VNAV Speed Goes Crazy

[kerke 0]

A perfect flight KBFI-KLAX goes bad when suddenly the aircraft slows down by itself to a scary slow speed and then decides to accelerate and overspeed. Left alone, the slow down and accelerate to overspeed pattern repeasts over and over again. The aircraft was cruising perfectly for over an hour on VNAV and LNAV at FL330 when the anomaly started.http://www.kerke.us/avsim/pmdg/slow.jpghttp://www.kerke.us/avsim/pmdg/overspeed.jpgAny ideas why this may have happened?Thank you in advance,Kerke---

[Guest dimas]

Hi, do you use ActiveSky? I have a problem that looks like this.. Aircraft slows down, then it accelerates to overspeed and then returns to cruise speed..

[Guest JoeMathews]

Hi,Has happened to me before. I think FS doesn't handle wind layers very well, I often have violent changes in speed and direction. Not being a real pilot I don't know if this is a possability in real life (any real pilots out there to comment?), to me it just seems like a naff simulation of wind; maybe a solution will come in the next version of FS. Pictures are always a good idea. Check out the wind direction and speed, in the top pic it's 312 at 90 then in the bottom pic it's swung straight at you at 91.Regards,Joe Mathews.

[Mats_J 2]

Kerke,This is definitely a wind problem. You have an almost 180

[Guest DP1]

For what it is worth, I would suspect the wind. A 90kt wind is quite powerful to say the least. What you could do to test and/or prevent this in the future is to set a key combination, in FSUIPC, to clear all weather. That way when and if it happens again you hit the key to clear the weather, then if that fixes things you can reload the wx and continue. I fly on line and clearing wx then refreshing wx in SB can be done without stopping the flight.Dave

[kerke 0]

>This is definitely a wind problem. You have an almost 180

[crvm 0]

And while you are at it, you cannot post screenshots that are of such SIZE both in dimention and kb on this forum OR Avsim's forums regardless of where the orginal resides. I have super fast DSL and it still took a bit to open.Best Wishes,[h4]Randy J. Smith[/h4]http://www.rawbw.com/~bdoolin/shinault/southparkcartmad.gif[h3]PMDG 747![/h3]Caution! Not a real pilot, but do play one on TV ;-)ASUS KV8 DLX | AMD 3200 64 | 1 GIG PC 3200 DDR | GIGABYTE 5700 ULTRA | ViewSonic VP192b 19" |

[Mats_J 2]

Kerke,Some question marks appears with your last statement. How can you have winds aloft if you don't download them? Are you using Custom weather or a preset weather set? Or mabe wx from a saved flight as you say it happened to you when flying from KBFI? The latter would make sense.Anyway. Here are the settings to use in FSUIPC to smooth wind changes in FS. You don't limit it per se but more limit the rate of change. I've discovered a change of 0.5 kts/sec or 0.5

[744pilot 0]

I can give some tips.-If you have the latest version of AS2004 (AS2004.5) then make sure you windsmoothing trough FSUIPS is on.-Always check your enroute WX on some WX charts because if it gets bumpty then you get this sort of things.Hope it works,

[kerke 0]

Mats, I only use the FS "Download weather and update every 15 minutes" feature. I configured my FSUIPC winds as per your sugestion and I'm flying the same route again to test it.Thanks a lot,PS: My apologies for the humongous pic size.

[kerke 0]

OK Mats, I just finished my test flight (KBFI-KLAX) using FSUIPC wind smoothing settings as per your screenshot. The results are better but still, on the LIN-AVE leg at FL330, winds now shifted 1 degree at a time around the 360 degree spectrum over and over again, and so VNAV speed decreased and increased with a noticeable engine spooling up and down back to almost idle while the winds shifted 360 degrees one degree at a time. I descended to FL290 but the results were not much better. At one point, close to AVE, winds settled back to normal (as in no constant wind direction changes).Here's the flight plan for those of you who wish to recreate this wind shifting anomaly: KBFI-SEA-J5-LKV-J67-LIN-J189-AVE.SADDE6-KLAX (FL330).It would be interesting to know weather real-world aircraft, specially the 737NG, behave the same way during sudden high-wind changes at cruise altitude.Thanks for your assistance,Kerke