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Guest Josve

PMDG 737-800 fuel prediction does not work?

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Guest Josve

Hi guys!I'm posting this question from a fellow simmer.I am flying one of those "delivery flights" and yesterday I flew a 7 hour leg from Anchorage to Sapporo, Japan. Yes, I needed to take 100% fuel, but per the fuel planner it was enough for the trip + alternate + reserve.On my way, the FMC told me I do not have enough fuel. I started observing carefully, and here are two screens while I was going to ATU, 260 nm out, the FMC shows me (FMC01.jpg) I will have 11.4 K lbs remaining at that way point. How is that possible if I now have 27.5 K lbs and I am burning 5.5 Klbs/hour flying at 450 knots ground speed?Well ... after I got to ATU (see FMC02.jpg), I actually had 24.2 K lbs! Also, at Sapporo I had 7 K Lbs left, just as I had planned before the flight.Something wrong with the algorithms when using the center tank maybe?- NeerajFMC01http://home.online.no/~johsvenn/artimages/div/fmc01_411.jpgFMC02http://home.online.no/~johsvenn/artimages/div/fmc02_899.jpgJohnny"I'LL BE BACK"[div align=center]http://www.avsim.com/hangar/fly/josve/aat.jpg ][/div

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Johnny, a search through this forum will reveal that this issue has been brought up numerous times.In a nutshell, what the PMDG development team stated was that the algorithm is fine, however it is VERY computational intensive and comsumes a lot of resources as it updates. What they have done is made this process conditional processing. If there are system resources available they start the tread up and continue to process until it is finished. On a long flight as you took from PANC to Japan the process can take up to a hour to get correct.I use FSBuild to plan flights, in its nav log and I can see how much fuel I should have at each waypoint and check it against the amount of fuel reported on my FMC. If you notice when the FMC reports insufficient fuel, it goes to zero amount quickly and then starts to climb back up to the correct amount slowly, that is a result of the conditional processing I was talking about.Hope this helps, the key is doing detailed flight planning.Bob


 

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Also, a small but very significant detail: if you want to use fuel prediction - do NOT use any time acceleration in FS - it will mess the PROG page calculations up completely.


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Guest

call me stupid, but how do you compute fuel using FSBuild? Do you just look at what it tells you the gross weight will be after each waypoint and figure out if you are 50,000 lbs lighter at the end then it decides you will burn that much fuel?

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Guest neeraj.pendse

Ah! Now I get it ... I was the person for whom Johnny posted this message, now I am trying to get into the forums as well. Wonder when this message will appear after being checked by the moderator.- Neeraj

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Guest G. Stone

>call me stupid, but how do you compute fuel using FSBuild? Do>you just look at what it tells you the gross weight will be>after each waypoint and figure out if you are 50,000 lbs>lighter at the end then it decides you will burn that much>fuel?FSBuild has a fuel burn column that you can use to compare. Take a look at this tutorial from the FSBuild website that includes all the information in the NavLog. It's only 4 pages long so it should be easy to find

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Guest neeraj.pendse

>Also, a small but very significant detail: if you want to use>fuel prediction - do NOT use any time acceleration in FS - it>will mess the PROG page calculations up completely.Now that's a gotcha for me: I am doing long flights, and guess what I am using to shorten the time! :-bang - Neeraj

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Guest Mickair
Johnny, a search through this forum will reveal that this issue has been brought up numerous times.In a nutshell, what the PMDG development team stated was that the algorithm is fine, however it is VERY computational intensive and comsumes a lot of resources as it updates. What they have done is made this process conditional processing. If there are system resources available they start the tread up and continue to process until it is finished. On a long flight as you took from PANC to Japan the process can take up to a hour to get correct.I use FSBuild to plan flights, in its nav log and I can see how much fuel I should have at each waypoint and check it against the amount of fuel reported on my FMC. If you notice when the FMC reports insufficient fuel, it goes to zero amount quickly and then starts to climb back up to the correct amount slowly, that is a result of the conditional processing I was talking about.Hope this helps, the key is doing detailed flight planning.Bob
Hey there,Today I flew a 5 hour 2300nm flight from KPVD to KSFO (737-700), and I got the insufficient fuel message during the first 2-2,5 hrs of the flight. After that, the figure climbed back up gradually just like you said, and I touched down with the right amount of fuel Is this a specific issue with longer flights I just have to deal with? There have been a lot of topics on the 'insufficient fuel warning' and the solution most heard is the one saying that the problem lies in the amount of reserve fuel on the PERF INIT page or carefull planning, though even when you change reserve fuel value to 0.1 the warning comes up, and I planned my fuel correctly with the Fuel Calculator for the PMDG 737. To be short: If I understand correctly the cause of my warning lies in the fact that the flight was long and the fuel calculating process algorithm from PMDG takes much more time to update on flights of this length.I hope somebody can clear this for me!I am enjoying your product very much!Kind regards,Bart

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