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Guest melf12

PSS (Native) B772LR - Landing weight?

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According to my VA's Operating Manual, the B772LR's Landing weight should NOT exceed 208.625 kgs. However, I have some 600 nm to TD at OMDB, my CDU Approach Ref page shows my Gross Weight to 211.4 and increasing!? At FL 390 I don't think anyone is getting on the aircraft... - does anyone know why/how the T7's GW is 'increasing?I could try Dumping fuel, but how is the GW increasing.Ken

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That's most likely due to an increasing amount of fuel left at your destination. If memory serves, it's a "feature" that PSS did not fix.Jim Harnes

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Thanks for your reply Jim,Very interesting? I made a 'rough and ready' fix by going into Fs9AircraftFuel and Payload, then reduced the fuel load. That seemed to work.I recorded my landing using Recorder - not played it back yet, be interesting to see if it improved my landing :)Ken

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Ken,Had a look at this again on the OMDB route {the last time it came up was during testing}. As Jim says, it is due to the changing FOG figure as the FMC constantly updates fuel useage.I found that in the cruise before TD and of course particularly when inserting the arrival runway and any changes to waypoint heights etc, the gross weight could increase marginally. But always on parallel to a similar FOG change. Once everything settled down without subsequent profile changes, the GW reduced as expected.This was with an ER. Just for interest, I'll try the LR today.John R

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Hello John, thanks for having another look at this problem.I had a memo from our BAv B777 Training Captain, he suggested I have 'another' look at the Standard Operating Manual for the B772LR.Wading through the SOP I found that the Gross Landing Weight must not exceed 208.265 Kgs. With about 600 nm to TD at Dubai, the GW was already 211.5 kgs and rising. Before dumping fuel I had a quick look at the CDU App Ref page, before moving on to fs9AircraftFuel Payload to 'dump fuel'. While doing that a thought crossed my mind, that the GW was moving down? I ignored that thought and dumped the fuel :) A pretty good landing resulted; and i'm pretty 'pernickety'!I'll see if I've got a .jpg of the TD.Ken

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Hello John,Did you find time to do that flight again?I can confirm that the Gross Weight does reduce, in the descent though! I've started to be a little more careful with my fuel load calculation, time will tell if that helps :) Ken

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Ken,Flew it in the LR with the same result. During the cruise, the GW can increase marginally as the system continually re-assesses fuel usage over the remaining distance. I assume the real 777 has a more sophisticated system for predicting landing weight {it costs a bit more than the PSS version}; even so, I suspect that it would suffer similar apparent anomalies as fuel usage rate or the approach profile change.The PSS 757 has the same facility although the anomalies are less marked {smaller engines etc}Of interest, the 747 {PMDG} does not attempt to predict landing weight. The Approach Page always shows current GW ie ZFW + current fuel state. I guess they decided to at least leave something for the pilot to do. It does provide a reminder to set the correct approach speed before the glidepath is captured.Overall without knowing a lot more detail about the real world 777 FMC, it is difficult to judge whether the PSS programming is correct or not. It certainly reacts as described in the manual and provides sensible and reasonably accurate predictions. Whilst I fly VATSIM, I am not a member of any VA so perhaps your 777 Training Captain will be able to give you some real world "gen". BTW, if you post your ZFW and start up fuel load, I would be interested in flying your profile.RegardsJohn

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You have certainly given it a 'good coat of looking at it' John. More that I could have expected.I'm doing the Heathrow to Dubai trip tomorrow, so I'll make a note of the information you require.I've got 'hooked' on this now. Despite what some people say, I think the PSS B772LR has a lot going for it, I would not part with it, it's the only aircraft I use nowadays. I'm comfortable with VNAV, LNAV etc, if I have a problem I revert to V/S. Never use the speedbrake, just bring her down nice and easy; need to start the descent further back than the T/D suggests, no problem. We have to keep and 'eye' on fuel usage, don't want a memo from the Chief Pilot :)We have a very good T7 Training Captain, I suspect he would point me at the Manual though, in this case :)Ken

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Hi John, here are all the weights for the B772LR Flight EGLL to OMDB.Total Fuel Load = 61061 KgsTaxi Weight = 242,496 KgsTakeoff Weight = 242,085 KgsLanding Weight 188,331 Kgs(Est)Zero Fuel Weight = 181,436 KgsTO Flaps 5 C of G = 28%TOD Gross Weight = 193.1I missed the Gross Weight, at the Arrival Gate - I forgot the CDU clears itself on landing??Fuel remaining, in the Main Tanks = 4.9 Left and Right.Let me know if I've missed something :)Conversion Formula lbs/kgs - 2.2046Ken

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Ken,Thanks, I'll give it a whirl tomorrow. Picked you up crossing Turkey this am after a Saturday lie in!!John R

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Hi John,"Picked you up crossing Turkey this am after a Saturday lie in!!" Did you see the B767 about 100nm behind me? He was 'bird dogging' me all the way from Germany to Dubai - couldn't catch me though :)I will be on the same Route tomorrow, got to get the 'hours' in!Ken

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