747-400 losing control during level flight due to weather/winds

[Byrna 0]

Hello,I did a search but could not find anything specific on this so I thought I'd post.I have flown my last two flights on the same route (KFJK - KSLC - New York to Salt Lake City) and with ASV5 (Active Sky 5) installed. I have noticed that when I accelerate simulation to 8X which is supported as per PMDG documentation (on the 744), occasionally, when the winds shift or become stronger, autopilot loses control, thrust gets reduced and the plane loses speed and a near-stall situation arises.I know the PMDG 744 autopilot apparently cuts off (as per documentation) if it detects things like an engine spoolin/shutting down and the 744 had problems with resuming from switching views and/or saves by having 1 or more engines temporarily spooling to very low N1 rates where it loses speed drastically but then manages to recover. After the patch (version 1.1), I have noticed in the readme file that the autopilot/autothrottle can disengage if engines spool or shut down, even if for a brief period.The result is struggling to get the plane back up to altitude and back to speed as the speed can go from a comfortable cruise of MACH 0.852 at 35,000 feet (which is well below max. alt) to 0.60 or near -danger speeds. Keeping the throttle lever at a very high manual setting of around 100% N1 should help but this is really crazy not to mention "dangerous" to be happening several times during a flight. Some people choose not to use accelerated simulation but then they are stuck with sleeping while the plane is flying and facing unknown "disasters" as they are not monitoring the plane. I choose to accelerate so I'm always there from beginning to end. Has anyone in PMDG duplicated these issues with accelerated simulation, weather programs and disengaging AT/AP? I even saw a post where default FS2004 weather causes the same loss of AT so this is not just an Active Sky-related issue.Any help would be appreciated.Can (John) Agbaba

[Byrna 0]

Would anyone from PMDG mind commenting on this please?I fly other add-ons like the PMDG 737NG and Active Sky 5 and have absolutely no problems...John

[crvm 0]

Do you have a reg ver or FSUIPC? There is a new version that helps smooth winds correctly since the last ver had some problems. I would also upgrade to ASV ver 6 since this is a free upgrade for users of ver 5. [h4]Randy J. Smith[/h4]AMD 64 4000+|ASUS K8V DELUXE|SAPPHIRE ATI X800XT PE|MUNCHKIN 3200|80 gig SATA|DELL 1905FP 19" LCD|TRACKir PRO|PFC JEPPESEN MOONEY YOKE|CH PRO PEDALS|

[rsrandazzo 6,353]

John-A couple of things:-> Use the search fuction in the forum- you'll find that this topic has been discussed before in great detail.-> Please refrain from comments like "anyone from PMDG care to comment on this?" It makes the poster appear to be demanding and imperious- which gives us the tendency to simply ignore the thread because you can't generally have a conversation with people who are imperious. Okay- this is a known problem with MSFS. It is not a problem with the 747-400, but is the result of a poor atmospheric change model within MSFS. ALL MSFS aircraft and addon aircraft exhibit this behavior- but the behavior is going to be more noticable the larger the airplane is- and the more realistic the flight model.I routinely operate the sim at 8x and even 16x without problems EXCEPT when the winds aloft/temperatures change too radically. No matter what weather importing program you use- they all have problems with the kludgy methods used by MSFS to model temperatures and wind.The flight model of this airplane is highly realistic- and as such if you are flying in rapidly altering conditions you will find that the airplane responds to the conditions correctly, and without prejudice. If you flew the airplane through such condition changes in real life- it would react the same way....If you flew these flights at normal time rates- you'd still notice some problems with spiking and wind shifts causing the autothrottles to struggle for airspeed control. This results usually from excessive temperature or wind changes upsetting the control laws of the autoflight system because the flight model reacts to the instantaneous change in the atmospherics...Flying these flights at 8x or even 16x- the changes appear even more dramatic- and can cause an upset from controlled flight in extreme cases.The only fix for this would have to come from Redmond, WA.....

[Guest CaptainJoe]

Hello,I have noticed this occuring even in 1x. What I do is I set the thrust mode to CLB even while at flight level. This will give the EEC enough room to increse the engine thrust high enough to be able to re gain lost airspeed. While I was watching the Virgin Air 747-400 DVD I noticed they had the thrust mode set to CLB at flight level. So I decided to try it and voila it fixed the airspeed issues I encounter when the wind speed changes.

[Tabs 2,790]

As Randy alluded to, the new Active Sky 6 has some options that help with this sort of issue, especially if you plan to operate long flights with the cruise phase happening overnight etc...

