Dan

 

To be consistent with prior flights I have included the contingency fuel in the required reserves. The last flight was conducted with no weather.

 

                             ZFW    TO Fuel   Req Rsr  ETA at T/C  Fuel Remng  ETA at T/D  Fuel Remng

 

VHHH-EDDP     436800   192560      20077         1350        16.2K lbs.         1352           18.1K lbs.

VHHH-PANC     506800   183351      26593         1216        23.7K lbs.         1215           35.1K lbs.

EDDP-KLAX      440000   195505      26272         1355        24.4K lbs.         1356           26.4K lbs.

The last one with no weather is the only one that you provide enough information to reproduce results, and the variance between FMS predicted fuel remaining and PFPX prediction is within 1%. Problem?

Simon and Leo

 

The data below is from a 777F flight EDDP-KLAX conducted with no wind.

 

TTL at engine start. 195.5

 

Remaining fuel at KLAX prior to takeoff. 24.4

 

T/C at BIBNU. TTL 183.8 PFPX 183.0 FMC 23.7

 

ADN TTL 165.8 PFPX 164.9 FMC 23.7

 

6230N TTL 135.9 PFPX 134.9 FMC 24.3

 

VBI TTL 66.6 PFPX 65.9 FMC 25.5

 

DDY TTL 47.7 PFPX 46.7 FMC 26.0

 

T/D TTL 29.1 PFPX 27.9 FMC 26.4

 

At cargo ramp TTL 25.4 PFPX 26.2

 

Once the contingency fuel of 14.5 is removed from the reserve amount, an increase from 9.2 to 11.9 doesn't look too bad. However, in the past the problem really comes into its own at high cargo weights of 180 to 210 not like 128.2 on this flight. But I believe getting the contingency out of the reserves is going to make a noticeable difference.

downscc, on 04 Oct 2015 - 11:38 AM, said:

 

The last one with no weather is the only one that you provide enough information to reproduce results, and the variance between FMS predicted fuel remaining and PFPX prediction is within 1%. Problem?

That is not a normal cargo flight. Cargo is usually in the 180 to 200000 lbs range not 128200lbs. Need to get back to the big loads and not the lightweight passenger plane.

 

Edit - Dan, Do you have any ideas on this junk that replaced the MD-11 image. This trash is from Apple. The image has not expired. It is still on ImageShack and my subscription is still in affect.

Dan

Taking into account post #57 by calzonister in which he stated that contingency fuel was not part of reserve fuel this what I am doing now. The general information is - plane is 777F, ZFW 480000 to 520000 lbs., fuel 180000-240000 lbs., no extra fuel, CI 85, no re-dispatch, and fuel policy is either U.S. Flag Jet or EU-OPS. Bizarre as it may sound I am using two different fuel biases. 92% for U.S. Flag Jet and 98% for EU-OPS. At the end of a flight the fuel remaining on the PROGRESS page is reasonably close to what PFPX shows as required. I might cut U.S. Flag Jet to 91% or even 90% to bring the fuel remaining more into line with what PFPX shows. Also, I might start carrying 1000-1500 lbs. extra fuel with EU-OPS since several times I have received an insufficient fuel warning at the beginning of a flight. This is about the best I can do with the FMC I have.

Hello everyone,

I've had this problem and it is most defenitly the product. I found a walkaround that works. Do you have FSUIPC purchased? If yes, try restarting your simulator and loading back your flight at your last saved point. I have tried this and the huge fuel usage has stopped. I've tried this walkaround at least 3 times already and its been working for me.Feel free to try this and let me know if it worked for you!

Cheers,

Bryan Cheung

 Do you have FSUIPC purchased?

Is this for the autosave feature? Once the flight is saved, FSX restarted and the save flight loaded, does the autosave feature of FSUIPC need to remain ticked for the duration of the flight or can it be turned off?

Yes it is for the autosave feature. You should turn it on for takeoff and for about 10 minutes after your TOC has started. Monitor your FMC and see if there is any huge decrease for fuel at destination. If yes, reload your flight to your last saved point. After you've loaded to the last saved point, monitor your FMC again and there shouldnt be any huge decrease for fuel at destination. You can then turn it off for the remaining duration of your flight.

 

Thanks. I will try this and see what happens.

