I've been having this problem and posted about it here and elsewhere, including the official forum:  

No one seems to have identified what it is aside from poor optimization of the sim itself. ☹️

Here's my proof that approach messes with your FPS 

https://forums.flightsimulator.com/c/bugs-and-issues/performance/211

This seems to happen at just about every airport I fly into.  If I restart the sim at the same airport FPS are back to normal.  Its frustrating.

It's probably some non-LOD'd vegetation combining with the buildings. I'm sort of able to reproduce the issue, not exactly, but sort of. If you turn the plane (or as he says change the approach), it changes. The reason it changes is because only the objects in the viewport are rendered in finality as drawcalls, so it's something with the # of drawcalls which is likely geometry or mesh related to a bad object in the SIM, or possibly the object has bad geometry and every time you hit that object in the cache enough it builds up the problem, it's not being flushed out correctly (so it's like stacking garbage). Otherwise, it might be a thread locking asynch issue combining or alone, hence the threads aren't in proper synch and something is waiting on something to update.

Edited May 11, 20215 yr by Alpine Scenery

Happened Last night . very short hop from LSZH-EDDL ..Framerates are sky high (45-50) at the start and by the time im on final im looking at 25fps and it doesn't go back up.

It doesn't seem to be related to how long the flight is, it seems random over certain areas that are fine some days, and not on other days.  I just TO out KPDX and while CPU load never exceeded 80% on the main thread, GPU load 82%, still had weird frame drops and stutters for a few minutes.

1 hour ago, Noel said:

It doesn't seem to be related to how long the flight is, it seems random over certain areas that are fine some days, and not on other days.  I just TO out KPDX and while CPU load never exceeded 80% on the main thread, GPU load 82%, still had weird frame drops and stutters for a few minutes.

Interesting, it seems to occur more around where heavy vegetation areas meet buildings, but maybe there are 2 separate issues here. However, I can reproduce the effect in dev mode with too many bushes and grass on the ground, but it doesn't happen every flight or every angle. It clears up on its own, so it may in fact be a cache state related issue where something isn't cleaning up at times. 

Others should also keep in mind that the LONGER you fly the more likely you are to encounter a random event by default, so in a sense every event has some time related component to it, that's why it's hard to declare if something is only related to time or not, but if it happens very early in the flight sometimes, then maybe not.

Edited May 12, 20215 yr by Alpine Scenery

At Monday I fly from Graz to Innsbruck and I got this too, that my frames goes down.

Also my Memory goes up to 30 GB (of 32 GB) and I got stutters too.

Yesterday was everything fine. Strange things happen.🤔

10 hours ago, Alpine Scenery said:

Interesting, it seems to occur more around where heavy vegetation areas meet buildings, but maybe there are 2 separate issues here. However, I can reproduce the effect in dev mode with too many bushes and grass on the ground, but it doesn't happen every flight or every angle. It clears up on its own, so it may in fact be a cache state related issue where something isn't cleaning up at times. 

Others should also keep in mind that the LONGER you fly the more likely you are to encounter a random event by default, so in a sense every event has some time related component to it, that's why it's hard to declare if something is only related to time or not, but if it happens very early in the flight sometimes, then maybe not.

And worth a look when it happens, sometimes, at server latency.  I took off 15m ago from Kuwait Intl OTW to Dubai Intl in the Citation L and all of a sudden major FPS drops in the high teens for several minutes, after which west coast server latency went from about 26ms where it normally is to 101ms.  I changed to east coast at 82ms and FPS returned to 30.  Shortly thereafter I looked again and west coast back to 27ms, so left it on Automatic.  During the big drops CPU load on the main thread was 28%, GPU 66% or so.

2 minutes ago, Noel said:

And worth a look when it happens, sometimes, at server latency.  I took off 15m ago from Kuwait Intl OTW to Dubai Intl in the Citation L and all of a sudden major FPS drops in the high teens for several minutes, after which west coast server latency went from about 26ms where it normally is to 101ms.  I changed to east coast at 82ms and FPS returned to 30.  Shortly thereafter I looked again and west coast back to 27ms, so left it on Automatic.  During the big drops CPU load on the main thread was 28%, GPU 66% or so.

That's probably another issue. FPS drop over time/on approach is usually about 10-15 FPS, in my experience and based on experience of some others. As I already mentioned, on the official forums somebody just sat on the apron for a longer period of time and the FPS dropped. In my experience, if I reload the sim on the same approach I already did I always get about 10-15 FPS more.

I can't imagine this is news to Asobo. I'm just afraid this is rooted in the code, and since they don't even acknowledge the issue, there's almost no chance this will get solved any time soon.

the problem is the gpu just goes dormant after a while and starts performing at 35% or less

3 minutes ago, devgrp said:

the problem is the gpu just goes dormant after a while and starts performing at 35% or less

Which indicates a threading or memory clean up issue usually, but hard to say for sure.

I guess I could look at my GPU usage when I can trigger the problem, and yes my FPS does drop to 15-20 only when I face the vegetation. When I turn the other way, the problem goes away. Also, the problem usually auto-resolves if I move around long enough or wait it out.

 

Edited May 12, 20215 yr by Alpine Scenery

39 minutes ago, Tomaz Drnovsek said:

That's probably another issue. FPS drop over time/on approach is usually about 10-15 FPS, in my experience and based on experience of some others. As I already mentioned, on the official forums somebody just sat on the apron for a longer period of time and the FPS dropped. In my experience, if I reload the sim on the same approach I already did I always get about 10-15 FPS more.

I can't imagine this is news to Asobo. I'm just afraid this is rooted in the code, and since they don't even acknowledge the issue, there's almost no chance this will get solved any time soon.

How long are you talking about on this Tomaz?  I think my longest flights are only about 3-3.5h and so far I don't think this is happening to me, but perhaps I confused this with random drops.  Some do seem less random and more region specific, and relatively small regions at that.  

7 minutes ago, Alpine Scenery said:

Which indicates a threading or memory clean up issue usually, but hard to say for sure.

I guess I could look at my GPU usage when I can trigger the problem, and yes my FPS does drop to 15-20 only when I face the vegetation. When I turn the other way, the problem goes away. Also, the problem usually auto-resolves if I move around long enough or wait it out.

 

Have you noticed any improvement w/ downgrading the vegetation sliders?

I'm not even clear on what the LOD sliders do to be honest.  I can dial them back to 120 from my default 200, and hardly can tell.  1440p screen.  68y/o eyes w/ good near vision however.

I just landed at dusk in Dubai and, since there are only six palm trees () and no other vegetation had absolutely no hitches all the way to touchdown, though my 8GB of VRAM was maxed.  I had one or two brief stutters from the GPU being near maxed and a brief 100% on the CPU main.  You may well be on to something!  If it's consistent among users it's worth a zendesk ticket perhaps.