How do I fix “Limited by main thread” in MSFS 2024?
“Limited by main thread” means Microsoft Flight Simulator 2024’s CPU simulation thread is taking longer to build each frame than the GPU. Lower Terrain Level of Detail, Objects Level of Detail and traffic first; then test without complex aircraft, add-ons or background utilities. It is a performance diagnosis, not an error that must disappear.
What does “Limited by main thread” mean?
The warning identifies the CPU’s main simulation thread as the frame-rate limiter at that moment. MSFS 2024 uses several CPU cores, but flight-model calculations, scenery preparation, traffic, avionics and other tasks must still be coordinated by a main thread.
The Developer Mode FPS display compares MainThread and GPU frame times. The higher time is holding back the next frame. At 60 fps each frame has about 16.7 milliseconds available; at 30 fps it has about 33.3 milliseconds.
Overall CPU utilisation can remain modest while one logical core is saturated, so Task Manager showing spare CPU capacity does not disprove a main-thread bottleneck. Brief spikes while scenery loads or traffic appears are normal. A sustained warning accompanied by low or uneven frame rates is the problem to address.
Fix the main-thread bottleneck step by step
Use a repeatable test flight and change one variable at a time, otherwise an aircraft, airport or traffic change can make a setting appear more effective than it really is.
- Establish an uncapped baseline. Use the same aircraft, airport, cockpit view, weather and time of day, then let the initial scenery loading settle. Temporarily disable V-Sync, external frame caps and frame generation while measuring so they do not obscure the underlying rendered frame rate.
- Lower Terrain Level of Detail first. Terrain LOD is usually the strongest CPU-side control, especially over cities and detailed airports. Reduce it in moderate steps while watching the
MainThreadframe time rather than relying only on the displayed fps. - Reduce Objects Level of Detail and traffic. Objects LOD increases the distance and quantity of scenery objects the CPU must prepare. AI or live aircraft, multiplayer traffic, airport activity, ground vehicles, road traffic and boats can all add simulation work.
- Separate aircraft load from scenery load. Test a simpler default aircraft at the same airport. If performance improves sharply, the original aircraft’s systems, avionics or displays are a major part of the load; if it does not, repeat the test away from the detailed airport.
- Test without third-party packages. Restart with an empty Community folder and disable non-essential packages where practical. Aircraft, avionics, traffic tools and overlapping scenery can consume main-thread time. Restore packages in batches, then narrow down the affected batch one item at a time.
- Remove background CPU competition. Close recording tools, browser video, overlays, traffic injectors and external panel applications for the test. Check that the CPU is not thermally throttling and that Windows is using an appropriate performance mode. Do not disable CPU cores or force processor affinity; those tweaks often make scheduling worse.
- Apply a sustainable frame cap after tuning. Set the cap slightly below the frame rate the system can maintain in demanding locations. This does not remove the CPU limit, but it gives the simulator headroom and often produces steadier frame pacing.
Which MSFS 2024 settings should you lower first?
Terrain LOD, Objects LOD and traffic provide the largest main-thread savings; resolution and render scaling mainly affect the GPU.
| Setting or workload | Main-thread impact | Best adjustment |
|---|---|---|
| Terrain Level of Detail | High | Lower first, particularly for large cities and major airports. |
| Objects Level of Detail | Moderate to high | Reduce when dense buildings, vegetation or airport objects cause the limit. |
| AI/live traffic and airport activity | High in busy areas | Lower densities and test with live or multiplayer traffic disabled. |
| Glass-cockpit refresh rate, where available | Aircraft-dependent | Reduce when the problem is much worse in complex glass-cockpit aircraft. |
| Resolution and render scaling | Low CPU impact | Leave alone unless the GPU frame time is also too high. |
| Textures, anti-aliasing and clouds | Primarily GPU-side | Do not use these as the first fix for a sustained main-thread limit. |
Setting names and grouping can change between simulator updates, but the CPU-versus-GPU distinction remains the same. Our broader MSFS 2024 FPS and performance checklist covers the rest of the graphics menu without sacrificing settings that do not affect this bottleneck.
Why does lowering resolution not fix it?
Lowering resolution does not reduce the simulation, traffic or scenery work performed by the main thread. It shortens GPU frame time, which can make the FPS display report an even clearer main-thread limit without making CPU performance worse.
When the GPU has spare capacity, you may be able to raise some GPU-heavy visual settings without losing frame rate. Frame generation can also make motion appear smoother on supported hardware, but it does not accelerate the underlying simulation, remove input latency or repair main-thread stutters.
Do you need a faster CPU?
A CPU upgrade is justified only when MSFS 2024 remains above your target frame time after testing lower LOD, reduced traffic, a simple aircraft, no third-party packages and minimal background software. Strong per-core gaming performance and suitable memory performance matter more here than a large core count alone.
Detailed airliners at large handcrafted airports can remain CPU-limited even on powerful systems. The practical goal is stable frame pacing at your chosen target, not forcing the warning to disappear in every location. Our guidance on balanced MSFS 2024 PC specifications and graphics settings helps distinguish a genuine hardware limit from an unbalanced setup.
If MainThread only spikes while turning the camera, approaching an airport or loading new terrain, investigate an add-on or scenery-streaming stall rather than treating it as a permanent CPU limit. When those spikes coincide with terrain remaining soft or failing to load, use these scenery-streaming and rolling-cache checks.