Yes it is for the autosave feature. You should turn it on for takeoff and for about 10 minutes after your TOC has started. Monitor your FMC and see if there is any huge decrease for fuel at destination. If yes, reload your flight to your last saved point. After you've loaded to the last saved point, monitor your FMC again and there shouldnt be any huge decrease for fuel at destination. You can then turn it off for the remaining duration of your flight.

 

Unfortunately your solution did not work for me. I did not think it would since your issue was decreasing fuel remaining and mine was increasing fuel remaining during the flight. I tried your solution on VHHH-KLAX flight of 12.5 hours. ETA increased by one minute and remaining fuel went from 30600 lbs. at T/C to 45000 lbs. at T/D. Right now I am using a different fuel bias for each type of fuel policy - 91% for U.S. Flag Jet and 97% for EU-OPS. I think that is about the best it is going to get for me.

Hello Michael

 

anything new on this "issue"? I seem to be having a similar problem, ableit rather recently, only the other way around where my 777 uses MORE than it should according to pfpx...like you i primarily fly the F model with rather big loads 

 

on a flight from KMEM to LFPG yesterday, planned with PFPX, weights winds etc. were matching perfectly, she used roughly 24% more fuel then she should have...really annoying

 

doing a bias evaluation in pfpx gives me 104% if that, which is not nearly enough to compensate...using the fly precisely profiles found on avsim...

on a flight from KMEM to LFPG yesterday, planned with PFPX, weights winds etc. were matching perfectly, she used roughly 24% more fuel then she should have...really annoying

 

24% is pretty significant. I find it hard to believe something like that would lie dormant for a few years before someone saw it.

 

Can you provide specific numbers? Weights, route, and so on?

Its only started to happen recently for some reason...I've been using the 777 pretty much since the day it came out and never had a problem with it thus far, using FSX:SE and soon gonna buy it for P3D v3

 

 

the route was: KMEM MEM BWG HNN HAR SAX PUT J42 BOS J575 TUSKY N145B PORTI 4750N 4840N 4930N 5020N SOMAX ATSUR RATKA UN512 LARLA UN521 NERLA UN491 BASIK UZ57 LATGO LATG6E LFPG

 

weights were fairly high, i don't have the exact numbers anymore since i don't keep past flights but the payload was around 92-93 tons and PFPX estimated around 75 tons of fuel, which turned up to be 85 tons actually used after the flight was done, checked via PROG page 2...that is 75 tons RELEASE fuel by PFPX...trip fuel was obviously a bit lower...

 

weather program for the sim is current version of ASN, weather source in PFPX is their online server so the winds matched pretty perfectly enroute

 

cruise alt was FL310 pretty much all the way through as PFPX didnt give me any step climbs

 

PFPX calculated remaining fuel to be somewhere around 11-12 tons and actual fuel left in the tank after arrival was 8.something

 

im sorry but that is as accurate as i can be...presently doing a flight from LFPG to OMDB which shows the same symptoms...i have accurate numbers for that one if you wish although that is still in progress

 

...cruise alt was FL310 pretty much all the way through as PFPX didnt give me any step climbs

 

That is part of the problem. While FL310 may have been an appropriate altitude at the beginning of your trip if you were heavily loaded, there is no way that a 777's optimum altitude would still be FL310 at the end of a transatlantic crossing from the US to Europe. I would expect an optimum altitude of at least FL370, if not FL390 by the time you reached European airspace eastbound.

 

Not sure why PFPX would not have specified step climbs. Did you select "optimum" for your altitude in the PFPX menu when planning your flight?

 

Also, did you import the forecast winds aloft into your FMS flight plan from ASN?

