This makes me wonder if we can “speedrun” reproducing the bug by pulling out the supersonic jets at ~FL400. 
though …i wonder also whether avionics could be an issue. C414 looks like it has the GNS530 which got a big update in SU12, and the HJet also got updated IIRC for the new G3000/G5000.
Could be a bug with mapping data being memory-leaked in the new system that didn’t used to happen?
I tried clearing the bug by rebooting the avionics through the CoherentGTDebugger and didn’t get the bugged state to clear.
Could test the distance traveled theory by loading up at an airport and chilling on the apron for 4 hours.
I use the TDS GTNXi when flying that plane. I’m not saying it’s not impossible that it COULD be avionics. I haven’t had the opportunity to test it enough to be able to say. The last 3 weeks have been rather busy for me and I’ve had little time to fly. The time I did have, I tried the bit of testing I did to see if I could reliably reproduce the performance degradation. And I have. I just haven’t had time to dig into it more or try with other planes.
Not a bad idea actually. I’ve actually never used accelerated time in the sim. Not even once. I should try on one of the longer HJet flights to see if the effect is the same as without it. I think that would actually settle if the issue is a function of time flown or distance travelled. Same for folks doing long haul in airliners who could potentially test this and report back.
Oh yeah that’s a much better idea than mine! You’ll be using the exact same plane & avionics…
Hello,
I had the same problem yesterday during a long flight (after 5 hours of flight). The fps started to drop suddenly. I was flying with the B58 black square mod.
I instantly got my fps back when I deactivated the experimental NanoVG option, but I lost both engines and could not restart the plane… annoying.
Can’t figure out how this is possible but I think the performance problem is avionics related.
Just made a 4 hour flight from Antalya to Brussels on vatsim. Used fenix a320.
Framerates start decreasing slowly and noticeable after about 2 hours. On final stutters start to occur BUT they disappeared almost completely at short final, landing and taxi.
What I have done earlier is made a fixed cache of the EBBR airport. But asobo really has to take a look at this bug.
I noticed that if I disconnect all peripherals (rudder, quadrant and yoke), the FPS recovers instantly. When connecting back, the FPS drops again.
Does the same happen to you?
Ok. Some surprising information. I normally fly only with vatsim. I fly always with a friend. We talk true discord the whole flight. Today I flew alone so discord was not running in the background. I used vatsim again like yesterday. Surprisingly I had nog decrease in framerate after the same 4 hour flight i did yesterday. When I googled I read that discord suffers a memory leak filling up the ram.
So maybe there are some people that run discord to while flying msfs? I’ll try next flight again without discord running. I’ll post the result here.
That’s a good find, but I never use discord and still see this drop.
I just completed a 10+ hour flight with no or very little performance degradation. I deliberately disabled multiplayer, Live Weather, and Real Time/AI traffic. There is always a performance impact when any traffic is used depending on the amount of traffic. This is probably because I use the built-in ATC and there is some additional processing done by ATC audio chatting with other aircraft.
I am having this issue, after just 1 hour of flight time sometimes. Cycling live weather off and then back on again in General Settings, Data fixes it temporarily, but if I have to do this for each flight.
Feedback logged! Glad to see the update
Same here
Should be one thread with all votes together 
Indeed, should be merged with the “Low framerates” thread. I’ve posted there a detailed analysis and 100% reproduceable scenario on 2 different systems with STOCK sim only.
Something to try for folks with this bug. I did a 16 hour long haul (KJFK - VHHH). I had a decrease from 45-50fps at departure to 30-35 fps by TOD. I completely disabled online functionality, applied settings. FPS returned to near 50. I returned to the menu, reenabled online functionality and for the most part, I retained the performance gain. Remained ~40fps and above all the way to parking. Haven’t had the time to try and replicate it a second time.
Thanks for the tip! When you say you disabled all online functionality, can you specifically tell us which items so we can verify? I’ll try it on my next long haul. Thanks!
When I say that I mean I literally disabled the setting “Online Functionality”.
Do you have the same issue if you follow the OP’s steps to reproduce it?
Yes
Provide extra information to complete the original description of the issue:
I have been having poor performance in general after the SU 12 update. I tried tweaking the graphics settings and the highest I am able to get in airports close to dense urban areas is only 25-30. 30 FPS previously used to be the lower limit and my FPS would be in the mid 30s or higher. I removed all scenery addons and still have low FPS.
If relevant, provide additional screenshots/video:
Not applicable.
I got the same problem, hope there will fix it. Is not playable no more 
I can confirm the issue. Yesterday planed and flew a long hall from KSFO-LPPT (10 hour plus) flight. Long before the second hour into it the fps started to drop and overall quality began to drop also.
Landed at LPPT with 8-10 FPS (started in KFSO with 32FPS). It´s becoming to be unbearable to fly the long halls.
Thank you