Hi. I'm flying some ultra-long-haul flights recently with my 772 and I always notice one thing. The fuel amount at destination on the CDU keeps decreasing. For example I've flown from OTBD to NZAA yesterday and after T/C my CDU said something about 16 tons of fuel at NZAA. The number kept decreasing and reached 9 tons before T/D. I haven't changed anything and I was doing step climbs without any delay. Right now I'am flying from NZAA to LEMG (two most separated major cities?). After T/C, CDU said 4.4 tons at LEMG, but soon I've got an 'Insufficient Fuel' message on the EICAS, and 0.0 fuel at LEMG on the CDU. This time I've decided to do something about it and I've reduced cost index, then reduced step size, and finally increased the tailwind. It helped, but just a little, and now I've still got the 'Insufficient Fuel' message.

Do you know why the fuel amount at dest is always decreasing, even when I make an airplane more fuel efficient and make the weather conditions better?

Am I doing something wrong (except taking more fuel on-board or perhaps not flying longest routes possible )?

Or maybe the autocruise increase fuel consumption (I do not fly 23-hour long flight in real time)?

 

Michał Trześniowski

Already being discussed here:

http://forum.avsim.net/topic/422714-fuel-scalar-in-t7-cfg/

Thanks, but that's not quite it. I'm not using PFPX, and the difference is between fuel amount at dest on CDU at T/C and later on, still on CDU. And I have less fuel than planned, rather than more fuel as in the topic you mentioned.

If you are using winds aloft and you are not inserting them into the LEGS>RTE DATA page you will find that the FMC will give erroneous remaining fuel. Someone correct me if I'm not mistaken. 

If everything is correctlly entered, the FMC will calculate fuel remaining (when still on the ground) of a flight in 0 wind conditions. After takeoff, the FMC will update it's predictions to the current wind. So if you enter a strong headwind at TOC, the FMC will calculate you fuel remaining based on that wind, for the remainder of the flight. This is so because you have not given it wind information to work with. On short flights you won't really notice it, but it can amount to a huge difference on long-haul flights.

 

Cheers,

I too am seeing this however I am using AS2012 during my flights so it is possible the winds have changed by the time I get to a point. Keep meaning to try with a set weather setup. Sounds like you are and still seeing it.

 

Perhaps I will try it tomorrow and make certain but it is a little annoying I must say.

I too am seeing this however I am using AS2012 during my flights so it is possible the winds have changed by the time I get to a point. Keep meaning to try with a set weather setup. Sounds like you are and still seeing it.

 

Perhaps I will try it tomorrow and make certain but it is a little annoying I must say.

What about trying a long flight with absolutely no weather?

What about trying a long flight with absolutely no weather?

 

Yes could do but it ain't half dull.

If you are using winds aloft and you are not inserting them into the LEGS>RTE DATA page you will find that the FMC will give erroneous remaining fuel. Someone correct me if I'm not mistaken. 

If everything is correctlly entered, the FMC will calculate fuel remaining (when still on the ground) of a flight in 0 wind conditions. After takeoff, the FMC will update it's predictions to the current wind. So if you enter a strong headwind at TOC, the FMC will calculate you fuel remaining based on that wind, for the remainder of the flight. This is so because you have not given it wind information to work with. On short flights you won't really notice it, but it can amount to a huge difference on long-haul flights.

 

Cheers,

I don't think that's the case. It seems like it, but I don't compare fuel at dest before takeoff and at T/D, but at T/C and at T/D, so the FMC already knows about the wind aloft. Plus when I make the tailwind stronger, the fuel amount at dest should increase. In fact it does, but not enough. On my last flight it went like this: 4.4 tons at T/C, decreasing to 1.9 (over something like 1000nm), then I increase tailwind by 20kts (jetstream ), no x-wind, it goes up to 2.0 then slowly down to 0.0. If I don't change the wind, the amount at T/C and T/D should be roughly the same, but I am sure it shouldn't decrease when the tailwind increases!

I will try tomorrow with no weather at all, and see is it still happening.

Yes could do but it ain't half dull.

 

It wasn't an assertion that you were dull, it was a suggestion to help you troubleshoot.  It's a valid suggestion.

It wasn't an assertion that you were dull, it was a suggestion to help you troubleshoot.  It's a valid suggestion.

 

I think he might have meant "dull" as in "boring" ...

I think he might have meant "dull" as in "boring" ...

 

Yes I did mean dull as in it would be very boring. :lol:

Yes I did mean dull as in it would be very boring. :lol:

 

Gotcha - yeah, kinda.  Worth a shot for troubleshooting, though.

I will try tomorrow with no weather at all, and see is it still happening.

I am still flying, but I can already say it's neither the weather, nor the AutoCruise.

 

Here's how it goes. FAOR-PANC, Cost Index: 25, Step size: RVSM, no weather at all.

Units are lbs x1000 this time.

Here's what the FMC said, and what I had done.

 

Before Taxi: Fuel at PANC - 34.4

During Climb: Fuel at PNAC - 32.7 (Probably the difference is the Taxi fuel)

At T/C (about 1700Z): Time/Fuel at PANC - 1228Z/32.7

 

Shortly after T/C I engaged Autocruise (up to x4)

 

1749Z: Time/Fuel at PANC - 1228Z/29.3

1952Z: Time/Fuel at PANC - 1232Z/10.5

 

1952Z - Autocruise OFF

 

2136Z: Time/Fuel at PANC - 1232Z/5.7

 

2141Z - Cost Index ->0, Step size ->1000 Autocruise ON

 

2141Z: Time/Fuel at PANC - 1234Z/6.1

0004Z: Time/Fuel at PANC - 1234Z/0.0; Insufficient Fuel on EICAS

 

So without the weather the problem still exists. As well as w/o Autocruise.

Any ideas?

 

 

Any ideas?

 

Are you using a particular saved panel state?

Are you running any external programs like FSPax, or any other program that could interfere with fuel?

Have you manually edited any files that could affect fuel?

 

That definitely way too extreme for it to be from the 777 itself.  I've done way too many flights with actual dispatch sheets and the fuel being spot on to believe that this is a problem with the 777.

Are you using a particular saved panel state?

Are you running any external programs like FSPax, or any other program that could interfere with fuel?

Have you manually edited any files that could affect fuel?

 

That definitely way too extreme for it to be from the 777 itself.  I've done way too many flights with actual dispatch sheets and the fuel being spot on to believe that this is a problem with the 777.

I always use the PMDG Cold and Dark, and follow the complete procedure from FCOM.

I don't use any external software that has something to do with fuel. All I have installed with FSX is acceleration, PMDG 747x, NGX, and 777x, and Aerosoft EGLL & EDDF (everything genuine).

I've only edited what was described in 777 introduction.