Why won’t FSX autopilot follow GPS or NAV mode?
In FSX and FSX: Steam Edition, the autopilot follows a GPS route only when the flight plan has an active leg, the panel’s NAV/GPS source is set to GPS, and NAV mode is armed from a sensible intercept heading. For VOR navigation, select NAV, tune NAV1, set the course, and intercept within range.
Which GPS/NAV settings should I use?
Match both the navigation source and the autopilot mode to the guidance you want; they are separate controls. The NAV/GPS source selector chooses which signal feeds the autopilot, while the NAV autopilot mode commands it to track that signal.
A mistake we see constantly is selecting NAV as the source because the pilot intends to use NAV mode. To follow the magenta GPS flight-plan line, the source must normally be GPS even though the autopilot button you press is NAV.
| What you want to follow | Source selection | Required setup | Autopilot mode |
|---|---|---|---|
| GPS flight plan | GPS | Active GPS leg and valid next waypoint | NAV |
| VOR radial | NAV | VOR in active NAV1, correct OBS course and usable reception | NAV |
| ILS localizer and glideslope | NAV | Localizer in active NAV1 and published inbound course selected | APR |
This applies to stock FSX aircraft and conventional add-ons. A complex aircraft with its own FMC, LNAV or custom autopilot may ignore the generic NAV/GPS switch; its route must be active in the aircraft’s own navigation system.
Make the FSX autopilot capture a GPS route
Use heading mode to establish a sensible intercept, then arm NAV only after confirming that the GPS is providing valid lateral guidance.
- Load and activate the route. Confirm that it appears in the aircraft’s GPS, not merely as a saved file. Our explanation of loading and activating a route in the built-in Flight Planner covers route selection and common waypoint problems.
- Check the active leg. The GPS should show a next waypoint and an active course, normally represented by a magenta leg. If it points behind the aircraft or selects the wrong segment, activate a suitable leg or use Direct-To for the waypoint you intend to track.
- Select GPS as the source. Look for a switch labelled NAV/GPS, GPS/NAV or a CDI source control. Set it to GPS before expecting NAV mode to follow the flight plan.
- Intercept the route with heading mode. Fly towards the active course rather than parallel to it or away from it. An intercept angle of roughly 20°–45° works well for most conventional FSX autopilots.
- Stabilise and engage the autopilot. Trim the aircraft, switch on the autopilot master and use HDG initially. Select altitude or vertical-speed modes separately if needed.
- Arm NAV mode. Depending on the panel, NAV may remain armed while heading mode flies the intercept. NAV should capture as the course deviation moves towards the centre.
- Confirm tracking. Check the mode annunciation and CDI rather than expecting the nose to point along the map line. The aircraft may crab into a crosswind while its ground track remains on course.
Why does NAV remain armed but never capture?
NAV usually remains armed because the aircraft is not approaching valid guidance from a capturable direction.
- Wrong source: GPS is selected while trying to track a VOR, or NAV is selected while trying to follow the GPS flight plan.
- No active GPS leg: A route can be displayed without the intended leg being active. Select a waypoint ahead and verify the desired track.
- Poor intercept: Heading mode is flying parallel to the course, away from it or from too far off to make a sensible capture. Turn towards the course and try again.
- GPS OBS mode: OBS or suspended sequencing can stop the GPS advancing as expected. Return it to normal leg sequencing unless you deliberately need OBS mode.
- Wrong radio: Most stock FSX autopilots use NAV1. Put the frequency in the active NAV1 window, not standby or NAV2, and confirm that the station is within reception range.
- Incorrect VOR course: Set the intended radial with the OBS and check the TO/FROM indication. The autopilot follows the selected course; it does not decide which radial you meant.
- Aircraft-specific logic: Test the same route in a stock aircraft. If that works, the add-on probably requires its own FMC, LNAV mode or navigation-source procedure.
- Repeated control commands: Check joystick buttons and keyboard assignments if NAV drops out, heading mode re-engages or the autopilot disconnects without command.
Why does it stop following GPS when I select an ILS?
It stops following the GPS route because an ILS requires the autopilot’s lateral source to change from GPS guidance to the NAV1 localizer signal.
Before intercept, select NAV as the source, tune the localizer into active NAV1, set the published inbound course and arm APR from a reasonable angle. Our complete FSX localizer and ILS intercept procedure explains the transition from GPS routing; if the localizer captures but the aircraft will not descend, use our glideslope capture fault checklist.
Does GPS or NAV mode control altitude and speed?
No. In the stock FSX autopilot, GPS and NAV provide lateral guidance only. Set altitude hold, vertical speed and power separately; use autothrottle only in an aircraft equipped with it.
Do not expect the generic autopilot to descend automatically at flight-plan waypoints. On an ILS, vertical guidance comes from the radio glideslope after APR capture, not from ordinary GPS or NAV tracking.