Learn how an aircraft autopilot works in flight simulators, how to set it up, what V/S means, and how to fix NAV, altitude and ILS capture.
In a flight simulator, an aircraft autopilot is a closed-loop software controller. It reads simulated attitude, heading, altitude, speed and navigation deviation, compares them with the active mode’s target, then commands pitch, roll or trim corrections repeatedly until the aircraft captures or holds the selected path.
This is a General flight-simulator explanation covering Microsoft Flight Simulator, X-Plane, FSX, Prepar3D and comparable platforms. Autopilot simulation ranges from basic simulator-native logic to detailed add-ons that reproduce flight-control computers, trim limits, engagement conditions and aircraft-specific mode behaviour.
How does autopilot simulation work behind the panel?
The autopilot continually measures the difference between what the aircraft is doing and what the active flight mode requires.
- Read the aircraft state: the system obtains attitude, heading, altitude, airspeed, vertical speed and navigation deviation from the simulator or an add-on’s own systems model.
- Identify the active modes: it checks which lateral and vertical commands are active, not merely which values have been entered on the panel.
- Calculate a correction: the controller determines the pitch or bank needed to reduce the difference between the present state and the target.
- Move the simulated controls: virtual servos command the ailerons, elevator or trim. The simulator then calculates the aerodynamic result.
- Measure the result again: the loop repeats, making smaller or larger corrections as wind, power, weight and aircraft configuration change.
The same closed-loop principle is used in real aircraft, although the fidelity of its simulation varies. Our explanation of real-aircraft sensors, servos and feedback loops covers the underlying engineering in more detail.
An autopilot cannot infer the pilot’s intention from a selected number alone. Setting 10,000 feet in the altitude window does not necessarily command a climb, and loading a route does not automatically activate NAV or LNAV. The mode annunciator, usually on the primary flight display, is the source of truth.
What are the flight director, autopilot and autothrottle?
These are related systems, but they do different jobs.
- Flight director: displays command bars showing the pitch and bank required by the selected modes. It does not move the controls by itself.
- Autopilot: moves the simulated controls to follow those commands or equivalent internal guidance.
- Autothrottle or autothrust: controls engine power when fitted and armed. Many general-aviation autopilots do not control the throttle.
- Yaw damper: reduces unwanted yaw. Normal autopilot turns are usually made by banking, not by steering directly with the rudder.
What do the different autopilot modes do?
Autopilot modes are grouped into lateral guidance, vertical guidance and, on suitably equipped aircraft, automatic thrust control.
| Mode | Control | Use |
|---|---|---|
HDG | Bank | Turns towards and holds the heading bug. Use it for vectors, manual course changes and route interception. |
NAV or LNAV | Bank | Tracks the selected radio, GPS or FMS course. The correct navigation source and route leg must be active. |
LOC | Bank | Captures and follows an ILS localiser or another supported localiser course. |
ALT | Pitch and trim | Holds or captures an altitude. Selecting a new altitude normally requires another mode to start the climb or descent. |
V/S or VS | Pitch | Maintains a selected vertical speed while the pilot monitors airspeed and power. |
FLC or IAS | Pitch | Maintains a selected airspeed during a climb or descent. Power strongly affects the resulting climb or descent rate. |
VNAV | Vertical path | Follows a calculated profile when the aircraft, flight plan and performance data support it. |
GS or GP | Pitch | Tracks an ILS glideslope or supported GPS glidepath after capture. |
SPD, THR or autothrust | Engine power | Controls thrust separately from the pitch and roll autopilot functions. |
Modes may be armed before they become active. For example, approach mode can arm both localiser and glideslope capture while heading and altitude modes remain active. The annunciations change only when capture conditions are met.
What is V/S on an autopilot?
V/S means vertical speed: the rate at which the aircraft climbs or descends, commonly displayed in feet per minute.
A positive setting commands a climb and a negative setting commands a descent. If you select +1000, the autopilot adjusts pitch to seek roughly 1,000 feet per minute upwards; selecting -1000 commands the equivalent descent. The exact sign and display format depend on the aircraft.
V/S mode protects neither airspeed nor engine performance. An excessive climb rate can make the autopilot raise the nose until the aircraft approaches a stall, while a steep descent with too much power can cause an overspeed. Use FLC or IAS when maintaining a safe airspeed is more important than holding a particular rate, and use V/S when the required rate is known and you can monitor speed closely.
How to set up autopilot in a flight simulator
Set up the navigation source, targets and modes before engaging the autopilot, then verify the actual annunciations rather than assuming the panel accepted every command.
- Power the required systems: confirm that the electrical system, avionics, relevant sensors and flight instruments are operating.
- Stabilise and trim the aircraft: establish a safe attitude and airspeed. Do not use the autopilot to recover from a stall, steep bank or badly out-of-trim condition.
- Prepare the navigation source: activate the intended GPS or FMS leg, or tune and identify the required radio aid. Select the correct GPS, FMS, VOR or localiser source.
- Set the targets: enter the required heading, altitude, airspeed or vertical speed. A target is not necessarily an active command.
