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Guest Emkay

Problems during climb with the 747-400

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Guest Emkay

HiI've recently been watching some IITV and other aviation videos that featured the 747, and they made me compelled to retry this 747 after long abandonment, but this time, I was successfully able to get the aircraft powered up and get the flightplan imported etc etc.Anyway, the main problems occur when I am well into my climb to my cruise altitude, as I get closer and closer to my altitude of 38000, the speed suddenly starts to fall below 230 knots which eventually ends up in the aircraft near stall, which activates that annoying scraping sound :(Anyway, int his particular flight I chose not to use VNAV since I don't completely understand it yet, is that the problem? Why does my aircraft start stalling as I get closer to cruise altitude? Decreasing the climb rate to -500 doesn't help either. Can someone input ont his and help me solve this annoying problem!Also, another problem I have is that when I set the sim rate to 8x every minute/30 seconds or so I get a caution sound, my speed selector is switched off and I get an FMC message saying something like "MAX ALT FL222" - what on earth does that mean? And why does my speed selector keep turning off when I set my sim rate to 8x? And again, is this because I have chosen not to use VNAV?Would kindly appreciate any help!

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Hi there,About your first problem, there could be more than one reasons for this, are you in VNav, do you have autothrottle armed and active, ...There are some more topic around here that discribe this problem in great detail, maybe take a look.And also, you said you have watched the video, but did you also watched the manuals ;-)About the sim rate, there are problems with the autopilot when using sim rates over +8 (its also in the manual) - so don't use this!Hope this helps a little bit?


Regards,

William Vrielynck

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Welcome to the forum... please sign your real name...rules is rules.FL380 might be too high for your weight, certainly since the FMC is squawking about it. A maxed-out (875,000lbs) 744 pax can be coaxed into climbing to about FL310. Your sim rate acceleration is just making a bad problem worse. VNAV has nothing to do with any of the problems you're having.I recommend that you lighten-up and fly some short routes until you learn how to fly her. Oh yes, read the book where it mentions sim rates.


Dan Downs KCRP

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Guest Emkay

Thanks for both of your replies. As you both rightly said, I consulted the manual to look for any information on simulation rate and after spending 10 minutes looking through each section of the manual, I was unable to find anything, can you direct me to which particular document the information about sim rate is? Also this happens at a sim rate of 8x, nothing more :) Is it usual for simmers to get their speed selector switched off and other parts of the autopilot during a sim rate of 8x?headley, I do have autothrottle armed and active, but I currently was not using VNAV on this flight, I set the autothrottle to maintain 270 knots throughout the climb, but it failed as I got closer. Also, since my aircraft wasn't even fully loaded, why did the FMC warn that the MAX ALT was FL222 or something close? Surely that's way too low?About the weight, my aircraft was not fully loaded at all, I was actually doing a flight from London to Dubai, and I loaded around 100,000kg of fuel I think it was, so nothing close to fully loaded!About read all the manuals, as much as I would love to absorb all the previous information conveyed in those documents, it seems too much of an elongated and daunting task, I like to consult manuals and support when I receive problems inflight, instead of having to know absolutely everything from the start :)

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Air density decreases with altitude, because of this your true air speed (TAS) will be faster than the indicated air speed (IAS).I can only presume that the speed you refer to (230kts) is taken from the speed tape on the LHS of the PFD, if so this is your IAS.You have encountered a problem that has existed since man began powered flight - a decaying IAS with increase in altitude.Modern Airliners use 'Mach' as the principle speed reference at high altitudes, this is displayed as a percentage of the speed of sound at the given altitude.Can I suggest you carefully study the AoM & perhaps research futher on flight dynamics, there are simply too many variables to discuss in a forum. As Dan says it may well be that you are far too heavy to be attempting a climb to 38000 feet, but I suspect there are also other factors also at play,Kind RegardsSteve Bell


Steve Bell

 

"Wise men talk because they have something to say.  Fools talk because they have to say something." - Plato (latterly attributed to Saul Bellow)

 

The most useful tool on the AVSIM Fora ... 'Mark forum as read'

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M Khan:I stand corrected. The manual (00-35) limits rates to x8. I have found that even this causes unstable throttle oscillations and limit my sim rates to x4.An IAS (CAS actually) of 270kts becomes 305KTAS (kts True Air Speed) at 8000, 358KTAS at FL180 and 495KTAS at FL360. If you were trying to hold 270KIAS that would be a problem in the climb, try switching to a Mach number of about 0.82 at about FL320 or try the recommended climb profile on the VNAV screen.


Dan Downs KCRP

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M Kan,As Dan said, there could indeed be a problem with your initial FL380 with your current weight!To determine the optimum FL for the current weight you can check your VNav-page 2 after you have configured the plane.In the VNAV-page 2 you will see bottom right the optimum and max FL for the current weight. You can also see the number of fuel you will still have when reaching your destination!If things are not OK you can still adapt fuel and cruise FL before take off! (changing weight is another thing as for this you have to run the loader and therefor you have to close the Sim. (I think).To determine the optimum fuel and altitude you can ofcoarse work you trough the manuals and charts - chapter 2: cruise and fuel planning - (like in real life) but i have found that this is not so accurate as the calculations done by the FMC.Hope this helps,


Regards,

William Vrielynck

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Guest Emkay

Thanks very much for the help. I will try out your suggestions :)If anyone does find a fix for the 8x instability issue, then please let me know!

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