Severe MainThread performance degradation during long flights – FPS collapse on approach

User Support Hub Install, Performance & Graphics
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1

Hello,

I am experiencing a severe and reproducible performance degradation during a flights in Microsoft Flight Simulator 2024.

At the beginning of a flight, the simulator runs normally with very high FPS. However, after several hours of flight, performance progressively deteriorates. The problem becomes especially severe during descent, approach and landing.

FPS can drop from well over 100 FPS to around 20–30 FPS, making the simulator practically unplayable.

When the problem occurs, the Developer Mode Performance Overlay shows:

  • Limited by: MainThread
  • MainThread: ~40.8 ms
  • Manipulators: ~15.2 ms
  • RdrThread: ~14.9 ms
  • CoherentGTUIThread: ~7.4 ms
  • Graphics Queue: ~43.4 ms
  • GPU usage: ~98%
  • GPU VRAM: ~14.7 / 16 GB
  • System RAM: ~28.2 / 31.1 GB

PC specifications:

  • CPU: AMD Ryzen 7 9800X3D
  • GPU: NVIDIA GeForce RTX 5070 Ti 16 GB
  • RAM: 32 GB DDR5
  • Resolution: 2560×1440
  • Main monitor: 240 Hz
  • Aircraft: iFly 737 MAX

I have already tested several possible causes:

  • Deleted/reset the Rolling Cache
  • Tested with airport/scenery add-ons disabled
  • Tested different monitor refresh rates, including 120 Hz
  • Tested with unnecessary add-ons disabled
  • Checked RAM and VRAM usage
  • Tested with Terrain LOD, Objects LOD and Buildings LOD set to 100

The problem still occurs.

The degradation appears progressively during the flight rather than being present from the beginning. After restarting the simulator, performance returns to normal.

The issue therefore appears to be related to a progressive degradation of MainThread performance during a flights.

I have also noticed that the Manipulators thread becomes significantly higher when the problem occurs.

This issue makes long-haul flights extremely difficult to complete, because performance can become severely degraded during the final approach despite having a high-end CPU and GPU.

Has anyone else experienced this specific MainThread / Manipulators degradation during long flights?

I would appreciate any information from the development team about whether this is a known issue.

2

Thank you for this report. We’ve moved your topic into the User Support Hub.

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3

In SU7 Beta is a fix in particular for long haul flights. Maybe it’s worth a try?

4

Asobo has now addressed this issue in SU7 Beta 1.9.12.0 with the following fix:

Fixed a memory leak in the visual transition, causing visual degradation after long flights.

I would recommend joining the SU7 beta and testing whether the issue is resolved in your case. Please also provide your feedback, especially after a long flight where the performance degradation normally occurs, in the thread below:
https://forums.flightsimulator.com/t/su7-beta-long-haul-feedback/776802