Fuel disagree

[JP59]

Hello,

From (I can't remember exactly when) some weeks, I have a strange problem. On every flight, after about 2 hours of flight, I have an FMC message "Fuel disagree - Prog 2". The calculated fuel is very below the totalizer fuel. I never had this problem before. So for every flight, I have to reset the calculated to manual. I wonder what is wrong. Any idea or help would be appreciated.

Cheers,

[GodAtum]

I'm getting the same too but not on every flight.

[Hardy Heinlin]

Hello.

The calculated fuel is very below the totalizer fuel.

How much?

What happens when you click on "Reset lag" on the Service page?


Regards,

|-|ardy

[JP59]

Hello Hardy,

I didn't wrote the exact values. I'll do it on my next flight and report. I remember an approximation of 5 tons but I'll report with exact values next time. I'll also try to reset lag and report. Many thanks.

[JP59]

Hello,

As requested, here are my observations during a L/R flight :

PW4056 PAX model
CYYZ to LFPG
Flight time : 06:20
Release fuel : 81437 Kgs
Fuel loaded with service page, direct entry in "Total fuel Qty" window
During cockpit preparation, CALC FUEL = TOTALIZER FUEL
Right after takeoff, slow drift of CLAC FUEL below TOTALIZER FUEL
After 3:35 of flight, FMC message "FUEL DISAGREE - PROG 2"
At this time : CALC FUEL = 42.0 / TOTALIZER FUEL = 46.1
On the service page, the window "Total ful Qty" shows 46123
RESET LAG button pressed : nothing happens
I reset the CALC FUEL to 46.1 MANUAL
The drift continues at the same rate
At LFPG FMC FUEL is 21.0 and TOTALIZER FUEL is 24.9
On the service page, the window "Total fuel Qty" shows 24915

Here is the EVENT RCD I made about 30 minutes after reset CALC FUEL. You can see the quantity is still drifting down :

http://www.hoppie.nl/forum/var/--Event_record_2015-JAN-22_13-45-02.situ

I hope this will help to find what's wrong.

Cheers,

[Hardy Heinlin]

Hi Jean-philippe,

did you use time acceleration?

Do you use any add-ons that influence any fuel related Q vars?


Regards,

|-|ardy

[Hardy Heinlin]

Right after takeoff, slow drift of CLAC FUEL below TOTALIZER FUEL

A slow drift is normal. Totalizer quantity lags behind calc quantity. This effect is intentional and realistic.

However, 4 tons is a bit too much. Did the difference increase mainly during stab tank transfer?


|-|

[JP59]

Hi Hardy,

I never use time acceleration, and do not have any add-on interfacing with PSX fuel. This flight was too short to load stab fuel, so I can't try this situation. Could it be a "bug" of PW4056 model ? I didn't wrote statistics, but I do not remember having this trouble with GE/RR models. But I also do not remember a PW flight without this problem.

[Peter Lang]

Could it be a "bug" of PW4056 model ?

no, I have the same experience here with RR engines. With time acceleration and without. But not on every flight.

When reading the posts I wondered if there is an association to the tremendous fuel flow of the APU and/or the jettison time which also is not "reliable".

But I had no time to investigate further in this. Just noticed and kept it in my brain for looking nearer on this item the next time.

Peter

[roccod]

Just to add to the debate, I get this same FUEL DISAGREE issue on many of my flights as well.  During the course of a longer flight (6+ hours), the disagreement between calculated and totalizer becomes very pronounced.

[Hardy Heinlin]

When reading the posts I wondered if there is an association to the tremendous fuel flow of the APU and/or the jettison time which also is not "reliable".

Hi Peter, what's wrong with the jettison time?

I know, the APU FF is too high in version 10.0.1. But that has nothing to do with the above fuel disagreement: the APU can use whatever it likes; in the moment when you start your engines and shut down the APU, the TOTAL and CALC values should agree.


Cheers,

|-|ardy

[Hardy Heinlin]

I will increase the lag rate by 30%. This should fix the problem.

I did this already in 10.0.1-alpha31 for the stab tank sensors, but not for the other tank sensors, because in 10.0.1 I increased the stab tank transfer rate only.


|-|

[Peter Lang]

Hi Peter, what's wrong with the jettison time?
-|ardy

Hi Hardy,
probably this is now fixed  
http://www.aerowinx.de/forum/topic.php?id=2536

I will watch out for further fuel disagree events and check if I can find more details. APU is shut down after check of flight controls.

Peter

[JP59]

I will increase the lag rate by 30%. This should fix the problem.

I did this already in 10.0.1-alpha31 for the stab tank sensors, but not for the other tank sensors, because in 10.0.1 I increased the stab tank transfer rate only.


|-|

Great. Thanks a lot.

[JP59]

Hello Hardy,

Unfortunately, I still have this problem with 10.0.2

Cheers,

[Hardy Heinlin]

Hello JP,

are you using a situ derived from an old situ of a previous flight of a previous flight of a previous flight ...?

Can you post the situ that you used to start your flight? Maybe your APU has already used too much (that bug is fixed), or do you let the APU run after engine start until takeoff or something?


Cheers,

|-|ardy

[JP59]

That's right. I still use old SITUS (aircraft well positioned at the gate for major airports). I'll try to create a fresh new SITU and report.

Here is the old SITU : http://www.hoppie.nl/forum/var/Projet_747_-_LFPG_-_Gate_E26.situ

About the APU, I start it about 10 minutes before push-back and shut it down just before to start taxi.

Thanks

[Hardy Heinlin]

Thanks. I see no problem in this situ.

For further analysis, could you please make ...

- a situ immediately after all engines are started.

- a situ immediately before pushing TOGA.

- a situ immediately before reaching CRZ ALT.

... and then post these 3 situs?

Just to be sure: does your server and do all your clients use 10.0.2?


Cheers,

|-|ardy

[JP59]

Hardy,

I confirm using 10.0.2 all over my network. On my next flight I'll start from a fresh new SITU created with 10.0.2 and press EVENT RCD at the moments you asked, and post on this thread.

[JP59]

Hi Hardy,

As requested, the SITU files. I just forgot to press EVENT RCD just before TOGA, because of the rush within the cockpit. I made an EVENT RCT on the initial climb, just after takeoff. Tell me if its ok for you or not.

Preflight : http://www.hoppie.nl/forum/var/Preflight.situ

Just before engines start : http://www.hoppie.nl/forum/var/Before_engine_start.situ

Just after engines start : http://www.hoppie.nl/forum/var/After_engines_start.situ

Initial climb : http://www.hoppie.nl/forum/var/Initial_climb.situ

Just before reaching CRZ ALT : http://www.hoppie.nl/forum/var/Before_reaching_cruise_altitude.situ

After 2h25 of flight (Fuel disagree FMC message) : http://www.hoppie.nl/forum/var/After_2h25_of_flight.situ

Regards,