Fuel at Destination prediction

[pcubine 143]

Michael, I've tried to reproduce but I do not see the same results. Walk me through the preflight for one of those flights and I will try again.

Dan

Those two flights were conducted in June of 2015. I don't remember any of the details like fuel bias, routes, cargo, etc. I do 777F flights every night so the details of any one particular flight are lost when I can OFP which I do the day the flight is done. All of the details kind of run together. However, I still have the details on this flight that I complete this morning.

 

Southern Air 777F EDDP-KLAX. I am not going to bore you with another hour by hour blow. Reserve required U.S. Flag Jet fuel policy is 26702 lbs. At TOC PROGRESS pages show ETA of 1549 and fuel remaining of 16500 lbs. at KLAX. A little over 10000 lbs. in the hole. Insufficient Fuel Warning. At T/D ETA was 1553 and fuel remaining at KLAX of 29000 lbs. which is 2300 lbs. more than required reserve.

 

I am sure that if the fuel bias was changed to 100% from 95% the Insufficient Fuel Warning message would disappear but then I would have way too much fuel in KLAX.

[downscc 1,327]

 

 

I would have way too much fuel in KLAX.

 

We're going to disagree on this point.  By way too much if you mean something like 30,000 lbs fuel remaining then I maintain that this is normal for some flights, and the reason that such flights are planned with redispatch decision points. Decreasing the fuel bias in PFPX so you get an answer you like is going to result in a fuel profile that is different from the profile used internally by the FMS.

 

Try using a fuel bias of 100% in PFPX. Accept any fuel remainging value that it computes and then compare with the FMS fuel remaining predictions. I suspect you will see a convergence of the data.

 

I just ran an example PFPX trip EDDP-KLAX auto-route (3% GC) no wind with 440 klbs ZFW.  The fuel release is 195.8 klbs and remaining 23.3 klbs; with a redispatch DP same route same weight the fuel release becomes 180.1 klbs and remaining 11.5 klbs.  This is with 100% fuel bias in a DAL 77L, bascially same performance as 777F.

 

Note the fuel remaining is cut by more than half.

[pcubine 143]

I just ran an example PFPX trip EDDP-KLAX auto-route (3% GC) no wind with 440 klbs ZFW. The fuel release is 195.8 klbs and remaining 23.3 klbs; with a redispatch DP same route same weight the fuel release becomes 180.1 klbs and remaining 11.5 klbs. This is with 100% fuel bias in a DAL 77L, bascially same performance as 777F.

I will try it in the next several days with a fuel bias of 100%. But I really don't see the point of using the 77LR when I don't fly it. For all I know it might work fine but that it not going to do me any good since I fly the 777F. If I used a ZFW of 440000 lbs. I can tell you right now the available fuel at KLAX is going to decrease during the flight.

 

Everything this week is to or from the Asia from KLAX, EDDF, EDDP, or a return trip. And since I don't use time acceleration I can't just crank out flights right and left. Tonight will be KLAX-VHHH and I will use a 100% fuel bias and carry no extra fuel. This coming weekend will be EDDP to KLAX and EDDF to KIAH.

[downscc 1,327]

For sure, use the 777F.... it's so close to the -200LR that they share the same type ID.

 

The 100% bias is key.  The only time you want to adjust that number is when the simulator is using a different fuel burn at a specific CI/speed, weight and altitude. See pg 25 PFPX manual.

 

When you set a bias of 95%, you are planning a flight for an aircraft that will have 95% of the trip fuel which also lowers the 10% Intl Contingency as well as the fuel for holding, alternates etc. You lower your total fuel release, which is why the FMS responds with an insufficient fuel warning, because the FMS has it's own fuel algorithms based on PMDG numbers. This is regardless of type flown or ZFW selected. Use any ZFW you want, but stick to 100% fuel bias unless you do a carefull evaluation at specific conditions to make the changes based on observations.

[barramundilure 152]

Hi Dan and Kyle

I noticed you have failed to address my situation as the thread starter and concentrated on Michaels issue. 

Am I to assume you simply don't have an answer to my particular issue with the fmc predictions at this time?

I have now gone to some lengths to give quite detailed information about flight times both forecast and actual, expected fuel over destination figures at pushback, take off, top of climb, top of descent and landing, winds, temperatures. The list goes on. 

None of these things account for the issue I am seeing in the software.

If you want to PM me with your email address I can photograph the full flight log with all the details entered for every waypoint throughout the flight if it makes it easier for you to see that I am describing a real issue.  It may not be the end of the world stuff, but it is there,

If you cant explain the issue that's fine but please do not simply put your head in the sand and say it isn't so.

