Learn how to switch an aircraft between GPS and NAV1/VLOC, verify the CDI source, and make the autopilot follow the selected guidance.
To switch a GPS-equipped aircraft between GPS and NAV1, use the CDI/source selector—labelled GPS/NAV, CDI, SRC or VLOC depending on the avionics. Prepare the destination source first, select it, verify the display or annunciator shows GPS or NAV1/VLOC, then arm the appropriate autopilot mode if required.
What does the GPS/NAV1 switch actually change?
The source selector changes which navigation system drives the course deviation indicator, HSI and, when coupled, the autopilot. It does not turn off the GPS, tune NAV1 or automatically engage the autopilot.
| Selected source | What the CDI or HSI follows | Typical use |
|---|---|---|
| GPS or FMS | The active GPS flight-plan leg or direct-to course | En-route GPS navigation and RNAV/GPS approaches |
| NAV1 or VLOC | The VOR radial or localizer received on NAV1 | VOR, localizer and ILS navigation |
On integrated aircraft, the GPS-derived source may be labelled FMS rather than GPS. NAV1 may appear as VLOC, meaning the first navigation receiver is supplying VOR or localizer guidance. These labels describe the guidance source, not an autopilot mode.
How do I switch from GPS to NAV1?
- Prepare NAV1. Put the required VOR or ILS frequency into the active NAV1 window, confirm that the station is received and identified, and set the required course. Our conventional radio-navigation walkthrough covers tuning, identification and course interception in more detail.
- Stabilise the aircraft. If the autopilot is already following GPS and the GPS and NAV1 needles disagree substantially, use heading mode before changing source. Otherwise, the aircraft may turn abruptly towards the newly selected course.
- Select NAV1 or VLOC. Press the GPS/NAV switch, CDI key, PFD softkey or source-selection control until the displayed source reads NAV1, NAV or VLOC.
- Verify the indication. Check the source label beside or above the CDI/HSI. Do not rely on needle movement alone; an invalid NAV signal may leave the indication flagged, parked or absent.
- Couple the autopilot if needed. Intercept the selected course, then arm NAV for VOR or localizer tracking, or APR for an ILS when appropriate. Confirm that the mode changes from armed to active.
To return to GPS navigation, make sure the intended flight-plan leg is active, select GPS or FMS as the CDI source, verify the source annunciation, and then arm the lateral navigation mode. Changing the source while hand-flying only changes the navigation display; it does not steer the aircraft.
Where is the GPS/NAV source selector?
The control location depends on the installed avionics, not simply the aircraft model.
- Traditional GPS and analogue CDI: a separate GPS/NAV switch is often fitted near the navigation instruments or GPS unit.
- Garmin GNS-style units: the CDI key normally alternates between GPS and VLOC guidance.
- Garmin G1000-style panels: the PFD CDI or source control cycles through GPS, NAV1 and sometimes NAV2. If the displayed source refuses to follow the route, our G1000 source-selection checks for X-Plane explain the common GPS-versus-VLOC problem.
- Airliners and other integrated panels: the selector may use FMS, VOR or LOC labels and may be assigned separately to each pilot's display.
For real-world flying, use the approved aircraft and avionics manuals because installations can differ even between two aircraft of the same type.
Why does the autopilot not follow the selected source?
Selecting GPS or NAV1 supplies guidance to the CDI, but the autopilot still needs the correct lateral mode and valid guidance to capture.
- The autopilot remains in HDG, ROL or another lateral mode rather than NAV or APR.
- NAV or APR is only armed; the aircraft has not reached a suitable intercept angle or capture zone.
- NAV1 is tuned in the standby window rather than the active window.
- The VOR or localizer is out of range, incorrectly tuned or not identified.
- GPS is selected, but no flight-plan leg or direct-to course is active.
- The source was changed on the other pilot's display while the autopilot is coupled to the opposite side.
- The simulator's GPS/NAV switch and autopilot NAV button have been confused. They are separate controls despite sharing similar labels.
This last mistake is especially common in older simulated panels: GPS selects the guidance source, while NAV commands the autopilot to track that source. The FSX GPS and NAV coupling checklist shows how those controls interact.
When should I switch from GPS to NAV1 for an ILS?
Switch to NAV1/VLOC before localizer capture unless the installed avionics are designed and configured to transfer sources automatically. GPS can guide the aircraft along the arrival and towards the approach, but the ILS localizer and glideslope come from the tuned navigation receiver.
- Tune and activate the ILS frequency in NAV1.
- Identify the station and set the published front course.
- Select NAV1 or VLOC while approaching the localizer intercept.
- Confirm that valid localizer guidance is displayed.
- Arm APR and monitor localizer and glideslope capture.
Some avionics can change automatically from GPS to VLOC during an activated ILS approach, but the pilot must still confirm the annunciated source. For the full sequence, including capture geometry and mode checks, see our MSFS 2024 ILS intercept and landing procedure.
Do not switch to NAV1 for an RNAV, GPS or LPV approach unless the published procedure and installed equipment specifically require it. Those approaches normally remain on GPS/FMS guidance through the final approach segment.