On final with a glideslope approach, occasionally the nose of my aircraft snaps up. As would be expected, airspeed bleeds off, she stalls, and into the ground she usually goes. Rarely recovery has been possible if the bird was far enough out and had enough altitude for the recovery.Please note that this is not a conventional stall. The action is instantaneous from a stable configuration with no warning and for no apparent reason. It is a snap action UP, not down as one would see from a conventional stall break.I posted this problem some time ago and others confirmed that they have seen the same thing. Unfortunately as far as I know nobody has been able to pinpoint the cause as of yet.I do not believe it is unique to anything obvious. It has happened with many aircraft (i.e. Freeware heavies and lights, PSS777, DFBaron, CitationX, etc. etc.). It also has happened at various speeds, interception altitudes, distances from the runway, and airports. I've noticed nothing one can sink his teeth into as evidence of the cause.It is also intermittent. It may not show up for weeks, or may occur on successive flights as it just did (think this is the first time. hope the frequency is not increasing).For one example, this occured yesterday on a flight with a PSS777 on an approach into PANC on a long flight from the East Coast.Moments ago, I completed an uneventfull 3 hour flight with the DF177 from KLWB (West Virginia) to Peachtree/Atlanta for the Sugarbowl (Go Mountaineers! Although I sure would appreciate some help from a couple of you Bulldogs). I was cleared for a long straight in approach on runway 20 and intercepted the glideslope at 4,000' MSL. After a smooth as satin descent for several mins. @ 70 knots and about 400 fpm the aircraft went wild (2 to 3 miles out). The nose snapped up. I have never paid attention to this before, but rather than an immediate loss of airspeed as one would expect, the airspeed instantly read something in excess of 160 knots. As would be expected from such a nose up attitude without enough altitude to recover, speed bled off and she crashed.Now the real kicker! Thanks to Pete's AutoSave provisions, I reentered the exact same approach about 20 miles out. Absolutely no problems at all. A beautiful crosswind approach to touch down. This has happened many times in the past. I cannot recreate the problem from the exact same conditions to investigate.Does anyone have any new idea as to the cause and solution of this action?Thanks:RTH1585368CFI

I assume that happens only on a coupled ILS approach and not, say, in cruise flight with the A/P engaged.If that is the case, you can rule out glitches caused by spyware protections etc. running in the background.Have you tried rebuilding your cfg file? I know it's a pain but have you tried an uninstall/reinstall of FS9?Hope you get it figured out.If nothing else works, you can just work on your "unusual attitude recovery " skills.You wrote: <>But if you zoomed upward 2-3 miles out and had 160kts airspeed, you should have had no difficulty in recovering. Given you nose up attitude, you should have assumed that the airspeed indicator was inaccurate and lowered the nose while adding full power (again under the assumption that the AI was faulty and that you might actually be near a stall.That should have accomplished a recovery with virtually no loss of altitude.Just pretend you are experiencing CAT or wake turbulance encounters, shout YEEEHAWWW and ride it out!!Kidding of course. Hope you get the problem solved.Regards,Jim

Thanks for the reply Jim.I believe I have tried everything you mention except reinstallation of FS9, which I don't even want to think about due to the complexity and number of addon's. I do have all of my original defaults backed up, so I hope that want be necessary anyway in order to troubleshoot if so desired.Concerning the stall bit and recovery. The increased airspeed is something I have never noticed before, and almost can't believe what I saw. The attitude of the aircraft is such that it does not shoot up relative to altitude in spite of the momentary increase in speed which might be considered a relative of an accelerated stall. Also, it is certainly not a matter of being near stall speed on approach although I will admit that I do normally as an old CFI firmly believe in slowing the bird down. As I mentioned in my original post, I have had this happen at various speeds. Intentially I have come in hot at times to see the same thing happen. It is always under totally stable conditions as a snap action upset.Thanks again for your comments.RTH1585368CFI

What are you using to set your weather? The only time that I've seen this happen it has been caused by wind. A sudden strong head wind could cause both the pitch-up and the indicated airspeed increase. MSFS downloaded weather seems to like to throw in a shallow surface layer of wind which can ruin a fine approach. You might turn on the wind indicator (Shift+z) and see if you can catch it in the act. R-

Interesting Point Ron:I have speculated on turning off fsmeteo to see if it could be causing the problem. I would have thought that a gust near 100 knots so near ground level would be unlikely, but who knows?I will try for a while with it turned off and/or monitor the text as you suggested. Unfortunately, with the intermittent occurances, I probably will still be second guessing as to whether it is just absent, or that was the cause. May be a good reason to consider the more popular weather program.Thanks for the input:RTH

RTH,This is a bit off the wall, but you're looking for something unconventional. As I see it, the common denominator (besides ILS/GS) is close proximity to an airport.Could it be something like an overheating issue? Do your frames go down during final approach? That could indicate a PC that's working harder, possibly due to increasing AI activity. During replay there is no AI activity, so the workload is reduced.Just a wild idea, but maybe it will tweak someone's memory and get you an answer.Regards,JerryH

