Today I was flying over the central europe, from EGLL to EHRD and eventually to LOWW.During cruise flight I had wind @ 108 kt and during the final approach the wind was only 22 kt. As reaction my plane started to accelerate desperately and even the LAND 3 feature ended with a crash at speed of 258 on the runway when it was 185 ( gently slowing down as usual ) few seconds before the abrupt A/P acceleration. Speed brakes did nothing but increasing the thrust by the A/P... to 85%.How comes the A/P drove my plane from an approaching speed of around 185 to accelerate to 258 and eventually heavily crashing under LAND 3 conditions ?I am using REX btw.How can I prevent the VNAV and LNAV driven by the A/P to behave in a such crazy way ? What could have been the cause ?It happened 2 times today on 3 flights...Thx

Well when you're on the (final) approach you shouldn't be in VNAV or LNAV any more, but rather in APP mode. Since you say you saw LAND 3 enabled I'm going to assume you were in APP though. Did the wind speed suddenly jump from 108 to 22? That would cause a very large, very sudden drop in airspeed, which the plane would attempt to compensate by an immediate increase of thrust.Hopefully someone with more experience can help you diagnose the problem further.In general though, if the A/P does something you don't understand or want, just switch it off and fly the plane by hand ;).John-Alan Pascoe

Yes I pressed VOR and then APP.Everything went fine for few seconds , the speed was usually slowing down and I was applying flaps accordingly to speed like I am used to do with no issues. The ILS ID was correct.The wind didn't abruptly go from 108 to 22, I had wind at 90-80-46 etc.. in between the descent along the STAR, that's the weird aspect.I thought it was a FSX mess but the next flight, different route btw, I had the very same behaviour. Every time is very windy my 737 behaves like a mad cow, I simply do not understand why she accelerates so much while down the G/S and she was keeping on doing that when she hardly crashed in LAND 3 mode.I usually land her manually but the acceleration started to be out of control earlier so I decided to see what a LAND 3 was able to do.....nothing... or even worse than before. Totally out of control and accelerating to 258 knots and 22 kt winds only.Is perhaps a REX bug or is that anything I can do to calm the 737 down during these kind of epilepsy attacks ?Is my bird the next subject of the National Geographic Mayday series episode ? I will FS Recoder the next flights, if I catch the weird behaviour on video I'll post them for sure.Thx

I am going to take a guess here that your using Default FSX Weather and have not tweaked your config files yet?

"Just" 22kts? 22kts is close to 25mph. 22kts is more than the crosswind and tailwind component allowed for auto lands, and very close to the max for auto lands with headwinds.Either way, could you make a video of your autoland? I'd be interested to see how you have the aircraft configured, and what the weather is doing.Lastly, how many autolands are you doing? (Not very realistic, but I know that's not what you're asking here.)

I am going to take a guess here that your using Default FSX Weather and have not tweaked your config files yet?

My FSX.cfg is really tweaked and I rarely have these " incidents ". I use REX weather and I set static weather wtihin FSX.And the decision to go LAND 3 was just to check if the A/P was able to exit or manage the situation ( just after when started to accelerate ) . In the reality I would have manually aborted the landing sooner rather than later.Other forumers reported weird behaviour of speed steps jumps of 50 knots just before landing, that's a REX bug but this one is new to me.To summarize, why the A/P set on LAND 3 was not able to slow the plane down and it kept on pushing the throttle to 85% when I had just captured the correct id G/S ? ( landing speed was 258 then she crashed )

My FSX.cfg is really tweaked

You have made these changes to your FSX.cfg and FSUIPC.ini ???

Make sure you also do the following.Open FSX.cfg and replace the current line in there with the line below.TurbulenceScale=0.500000Open FSUIPC.ini and replace the current lines in there with the lines below.TurbulenceRate=0.5,2.5TurbulenceDivisor=40,40,80,80Use the latest version of FSUIPC whether it is registered or not.

If your using REX Weather you should also disable turbulence either with FSUIPC Registered or in FSX if you do not have the registered version.Load the Rex Weather engine and then FSX and leave the FSX weather settings alone. If you do this correctly and then check FSX Weather you will noticethe User Defined Weather will be checked and this is normal. If you click on something else your overiding the REX Weather Engine which defeats the point of using it in the first place.

