Fix FSX Boeing 737 speed hold: arm autothrottle, engage airspeed hold, stop throttle-axis overrides, and correct climb or descent limits.
In FSX’s default Boeing 737-800, selecting a target speed does not activate speed hold. Arm the autothrottle, then engage the SPEED/airspeed-hold mode. If it still fails, a throttle axis may be overriding it, or the aircraft may lack enough thrust—or be descending too steeply—for autothrottle alone to maintain speed.
How do you activate speed hold in the FSX 737?
The default 737 needs both the A/T ARM switch and the SPEED mode engaged. Turning the speed selector only changes the target displayed in the window; it does not command the throttles.
- Stabilise the aircraft. Begin in level flight or a modest climb or descent so the system is not trying to recover from a large speed error.
- Select the target speed. Check that the MCP is displaying indicated airspeed rather than Mach before entering a value in knots.
- Arm the autothrottle. Move the A/T ARM switch to the armed position or press
Shift+R. - Engage airspeed hold. Press the MCP SPEED button or use
Ctrl+R. The keyboard command is a toggle, so pressing it repeatedly can switch the mode off again. - Leave the physical throttle still. Watch the virtual thrust levers and the aircraft’s speed trend. Movement may not be immediate if the aircraft is already close to the selected speed.
Our FSX control and keyboard-command reference lists the autothrottle-arm and airspeed-hold assignments if you need to check or remap them.
Why does the 737 still gain or lose speed?
Speed hold can command thrust only within the aircraft’s available power range. It cannot correct every climb or descent profile.
| Symptom | Likely cause | Fix |
|---|---|---|
| The selected speed changes, but thrust does not | A/T is not armed or SPEED mode is not engaged | Arm A/T, then activate SPEED; do not merely turn the selector |
| Speed falls while climbing at high thrust | The selected climb rate or pitch is too aggressive | Reduce vertical speed or lower the nose and allow the aircraft to accelerate |
| Speed rises during descent with thrust at idle | The descent is too steep for idle thrust to control | Reduce the descent rate, descend earlier or use the speedbrake within normal limits |
| Virtual throttles jump or hunt | A noisy or recently moved hardware throttle is overwriting autothrottle commands | Keep the axis still, recalibrate it and increase its null zone if necessary |
| The target appears as a decimal Mach value | The MCP is in Mach mode rather than IAS mode | Switch back to IAS when selecting a target in knots |
A non-motorised throttle quadrant will not physically move when FSX changes the virtual levers. That is normal. However, axis noise can keep sending new throttle positions to the simulator, causing the autothrottle and hardware to fight each other.
Does the autopilot master have to be on?
The default FSX 737’s autothrottle can control thrust separately from the autopilot master, but engaging the autopilot does not automatically enable speed hold. You must still arm A/T and select SPEED.
Vertical modes also matter. A demanding vertical-speed command can make the autopilot pitch up until the autothrottle reaches maximum thrust, after which airspeed falls. During descent, the reverse happens: once thrust reaches idle, autothrottle cannot slow an aircraft being driven downhill too quickly.
Do GPS, NAV or heading modes control speed?
GPS, NAV and heading modes control the aircraft’s lateral path, not its thrust or airspeed. Speed must be managed separately through autothrottle or manual power; our explanation of GPS and NAV autopilot behaviour in FSX separates these functions.
Does this fix apply to add-on Boeing 737s?
These steps apply directly to the default Boeing 737-800 in boxed FSX and FSX: Steam Edition. Advanced add-on 737s may replace FSX’s standard autopilot logic, ignore its keyboard shortcuts and use simulated modes such as MCP speed or VNAV speed instead.
For those aircraft, operate the cockpit controls according to the add-on’s documentation and confirm the active thrust mode rather than relying only on the selected-speed window. Our breakdown of 737 autothrottle and speed-mode behaviour explains how those modes divide control between thrust, pitch and the flight-management system.