Fuel at Destination prediction

[pcubine 143]

copped some stick

Tim

What does this mean?

 

Thanks

Michael

 

If you downgrade to V1.10.6370 the problem is gone.

Is that the version prior to the VAS leakage fix?

[barramundilure 152]

Copping stick is an Australian term for getting some criticism Michael. 

Cheers

Tim

[Robinnn 13]

Is that the version prior to the VAS leakage fix?

 

Don't know, I never had VAS leakage with any version.

[downscc 1,327]

There appears to be a 400kg/hr reduction in fuel on arrival or increased fuel flow if you like that I cannot account for. It was not a problem before and now it is.

 

Keep a log of your flight. It's easy if you are already using PFPX.  Here is my KLAXZSPD flight from yesterday, show me the details for a flight where you have fuel consumption error:

DELTA AIR LINES  DL FLIGHTPLAN - IFR  DAL185  N702DN  KLAX-ZSPD
--------------------------------------------------------------------------------
ALL WEIGHTS IN POUNDS (LB)                                       STD 25SEP/2015Z
--------------------------------------------------------------------------------
OFP 1 - PREPARED 26SEP/1627Z BY DANIEL DOWNS (DD)

DL185/DAL185        N702DN/B777-2LR GE  SEL/              ROUTE:      KLAXZSPD01

DEP: KLAX/LAX 25R   ELEV   128 FT   MACH:       M.84      TTL G/C DIST:  5630 NM
ARR: ZSPD/PVG 16L   ELEV    13 FT   INIT ALT:   FL320     TTL F/P DIST:  5806 NM
                                    FUEL BIAS:  100.0%    TTL AIR DIST:  6384 NM
                                                          AVG WIND CMP: HD044 KT
ALT: ZSWX/WUX 21    ELEV    16 FT   102 NM
--------------------------------------------------------------------------------
CONFIG      DOW  PAX   CARGO   TOTAL   ULOAD LIM             ZFW     TOW     LDW
STANDARD 344244  218   50917   94553   22103 ZFW     MAX  460900  766000  492000
                                                     PLN  438797  668297  455107
                                                     ACT  438800  668800  454200
****************************** RE-DISPATCH PLANNING ****************************

INIT RELEASE KLAX TO RJNS SUBJECT TO INFLT RE-DISPATCH ONTO ZSPD OVER KAGIS

FUEL BURN FROM KLAX  TO KAGIS 179479
PLAN REMAINING OVER     KAGIS  50021          ACT REMAINING OVER KAGIS .52362..
--------------------------------------------------------------------------------
REQD OVER KAGIS TO DEST ZSPD   49966
                TO ALTN RJNS   40641          RD EXTRA FUEL      55

********************************************************************************


               FUEL    CORR    ENDUR
TRIP         213190  ........  13:09
10 PCT         3522  ........  00:16
ALTN ZSWX      5850  ........  00:20
INTL HOLD      6883  ........  00:30
MIN T/O      229445  ........  14:15
EXTRA            55  ........  00:00
TAXI           1425  ........  00:25
RELEASE      230925  ........  14:40  ACT FUEL LOADED 230,958 LBS

KLAX/LAX   STD 20:15   ETD 20:15  ACT OFBL 20+16    EST T/O 20:40  ACT T/O 20+25
ZSPD/PVG   STA 09:45   ETA 10:04  ACT ONBL 09+42    EST LDG 09:49  ACT LDG 09+38
                                  TTL BLCK 13+26                   TTL FLT 13+13
PLANNED FREM 15.5 ACT 15.2

********************************************************************************

ATC ROUTE: N0502F320 VTU5 RZS DCT LIBBO DCT BRINY DCT BOARS DCT AMAKR DCT REDWD
           DCT UNVER DCT 42N130W 45N140W/N0489F340 47N150W 48N160W
           49N170W/N0485F360 49N180E 47N170E 43N160E/N0488F380 DCT EMRON OTR9
           AVBET OTR11 KAGIS Y51 INUBO Y16 CHINO Y88 CUE Y28 ISAKY Y60 ONIKU
           A593 DUMET DUM21A

