Why is the autopilot not working in FlightGear?

FlightGear’s autopilot usually does not work because the chosen aircraft has no functional AP, avionics power is off, the flight director rather than the servos is engaged, the aircraft is untrimmed, or a controller is overriding it. Stabilise in safe flight, test HDG first, then diagnose NAV or approach modes separately.

How do I get the FlightGear autopilot working?

The quickest reliable test is a small heading change in stable, trimmed flight using the aircraft’s virtual-cockpit controls.

1. Climb to a safe testing altitude. Use calm weather, normal simulation speed and a sensible cruise airspeed. Do not diagnose an autopilot close to the ground, near a stall or during a steep turn.
2. Confirm that this aircraft has a working autopilot. FlightGear aircraft do not share one universal system. Some have detailed custom units, some offer basic stabilisation, and some cockpit controls are decorative or incomplete. Check the aircraft’s help, checklist and included documentation.
3. Supply the required power. Start the aircraft normally and check the battery, generator or alternator, avionics bus, autopilot master, servo switches and relevant breakers where modelled. A partly illuminated panel does not prove that the autopilot has power.
4. Stabilise and trim. Establish straight-and-level flight with an appropriate power setting. Reduce control pressure and trim the aircraft before asking the servos to take over.
5. Set the heading bug to the present heading. Select HDG mode and engage the AP according to that aircraft’s procedure. The order varies: some systems accept the mode before AP engagement, while others expect the AP first.
6. Check the active annunciations. Confirm that both AP and HDG are active, not merely selected or armed. The flight director only moves guidance bars; it does not move the controls unless the autopilot servos are also engaged.
7. Command a modest turn. Move the heading bug 10–20 degrees to either side. Be certain that you are moving the heading bug rather than the course or OBS pointer.
8. Add one mode at a time. Once HDG works, test altitude hold while level. Leave GPS, NAV and approach capture until the basic pitch-and-roll system is proven.

Nothing happens: why does the AP light not come on?

If the AP control gives no indication at all, the likely causes are missing power, the wrong command, a held disconnect input or an aircraft without a modelled autopilot.

Very short reports such as werkt niet or dit werkt ook niet in Dutch, passiert nichts in German, den lyser inte in Swedish and non riesco in Italian need the same first distinction: does the AP fail to engage, or does it engage without controlling the aircraft? If the result is “no, nothing happens”, start with the power and command path.

A mistake we see constantly is assuming that FlightGear’s generic command and every aircraft’s panel operate the same properties. Detailed aircraft can use custom XML and Nasal logic, so the cockpit button may work when a generic shortcut does not. Our guide to mapping and testing FlightGear keyboard and controller commands explains how to find duplicate or incorrect assignments.

The AP light is on, but why is the aircraft still not turning?

An illuminated AP master does not guarantee that a lateral mode is active or that a turn has been commanded.

• Move the heading bug. If it remains on the present heading, HDG mode is correctly commanding no turn.
• Use the correct pointer. The heading bug commands HDG mode; the course or OBS selector normally sets a VOR, localiser or displayed course.
• Confirm HDG is active. A button light can mean selected or armed. Use the aircraft’s mode annunciator rather than assuming every panel follows the same colour convention.
• Engage the servos. Moving flight-director bars with no aircraft response means the FD is providing visual guidance while the AP is not flying.
• Release manual input. A noisy roll axis, held key or off-centre controller can override, fight or immediately disconnect the autopilot.
• Try the cockpit control. If a generic autopilot dialog or shortcut changes nothing, operate the aircraft’s modelled AP and HDG controls directly.

If AP and HDG are both active, the heading bug has moved and the aircraft is still not turning, disconnect external controllers and restart FlightGear before retesting. Reconnect one device at a time if the clean test works.

Why will FlightGear not follow NAV, GPS or an ILS?

NAV and approach modes require the correct navigation source, a valid signal, an active course or route leg and suitable capture geometry.

Why is a loaded flight plan not being followed?