I have also not played with fuel bias in the planning software and yet the problem appears to have only started recently. 

Sincerely

Tim Carter

[downscc 1,327]

Sorry Tim, valid complaint.

 

Any unexpected loss of fuel remaining at a constant rate is not normal. The was a bug in an earlier version of PMDG 777 that only happened in specific cases, and that problem has been solved with current version.  I believe one or two posts alluded to this and I don't recall your response. I apologize if you have already confirmed you have current version 1.10.6492.

 

If you have current version and you are loosing 400 kg/hr then next step is a flight with no weather, carefully documented such that anybody else could reproduce the exact same flight and compare results. Please be sure that the results are reproducible.  Hopefully in attempting to reproduce the problem we will figure out what's causing it.

 

You have mentioned three flights I believe, but only the highlights describing your problem. Give us a flight, weights, fuel release, route of flight, etc., such that it can be reproduced. We'll see what can be found.

[barramundilure 152]

Hi Dan

Thanks for your comments.  I have the full flightplan log here.  How would I go about posting it here? Can I post jpegs of each page?

It has all the data you mention.

Must admit I hadn't thought of doing a flight no wx and seeing if the problem is still present.  I wonder how long the flight would be to be a valid test.

Just checked my versions and they are definitely up to date.

 

Sincerely

Tim Carter

[pcubine 143]

The 100% bias is key. The only time you want to adjust that number is when the simulator is using a different fuel burn at a specific CI/speed, weight and altitude. See pg 25 PFPX manual.

Page 25 of what manual? I don't see anything in the Introduction or FCOM1

[pcubine 143]

Must admit I hadn't thought of doing a flight no wx and seeing if the problem is still present. I wonder how long the flight would be to be a valid test.

Flights without weather are probably the most boring thing you can do in FSX. Don't even start your weather engine. Make certain PFPX or whatever you are using for flight planning has no connection to any weather server and then verify that each waypoint shows 000/00 for wind. Use FSX weather option "Clear Skies." This should give you a standard day with no winds. I don't use time acceleration, traffic, or auto stepclimbs.

 

When I was testing for VAS leakage flight times were 10, 12, and 16 hours. With this FMC issue I have done a 10 and a 12 hour flight. Maybe pick one or two flights that you reported problems with and fly those.

[scandinavian13 5,192]

 

 

How would I go about posting it here? Can I post jpegs of each page?

 

http://www.avsim.com/topic/441765-posting-images-in-avsim-forums-how-to/

[downscc 1,327]

 

 

Page 25 of what manual? I don't see anything in the Introduction or FCOM1

 

Michael, the PFPX manual. Not PMDG. I was pointing you to the section on how to adjust fuel bias in PFPX using the evaluation tool.

 

 

I have the full flightplan log here. How would I go about posting it here? Can I post jpegs of each page?

It has all the data you mention.

 

It would be hard to reproduce a flight flown with weather, getting the exact same weather would be possible depending on the wx you used, but it complicates things. Keep it simple. Here are a few things that help reproducing a flight:

• Flightplan full route ORIG-DEST including STAR and IAP
• No wx or add-on traffic or AI traffic
• Preflight fuel release and ZFW.

This boils it down to something that can reproduced for any given PMDG 777 variant (of course you have to include if L F or ER).  The flight log can be something very simple, for example actual total elasped time (easy using digital clock option in the 777) and fuel remaining at each fix. A long flight would not require this data at each fix, but once an hour would be sufficient. The flight can be flown in accelerated time, and changed to real time later if something interesting warrants the closer look. Keep it simple.

 

How long a flight? Long enough to establish there is a reproducable problem. At least a 5% unexplained loss of fuel as a minimum I'd think. Use your judgement.

[pcubine 143]

Michael, the PFPX manual.

Sorry for the stupid question. Yes I used that sometime last year for the 777F, NGX, MD-11F but I was not satisfied with results for any of the three planes.

[Patco Lch 1,465]

Micheal,

I love being a member FedEx V so I can fly the 777F but I take my hat of to you for flying them route with no time compression and the reporting you do. Great work.

David,Thanks for the SWA flow for NGX FS2CREW. Very usefull.

[pcubine 143]

David,Thanks for the SWA flow for NGX FS2CREW. Very usefull.

Does this thread look like it is about the NGX or FS2CREW? I think it would have been best to send David a PM or add this reply to thread you got the information from.

[scandinavian13 5,192]

Does this thread look like it is about the NGX or FS2CREW? I think it would have been best to send David a PM or add this reply to thread you got the information from.

 

Clearly wasn't a hijack, and was simple comment. No need to further distract the thread by adding more attention to it. Nor is there reason to get upset about it.