--------------------------------------------------------------------------------
AWY      WAYPOINT   MT    ALT  WND/VEL   TAS  DIST  FUEL REM / USED   LEG   ACC
         NAME             TMP     FREQ    GS   REM  POSITION          ETO / ATO
--------------------------------------------------------------------------------
         KLAX/25R         128                          229.5 /   1.4 FMS FREM 22.7 PREFLT
         LOS ANGELES INTL                     5806  N3356.4 W11823.0 ...../.....
                                                                                  DEST  ACT
                                                                                  FREM  FREM
                                                                                  PRED  DELTA
                                         ACTUAL>>      214.8 /  16.1       00+28  20.8  + 2.0
DCT      LIBBO     299  FL320  225/047   501    88     212.8 /  18.1   10  00:30
-KZOA                     -38            495  5593  N3600.0 W12150.0 ...../.....

                                                       194.4 /  38.7       01+35  20.6  + 2.1
DCT      42N30     293  FL320  226/078   497   170     192.3 /  38.7   21  01:37
         42N130W          -43            477  5050  N4200.0 W13000.0 ...../.....

                                                       175.8 /  55.1       02+35  20.4  + 1.9
DCT      45N40     278  FL320  265/048   494   471     173.9 /  57.0 0102  02:39
         45N140W          -45            450  4579  N4500.0 W14000.0 ...../.....               FMS
                                                                                               ETA
                                                       159.4 /  71.6       03+31  20.5  + 3.0  0917
DCT      47N50     272  FL340  296/070   489   326     156.4 /  74.5   45  03:38
         47N150W          -49            421  4145  N4700.0 W15000.0 ...../.....

                                                       144.3 /  86.7       04+24  20.4  + 3.9  0917
DCT      48N60     267  FL340  286/049   491   410     140.4 /  90.5   58  04:36
         48N160W          -47            443  3734  N4800.0 W16000.0 ...../.....

                                                       129.9 / 101.1       05+16  18.9  + 4.0  0926 selected STAR
DCT      49N70     268  FL340  224/043   490   402     125.9 / 105.0   53  05:29
         49N170W          -48            461  3332  N4900.0 W17000.0 ...../.....

                                                       115.9 / 115.1       06+07  18.8  + 4.0  0926
DCT      49E80     263  FL360  220/030   486   144     111.9 / 119.0   19  06:20
         49N180E          -52            464  2938  N4900.0 E18000.0 ...../.....

                                                       101.9 / 129.0       06+59  17.3  + 4.0  0932 updated WINDS
DCT      47E70     253  FL360  241/025   486   419      97.9 / 133.1   55  07:15
         47N170E          -52            461  2518  N4700.0 E17000.0 ...../.....

                                                        57.5 / 173.5       09+56  17.2  + 2.6  0932
OTR9     AVBET     248  FL380  260/074   490   247      54.9 / 176.0   35  10:08
                          -49            420  1241  N3608.5 E14528.0 ...../.....

******************************** RE-DISPATCH FIX *******************************
                                                        52.4 / 178.6       10+18  17.1  + 2.4  0932
OTR11    KAGIS     273  FL380  264/074   490    64      50.0 / 180.9   09  10:28
                          -49            416  1098  N3549.2 E14233.8 ...../.....
********************************************************************************

                                                        36.4 / 194.6       11+27  16.9  + 2.2  0933
Y28      WASYU     256  FL380  261/078   491    12      34.2 / 196.7   02  11:36
                          -48            414   633  N3428.3 E13323.0 ...../.....

My last logging was close to 100 nm before descent.

[pcubine 143]

I fly the 77L a lot more than the 77W and I have never had an insufficient fuel warning before takeoff. This is a big red flag that your flight planning has a problem.

Dan

Below is some information on a flight I completed this morning. As you can see I started the flight with less than the reserve fuel according to the PROGRESS page so there were insufficient fuel in the FMC. I changed the reserves on the INIT page to 5000 lbs. to get rid of the warning. As the flight progressed to Houston you can see that the remaining fuel at landing increased until it was right at required reserves.