Loading a route does not engage the autopilot, select GPS as the CDI source or guarantee that the required leg is active. Use the route manager and avionics appropriate to the aircraft; our instructions for loading a plan and activating the intended route leg cover that part of the setup.

After activation, select GPS as the navigation source where the panel provides a NAV/GPS or CDI selector. Intercept the route rather than expecting NAV mode to recover from any position. For differences between aircraft panels, see our explanation of selecting the GPS source and making NAV follow it.

Why will the ILS not capture?

An ILS requires the correct active frequency, receiver and inbound course where that equipment uses one. Intercept the localiser from the front at a modest angle and approach the glideslope from below with a valid deviation indication.

APPR cannot capture a signal that is out of range, behind the aircraft or absent from the simulator’s navigation database. If the expected VOR, ILS or procedure is missing or has different data, correct it by checking and updating FlightGear’s navigation data, not by reinstalling the autopilot.

Why does altitude hold not climb to the selected altitude?

On many aircraft, ALT mode captures the aircraft’s present altitude rather than commanding the number shown in the altitude selector.

To climb or descend, use whichever vertical mode that aircraft actually supports, such as vertical speed, pitch, indicated airspeed or flight-level change, then arm or select altitude capture if required. Mode names and sequencing vary, so the aircraft documentation takes priority over a generic procedure.

The autopilot usually controls pitch and roll, not engine power. Set and monitor power yourself unless the aircraft has a separately modelled autothrottle. Disconnect and recover manually if airspeed approaches a stall or overspeed.

Why does the autopilot disconnect, oscillate or fight the controls?

Repeated disconnects or oscillation normally indicate poor trim, unstable flight, conflicting controller input or an aircraft-specific control-loop problem.

• Trim close to the desired attitude before engagement. Do not hold continuous stick or yoke pressure against the servos.
• Check that pitch, roll and trim are each assigned to only one intended device. An unused joystick can still send small axis spikes.
• Verify that an AP disconnect button or keyboard command is not stuck or duplicated.
• Use a normal airspeed and power setting. The autopilot cannot indefinitely correct a near-stall, overspeed or badly unbalanced aircraft.
• Test at normal simulation speed in calm weather. Turbulence, time acceleration and uneven frame delivery make control-loop behaviour harder to diagnose.
• Avoid moving manual trim while the AP is engaged unless the aircraft’s procedure calls for it; some systems treat trim input as a disconnect command.

If only one aircraft oscillates while another remains stable under the same conditions, the likely problem is that aircraft’s autopilot tuning, compatibility or files rather than a global FlightGear setting.

None of these fix it: is the aircraft or FlightGear at fault?

A controlled comparison will show whether the fault follows one aircraft, one input device or the whole FlightGear installation.

1. Back up the user configuration. Do not permanently delete settings while diagnosing the problem.
2. Start a clean session. Use calm weather, normal simulation speed, disabled failures and a supplied aircraft whose documentation confirms that it has an autopilot.
3. Disconnect external controllers before launch. Fly with keyboard or mouse controls, stabilise at a safe altitude and operate the virtual-cockpit AP.
4. Test only HDG. Set the bug to the present heading, engage AP and HDG, then move the bug by 10–20 degrees.
5. Compare another aircraft. If this one aircraft alone fails, check that its package matches the FlightGear build and reinstall the aircraft if files may be incomplete.
6. Restore devices and settings gradually. Reconnect one controller and recreate one assignment group at a time until the fault returns.
7. Inspect the log immediately after engagement. Missing XML resources, Nasal runtime errors or unresolved aircraft components point to an incomplete or incompatible package.

Does the clean aircraft hold HDG? Yes: the basic autopilot path works, so troubleshoot the failed aircraft, navigation source or capture setup. No: temporarily move the backed-up user configuration and retest with fresh settings. If every supplied aircraft still fails without controllers, repair the matching FlightGear program and base-data installation rather than changing route or GPS settings.