I don't know if the community has ever examined this phenomenon fully. Over the years I've seen posts about cruising along at altitude on autopilot and all of a sudden the plane has violent oscillations in roll and then whips over into a death dive, usually being flung to one side, either left or the right until the heading has changed drastically:

I don't think all sim aircraft capable of flying several miles up have this happen. I'm just wondering if the answer is "out there". No, not switching to another flight sim entirely! I was just testing out Concorde, trying to get her to Mach 2 whilst heading out of Sydney and pointed at Hawaii...

This phenomenon has happened to me before. Once I was flying the freeware Piaggio P180 Avanti at FL410, (can't recall where i was flying it) another time I was flying the freeware Me264 Amerika Bomber from the Azores to New York and the "invisible hurricane" hit me at about 20000 feet. I do know that I was using FSOpen Clouds to inject real world METARS into the sim... AHA you say.. Not quite... I have winds aloft activated, BUT I have FSUIPC running to smooth the effects.. The first time Concorde did this I "recovered" even though IRL she'd have been a large fireball and bits, got her back up from 35000 feet or so (I have collision detection turned off - that's another FSX story!) and once more cruising at M2.0 at 55k feet and rising slowly, not caring about the bucket loads of fuel burned, I wanted to carry on with the experiment. I then TURNED OFF user defined weather in the sim and selected Fair weather. Winds were now showing 256 degrees at 25 knots...Yet after a few more minutes, Concorde did the same thing all over again..

Years ago I altered the Turbulence scale from 1.0 to 0.8 in the fsx.cfg file to lessen the exaggerated default sim, yet could random turbulence enabled from FSUIPC cause the upset?

Is this purely a winds aloft issue which FSUIPC cannot alleviate properly? Note that I've had many, many airliner flights with weather and winds aloft active. Are there just some places on the FSX globe where the invisible weather will slap you silly without deliberately loading up a hurricane or storm cell?

Any long time users of FSX, I'd appreciate some discussion. I believe (hope) I'm not the only one and that this "issue" has been documented, but my google-fu has failed to find it. Cheers.

Yes, I'm a little miffed my new payware toy experience has been marred by the screwy, old simulator! 

The sim rate wasn't over 4x (if you increase it), was it?  I have found anything over 4x really screws up airliners in autopilot cruise.

Keep in mind if you have real-time weather injection, it will still override the default FSX weather.  You need to stop or quit the feature injecting weather.

For real-time weather, do you know how to look up wind aloft speeds?  Your route may simply be too windy to fly for that particular day.  I recently flew from Orlando to Los Angeles (east and west coasts of the States) and had a 80 knots headwind for most of my cruise.  That would be considered a Category 1 hurricane!

I don't think it has anything to do with the aircraft you were trying to use.  Perhaps write down the routes and approximate locations where you encountered issues and we could try the same routes to verify it in case it may simply be a buggy location.  I was thinking it may have been a bug at too high a flight level, but you experienced the same issue at FL200.

@TextRich no the sim was in real time. Like you, I'm aware of that rate increase instability.

I've had severely strong winds aloft with no "hand of God" effect. One MD-11 flight had a headwind of over 100 knots at one point, she just altered her track to stay on course with no effect other than a slow speed over the ground...

I often notice what I'd term a "conflict" of METARs in that the wind direction and speed rapidly varies by a couple of degrees and couple of knots back and forth for a considerable time (usually over open water...). I'm assuming that this is FSUIPC doing its job in smoothing out the wind. Prior to having FSUIPC I used to get the old FSX "headwind instantly turning into a tail wind" and back again, thus stalling the plane and then giving me an overspeed warning.

Note that once I've encountered the phenomenon, disabled the AP and AT and tried to recover manually, I'm still battling against the unseen!  For example, full right stick almost allows me to get straight and level, before the plane snaps into a right roll, then I'm at full left stick, fighting the other way.

EDIT - perhaps try flying a route from the Azores direct to NYC at about 20000 feet. I cannot recall the route in the Avanti, but that may have been somewhere over Europe from the UK..

As for Concorde I headed out of Sydney at about 45-40 degrees getting to over FL550 ..

Edited November 2, 20205 yr by HighBypass

I tried again out of Sydney with a Concorde. Here's a screenshot of when the upset first began..she was at just under Mach 2 and about 55000 feet with a 100fpm climb rate. I had not selected "download winds aloft data" in FSX. I was running FSOpen Clouds. I do have REX4 w/ soft clouds enabled but that's just a texture program and not a weather injector.. I should have taken a simulator shot, not that you'd have seen the degrees and wind rapidly glitching back and forth (Ctrl-Z) .

I won't have time personally to fly for a week or so, but it's on my to-do list to try the Azores-NYC route since I don't use a Concorde.  Have you tried flying the routes WITHOUT using any weather add-on - just the default weather?  In addition, have you tried flying with a different weather engine?

I haven't tried a different engine. I shall try with just default weather (fair weather preset) and see what happens, thanks 🍻

I've managed to complete a full Trans Atlantic flight in default fair weather. However the was some "turbulence" climbing supersonic west of Ireland and then another bout of it when descending and decelerating near the US coast at about 39000 feet. However, not enough to flip her over. I'm sure I turned off any effects in FSUIPC..  I may try again with weather active.

Another transatlantic flight completed - west to east this time. I might have found the right combination to live with the phenomenon on my setup! It doesn't go away, but the plane appears to deal with it and not resorting to a death wobble and rollover. I shall of course do more airliner flights in subsonic aircraft also.

I do not have the FSX option for downloading winds aloft ticked. I used FS Open Clouds to inject the weather into the sim which does give me a jetstream etc. In FSUIPC I ticked suppress turbulence gusts and variance. I had the upset as my previous post when climbing away from the US east coast and then whilst in cruise approaching Ireland at FL580. The altimeter was twitching between 58300 and 57400 or so and the plane was banking left & right for quite some time.

Overall the flight in between was smooth and I had a quartering tailwind of 99 knots for most of it.

i just gave Azores-New York a try with default weather (and the usual weather fixes in FSUIPC 4).  I flew the default 747-400 at FL 370.  I had no issues at all, even with the sim rate at 4x for most of the cruising phase.  So I am thinking that if it was an issue with the default simulator, Microsoft would have discovered and fixed it before its expansion pack.  I think it had to do with your weather add-on.  For example you may have realistic turbulences enabled in one add-on and also  in the other add-on, which could double the effect of your turbulences.

FSOpen Clouds does use real world winds aloft data above 6000 feet and I can turn that on or off. I believe that is the only weather add-on I have and I turned off FSX's winds aloft option. REX4 & Soft Clouds - my other more realistic add-on for the skies on my setup, is just a texture library and does not have its own weather engine.

As you suppose, the way winds aloft data is used by FSOpen may cause some anomalies at cruise alts.