 

As for the 13000 lbs. above reserves at KLAX - that included 10000 lbs. extra fuel carried from VHHH-KLAX. BTW the 10000 lbs. was included in the insufficient fuel warning at VHHH prior to takeoff. Without it, I would have really been in the hole.

 

I think the plane always has enough fuel as long as PFPX is used for planning and the winds don't go crazy enroute. During the flight your method shows that it does. My method shows that it does at the end of the flight. Why can't the two agree? Because the FMC PROGRESS page fuel remaining is either getting incorrect data from somewhere or it can't calculate the correct data.

 

----Flight Referred to Above----

EDDF-KIAH 205000 lbs. cargo, EU-OPS fuel policy, fuel bias 95%, release fuel 184499, reserve required 22418, PROGRESS page prior to takeoff fuel remaining at KIAH 9900 lbs, headwind comp 4 kts.

PROGRESS page at TOC - ETA 1304 fuel remaining at KIAH 9100 lbs.

PROGRESS page at 1 hour - ETA 1305 fuel remaining at KIAH 9800 lbs.

PROGRESS page at 2 hours - ETA 1304 fuel remaining at KIAH 11600 lbs.

PROGRESS page at 3 hours - ETA 1307 fuel remaining at KIAH 12800 lbs.

PROGRESS page at 4 hours - not at PC.

PROGRESS page at 5 hours - not at PC.

PROGRESS page at 6 hours - not at PC.

PROGRESS page at 7 hours - ETA 1310 fuel remaining at KIAH 17800 lbs.

PROGRESS page at 8 hours - ETA 1308 fuel remaining at KIAH 19300 lbs.

PROGRESS page at 9 hours - ETA 1308 fuel remaining at KIAH 21000 lbs.

PROGRESS page at T/D - ETA 1307 fuel remaining at KIAH 22300 lbs.

[downscc 1,327]

Your fuel bias adjustment of 95%? How did you arrive at that? I am looking for a reason why your fuel remain predicted is much less than plan.

 

I have never see a fuel warning when using PFPX fuel loads. Gotta be something in the way you have things configured.  EDIT:  I've tried the fuel adjustments in PFPX and usually only tweaked 3% or less and over the long run I just leave it at 100% now.

[pcubine 143]

Your fuel bias adjustment of 95%? How did you arrive at that?

Trial and error. Trying to come up with a bias and free fuel that work in the FMC on both ends of the flight.

 

Gotta be something in the way you have things configured.

So what is configured wrong with the flight to Houston. I arrived with required reserves. It's just that I had to takeoff with insufficient fuel according to the FMC.

[downscc 1,327]

I don't understand a couple of things that you do. The fuel bias already mentioned is one, because my experience is leaving fuel bias at 100% consistently works best. Then there is the planning.  I have just finished preflight with a PMDG B77L in UAL colors at gate A20 EDDF getting ready for UA47. This is flown by the company in a shiny new B789 but simming with the B77L works for me.

 

You said you have a payload of 205000 lbs, I max out the ZFW with a payload of 116,656 lbs. Maybe that's the diff between 777F and -200LR? You are using EU Ops fuel policy, I am using US Flag, no biggy.

 

So, at max ZFW of 460.9 klbs and a route that varies from great circle distance by 2% (Using NAT A) there will be differences between our preflight but I do not have a problem with FMS prediction.

 

My release fuel is higher at 194,679 lbs but that could be route and weather variations (I am using historical weather with an off block time of 271150 UTC. The planned fuel remaining is 27.6 lbs and the FMS Progress page indicates 27.3 klbs at KIAH. That is a perfectly reasonable variance.

