FlightGear autopilot not working? Diagnose power, flight modes, GPS/NAV setup, engagement limits and controller conflicts with practical fixes.
FlightGear’s autopilot usually fails because the aircraft does not model one, the system lacks electrical power, the aircraft is outside engagement limits, a flight mode is not active, or a controller axis is overriding it. Stabilise the aircraft, verify power and mode annunciations, then remove conflicting inputs and test one mode at a time.
How do I get FlightGear’s autopilot working?
Start with heading hold in stable flight; it is the simplest way to separate an autopilot fault from a navigation or approach setup error.
- Confirm that the aircraft has a functional autopilot. FlightGear aircraft vary widely. Some have a fully modelled unit, some provide only basic stabilisation, and others have cockpit switches that are decorative or incomplete. Check the aircraft’s help, checklist or included documentation.
- Supply electrical power. Start the aircraft normally and switch on the required battery, generator or alternator, avionics bus and autopilot controls. A depleted battery, failed generator or pulled breaker can prevent engagement even when the panel remains partly illuminated.
- Establish stable flight. Hand-fly to a safe altitude, set a sensible airspeed and power setting, trim the aircraft, and reduce the bank and pitch angle. Many systems reject engagement outside their permitted attitude or speed range.
- Remove conflicting control inputs. Centre the yoke or stick, release keyboard controls and check for duplicate or noisy axis assignments. If necessary, test with external controllers disconnected before launching FlightGear. Our FlightGear keybinding and command reference helps identify an incorrect shortcut or competing assignment.
- Test heading mode first. Place the heading bug on the present heading, select HDG mode and engage the autopilot. Confirm that HDG and AP appear as active modes; selecting the flight director alone only displays guidance cues.
- Add altitude hold. Once heading mode works, select altitude hold while already level and trimmed. Do not assume that entering a target altitude will command a climb or descent.
- Test NAV or approach mode last. Only move on after basic heading and altitude control work. This keeps GPS, VOR and ILS configuration errors out of the initial diagnosis.
Why will the autopilot not engage or stay engaged?
An autopilot that refuses to latch usually lacks power, sees an invalid aircraft state or receives an immediate manual-control command.
| Symptom | Likely cause | What to check |
|---|---|---|
| AP control does nothing | No modelled autopilot, missing electrical power or wrong command | Aircraft documentation, electrical buses, breakers and command binding |
| AP engages and disconnects immediately | Joystick movement, noisy axis, excessive attitude, stall condition or system failure | Control indicators, airspeed, trim, bank angle and failure settings |
| Flight-director bars move but aircraft does not | FD is on but the servos are not engaged | Separate AP master or servo control and active-mode annunciations |
| AP is illuminated but ignores panel selections | Generic command is being used with an aircraft-specific system | Use that aircraft’s virtual-cockpit controls and documented procedures |
| Aircraft pitches or banks sharply | Poor trim, unsuitable speed, conflicting input or an aircraft implementation problem | Disconnect, recover manually, stabilise and retry with one mode |
A common FlightGear mistake is treating the generic autopilot interface and every aircraft’s panel as interchangeable. Detailed aircraft may use custom XML and Nasal logic, so a generic shortcut can fail even though clicking the modelled cockpit control works.
Why does heading, GPS or ILS mode not capture?
NAV and approach modes need the correct navigation source, a valid signal and suitable interception geometry; engaging AP alone does not provide those conditions.
Why does heading mode turn the wrong way?
HDG mode follows the heading bug, not the aircraft’s present heading or a loaded route. Set the bug where you want the aircraft to turn and confirm HDG is active rather than merely armed.
Why will FlightGear not follow the GPS route?
Select GPS as the CDI or navigation source if the aircraft provides a NAV/GPS selector, activate the required route leg, and bring the aircraft close enough to intercept it. A loaded flight plan is not always an active navigation leg, and NAV mode may remain armed until the course-deviation signal meets its capture conditions.
Why will approach mode not capture the ILS?
Tune the correct ILS frequency, select the appropriate navigation receiver, set the inbound course where the equipment requires it, and intercept the localiser at a modest angle. For glideslope capture, approach from below with a valid glideslope indication. APPR mode cannot capture an unavailable signal or correct a badly positioned approach.
Why does altitude mode not climb to the selected altitude?
On many autopilots, ALT mode holds the altitude at which it becomes active. Setting an altitude preselector does not necessarily start a climb; select a supported vertical-speed, pitch, IAS or flight-level-change mode as appropriate for that aircraft.
The autopilot normally controls pitch and roll, not engine power. Set enough power to maintain a safe speed and watch for a stall or overspeed. If the physical throttle jumps or has duplicate assignments, apply the controller-axis checks in our FlightGear throttle troubleshooting guide; the same binding conflicts can upset autopilot operation.
Why does the autopilot oscillate or fight the controls?
Oscillation means the system is receiving unstable input, has insufficient control authority or is being asked to recover from a poorly trimmed condition.
- Trim close to straight-and-level flight before engagement, then release sustained stick or yoke pressure.
- Use an appropriate airspeed and power setting; the autopilot cannot compensate indefinitely for a near-stall or overspeed condition.
- Assign each pitch, roll and trim axis to one device only. Small spikes from an unused controller can make the servos hunt or disconnect.
- Diagnose the problem at normal simulation speed and in calm weather. Time acceleration, turbulence and very uneven frame delivery make control-loop behaviour harder to assess.
- If only one aircraft oscillates under the same conditions, its autopilot tuning or compatibility is the likely cause rather than FlightGear’s global settings.
How can I tell whether the aircraft or FlightGear is at fault?
A clean comparison test will show whether the failure follows one aircraft, one controller or the whole simulator.
- Start a fresh session in calm conditions with failures disabled and a supplied aircraft known to include an autopilot.
- Launch with external controllers disconnected, then use the cockpit controls to test only HDG mode in stable flight.
- If that works, reconnect one controller and restore assignments one at a time.
- If the problem occurs only in a downloaded aircraft, check that the aircraft package is intended for the FlightGear build being used and reinstall that package if its files may be incomplete.
- If every aircraft fails, back up the user settings and temporarily reset or move the configuration rather than deleting it permanently. Recreate only the essential controls before retesting.
For an aircraft-specific failure, inspect FlightGear’s log after attempting engagement. Errors referring to missing XML resources, Nasal modules or aircraft properties point to an incomplete or incompatible aircraft package. If basic heading hold works in a clean aircraft but NAV does not, leave the installation alone and correct the navigation source, route activation or interception setup instead.