Learn how an aircraft autopilot works in flight simulators, which modes to use, how to engage it correctly, and why it may ignore your route.
An aircraft autopilot is a closed-loop control system that moves the flight controls to hold selected targets such as heading, altitude, speed or a navigation path. In flight simulators, software reads the simulated aircraft state, compares it with the active mode’s target, applies control inputs and repeats that correction many times per second.
This principle is shared by general-purpose simulators including Microsoft Flight Simulator, X-Plane, FSX and Prepar3D. What changes is the depth: a simple aircraft may approximate the controls, while a detailed add-on can reproduce flight-control computers, mode logic, trim limits and automatic disconnect conditions.
How does autopilot control a simulated aircraft?
The autopilot continuously measures an error and commands the aircraft towards the selected target.
- Sense the aircraft state: the system reads attitude, heading, altitude, airspeed, vertical speed and navigation deviation from the simulator or the add-on’s own systems model.
- Check the active modes: it determines what has actually been commanded, such as heading hold, altitude hold, vertical speed or route navigation.
- Calculate a correction: the controller requests an appropriate pitch or bank angle, then commands the virtual control surfaces or servos.
- Apply aircraft physics: the simulator calculates how aerodynamics, engine thrust, weight, weather and control movement alter the aircraft.
- Repeat the feedback loop: the autopilot measures the new result and makes another correction.
This is part of the repeating physics and systems loop that turns control inputs into simulated motion. Poor aircraft modelling, conflicting hardware inputs or an unstable simulation rate can therefore affect autopilot behaviour.
What do the different autopilot modes control?
Autopilot modes are divided mainly into lateral guidance, vertical guidance and, where fitted, automatic thrust control.
| Control area | Common modes | What they do |
|---|---|---|
| Lateral | HDG, NAV, LNAV, LOC | Control bank to follow the heading bug, a radio course, an FMS route or an ILS localiser. |
| Vertical | ALT, VS, FLC/IAS, VNAV, GS/GP | Control pitch to hold altitude, maintain a vertical speed or airspeed, follow a calculated profile, or track an approach glide path. |
| Thrust | SPD, THR, autothrottle or autothrust | Adjust engine power. This is normally a separate system even when integrated with the autopilot. |
| Yaw | Yaw damper or automatic rudder functions | Dampen unwanted yaw. Ordinary heading changes are normally made with bank rather than direct rudder steering. |
The flight director is separate too: its command bars show the pitch and bank that satisfy the selected modes, but they do not move the controls unless the autopilot is engaged. The mode annunciator, often called the Flight Mode Annunciator or FMA, is the source of truth. A value displayed in the altitude or heading selector is not necessarily an active command.
Which autopilot mode should I use?
Choose the mode according to the path you need the aircraft to follow, not simply the number displayed on the control panel.
- Heading mode: use it for radar vectors, manual route changes and intercepting a navigation course.
- NAV or LNAV: use it when the correct GPS, FMS or radio-navigation source is selected and the intended route leg is active.
- Altitude hold: use it to remain at the present or captured altitude. Merely selecting a new altitude usually does not initiate a climb or descent.
- Vertical speed: use it when a specific climb or descent rate matters, but monitor airspeed. Excessive vertical speed can produce a stall in a climb or an overspeed in a descent.
- FLC or IAS mode: use it when maintaining a safe climb or descent speed is the priority. Pitch controls speed; power determines much of the resulting performance, unless an integrated thrust system manages it.
- VNAV: use it only when the aircraft supports the mode and the flight plan contains valid altitude constraints and performance data.
- Approach mode: arm it for a properly configured localiser and glideslope or supported GPS approach. It is not a general-purpose descent or automatic landing button.
For route legs, altitude constraints and approach sequencing, our practical IFR flying workflow explains where these modes fit into a complete simulated flight.
How do I engage the autopilot correctly?
Engage the autopilot only after configuring the guidance and placing the aircraft within its permitted attitude, speed and trim range.
- Stabilise and trim: establish a safe speed and attitude. Autopilot is not a recovery system for a stall, steep bank or badly out-of-trim aircraft.
- Prepare navigation: load and activate the route or tune the required radio aid. Select the correct GPS/FMS or VOR/LOC source.
- Set the targets: enter the required heading, altitude, speed or vertical rate.
- Select or arm the modes: choose the lateral and vertical guidance you want. Switch on the flight director where the aircraft requires it.
- Engage the autopilot: use the aircraft’s autopilot master or channel button after satisfying its engagement conditions.
- Verify the annunciations: confirm which modes are active and which are merely armed. Continue monitoring speed, altitude and flight-path changes.
Airbus-style systems add managed and selected modes, so the control position alone can be misleading. Our worked MSFS A320 autopilot example shows how those modes and their FMA indications differ.
Why is the autopilot not following my route or altitude?
An autopilot usually ignores a route or altitude because the wrong mode, navigation source or flight-plan leg is active—not because the autopilot is completely broken.
| Symptom | Likely cause and fix |
|---|---|
| Autopilot will not engage | Check electrical power, avionics, autopilot master, valid sensor data and aircraft attitude. Remove any stuck disconnect assignment and centre noisy controls. |
| Aircraft holds heading instead of following the route | HDG is active, or the wrong navigation source is selected. Activate the intended route leg, select GPS/FMS guidance and engage or arm NAV/LNAV. |
| Aircraft turns in the wrong direction | Check the heading bug, active waypoint, route discontinuities and direct-to selection. For radio navigation, verify the frequency, course and source. |
| Selected altitude is ignored | A selected altitude is normally a capture target, not a climb command. Use VS, FLC or supported VNAV, and confirm that altitude capture is armed. |
| Autopilot oscillates or hunts | Look for conflicting axis assignments, controller noise, extreme turbulence, poor trim, unrealistic time acceleration or an aircraft-specific systems fault. |
| Localiser captures but glideslope does not | Approach mode may not be armed, the aircraft may be above the glide path, or the wrong frequency or navigation source may be selected. Intercept from a sensible angle and normally from below. |
| Autopilot disconnects unexpectedly | Manual trim, large control inputs, excessive attitude, invalid sensor data or a bound disconnect switch can trigger disengagement. The exact limits depend on the aircraft. |
| Throttle does not move | Autothrottle or autothrust is a separate system. Arm and configure it if fitted; many general-aviation autopilots require manual power control. |
Aircraft-specific logic matters, particularly in detailed airliners. For that type, use the A320 engagement, mode and autothrust checks for MSFS rather than applying generic autopilot assumptions.
Can autopilot land the aircraft?
Some simulated aircraft can perform an autoland, but engaging approach mode does not automatically mean the aircraft will land itself.
A normal coupled approach may track the localiser and glideslope only until the pilot disconnects and lands manually. Autoland additionally requires suitable aircraft logic, the correct approach capability, valid radio-altimeter data and modelled flare and rollout modes. The runway having an ILS is not enough on its own.
Check the mode annunciations for the aircraft’s expected landing, flare and rollout indications. If those modes are absent, plan to disconnect at a safe point, take control, set power as required and trim the aircraft rather than trying to overpower an engaged autopilot.