "Phantom" Wing Fuel assymetry problem, still being addressed by Boeing (which yours truly experienced last night).
Geragau did point out that whilst the "soft reboot" does much to realign the computed fuel with the Totaliser, they tended to drift apart again thereafter (much like INS after a DME update). What he says is TRUE, BUT, although the in-flight discrepancies might begin again, the more important to me is the PREDICTED Fuel at arrival, and, it is my observation that even though in-flight differences may slowly recommence, the Predicted Arrival Fuel is MUCH more in line with reality.
Three FQI oddities for the aircraft, I say again Be Careful .....
Regards,
Old Smokey
In my original post, I did describe the "soft reboot" fix (which works), but don't forget that we have three possible reasons for strange B777 fuel indications, i.e.
(1) A VNAV problem being addressed by Boeing, the "soft reboot",
(2) Suspect FQI for the centre tank in some instances,
(3) The "Phantom" Wing Fuel assymetry problem, still being addressed by Boeing (which yours truly experienced last night).
Geragau did point out that whilst the "soft reboot" does much to realign the computed fuel with the Totaliser, they tended to drift apart again thereafter (much like INS after a DME update). What he says is TRUE, BUT, although the in-flight discrepancies might begin again, the more important to me is the PREDICTED Fuel at arrival, and, it is my observation that even though in-flight differences may slowly recommence, the Predicted Arrival Fuel is MUCH more in line with reality.
Three FQI oddities for the aircraft, I say again Be Careful .....
Regards,
Old Smokey
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Real time ACARS maintenance reports
Woodyspooney mentioned real time maintenance data to maintenance control...........is this an every practice? Do ACARS datalink download full real time aircraft performance data to maintenance control all the time or only when there is an anomaly as claimed in the recent Air France 330 AF447 case over the pond?
Another way to check the rate of change from the Totalizer to Calculated is as follows:
First take note of Calculated value and Totalizer value.
On the PERF INIT page, type the Totalizer value onto the scratch pad and line select it over Calculated figure then execute. 'MAN' will replace 'CALC'
Then select DELETE and line select over the same figure and execute. 'CALC' will return.
Now they are synched. Then each hour you can monitor the rate of change.
You will be surprised how much this the rate does vary over a long flight.
halas
First take note of Calculated value and Totalizer value.
On the PERF INIT page, type the Totalizer value onto the scratch pad and line select it over Calculated figure then execute. 'MAN' will replace 'CALC'
Then select DELETE and line select over the same figure and execute. 'CALC' will return.
Now they are synched. Then each hour you can monitor the rate of change.
You will be surprised how much this the rate does vary over a long flight.
halas
