Stuttering Masterclass

Estimated Lesson Time: 60–70 Minutes

Lesson Overview

One of the most frustrating issues in Microsoft Flight Simulator isn’t necessarily low FPS—it’s stuttering.

Many users assume that if they can achieve 60 FPS or more, their simulator should feel perfectly smooth. However, this is often not the case.

A simulator can report a high average frame rate while still feeling inconsistent due to irregular frame delivery.

Likewise, another system may only achieve 40 FPS yet feel exceptionally smooth because each frame is delivered consistently.

Understanding the difference between frame rate and frame pacing is one of the biggest steps towards becoming a professional Microsoft Flight Simulator optimiser.

In this lesson, you’ll learn how to identify different types of stutters, understand what causes them and apply a structured troubleshooting process to isolate the underlying problem.

By the end of this lesson, you’ll be able to determine whether a stutter is caused by the CPU, GPU, scenery streaming, VRAM, thermal throttling, background tasks or third-party add-ons.

Lesson Objectives

By the end of this lesson you will understand:

The difference between low FPS and stuttering.

Micro-stutters.

Major stutters.

Frame pacing.

Shader compilation.

CPU spikes.

GPU spikes.

Streaming stutters.

Rolling Cache.

Add-ons.

AI traffic.

Glass cockpit refresh.

VRAM saturation.

Thermal throttling.

Windows background activity.

How to diagnose the true cause of a stutter.

What Is a Stutter?

A stutter occurs when one or more frames take significantly longer to render than the surrounding frames.

Imagine a simulator normally rendering frames every 16 milliseconds.

Suddenly, one frame takes 80 milliseconds.

The result is a noticeable pause.

Even if average FPS remains high, that delayed frame creates the feeling of a stutter.

The key point is this:

Stutters are caused by inconsistent frame delivery, not simply low FPS.

FPS vs Smoothness

Consider these two examples:

Example A

60 FPS

Frame times:

16ms

The simulator feels smooth.

Example B

60 FPS average

Frame times:

16ms

72ms

16ms

Average FPS is still close to 60.

But the 72ms frame causes a noticeable hitch.

This is why average FPS should never be used as the only measure of performance.

Micro-Stutters

Micro-stutters are small interruptions that last only a fraction of a second.

Symptoms include:

Slight hesitation while panning.
Small pauses during taxi.
Minor hitches during turns.
Tiny interruptions when scenery loads.

Common causes:

CPU spikes.
Background tasks.
AI traffic.
Shader compilation.
Streaming scenery.

Although brief, repeated micro-stutters make the simulator feel inconsistent.

Major Stutters

Major stutters are much larger pauses.

They may last several hundred milliseconds or even several seconds.

Symptoms include:

Simulator freezing briefly.
Aircraft appearing to jump forward.
Long pauses during loading.
Heavy interruptions while flying.

Major stutters usually indicate a larger issue such as:

Running out of VRAM.
Severe CPU overload.
Storage delays.
Driver problems.
Add-on conflicts.

Frame Pacing

Frame pacing describes how evenly frames are delivered.

Good frame pacing:

16ms

Poor frame pacing:

16ms

18ms

55ms

17ms

80ms

The average FPS may appear acceptable, but the uneven delivery creates visible stutters.

Professional optimisation aims for consistent frame times, not simply the highest FPS.

Shader Compilation

Modern graphics drivers compile shaders when new graphical effects are encountered.

Examples include:

New airports.
New aircraft.
Simulator updates.
Driver updates.

The first flight after a driver or simulator update may contain additional shader-related stutters.

These often reduce after several flights as the shader cache is rebuilt.

If shader-related stutters persist after multiple flights, investigate your shader cache configuration.

CPU Spikes

The CPU performs many tasks simultaneously:

Aircraft systems.
Flight model.
Terrain calculations.
AI traffic.
Glass cockpit updates.
Object management.

Occasionally one task temporarily demands significantly more processing time.

