Learn how to use FSX time acceleration safely and prevent autopilot, fuel, scenery, performance and approach problems.
In FSX and FSX: Steam Edition, press R then + or - to change the simulation rate. Increase it one step at a time, use modest acceleration only in stable cruise, and return to 1× before turns, descents, weather changes or busy airspace. Higher rates can upset the autopilot, systems, scenery loading and ATC.
How do I change the simulation rate in FSX?
The default method is to select the simulation-rate control and then increase or decrease its value.
- Stabilise the aircraft: finish any climb or turn and confirm that the aircraft is properly trimmed or established on autopilot.
- Select simulation rate: press
R. - Increase or decrease it: press
+to accelerate or-to slow down. On many keyboards, plus shares the=/+key. - Check the displayed rate: FSX briefly shows the selected value. Make one change at a time rather than holding the key down.
- Return to normal: use
Rand-, watching the indication so that you stop at1×rather than dropping below normal speed.
Our printable FSX keyboard-command reference lists the relevant shortcuts. If the keys do nothing, regain focus on the main simulator window and check whether a custom profile has replaced them; our guide to checking and remapping FSX controls explains where to correct the assignments.
This is the built-in simulation-rate control. It is unrelated to the separate FSX Acceleration expansion pack.
What simulation rate is safe in FSX?
There is no universal safe maximum because the aircraft, add-ons, weather, traffic and frame rate all affect stability.
| Rate | Suitable use | Main caution |
|---|---|---|
1× | All phases of flight | Use for departures, arrivals, manoeuvring and demanding weather |
2× | Established cruise | The best starting point for most flights; continue monitoring the autopilot |
4× | Long, straight cruise with smooth performance | May expose autopilot, scenery or add-on system limitations |
8× and above | Only simple aircraft in very stable conditions | Often unreliable with complex aircraft, heavy scenery, AI traffic or changing weather |
These are practical limits, not guarantees. Some complex add-on aircraft permit only normal speed or a modest increase, so follow the aircraft manual when it specifies a maximum simulation rate.
Can I use FSX time acceleration with autopilot?
Yes, but engage time acceleration only after the autopilot has captured its lateral mode and altitude.
A mistake we see constantly is selecting a high rate while the aircraft is still intercepting a course, levelling from a climb or entering a turn. At accelerated time, each correction covers more simulated movement before the next visible update. The aircraft may weave, overshoot altitude or bank increasingly hard.
If that happens, reduce the rate immediately to 1×. Disconnect the autopilot if necessary, stabilise the aircraft manually, then re-engage it after the flight path is under control. Use a lower maximum rate for the rest of that flight.
Does time acceleration affect fuel and aircraft systems?
Simulation rate advances fuel consumption, engine operation, the flight clock, distance travelled and most aircraft systems along with the aeroplane.
If FSX sustains 4×, one simulated hour passes in about 15 minutes of real time and the aircraft still uses approximately an hour's cruise fuel. Time acceleration is not teleportation, so check fuel quantity and reserves before leaving the flight unattended.
Add-on gauges, failure logic and system timers may not behave correctly at rates their developers did not support. Watch engine indications, fuel balance, pressurisation and navigation modes after every increase.
Why does FSX stutter or show blurry scenery at high rates?
Higher simulation rates give FSX less real time to process aircraft logic, AI traffic, weather and scenery loading for each mile flown.
If terrain becomes blurry, the frame rate collapses or the simulator stops making smooth progress, return to 1× and let the scene settle. Reducing traffic, scenery complexity or demanding weather can help; use our FSX performance-tuning steps rather than trying to force a higher rate through an already overloaded scenario.
Selecting 8× also does not guarantee eight times the progress when the computer cannot process the flight quickly enough.
When should I return to normal speed?
Return to 1× before top of descent, significant turns, route changes, weather transitions or any phase requiring close ATC attention.
- Confirm the aircraft is stable at normal speed before beginning the descent.
- Check position, remaining fuel, altitude settings and the programmed approach.
- Use normal speed before expected ATC hand-offs or descent instructions.
- Do not carry time acceleration into an instrument approach, traffic pattern or landing.
For long cruise segments, the safest routine is simple: establish the aircraft, try 2×, monitor it, and increase further only when both the aircraft and FSX remain completely stable.