Dan

 

I am going to list the first 3 flights with fuel bias at 100%, CI 85 and flying the 777F.  I don't want to inundate you with too many flights at one time. I think I still have 3 flights to do. These three flights were generated using PFPX with ASN as the weather source and ASN was also used for weather in the sim. Flights 2 and 3 showed insufficient fuel prior to takeoff and at T/C after runway approach and STAR were entered into the FMC. Flight 1 was U.S. Flag Jet Fuel Policy and 2 and 3 were EU-OPS Fuel Policy. More to come later. 

 

 

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

KLAX-VHHH     142500   294367    36852           0658         38.7K lbs.        0703           45.4K lbs.

 

EDDP-RJAA     195000   209446    24228           1400         15.5K lbs.        1357           30.4K lbs.

 

RJAA-EDDP     220000   226984    24321           1517         23.4K lbs.        1513           38.2K lbs.

 

 

 

I don't know what to suggest. I did the EDDF-KIAH flight yesterday and the fuel remaining was within 1000 lbs of planned, using same conditions as you mention: US Flag, ASN, PFPX fuel bias 100%, etc. Exceptions: 77L and my CI was 220.

 

If you give the enough to go on I'll try to reproduce the exact same flight in same variant, but that would have to be with no weather.  Speaking of weather, which might be a consideration, I almost always plan a flight that occurred withing the past 24 hrs and set ASN to be slaved to P3D time. For example, it is about 2000z right now so I would be planning a Westbound Atlantic trip leaving the blocks at maybe 1200z. I do this for several reasons, one of which is my flights occur in the same weather conditions as the flight I am mimicking.  Anyway, eventually we'll figure out why your fuel remaining is significantly higher than planned. There's a reason, we just need to nail it.

 

Req Rsr meaning?  TO Fuel same as Fuel Released or Min Req Takeoff? Easier to follow ZFW than payloads, since same payload can have different ZFW in different airframes.

Dan

 

Req Rsr is required reserves consisting of cont, altn, and final per PFPX OFP. TO Fuel same as Min Req Takeoff. Roger on the ZFW.

Just to be clear here -- because I'm getting slightly confused:

 

Are we talking about actual fuel remaining in the tanks on stand at destination (taken from the EICAS fuel totalizer) or an FMC fuel remaining prediction?

Just to be clear here -- because I'm getting slightly confused:

 

Are we talking about actual fuel remaining in the tanks on stand at destination (taken from the EICAS fuel totalizer) or an FMC fuel remaining prediction?

FMC fuel remaining prediction at T/C and T/D.

Thought so, thank you.

 

Would be interested to know how your actual figures (taken directly from the totalizer -- ignoring the FMC altogether) match up with the PFPX plan. Assuming you're arriving with a value reasonably close to that planned by PFPX, I think we can safely ignore all this stuff about PFPX fuel biases, weather injection and so on. The problem, as I understand it, is the predictions and not the actual. Is that right?

 

The question is then what is going on in the FMC to make the predictions wrong. Granny/eggs etc but:

- Are you entering updated winds for each waypoint in to the FMC prior to departure? Are they still there at T/C if you check the RTE DATA pages (Just in case for some reason they're getting deleted)? This is the main reason I can think of for the FMC's predictions being wrong. However, I find it odd that the predictions are also wrong on westbound flights (where an FMC assuming nil wind is highly unlikely to give you an INSUFFICIENT FUEL message prior to departure, though I find that particular message to be fairly common on eastbounds before representative winds have been entered).

- You say the problem tends to appear after entering runway/approach/STAR -- silly question again but my first thought if I modified the route and suddenly the FMC's predictions went wonky would be some sort of error in the distance calculation. I know this is happening at multiple destinations, but who knows -- maybe there's something strange about the way the FMC is recalculating the distance to run? Likewise, have you checked on the LEGS page to see what speeds and altitudes are being predicted along the route (and particularly as you approach the STAR?) I know the PMDG 747 would sometimes give a blank time/fuel at destination if it couldn't calculate a proper descent path for some reason (usually an unattainable constraint somewhere) -- maybe something similar is happening here?