You have made these changes to your FSX.cfg and FSUIPC.ini ???If your using REX Weather you should also disable turbulence either with FSUIPC Registered or in FSX if you do not have the registered version.Load the Rex Weather engine and then FSX and leave the FSX weather settings alone. If you do this correctly and then check FSX Weather you will noticethe User Defined Weather will be checked and this is normal. If you click on something else your overiding the REX Weather Engine which defeats the point of using it in the first place.

Hi Paul,thanks a lot for your suggestions.I do not have FSUIPC. I'll check what you have indicated and I guess that even if I miss FSUIPC I have to set the turbolence value in the fsx.cfg as you reported , correct ?Thx mate

Yes you would change the value in FSX.cfg and and then when in FSX you go to the weather settings tab and check that box that disables turbulence and thermal effects on aircraft.

I would like to backup what ZachLW said about "Just 22kts."RW CATII ops at my company have wind limitations of:20 kts Headwind15 kts Crosswind10 kts TailwindThat is for CATII ops with no autothrottle. I would imagine the limitations for full autoland are even tighter. I don't know whether it's a glitch in the PMDG software or the FSX weather engine. Those limitations are there to avoid situations like the one you have been experiencing. Maybe the RW 737 might start struggling just like that with similar conditions.I know you said that you were just checking it out to see how the NGX would perform in those conditions, and I think you may have found out. Espicially if you're having the similar experiences on different approaches at different airports with similar conditions. RW those limitations are hard rules. Line pilots don't get to go check out what will happen, so there probably are only a small handful of people at Boeing who've legally attempted high wind coupled landings like that.

popping into my head you are in MCP SPD mode for the autothrottle, right?Its actually a thing one of my "students" did, letting VNAV control the speed all the way to the runway led to some awry results.

Thanks guys for suggestions.Beside being you right I think the problem is a consequence of setting that under some circumstances may exploit a kind of " bug " , may that is related to the turbulence value altered into the fsx.cfg file, I am investigating and I have done the corrections suggested by Paul.Back to ccarter06 you are right, even if I have to say that I assume a wind of 22 knots, even if not so light, it may lead to some consequences yes but I don't think an acceleration from 180 to 258 while down the G/S, I am thinking more of a software ( FSX or REX ) bug there.And to Fabo, I do not know if I understood you right but the VNAV was turned off after the APP was turned on. I was manually selecting the speed via the A/T and setting the speed bug setting to something around 150-160 or so and when decelerating, then all of a sudden it started to accelerate. I only regret that my FS Recorder was turned off.Anyway posting here with you guys I keep on learning every day more and more, thanks a lot to everybody.

Wind shifts in fsx will do all sorts of magic to your airspeed. I use AS2012 for weather now. The ngx flies perfect VNAV profiles without massive speed changes.I guess your have some more fine tweaking to do. Don't think the ngx is to blame.

For me... REX weather, registered FSUIPC.FSUIPC wind smoothing enabled, at 8 knots per second.The suppress turbulence box ticked in FSUIPC. Result...Very good indeed.And i still get some turbulence, quite realistic i would say.Nothing else required.

Today I was flying over the central europe, from EGLL to EHRD and eventually to LOWW.During cruise flight I had wind @ 108 kt and during the final approach the wind was only 22 kt. As reaction my plane started to accelerate desperately and even the LAND 3 feature ended with a crash at speed of 258 on the runway when it was 185 ( gently slowing down as usual ) few seconds before the abrupt A/P acceleration. Speed brakes did nothing but increasing the thrust by the A/P... to 85%.How comes the A/P drove my plane from an approaching speed of around 185 to accelerate to 258 and eventually heavily crashing under LAND 3 conditions ?I am using REX btw.How can I prevent the VNAV and LNAV driven by the A/P to behave in a such crazy way ? What could have been the cause ?It happened 2 times today on 3 flights...Thx

Become a real pilot. Do a manual landing :(