[jeehaa 0]

I have the same problem and it happens to the 737ng as well. As we are not allowed to increase simulation rate online, I fly it at 1x SR.What happens is this: During climb / cruize / descend, the variability of the winds (knots and direction) is so big that the autopilot will disconnect vnav or the plane stalls, eventhough the trottles are set to full (A/T or manual; the same for both). In other aircraft (payware) I don't have this problem at all. I remember that I had this problem with the activesky 2004 series but it suddenly disappeared. Now with the 744 and the 1.10 patch installed, the problem is back, for the 737ng and 744 as well.Kind Regards,Jan Herman Kloppenborg

[Byrna 0]

Hello Captain Joe,I do something similar - since autothrottle DOES disconnect to an ARMED but DISENGAGED state, when this happens, I make sure the actual position of my throttles on my CH flight yoke are very high - near max. to ensure throttle does not reduce much but the CLIMB idea is a good one too. Except of course, that in very long range flights (e.g. Montreal - Hong Kong which is barely doable with the 744), this will probably result in higher fuel consumption and running out of fuel.Thanks for the tip.John

[Byrna 0]

Robert,Thank-you for your informative reply regarding issues with FS weather modeling.Firstly, I STARTED my post by stating that I could not find anything when I used the search button. I always do searches BEFORE posting anything. If you care to provide what keywords can be used which bring up legitimate search results, perhaps that would be more helpful than simply stating "use the search button". Second, as stated below by Jan, the problem I mentioned did NOT happen UNTIL I too installed the 1.1 update. Before the update to 1.1 the only thing which happened was a brief disconnection of autothrottle but never a descent and mess of this magnitude. It is nice to know this is an FS2004 issue. I just thought that ASV5 (I'll be upgrading to AS 6 soon) had sorted out these issues with wind smoothing. It is clearly observable that sudden wind intensity and direction shifts cause this behaviour so I'll have to make sure to understand how to best configure AS 6 when I upgrade.Also, I use FSUIPC registered version 3.5.0. I have not upgrade to 3.5.1 (I believe this is the latest).I'll try to upgrade to AS 6 and then try to understand how to adjust FSUIPC settings (if still required).One last observation: Perhaps if FS2004's limitations can cause such a complete loss of control of a very precisely modeled aircraft like the PMDG 744, it may be better NOT to model every detail of the 744 flight model with such accuracy so that it is NOT so sensitive to the known issues within FS2004. But I guess this may not be possible without a complete re-write of the FDEs and may even detract from the enjoyment of your amazing aicraft. It's one thing being realistic and this is a wonderful gift to use from PMDG, but if this realism causes problems like this, I guess either we'll have to learn to live with it and try to adjust FSUIPC/Active Sky settings or the FDE's can perhaps be modified (if at all possible).Just a thought... Hope Microsoft, for once, brings out a bug-free, stable, well-modeled (weather, aircraft, panels etc...) FS2006 (FS10) next year. It will reduce the headaches of developers like PMDG and users like us alike.John

[Guest SIX]

First off, if I am walking away from the computer for a bit, I clear my weather by hitting CTRL+W, my assigned key for clearning WX in FSUIPC hotkey settings. Sometimes the plane will have no headwind, or maybe even a tail wind, but there has been an atmospheric change (maybe pressure, I don't know) and the bird will slowly go into a stall. When i return, I restart Activesky and continue with the weather simulation.I suggest when you have simrate of any speed on you turn the weather off.Wilson HinesMy Blog: http://www.wilsonhines.com --------------------------------------http://www.precisionmanuals.com/images/forum/747400.jpghttp://www.precisionmanuals.com/images/forum/pmdg_744F.jpghttp://online.vatsimindicators.net/837438/3074.png

[Byrna 0]

Hello Wilson and thanks for the workaround. But I have other add-ons, including the PMDG 737NG series and PSS 772LR and NEVER have I had an auto-pilot disconnect on me during accelerated simulation. So it's pretty obvious that the problem is with the autopilot logic in the 744, even if it IS realistic for real life - it is not realistic given the limitations of FS2004 and hence autopilot disconnect when throttles are below a certain N1 should be disabled completely by PMDG. That will not in any effect the enjoyment of the sim and in fact, will make it much more enjoyable as the plane will not fall from the sky everytime a little wind hits. I have FSUIPC and ASV6 wind smoothing settings adjusted but still get autopilot disconnecting but ONLY on the 744, not on the 737NG, not on the PSS772LR not on the PSS Airbuses.Hope that is clear enough.John

[Byrna 0]

Hello PMDG staff,I wanted to quote the specific section from the PMDG 744 manual to see if I understand why the autothtottle disconnects on the 744 and wanted to ask if there was any way to fix this without sacrificing the beautiful handling of the 744. Here is the section that has made me insist so much on this autothrottle disconnect issue (from page 8-8 of the manual):"The autothrottle will disconnect in any situation where a fault is detected in the engaged authrottle mode... The autothrottle will also disengage if more than one engine fails in flight..." I believe I had read somewhere that if the N1% falls below a certain number, then autothrottle may also disengage. Is this true? And is it possible for PMDG to modifying the auto-throttle logic so that it won't disengage as per above conditions but without sacrificing any of the FDE performance on the 744?Hoping you'll reply.John

[drdickie 2]

The latest FSUIPC is 3.53, and there is a later, beta version available through Peter Dowson's forum.

[Guest SKireyev]

John--The new version of AS6 has an option to force constant temp and constant pressure for the route that you import in before flying. This takes care of the problem you have described. I have never had to adjust wind settings within FSUIPC or AS after checking those two options. I don't think having to use this route is realistic, but then again abrupt temp and pressure drops aren't either, so I'd take a good flight model over a bad weather model any day.Cheers,

[michal 44]

>so I'd take a good flight model>over a bad weather model any day.Well said. :-)Michael J.http://www.precisionmanuals.com/images/forum/pmdg_744F.jpghttp://sales.hifisim.com/pub-download/asv6-banner-beta.jpg