- Select the lateral and vertical modes: choose
HDG,NAVor another lateral mode, plusVS,FLC,VNAVor altitude hold as appropriate. - Engage the autopilot: use the master or channel control only when the aircraft is within its modelled engagement limits.
- Read the mode annunciator: confirm which modes are active and which are armed. Watch the first control response, airspeed and trim movement.
Pressing the autopilot master alone may engage basic roll and pitch modes rather than route and altitude guidance. Labels such as ROL, PIT or ALT tell you what it is actually doing. Detailed Airbus-style systems also distinguish between selected and managed guidance, so control-panel position alone can be misleading.
If you need to override the system, disconnect it first and then take control. Fighting an engaged autopilot with the joystick or trim can produce abrupt movement when it disconnects.
Why is the autopilot not following my route or altitude?
The usual cause is an incorrect mode, navigation source or active flight-plan leg rather than a completely broken autopilot.
| Symptom | Checks and fixes |
|---|---|
| Autopilot will not engage | Check electrical and avionics power, flight-director requirements, valid sensor data, trim, airspeed and attitude. Look for a stuck disconnect binding or a modelled system failure. |
| Aircraft holds its wings level instead of turning | The autopilot may be in a basic roll mode. Select HDG, NAV or the aircraft’s equivalent and confirm the new annunciation. |
| Aircraft holds heading instead of following the route | Confirm that NAV or LNAV is active, the CDI or guidance source is set to GPS/FMS, and the intended route leg is active without a discontinuity. |
| Aircraft turns towards the wrong waypoint | Check the active leg, heading bug, direct-to selection and flight-plan sequencing. For radio navigation, verify the tuned frequency, selected course and navigation source. |
| Selected altitude is ignored | The altitude selector normally establishes a capture target. Select VS, FLC or supported VNAV to begin the climb or descent, then confirm altitude capture is armed. |
| Aircraft pitches sharply when autopilot is engaged | The aircraft may be badly trimmed or far from the flight director command. Stabilise and trim manually before trying again. |
| Autopilot oscillates or hunts | Return to normal simulation rate, reduce extreme turbulence and check for duplicate pitch, roll or trim assignments. Controller noise and a poor aircraft flight model can also cause repeated corrections. |
| Autopilot disconnects unexpectedly | Check for large manual control inputs, manual trim movement, excessive attitude, invalid sensor data and duplicate disconnect bindings. Limits vary between aircraft. |
| Localiser captures but glideslope does not | Arm approach mode, verify the ILS frequency and source, and intercept the glideslope from below at a sensible angle. Being above it is a common reason for failed capture. |
| The throttle does not move | Autothrottle or autothrust is separate from the autopilot. Arm and configure it if the aircraft has it; otherwise manage power manually. |
Also check whether pilot-assistance features, AI control or hardware profiles are issuing competing inputs. If failures are enabled, electrical, sensor or servo faults may prevent engagement; our guide to how random simulator failures are modelled and triggered explains what to inspect.
I set it up — zrobiłem to — but it still does not work
The Polish phrase zrobiłem to means “I did it”; for autopilot troubleshooting, the next step is to isolate the problem instead of pressing more mode buttons.
- Return to normal conditions: use normal simulation rate, moderate weather and no intentional failures.
- Disconnect and stabilise: hand-fly straight and level at a safe speed, then trim the aircraft.
- Check controller assignments: remove duplicate axes and inspect bindings for autopilot disconnect, electric trim and assistance controls.
- Rebuild the guidance: select one valid navigation source and active leg, then set one lateral and one vertical mode.
- Engage and read the annunciations: if the expected mode does not appear, the aircraft has not accepted it. Investigate that condition rather than the selected panel value.
- Compare aircraft: if a simple default aircraft works under the same conditions but a detailed add-on does not, the likely cause is aircraft-specific configuration, state or systems logic.
Can autopilot land the aircraft?
Some simulated aircraft support autoland, but approach mode by itself does not mean the aircraft will land automatically.
A coupled ILS approach usually tracks the localiser and glideslope while the pilot manages configuration, speed and monitoring. Autoland additionally requires an aircraft with modelled flare and rollout logic, suitable navigation signals, the required autopilot configuration and the expected landing-mode annunciations. Some aircraft require more than one autopilot channel; others do not support autoland at all.
A GPS glidepath marked GP should not be assumed to provide autoland capability. If the expected landing, flare or rollout modes do not appear, plan to disconnect at a safe point and land manually. Our step-by-step simulator ILS procedure explains localiser and glideslope interception without treating approach mode as an automatic landing button.
Are ANO and IFS autopilot modes?
No. Neither ANO nor IFS is a universal autopilot mode annunciation.
In UK aviation material, ANO usually refers to the Air Navigation Order, not an autopilot control. IFS is used as a product- or system-level abbreviation in different contexts, but it has no single standard cockpit meaning. If either appears in an aircraft add-on or document, use that aircraft’s legend or manual rather than guessing from the letters.
Standard annunciations such as HDG, NAV, ALT, V/S, LOC and GS describe active or armed guidance. Unfamiliar abbreviations outside the mode annunciator may refer to equipment, regulations, training material or the add-on itself.