Understand autopilot NAV mode, how to arm and capture it, which source it follows, and why it may stay armed or turn the wrong way.
In real-world aviation, NAV mode makes the autopilot intercept and track lateral guidance from the selected navigation source—typically a VOR, GPS or flight-management-system route—rather than hold a fixed heading. Select and verify the source, establish a sensible intercept, arm NAV, then confirm that NAV changes from armed to active.
NAV is normally a lateral mode. It reads course-deviation or steering commands, banks to intercept them, and then corrects for wind to remain on the path. It does not tune a station, select GPS instead of VLOC, activate a flight-plan leg or hold altitude.
Labels vary between installations: an airliner may call the equivalent mode LNAV or managed navigation, while a general-aviation unit may display NAV, GPS, VOR or LOC after capture. We treat the flight-mode annunciator as the source of truth. Our explanation of autopilot feedback, selected targets and mode annunciations covers the underlying control logic.
How do I use autopilot NAV mode?
Use NAV only after the navigation source and intended course are correctly configured; pressing the NAV button does not perform that setup for you. In an actual aircraft, the approved flight manual and autopilot supplement take precedence over this general sequence.
- Select the navigation source. Check the CDI or HSI indication for
GPS,FMS,VLOCorNAV. Do not assume that tuning a frequency automatically changes the source. - Prepare valid guidance. For GPS or FMS navigation, load and activate the intended leg and check the next waypoint. For VOR navigation, tune and identify the station, set the required course with the OBS or course selector, and confirm the expected TO/FROM indication. Simmers can use our procedure for tuning and intercepting VOR guidance to practise the complete sequence.
- Establish an intercept. Use HDG mode to point the aircraft towards the desired course at a manageable angle. Capture limits depend on the installation, so do not expect NAV to recover reliably from a distant parallel track or an abrupt high-angle crossing.
- Engage and arm the mode. Engage the flight director or autopilot as appropriate, then select NAV. Some systems activate it immediately when close to the path; others leave HDG active while NAV waits in the armed state.
- Confirm capture. Read the flight-mode annunciator. NAV, GPS, VOR, LOC or LNAV must move to the active lateral-mode position; a lit button alone is not proof that the course has been captured.
- Monitor the result. Check that CDI deviation is reducing, the commanded bank is sensible and the aircraft is following the intended leg. Continue monitoring at waypoint changes and during VOR station passage, where guidance can become sensitive or temporarily unreliable.
Which navigation source does NAV mode follow?
NAV follows the source selected for the CDI, HSI or autopilot steering input, not necessarily the source that has merely been tuned or displayed elsewhere.
| Source | Required setup | What NAV follows |
|---|---|---|
| GPS or FMS | Select GPS/FMS and activate the correct route leg | The active lateral route and its waypoint sequencing |
| VOR | Select VLOC/NAV, tune and identify the station, then set the course | The selected VOR course represented by the CDI |
| Localiser | Select VLOC/LOC and tune the correct approach frequency | Installation-dependent lateral localiser guidance; APPR is normally used for a coupled ILS |
| GPSS retrofit | Follow the equipment-specific selector procedure | GPS steering may be supplied through HDG mode rather than the autopilot's NAV channel |
With a GPS in normal waypoint-sequencing mode, turning the OBS or course knob usually does not redefine the active leg. With a VOR, the selected course is fundamental. GPS OBS mode is an exception because it creates a chosen course to or from the selected waypoint.
An ordinary ADF needle is not a selectable NAV steering source on most autopilots. NDB tracking normally requires manual heading corrections unless the aircraft has an explicit ADF-coupling facility.
What is the difference between NAV and HDG mode?
HDG mode follows the heading bug, while NAV mode follows a radio or computed ground path. HDG therefore maintains the selected magnetic heading; NAV changes heading as necessary to intercept the course and compensate for crosswind.
Choose HDG for vectors, temporary deviations and establishing an intercept. Choose NAV once the intended navigation guidance is valid and you want the aircraft to capture and track it. NAV does not inherently know where you want to go—it follows whatever valid source and leg you have selected.
What do armed and active NAV mean?
Armed NAV means the autopilot is waiting to meet its capture conditions; active NAV means it is commanding bank to intercept or track the guidance. While NAV is armed, another lateral mode such as HDG or ROL may remain active.
Colours, labels and annunciator positions differ, so do not rely on a universal rule such as white meaning armed and green meaning active. The KAP 140 button and annunciator walkthrough shows how arming and capture work on one common general-aviation autopilot.
Why won't autopilot NAV mode capture?
NAV usually stays armed because the selected guidance is invalid, the aircraft is outside the capture geometry, or the autopilot is listening to a different source than the pilot expects.
- Wrong CDI source: change from VLOC to GPS/FMS for a GPS route, or from GPS to VLOC for a VOR or localiser.
- No valid signal: verify the radio frequency, station identification and reception range. A tuned frequency alone does not guarantee usable guidance.
- Wrong course or leg: check the OBS setting, TO/FROM sense, active waypoint, route discontinuities and any GPS OBS or SUSP condition.
- Poor intercept geometry: use HDG mode to establish a shallower, closer intercept, then arm NAV again according to the equipment procedure.
- Flight director only: the command bars can show NAV steering while the aircraft does nothing automatically if the autopilot servos are not engaged.
- Unexpected GPSS logic: some retrofit installations require the autopilot to remain in HDG while a separate GPSS unit supplies steering commands.
- Simulator control conflict: duplicate button or keyboard assignments can select and immediately cancel NAV. A mistake we see constantly is watching the button rather than checking the active-mode annunciation.
Does NAV mode control altitude or fly an ILS?
NAV mode normally controls lateral steering only; altitude, vertical speed, airspeed and vertical path require separate modes such as ALT, VS, FLC, VNAV, GS or GP. A lateral NAV mode and a vertical mode can operate together.
For an ILS, use LOC or APPR as specified by the aircraft's procedure. NAV may track the localiser on some installations, but it should not be assumed to arm or capture the glideslope. Our guidance on the correct point to arm ILS approach mode explains the required intercept and capture sequence.