I'm not complaining about any of this, and I know that operational factors lead to differences from the planned performance. And the third variable was the route: there were certainly some deviations from the flight plan as the aircraft got closer to the terminal area. Another was the weather, as the local conditions begin to become more determinative than the wind corridor. One was the vertical profile: I couldn't maintain M0.84/340 in a constant descent the whole way from F元90 to the ground without intermediate level-offs. There were three variables that changed, for sure. Yes, winds were uplinked for both cruise and descent.Ĥ. (Hardy: Very powerful feature, by the way, thanks for it.)ģ. Yes, the expected STAR waypoints were in the OFP and in the FMC.Ģ. In this case, should I just assume that TOPCAT isn't perfect and that PSX has the better numbers? Or should I trust TOPCAT in the same way that one would trust the OFP's number for V2 over the FMC value (since the dispatch office has more data to feed into the equation than the FMC does)?ġ. In other words, feeding the PSX weather into TOPCAT, with the same derate, and same runway, calculating N1 for takeoff might give 102.3% in TOPCAT, whereas the FMC commands 104.1%. I note that the N1 predictions for the GE engines are off by a percent or two when compared to the N1 commanded by the FMC. But just in case you or someone else does. My second question has to do with TOPCAT and I understand that you may not have any idea here. So my question is this: given what you know about PFPX, should I expect that the fuel burn would be as predicted under ideal circumstances? Or are there any known issues with fuel predictions in the final phase of the flight? Could be any number of factors here - weather, primarily, or unpredicted time spent at intermediate altitudes, the speed schedule in the descent, etc. However, in each case, the approach (starting at TOD and going until landing) took about 6000 more lbs of fuel than predicted by PFPX. I'm using the latest version of your 747-400 passenger GE performance file for PFPX, and the agreement was really excellent throughout the whole cruise portion. Normally I can't finish a full 15-hour flight but I was able to do this a time or two in the last few weeks, and I noticed that PSX and PFPX were basically in full agreement about the fuel consumption enroute. Steve, I have two quick questions for you.įirst, I had the pleasure of flying some full long-haul flights in PSX recently.
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