The winds by waypoint are requested at the ramp prior to pushback. The fuel remaining is checked in the FMC just prior to line up. And the winds are request again at T/C and the fuel remaining is checked in the FMC. I only consider the fuel remaining between T/C and T/D because there are too many variables such as speed/altitude constraints which might or might not be waived by ATC.

 

I enter the runway approach/STAR during the climb to cruise and I have only seen it  move the remaining fuel from a plus to a minus if a  German airport is the destination. In particular if EDDF is the destination and a transition is used. The transitions can add up to 10-15 minutes to estimated flight time.

The winds by waypoint are requested at the ramp prior to pushback. The fuel remaining is checked in the FMC just prior to line up. And the winds are request again at T/C and the fuel remaining is checked in the FMC. I only consider the fuel remaining between T/C and T/D because there are too many variables such as speed/altitude constraints which might or might not be waived by ATC.

 

I enter the runway approach/STAR during the climb to cruise and I have only seen it  move the remaining fuel from a plus to a minus if a  German airport is the destination. In particular if EDDF is the destination and a transition is used. The transitions can add up to 10-15 minutes to estimated flight time.

 

Thanks Michael -- but what about the totalizer?

 

What I am trying to do is establish whether the issue is with the actual burn (which will be reflected on the totalizer) or the predicted burn (which is what the FMC gives you, and so like any calculator if the data is wrong -- either because of something you've fed it erroneously or some other input it's reading erroneously) it will be wrong.

 

If your PMDG 777 is actually burning less or more fuel than expected (as in: PFPX says load 220,000lbs and plan to land with 26,000lbs, and load 220,000lbs but when checking the actual amount of fuel in the tanks - via the totalizer, not the FMC -- after landing you actually have 33,000lbs remaining), that is one thing. If it is burning the same amount of fuel as everybody else's but the FMC fuel predictions are wrong, then that's another issue entirely.

 

If the actual burn is in line with the paper flight plan, then talking about wind, weather and PFPX bias figures is irrelevant. The issue is with the FMC itself and either the way it is performing the calculations or the data it is receiving (either manually input or sensed). If, on the other hand, the actual burn is off for some reason then it's unsurprising that the FMC is getting it wrong because it's basing its predictions on a particular mathematical model and the actual data is significantly divergent from this, and therefore it is having to update its predictions constantly. This would more likely indicate some sort of underlying problem with the way your PMDG 777 is operating.

Thanks Michael -- but what about the totalizer?

 

I believe I have compared the FMC and the totalizer once. However the FMC was at T/D and the totalizer was when I had taxied off the runway. They were close when I take into account that the comparison was done at two different places. Next time I will check them both maybe a mile from touchdown or would you recommend another location for the comparison?

I would record:

 

Total fuel on board from the totaliser before engine start.

 

Totaliser fuel at a convenient waypoint just after TOC, compared with the PFPX flight plan fuel at that point and the FMC fuel remaining prediction.

 

The same prior to TOD (and it wouldn't hurt to do some enroute if possible to get a picture of how the actual burn is progressing compared to the PFPX plan)

 

Totaliser fuel remaining after shutdown (and compared to the PFPX planned remaining figure).

 

That way we can compare the actual vs planned burn vs FMC predictions.

 

Thanks!

That way we can compare the actual vs planned burn vs FMC predictions.

 

 

Simon

In accordance with your suggestion I am furnishing you with the following information:

 

(1) General Info. VHHH-PANC, 777F, CI 85, fuel bias 100.0%, cargo 195000 lbs., and average wind component per PFPX TL 037.

(2) TTL (totalizer) before engine start 184.4

(3) Fuel remaining before takeoff 25.4, required reserves at PANC 26.6. Insufficient fuel warning in FMC and on EICAS.

(3) At T/C fuel per TTL 171.3, PFPX 171.3, fuel remaining PANC 23.7

(4) Fuel at 4 waypoints during flight  SHR      TTL 158.8, PFPX 156.5, remaining at PANC 24.6

                                                          LURED TTL 119.3, PFPX 113.1, remaining at PANC 26.9

                                                           RUSOR TTL 57.5, PFPX  42.9, remaining at PANC 33.6

                                                           ENEGU TTL 49.7, PFPX  40.3, remaining at PANC 34.2

(5) At T/D per TTL 37.9, PFPX 28.3, remaining at PANC 35.1.