Thanks Jerry:Boy, I couldn't agree more that it is a bit off the wall. On a couple of posts quite some time back, I did however get some response that there were others that had seen this action.I don't believe this is a heat issue but I certainly will check it out. It has happened at minor airport locations where AI traffic was at a minimum. I don't remember whether it has happened when AI traffic and enhanced weather were both turned off or not, but I will reduce the load and bring my system temp. gauges back into my tray and check it out. Your guess is about as good as anybody elses at this stage. Thanks again:RTH

No. This has nothing to do with hardware, installation, etc.FSMeteo uses downloaded meterological data. These data are correct. When the winds aloft are different from surface winds, this is a wind shear. If the wind is a headwind you will see a increase in indicated airspeed. If the wind is from behind the aircraft, you will see a decrease in the indicated airspeed. In the real-world, sometimes these differences between surface and winds aloft really can be quite extreme. FSMeteo, to my knowledge, doesn't use a smoothing algorithm (I could be wrong about this) so it would be expected that, using these data (showing winds aloft to be from a specific direction and speed and surface winds to be from a different direction and speed) the wind shear would be quite abrupt. A 30 knot wind shear is not that unusual and a 70 knot wind shear is not unheard of. Remember, wind shear is a combination of both change in direction and wind velocity, so a 30 knot headwind changing to a 30 knot tailwind = 60 knot wind shear.Why is there a difference between surface and winds aloft data? Winds aloft are predictions and surface winds are actual hourly observations. Moreover, winds aloft predictions are made for altitudes 3000 feet and above AGL. Below that altitude, predictions for winds aloft are not generated. Winds aloft forcasts are made 4 times each day at 3 hour intervals, and surface winds are reported each hour. Moreover, winds aloft are reported in reference to true north and surface directions are reported relative to magnetic north. So there is considerable opportunity for a discrepancy between surface and winds aloft data in both wind direction and magnitude.Atmosperic events (wind shear, turbulence, icing, etc.) are exaggerated to various degrees by different weather add-ons (e.g. FSMeteo, ActiveSky, WeatherMaker Pro, etc.) For example, the icing algorithm in WeatherMaker Pro, I think, is much more aggressive than in ActiveSky.Some notes about handling wind shear. In the real world pilots are taught to go-around when encountering wind shear. Don't just 'ride it out'. Go-around is a specific sequence of steps. In the Cardinal 177, this means pitch up to normal climb attitude, prop forward, full power, carb heat in, gear up and climb at best angle of climb speed (which in the C177 should be around 63-67 KIAS, consult the documentation and look for a term called Vx).Finally, you should be flying your approach at 90, not 70 KIAS. 90 is a more suitable speed for sequencing, and gives you more energy for establishing a climb when you do encounter wind shear, among other reasons.

Thanks for the reply Cindy:I too doubt that fsmeteo has anything to do with anything here, but am at the monkey and banana stage now. (Press a button and see if you get a banana).If I am not mistaken, a few tweaks in FSUIPC should dampen some of the wind effects you are talking about, but I am not sure. I agree in general with most of what you say, however, this is a relatively recent occurance. I have had MSFS since the old 5" floppies and NEVER had this problem until the past few months. As an old CFI I have been fortunate enough to have never encountered wind shear of a magnitude that was significant, although I do not intend to belittle the possibility at all. It certainly should not be as common as I am finding presently in MSFS.Relative to my 70 knot approach speed, coming from the old school I respectfully question this, but will do a little checking in the aircraft specs. Could be mistaken. Certainly in a 172, 90 knots is a bit hot from my old world school at least.In any case, this is academic to the problem in question. As I said in my original post, I have had the problem occur at various speeds. I have intentially come in hot not necessarily in the Cardinal (first time in a long time I flew this bird) and the same thing happened.Again, thank you for your comments.RTH

Are you limiting the rates of wind speed and direction change with the wind transitions option in FSUIPC? You can limit the rate of change of winds...and also set a threshold beyond which bad wind data is thrown out. It's one of the many improvements FSUIPC makes to the FS experience...so basic for me now that I can't remember the last time I saw a problem like this.Sounds like maybe your wx add-on is spiking the winds...the smoothing option should keep it controllable.CheersBob ScottATP IMEL Gulfstream II-III-IV-V L-300Santiago de Chile

Thanks Bob:I implemented the items you suggested just before seeing your reply. We will see what the result is in time.Thanks again:RTH

Thank you for your awfully nice reply. I didn't see that you are a CFI in your signature I apologize for sounding high-handed in my original post. I am very respectful of you and others in the AVSIM community. Hope any ideas I could offer were of help. Best regards.

No problem, No offense taken, and no appology needed!I appreciate your comments and your kind attitude.RTH

Update:For what it might be worth, I now turn fsmeteo off before beginning a final approach. Since I have done this, I have not had the problem described in the original post happen again. This makes little difference to anything weatherwize as current conditions are retained, and there is little probability that there would be significant change in the ten to fifteen mins. the approach will add.For anyone implementing third party weather, I would suggest giving this a try if you are seeing this problem occur. MSFS originated weather may do the same thing, I don't know; but I am not sure there is a way to retain your current weather conditions without leaving it on. Time will tell if this was the problem, but again, this seems to be the solution thus far (for me at any rate).Good luck and happy flying:RTH