 

Even if PFPX did not give you step climbs, you can determine when to perform them while enroute, by referring to the current optimum altitude on the FMS CRZ page, or by enabling the PMDG auto step climb option.

yes Jim i'm aware, not sure why PFPX didnt give me step climbs...doesnt seem to do so when the plane is overly heavy, however even if i DO climb which i did during that mem-cdg flight towards the end the numbers didnt change

 

i just completed said flight to dubai and i had the exact same problem where the plane would use way too much fuel and the predicted fuel on the prog page would steadily decrease...here are all the numbers:

 

ROUTE: LANV1G LANVI UM164 EPL UN491 DEGES UN871 GAPTO UT23 DIMLO DCT INVED UM747 NEKUL UM859 RONBU M859 ODERO UP975 KATUT UM688 SIDAD R784 IMDAT B416 DESDI DESD8D

 

Weather: ASN for the Sim, PFPX own server for planning

 

PAYLOAD: 97954kgs

 

               FUEL    CORR    ENDUR
TRIP          61795  ........  06:03 
10 PCT         5564  ........  00:36
ALTN OOMS      6304  ........  00:34
INTL HOLD      2725  ........  00:30
MIN T/O       76388  ........  07:43      
EXTRA             0  ........  00:00       
TAXI            330  ........  00:10       
RELEASE       76718  ........  07:53 

that is with a bias of 124% (!!!) in PFPX and exactly what i loaded...

 

after landing on the FMC progress page 2: LEFT 44.7 RIGHT 44.7 TOTAL USED: 89.4....remaining fuel in the tanks after landing: 4.2

 

needless to say i had to add fuel during the flight else i would not have made it. 

 

wind data for the route was loaded in the fmc, i flew exactly the CI i defined which was 85 and i flew at exactly the levels PFPX gave me which was FL310 for the entire flight.

 

and yes PFPX does account for staying at the same altitude and calculates fuel accordingly

 

 

on a further note: i did some fuel burn timing during the flight, both engines show 4.0 for FF pretty much the entire flight which is fine hower: looking at the total fuel and clocking it for 1 minute results in roughly 200kgs per minute which streteched over an hour is 12.000kgs...not the 8000 it should do

Again, I cannot overemphasize the necessity of performing step climbs at the appropriate times. Even if PFPX is holding you at FL310 for the entire flight, the FMS in the aircraft has very different expectations. The amount of fuel that the FMS is predicting on landing at the beginning of your flight is based on the assumption (by the FMS) that you will climb while enroute to fly at the optimum altitude for the aircraft's weight as fuel burns off. If you fail to do so, then the FMS remaining fuel prediction is going to continuously be revised downwards as you proceed enroute. While FL310 may be appropriate at the beginning of a long flight, there is no way that it would be an appropriate or efficient altitude when you are 2000 or 3000 miles into a long flight.

 

I think you are putting too much stock in what PFPX is telling you. It is an excellent program, but it is not perfect. The fact that it is holding you at FL310 for 2000 or 3000 miles is a clear indication that something is definitely wrong. The accuracy of PFPX depends very much on the aircraft profile that you using, and not all PFPX profiles are created equal. Some are very simplified, with a minimal amount of data for aircraft performance at different weights and altitudes, while others are extremely complex, with many, many pages of performance tables for a wide variety of weight/altitude/speed combinations.

 

In any case, even the very best PFPX profiles cannot equal the performance data contained within the actual PMDG FMS code itself, which came directly from Boeing.

 

Even if you do not enter step climb information into the FMS, it (the FMS) will tell you when to go up an additional 2000 feet, by keeping tabs on the optimum flight level prediction on the CRZ page, or by enabling automatic step climbs in the PMDG menu accessible in the FMS.

 

Now having said all that, I can't rule out that there MAY not be some sort of bug in the fuel flow in your particular installation. You said that you measured fuel consumption over a 1-minute period, and extrapolated that forward over 1 hour. While that is a valid exercise, I would suggest measuring actual fuel burn off for at least 15 minutes before doing any forward-looking calculations. 200KG in one minute seems almost impossible even at 31,000 feet, unless you were running the engines a absolute maximum thrust.

I'm gonna measure it over a longer period on the next flight which will be OMDB-EDDP and we'll see, with the recommended FMC steps

 

fwiw the N1 during cruise is steadily around the 80-85% mark, using a CI of 85 pretty much always as i said above 

 

what i find even more curious is that this problem occured only very recently...up to now it has all been perfectly fine and the numbers matched up within an acceptable tolerance, doing some googling i'm not the only one with a "the plane uses too much or too little fuel" problem

 

i've tried different calculations with different profiles and they're all pretty equal in the results they produce, generally i'm just baffled by this issue as you can imagine and i'm sure there is a solution

 

lets be honest the chances of the issue being with the actual aircraft are quite slim i would imagine