(6) TTL after engine shutdown 32.6, PFPX 26.6. This could be meaningless since PFPX didn't have the STAR in it's route and the runway was changed from 13 to 07L while on the STAR .

 

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.

 

 

Dan

I think I will do this flight tonight but without any redispatch. 

Dan

 

Req Rsr is required reserves consisting of cont, altn, and final per PFPX OFP. TO Fuel same as Min Req Takeoff. Roger on the ZFW.

 

Michael,

 

Not that this is in any way related to your fuel at destination issue, but contingency is never part of the reserve value! It is contingency fuel and just that. In fact it can be burned in its entirety from the moment the fuel bowser is disconnected, hence it is not part of the trip, let alone minimum takeoff fuel. 

 

As its purpose is to account for contingencies from the moment the fuel bowser is disconnected, the fuel at destination on a flight plan will never include the contingency value. That is, it assumes that all of it will be burned which typically of course is not the case.

 

Regardless, your reserve fuel value will consist of 30 minute reserve + alternate fuel + (a small nominal buffer if you want to get the insufficient fuel warning before it actually goes below 30 minute reserve + alternate ).

 

In summary

 

Reserve: 

 

30 Minutes + Alternate + ( for some operators HOLD fuel).

 

In summary

 

Reserve: 

 

30 Minutes + Alternate + ( for some operators HOLD fuel).

 

Thanks for the information.

Simon

In accordance with your suggestion I am furnishing you with the following information:

 

(1) General Info. VHHH-PANC, 777F, CI 85, fuel bias 100.0%, cargo 195000 lbs., and average wind component per PFPX TL 037.

(2) TTL (totalizer) before engine start 184.4

(3) Fuel remaining before takeoff 25.4, required reserves at PANC 26.6. Insufficient fuel warning in FMC and on EICAS.

(3) At T/C fuel per TTL 171.3, PFPX 171.3, fuel remaining PANC 23.7

(4) Fuel at 4 waypoints during flight  SHR      TTL 158.8, PFPX 156.5, remaining at PANC 24.6

                                                          LURED TTL 119.3, PFPX 113.1, remaining at PANC 26.9

                                                           RUSOR TTL 57.5, PFPX  42.9, remaining at PANC 33.6

                                                           ENEGU TTL 49.7, PFPX  40.3, remaining at PANC 34.2

(5) At T/D per TTL 37.9, PFPX 28.3, remaining at PANC 35.1.

(6) TTL after engine shutdown 32.6, PFPX 26.6. This could be meaningless since PFPX didn't have the STAR in it's route and the runway was changed from 13 to 07L while on the STAR .

Dan

I think I will do this flight tonight but without any redispatch. 

 

 

To be clear: according to PFPX you were to arrive with 26.6, but you ended up arriving with 32.6? However at T/C your fuel remaining was showing 23.7?

 

Furthermore, as the flight progresses your fuel at destination continues to increase and as seems always ends up above what your flight plan shows at destination (that being a good thing of course).

 

That raises a red flag because the FMC is expecting less favorable conditions for the flight, while you are on the ground and at T/C, however as the actual burn never lies, and the flight progresses the FMC finds it ended up having more fuel than expected. Which points to a discrepancy in the information supplied to the FMC.

 

What FL's did you fly from the first one at T/C and the subsequent step climbs? What FL's did you have in the RTE DATA Wind page?

 

 

 

What FL's did you fly from the first one at T/C and the subsequent step climbs? What FL's did you have in the RTE DATA Wind page?

 

 

T/C, FL310, FL330, FL350, T/D. Since I no longer have then RTE DATA Wind page available I can only guess at the levels based on past experience. The levels begin at FL290 and end at FL370 unless I delete a level an add a level which I did not do on this flight. Most flights are in the low to mid 30's because I carry about 180000 to 205000 lbs. of cargo. There are only a few flights that I go higher than FL360-370. The flight I am doing now has no weather so this will not be a consideration.