 

Now the trick is to figure out why your configuration is giving you fits with FMS predicted remaining fuel.  Right off the bat there are a couple of things that will vary the FMS guess from the PFPX plan first of all being winds. I've noticed that the FMS uploads winds up to FL350 so if you are higher you may want to adjust the legs wind levels. Also, if the flight is > 6 hr then the forecast period for the winds you've loaded has expired. Selection of an arrival while enroute instead of during preflight is another source of variance. However, taken all the things I know will cause the FMS fuel reminaing forecast to vary does not come close to the error you are seeing. Since we are both using the same PMDG product, on the same route, I must presume the variance is caused by something different in your setup that we haven't discussed.

[bjratchf 80]

I am perplexed at the importance given the FMS fuel remaining prediction.  The important number is the fuel on board at a waypoint compared to planned fuel on board at that waypoint.  If you are at a decision point the choice to proceed or divert is based on fuel remaining. Never would you divert because the FMS prediction was not in agreement with the predicted fuel remaining.

 

If your gonna spend time on subject, I recommend you start logging your flights. I save a .txt copy of the PFPX flight plan and use my favorite text editor to enter the actual times, fuel numbers and weather at each waypoint.  I also post in the margin the time variance and FMS fuel remaining prediction so I can see how that relates to the route data. Gives me something to do on long flights.

 

What I have found, and mentioned here several time on similar threads, is that the FMS prediction is sensitive to elasped time performance.  Makes sense, the engine burn rate is predictable but time in the air is the variable that is hardest to predict.

 

I just added Imagine Sim ZSPD Shanghai Pudong to my airport inventory so maybe this weekend I'll make a trip over there and keep a log for discussion.

 

Dan, what text editor do you like to use? I would always print out flightplans, but I like to keep a paperless environment. The problem I've had with PFPX is in its export function- the flightlog doesn't line up in an organized manner in any text editors I've used, so I simply eyeball everything to make sure fuel is still in check for the flight. 

[barramundilure 152]

Hi Dan

My problem is a little different in that I am landing with less fuel than originally predicted.

I did a flight OTHH-VTBS yesterday in the B77W and kept a detailed log of Altitude, Wind Speed and direction estimated fuel at destination etc.

Prior to Taxi my landing estimated fuel was 14,600Kg.  On Take Off it was 14,000kg.  At top of climb the estimate on landing was 13,600kg.  My PFPX flight plan estimated a landing fuel of 12,200kg.

I logged ever waypoint and watched the predicted fuel at destination roll down at the 400Kg/hr mentioned until at top of descent my estimated fuel on landing was 12000kg.  By the time I landed and the STAR was pretty direct. I landed with 10,400kg.

The flight time was 2 minutes longer than expected at 6hr 02min.  Temperature and wind speeds and direction all very close to the flight plan forecast.  Can photograph the log sector by sector if it helps. 

This is the problem I am facing. 

It was never a problem until recently and don't know the cause or solution.

Regards

Tim Carter

[scandinavian13 5,192]

If you're wanting to add a little more attention to this, you should really do this a little more scientifically. As of right now, it looks like there's simply a misunderstanding of the FMC features, a misunderstanding of PFPX, and a misunderstanding of the idea of contingency fuel and why there's an 'actual' column on the dispatch paperwork.

 

If you're using real world wind, remember that wind data is a forecast product (seriously, go look: http://aviationweather.gov/), and not an actual observation. This is actually an issue identified by the industry as an example of benefits gained through things like SWIM. The data just isn't as perfect as people think. It's obviously good enough for planning purposes, but it's not a direct observation like some mistakenly believe.

 

Granted, in the sim the data is whatever the weather engine reports, which is likely pulled right off those forecasts as "actual." Still, this data may change over the course of the flight, which will affect planned versus actual. Additionally, depending on which flight levels are being reported, and what flight levels you're actually cruising, there may be variance in that data. In those cases, you would probably see creep in the data.