This creates a CPU spike.

Symptoms include:

MainThread limitation.
Sudden frame-time spikes.
Stutters without GPU saturation.

CPU spikes commonly occur:

During approach.
At busy airports.
When AI traffic becomes active.
When many objects load simultaneously.

GPU Spikes

The GPU may also experience sudden increases in workload.

Examples include:

Large cloud formations.
Heavy reflections.
Night lighting.
Dense photogrammetry.
High-resolution scenery.

When the GPU suddenly requires additional rendering time, frame delivery becomes uneven.

Unlike a CPU bottleneck, GPU spikes usually coincide with GPU utilisation approaching 100%.

Streaming Stutters

Microsoft Flight Simulator continuously streams scenery while you fly.

This includes:

Terrain.
Satellite imagery.
Buildings.
Trees.
Roads.
Photogrammetry.

If the simulator cannot receive or process this data quickly enough, temporary pauses may occur.

Streaming-related stutters often appear:

Over large cities.
During rapid descents.
When entering new scenery areas.
During fast aircraft operations.

Rolling Cache

Rolling Cache stores recently downloaded scenery locally.

If functioning correctly, it can reduce repeated downloads when revisiting familiar areas.

However, outdated or corrupted cache data may contribute to streaming inconsistencies.

If you suspect Rolling Cache involvement:

Test with it enabled.
Test with it disabled.

Always compare using the same benchmark flight.

Add-ons

Third-party add-ons can generate stutters in different ways.

Examples:

CPU intensive:

FSLTL.
GSX.
BeyondATC.
Complex aircraft.

GPU intensive:

Premium airports.
Large scenery packages.
High-resolution textures.

Always consider recently installed add-ons when diagnosing new stutters.

AI Traffic

Every AI aircraft requires:

Flight calculations.
Taxi logic.
Lighting.
Position updates.
Collision avoidance.

High traffic density significantly increases CPU workload.

Typical symptoms include:

Stutters while taxiing.
Frame-time spikes near terminals.
Reduced 1% lows.

Glass Cockpit Updates

Modern airliners contain multiple high-refresh displays.

Examples:

Garmin avionics.
Airbus ECAM.
Boeing displays.
Navigation displays.
Flight management systems.

Higher display refresh rates require additional CPU processing.

Reducing Glass Cockpit Refresh Rate may improve frame consistency on CPU-limited systems.

VRAM Saturation

When VRAM becomes full, the GPU must constantly move textures between system memory and video memory.

Symptoms include:

Texture pop-in.
Major stutters.
Delayed scenery loading.
Significant frame-time spikes.

Monitor VRAM usage carefully during benchmark flights.

Thermal Throttling

High temperatures may cause:

CPU clock reductions.

GPU clock reductions.

Reduced performance.

Frame pacing issues.

Thermal throttling often develops gradually during longer flights.

Monitor:

CPU temperatures.
GPU temperatures.
Clock speeds.

Windows Background Tasks

Even a well-optimised PC continues to perform background work.

Examples include:

Windows Update.
Antivirus scans.
Search indexing.
OneDrive synchronisation.
Scheduled maintenance.

If these tasks begin during flight, temporary stutters may occur.

Review Task Manager and Resource Monitor if unexplained stutters appear.

Identifying the Cause

Ask yourself:

Does the stutter occur:

Only once?

Repeatedly?

At one airport?

Every airport?

With one aircraft?

Only during approach?

Only after updates?

Only with AI traffic?

The answers narrow the investigation dramatically.

Professional Stutter Diagnosis Workflow

Step 1

Run your permanent benchmark.

Step 2

Record:

Average FPS.
1% lows.
Frame times.
GPU utilisation.
VRAM usage.
MainThread status.
CPU temperature.
GPU temperature.

Step 3

Identify exactly where the stutters occur.

For example:

Pushback.
Taxi.
Take-off.
Climb.
Cruise.
Descent.
Approach.
Landing.

