767-300 fmc

[dfish]

After recieving a "Fuel disagree Progress 2/2" message in the FMS scratchpad, what actions are taken? if any? Fuel status at the time was 40K in wing tank and 0 in center.

Dave F.

[Spanner Turner]

Fuel Quantity Processor
The value of FMC calculated fuel quantity is set equal to the total
fuel quantity from the fuel quantity processor when the airplane is on
the ground and there is no fuel flow. When fuel flow begins, the
initial fuel quantity value is saved for all future calculations and the
fuel flow input data from the EICAS computer is integrated, summed
and saved. FMC calculated fuel is computed by subtracting the fuel
flow sum from the initial fuel quantity value. Throughout the flight,
the difference between FMC calculated fuel and total fuel quantity is
computed. If the difference exceeds 1360 kgs, a CDU alert message
is generated (FUEL DISAGREE - Prog Pg 2). To avoid false alarms
due to slosh during maneuvers the fuel discrepancy must exceed 910
kgs for 6 minutes before the 1360 kg threshold is checked.


After recieving a "Fuel disagree Progress 2/2" message in the FMS scratchpad, what actions are taken?



Not sure what actions, I guess you could look for a possible fuel leak.
I.E If you started with 50k, and your fuel Totaliser is now indicating 40k, yet the left eng fuel flow transmitter has counted 4k used and the right eng fuel flow transmitter has counted 4k (8k total burn) what has happened to the other 2k??

One of a few things is the prob here.

1) one of the fuel flow transmitters is inaccurate.
2)The fuel quantity indication system is inaccurate.
3) Fuel is being lost somewhere.
4)EICAS computer is sending bad info to FMC
5)FMC is stuffing up its calculations.

This defect pops up from time to time and we generally replace one of the eng fuel flow transmitters.

[Spanner Turner]

Further info on FMC progress page, if you can determine if it's the Totaliser system or the Fuel Flow Transmitter system you can inhibit their input into calculations as per the instructions highlighted below.


Progress Page 2/2 is accessed by pressing NEXT PAGE key when on
Progress Page 1/2.
Data Fields
1L-1R WIND COMPONENTS/WIND VECTOR
2L XTK ERROR - Displays current cross track error.
3L-3R TAS/SAT - Displays current true airspeed and static air
temperature.
5L Blank unless there is a 1360 kg discrepancy between the totalizer
and calculated fuel values. If a discrepancy occurs, the line select
fields are formatted as shown. Line selection causes the system to
use the fuel totalizer input and inhibits the calculation of fuel used
based on fuel flow. Line 6R, CALCULATED FUEL, blanks if 5L is
selected.
2R VTK ERROR - Displays current vertical track error with respect
to a path descent. (Blank when descent not active.)
5R Same as 5L except that selection causes the system to use the
calculated fuel and inhibits the totalizer input. Line 6L, TOTALIZER
FUEL, blanks if 5R is selected.
6L-6R Manual entry of fuel quantity on the PERF INIT page is
propagated to line 6R and is the initial value of fuel quantity used.
Line 6L is blank and subsequent totalizer inputs are ignored.

[Capt Fathom]

After recieving a "Fuel disagree Progress 2/2" message in the FMS scratchpad, what actions are taken?
Is it a non normal checklist item? Maybe not all airlines have it as such!

[Check Airman]

"The value of FMC calculated fuel quantity is set equal to the total fuel quantity from the fuel quantity processor when the airplane is on the ground and there is no fuel flow."

Hope you don't mind if I introduce a little drift. Say you're off to a field with no ground services, and when you get there, you discover that the APU is now inop, so you keep one engine running for the (short) turnaround. After you load the FMC with the new route etc., how is the Totalizer / Calculated fuel affected, since you always had a fuel flow? Suppose you need to refuel?

I know that this is a bit of a stretch, definitely improbable, but not impossible.

[downsouth]

I know that this is a bit of a stretch, definitely improbable, but not impossible.

Well, there's a procedure for the Airbus 320 where by you have to reset a few C/Bs in order to reset the fuel used to cero... I've never flew a boeing (unfortunatelly) but maybe there's some similar procedure to deal with that improbable (but not impossible) situation...

[dfish]

Thanks for the feedback gentlemen.

Dave F.

[oncenterline]

Maybe a little offtopic, but how do you put 40.000 kilograms of fuel into the wing tanks of a 767-300? I thought it is around 37 tons max. Or did you mean 40k liters (or even 40k lbs)?

[dfish]

That would be 40k Pounds.

Dave F.

[Short_Circuit]

Write a log entry and let me look at it, don't know what your SOP is in F/D. it is common enough not to be concerned unless you have a very tight fuel load.

[yoohoo748]

Umm... QRH to rule out or to confirm fuel leak, select totalizer or calculated based on your findings. As far as what to do after you land after your flight, consult your trusty MEL and you will be sure to find all the good stuff that needs to be done. ie: manual fuel drip check. I do believe that would involve an AME. Doing a drip check is one of the most fool proof ways of determining whether or not we used more fuel than planned and that was recorded by the FMS.
Short_Circuit: I think I agree with you, but to clarify bout not being concerned with being 'tight' on fuel, I know where I come from that we are not in the habit of carrying around loads of extra fuel for no apparent reason. Take what is required (due consideration to weather, anticipated traffic and contingencies); tankering only if fuel is at a premium at our planned destination. Drips are deemed to be accurate, that is where we would be making our fuel decisions from. Yeah? Yeah sure!!
Engine running while boarding and loading baggage? which one would you shut down? assuming there are no ground services I would also expect to be using stairs as apposed to an air bridge. Which one would you be shutting down? Suck the men and luggage into the engine or perhaps the little old lady with the poodle trying to make it to the stairs. I can see the headlines now... Poodle gets sucked into jet engine after chasing after owners wig! I'm sure this does happen in some parts of the world, but nowhere i have seen, and I've been to some rough places. That being said, I'm sure it does happen.
Solution... shut right down, deal with freight, start it back up, shut left down, deal with pax. Do-able, but come one... not the a/c designed for the bush now is it. Fuel... as far as I can tell, you might be able to reset the FMS by flipping the dates, or a couple breakers. Not sure.