 

As an example, down at ROA right now, the wind is:

ROA 1120 1518+13 1612+10 1808+04 1913-09 2621-18 243334 283143 294256

 

If the highest level being presented to the FMC is FL350 (the "283143" above is the AWC's FL340 data), and you're cruising up at FL390 (the "294256" above), then that 11 knot difference with a 10 degree offset will manifest itself in a creep in the data. Math proof  (assuming 475 TAS, heading 270):

 

Distance - Forecast Time - Actual Time - Diff - Fuel (Lbs, assuming 15000/hr)

0500 - 01:07 - 01:08 - 00:01 - 0353

1000 - 02:15 - 02:17 - 00:02 - 0707

1500 - 03:22 - 03:26 - 00:04 - 1061

2000 - 04:30 - 04:35 - 00:05 - 1415

2500 - 05:37 - 05:44 - 00:07 - 1769

3000 - 06:45 - 06:53 - 00:08 - 2122

 

As you can see, even a relatively minor change of 10 degrees and 11 knots between the forecast and actual can throw off the predictions. While these are example numbers from a quick and rough calculation, the concept is shown: forecast values that diverge from actual values over long distances will have a significant affect on the destination predictions. On a 7 hour flight (pretty average for the 777), a minor deviation (10 degrees and 11 knots) results in about 2.0 less in the tanks. If the deviation is more significant, you'll see a larger delta.

 

This seems to me like it's more of the cause of the discrepancy at the moment, unless people have been controlling for variables reliably.

[pcubine 143]

This seems to me like it's more of the cause of the discrepancy at the moment, unless people have been controlling for variables reliably.

These two flights in post #3 of this thread were conducted under controlled conditions.

 

Two flights using 777F EDDP-KLAX (#1) and EDDF-KIAH (#2) with no weather, no time compression and auto step climbs. About 12 hrs. and 10 hrs. in duration.

 

Flight #1 T/C ETA is 1545 and fuel remaining at KLAX is 17900 lbs. T/D ETA is 1546 and fuel remaining at KLAX 14300 lbs.

 

Flight #2 T/C ETA is 1136 and fuel remaining at KIAH is 21700 lbs. T/D ETA is 1136 and fuel remaining at KIAH is 34000 lbs.

 

All of these times and fuel remaining are as reported on the PROGRESS page of the FMC. So #1 the fuel remaining decreased and #2 it increased. The only difference was #1 had a cargo payload of 100000 lbs. and #2 had a cargo payload of 1950000 lbs.

[downscc 1,327]

Dan, what text editor do you like to use? I would always print out flightplans, but I like to keep a paperless environment. The problem I've had with PFPX is in its export function- the flightlog doesn't line up in an organized manner in any text editors I've used, so I simply eyeball everything to make sure fuel is still in check for the flight. 

I use Ultra Edit from IDM. It's a little pricy but it does everything but make coffee. It can be used to generate code in most any language (eg c, Java or HTML), display binary in hex format and is very easy to use. I don't use most of the features but it sure is a good text editor.

 

 

 

Flight #1 T/C ETA is 1545 and fuel remaining at KLAX is 17900 lbs. T/D ETA is 1546 and fuel remaining at KLAX 14300 lbs.

 

Flight #2 T/C ETA is 1136 and fuel remaining at KIAH is 21700 lbs. T/D ETA is 1136 and fuel remaining at KIAH is 34000 lbs.

 

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.

[scandinavian13 5,192]

 

 

I use Ultra Edit from IDM. It's a little pricy but it does everything but make coffee. It can be used to generate code in most any language (eg c, Java or HTML), display binary in hex format and is very easy to use. I don't use most of the features but it sure is a good text editor.

 

Sounds a lot like Notepad++

 

Ryan recommended that one for me when I started working the support queue.

[downscc 1,327]

Notepad++ is free, a better recommendation for hobby use. I'd probably go that route too if I hadn't already purchased UltraEdit.  I first started with UltraEdit more than a decade ago, back then it was only a few bucks and came with two other useful programs UltraCompare (powerful file comparison tool) and UltraSecurity (secure delete, something the Clinton's should have used). Well with commercial success came the increase in cost and I'm not sure I'll pay for the next major release. I do really like the user interface, professional easy to use, powerful macro utility, text columns etc etc... but it's not free LOL.