Patterns often reveal the underlying cause.

Step 4

Form a hypothesis.

Example:

“The simulator only stutters during approach into heavy airports while MainThread is limited.”

Step 5

Change one variable.

Repeat the benchmark.

Step 6

Confirm whether the stutter:

Improved.
Remained unchanged.
Became worse.

Worked Example

Problem

Heavy stutters while taxiing at Heathrow.

Measurements

GPU utilisation:

71%

VRAM:

11 GB of 16 GB

MainThread:

Limited

CPU temperature:

63°C

GPU temperature:

67°C

Analysis

GPU is not saturated.

Temperatures are normal.

VRAM has headroom.

MainThread limitation is significant.

Likely causes:

AI traffic.
Airport workers.
Ground vehicles.
Object density.

Test

Reduce AI traffic only.

Repeat benchmark.

Result

Frame pacing improves.

Taxi stutters largely disappear.

Conclusion:

The primary cause was excessive AI traffic increasing CPU workload.

Common Mistakes

Chasing FPS instead of smoothness.

Ignoring frame times.

Testing multiple settings simultaneously.

Forgetting shader compilation after updates.

Ignoring VRAM usage.

Assuming every stutter is GPU related.

Leaving background tasks unchecked.

Student Exercise

Today you’re going to identify every stutter during your benchmark flight.

Step 1

Run your permanent benchmark.

Step 2

Record every location where stutters occur.

Examples:

Taxi.
Rotation.
Climb.
Cruise.
Descent.
Approach.
Landing.

Step 3

For each stutter, record:

Average FPS.
1% lows.
Frame times.
GPU utilisation.
MainThread status.
VRAM usage.
CPU temperature.
GPU temperature.

Step 4

Determine the most likely cause.

Support your diagnosis with evidence.

Step 5

Make one relevant change.

Repeat the benchmark.

Document whether the stutter improved.

Stutter Analysis Report

Benchmark Conditions

Airport:

Aircraft:

Weather:

Graphics Profile:

Stutter Locations

Taxi:

Take-off:

Climb:

Cruise:

Approach:

Landing:

Performance Data

Average FPS:

1% Lows:

Frame Times:

GPU Utilisation:

VRAM Usage:

MainThread Status:

CPU Temperature:

GPU Temperature:

Diagnosis

Most Likely Cause:

Evidence:

Optimisation Tested

Single Change:

Result

Stutter Improved?

Yes / No / Partially

Final Conclusion

Confirmed Cause:

Student Checklist

Benchmark completed.

Every stutter location recorded.

Frame times monitored.

MainThread checked.

GPU utilisation recorded.

VRAM monitored.

One optimisation tested.

Results documented.

Lesson Summary

Congratulations.

You now understand that stuttering is fundamentally a frame-time consistency problem rather than simply a frame-rate problem.

Remember:

Smooth frame pacing is often more important than achieving the highest average FPS.
Micro-stutters and major stutters have different characteristics and may point to different underlying causes.
CPU spikes, GPU spikes, streaming, AI traffic, shader compilation, VRAM saturation and background tasks can all interrupt frame delivery.
Identifying where and when stutters occur provides valuable clues that help isolate the true cause.
Professional troubleshooting relies on repeatable benchmarks, careful measurement and changing one variable at a time.

Knowledge Check

What is the difference between low FPS and stuttering?
Why can a simulator with a high average FPS still feel unsmooth?
What are the common causes of micro-stutters?
How do CPU spikes differ from GPU spikes?
Why might shader compilation introduce temporary stutters?
How can VRAM saturation affect frame pacing?
Why should you record the exact location where a stutter occurs during a benchmark flight?
How can AI traffic and glass cockpit updates contribute to inconsistent frame delivery?
Why is changing one variable at a time essential when diagnosing stutters?
Based on your benchmark, what was the most likely cause of the stutters you observed, and what evidence supports your conclusion?

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