How do I use time acceleration in X-Plane 12?

To use time acceleration in X-Plane 12, stabilise the aircraft—preferably on autopilot—then use the default Alt+T shortcut to increase simulation speed and Alt+R to reduce it. Ctrl+T and Ctrl+R control ground-speed acceleration. Increase the rate gradually, monitor the flight, and return to 1× before descent, traffic or difficult weather.

How do I fast-forward a flight safely?

The safest method is to engage acceleration only during a stable, straight cruise with the aircraft correctly trimmed and the autopilot following the intended route.

1. Stabilise the aircraft. Reach cruise altitude, confirm the autopilot is holding altitude and course, and resolve any route discontinuities or pending altitude constraints.
2. Increase simulation speed. Tap Alt+T once, then allow the aircraft to settle before selecting a higher rate. Use Alt+R to step it back down.
3. Watch the flight instruments. Check altitude, vertical speed, heading, engine indications and distance to the next waypoint. Do not leave an accelerated flight unattended.
4. Use ground-speed acceleration when appropriate. Ctrl+T covers distance faster without simply accelerating every simulator process in the same way. Reduce it with Ctrl+R.
5. Return to 1× early. Normalise both controls if you used them together; reducing simulation speed does not necessarily cancel ground-speed acceleration.

On a Mac keyboard, Option is the equivalent of Alt. If the shortcuts do nothing, open X-Plane 12's control settings and search for sim speed and ground speed. Our reference list of established X-Plane time-control commands is useful for checking the standard bindings, although your own assignments take precedence.

What is the difference between simulation speed and ground speed?

Simulation speed accelerates the simulator's passage of time, while ground-speed acceleration primarily makes the aircraft cover distance more quickly relative to the world.

Ground-speed acceleration is not extra throttle and should not produce an equivalent jump in indicated airspeed. Neither mode skips directly to a waypoint: X-Plane still flies the route, so sharp turns, terrain and descent points can arrive surprisingly quickly. Combining both modes can multiply the effective travel rate and is rarely necessary.

Why won't X-Plane 12 hold the selected acceleration?

X-Plane can only deliver a higher simulation rate if the computer has enough processing capacity to calculate the extra flight-model work.

• Low frame rate: A selected multiplier is a request, not a guarantee. Reduce the rate, graphics load, complex weather or AI traffic if the simulator clock is advancing more slowly than expected.
• Autopilot oscillation: Some aircraft begin porpoising, hunting for the selected heading or overshooting waypoints at higher rates. Return towards 1× or try ground-speed acceleration instead.
• Add-on limitations: Aircraft and plugins may use timers that do not scale cleanly, deliberately restrict acceleration or reset it to normal. If a default aircraft works but an add-on does not, the add-on is probably controlling the rate.
• Wrong control reduced: Alt+R reduces simulation speed; Ctrl+R reduces ground speed. If both were increased, both must be restored.

When should I switch back to normal speed?

Return to 1× well before top of descent, a major course change, controlled traffic, mountainous terrain or deteriorating weather.

An FMS top-of-descent marker does not stop time acceleration automatically. A mistake we see constantly is waiting until the marker is reached, then discovering that the aircraft has passed an altitude constraint before the crew can react. Avoid acceleration during take-off, approach and landing, and reduce it before changing autopilot modes or capturing a new altitude.

Does time acceleration affect weather and ATC?

Simulation-speed acceleration advances the simulator clock and lighting, but live weather does not become a forecast of future real-world conditions.

Weather downloads continue to reflect available real-world observations rather than meteorological data from the accelerated future. We explain the distinction in our guide to how time changes interact with X-Plane 12 live weather.

Built-in ATC continues issuing calls and instructions, which can become easy to miss at high rates. Return to 1× before expected clearances or arrival sequencing; our advice on operating X-Plane 12's built-in ATC covers the normal radio workflow.

For online flying, remain at 1× unless the network rules and controller explicitly permit acceleration. It can cause conflicts because your aircraft reaches fixes much earlier than expected; see our X-Plane 12 VATSIM operating guidance before using any time controls while connected.