How does an autopilot follow a flight plan in a simulator?

In real-world aviation and flight simulators, an autopilot follows a flight plan only after the GPS or FMS has an active route, the correct navigation source is selected, and NAV or LNAV mode captures that guidance. It then commands bank to reduce track error; altitude, speed and descent require separate modes.

What is the autopilot actually following?

The autopilot follows lateral steering guidance, not the waypoint list itself. The GPS or flight management system identifies the active leg, calculates the desired track and cross-track error, then sends guidance to the flight director or autopilot.

A basic general-aviation autopilot may steer towards the centre of a GPS course using CDI deviation. An airliner FMS usually supplies roll-steering commands through LNAV. In both cases, the autopilot adjusts bank to intercept and maintain the route while compensating for wind; it does not independently choose which waypoint should come next.

Our explanation of how GPS, inertial and radio-navigation systems generate guidance covers the systems behind that process.

What must be set before autopilot can follow the route?

A valid active leg, the matching navigation source and suitable capture geometry must all be present.

1. Load and check the route. Confirm that the flight plan appears in the aircraft’s own GPS or FMS, with the expected waypoint order and no unresolved discontinuity. A route filed with ATC or drawn on a simulator map does not always populate a complex add-on aircraft’s FMS. See our practical flight-plan setup process if the route has not yet been entered.
2. Activate the route or correct leg. Highlighting a waypoint is not the same as activating it. The avionics should show a defined active leg from one waypoint to the next. If the aircraft is already off route, activate an appropriate leg or use Direct-To carefully; Direct-To normally bypasses earlier waypoints.
3. Select GPS or FMS as the navigation source. The CDI or primary flight display should identify GPS, FMS or the equivalent source. If it shows VOR, LOC or VLOC, NAV mode will follow radio guidance rather than the magenta flight-plan line.
4. Establish an intercept. Use heading mode or hand-fly towards the active leg at a modest intercept angle. Some systems will not capture a course from far away, from the wrong side or while flying almost parallel to it.
5. Arm NAV or LNAV and verify capture. Engage the flight director and autopilot as required by the aircraft, then select the route-following mode. Read the flight-mode annunciator: an armed mode is waiting to capture, while an active mode is actually steering.
6. Monitor waypoint sequencing. Check that the active waypoint advances at each turn. A vector leg, route discontinuity, OBS mode or suspended sequencing can stop automatic progression.

Which autopilot mode follows a flight plan?

Use the lateral mode that corresponds to the navigation source producing the route guidance.

Mode names vary. Many light-aircraft panels use NAV for both GPS and radio tracking, airliners usually call flight-plan tracking LNAV, and some older installations receive GPS roll steering through a GPSS function.

Will autopilot follow altitude and speed restrictions?

NAV and LNAV normally control the lateral path only; they do not automatically follow every altitude or speed printed in the flight plan.

• Altitude hold maintains the selected altitude.
• Vertical speed or flight-level change climbs or descends towards a selected altitude under pilot supervision.
• VNAV can follow calculated climb or descent paths when the aircraft supports it, the performance data and restrictions are valid, and the appropriate vertical mode is armed.
• Autothrottle or autothrust controls speed when fitted and engaged. An ordinary autopilot does not move the throttles.

Altitude entries in a simulator flight plan may be planning data rather than commands. Even with VNAV, the pilot must set or authorise the cleared altitude according to the aircraft’s operating logic.

Why is the autopilot not following the flight plan?

Most failures come from the wrong navigation source, an inactive leg or a route mode that is armed but has not captured.

• The aircraft remains on the heading bug: HDG is still active. Arm NAV or LNAV and intercept the active route.
• NAV turns towards a VOR or localiser: the source is set to VLOC rather than GPS/FMS. This is especially common in older simulator panels; our FSX checks for GPS source selection and NAV capture cover that arrangement.
• The route is visible but no leg is active: activate the flight plan, the next suitable leg or a Direct-To waypoint. Merely displaying the map does not create steering guidance.
• The mode stays armed: reduce the intercept distance and angle, confirm the correct source, then approach the course using heading mode.
• The aircraft flies past a waypoint: look for OBS, SUSP, manual sequencing, a vector leg or a route discontinuity. For glass cockpits, our G1000 guidance on active waypoints and OBS/SUSP in X-Plane explains the same failure chain.
• The aircraft cuts the corner before a waypoint: that may be normal fly-by turn anticipation rather than an error. Fly-over waypoints are treated differently.
• The flight director bars move but the aircraft does not: the flight director is providing commands, but the autopilot itself is not engaged or has disconnected.
• The route in the cockpit differs from the simulator route: the aircraft’s FMS and the simulator’s planning or ATC system are using separate copies. Edit or reload the route in the avionics that actually supplies autopilot guidance.
• The autopilot disconnects or fights the controls: check for manual control input, duplicate axis bindings, trim problems or an aircraft state outside the autopilot’s engagement limits.

A reliable recovery is to select heading mode, stabilise the aircraft, confirm the active leg and GPS/FMS source, steer onto an intercept, arm NAV or LNAV, and watch the annunciator change from armed to active. Once captured, verify that the next waypoint sequences correctly before attending to the vertical modes.