What do NAV and APP autopilot modes do in flight simulators?

In a flight simulator, NAV mode steers the aircraft laterally along the selected navigation source, such as a VOR radial, localiser or GPS/FMS route. APP (approach) mode arms or captures both localiser and glideslope guidance for an ILS, or compatible lateral and vertical guidance for a supported RNAV approach.

What is the difference between NAV and APP mode?

NAV provides lateral guidance; APP adds approach-specific lateral and, where available, vertical capture. The exact labels vary: some panels use APR or APPR, while airliners may separate LNAV, LOC and APP.

NAV does not always mean NAV1. It follows whichever source is driving the course deviation indicator: GPS/FMS, NAV1, NAV2 or another source supported by that aircraft. This source-selection detail causes many failed captures.

NAV can often track an ILS localiser, but it normally will not capture the glideslope. APP arms the additional vertical mode. Our basic autopilot mode workflow explains how heading, altitude and navigation modes interact.

For RNAV approaches, APP behaviour depends on the avionics and procedure. An approach with an authorised, modelled glidepath may show GP capture; an LNAV-only approach has no vertical path for APP to follow. The practical differences are covered in our comparison of ILS and RNAV guidance.

When should I switch from NAV to APP?

Use NAV while following the route or positioning for the approach, then arm APP before intercepting final approach guidance.

1. Identify the approach type. Confirm whether it is an ILS, localiser-only or RNAV procedure and whether vertical guidance is available.
2. Configure the navigation source. Tune and identify the ILS where required, set the inbound course if the avionics need it, and select the correct CDI source. For a conventional ILS this is normally VLOC or the NAV radio rather than GPS, although integrated avionics may switch automatically. See our explanation of choosing GPS or NAV for an ILS.
3. Establish a sensible intercept. Approach the final course at the published altitude and a moderate intercept angle. Intercept an ILS glideslope from below.
4. Arm APP. Press APP or APR before reaching the localiser and glideslope, then check the flight-mode annunciator rather than relying only on the button light.
5. Monitor the capture. Confirm that the armed lateral mode becomes active, followed by GS or GP. Continue controlling speed, power, flaps and landing gear.

There is no universal requirement to press NAV first. Heading mode can take the aircraft to the intercept, after which APP captures the approach. If NAV has already captured the localiser, selecting APP commonly retains lateral tracking and arms the glideslope.

How can I tell whether NAV or APP has captured?

The flight-mode annunciator is the authoritative indication of what the autopilot is actually doing.

An armed mode is waiting for valid guidance and suitable capture geometry; an active mode is controlling the aircraft. Many displays use white for armed modes and green for active ones, but colours and abbreviations vary between aircraft.

• NAV, LOC or LNAV active means lateral guidance has captured.
• GS active means an ILS glideslope has captured.
• GP active usually means an RNAV glidepath has captured.
• ALT active with GS armed means the aircraft should hold altitude until it meets the glideslope.

A centred needle alone does not prove that the autopilot has captured it. The flight director can also display steering commands while the autopilot master is off, leaving the pilot to follow those commands manually.

Why will APP mode not capture the localiser or glideslope?

APP usually fails to capture because the navigation source, signal, approach geometry or armed mode is wrong.

• Wrong source: GPS remains selected while attempting to capture a radio-based ILS.
• Incorrect setup: The wrong ILS frequency, runway, inbound course or approach has been selected.
• Poor intercept geometry: The aircraft reaches the localiser too fast, too close, or at an excessive intercept angle.
• Above the glideslope: Many autopilots will not capture properly from above. Return to an appropriate published intercept rather than forcing a steep descent.
• No vertical guidance: A localiser-only, VOR or LNAV-only procedure cannot provide a glideslope or glidepath.
• Mode merely armed: APP has been selected, but the aircraft has not yet entered the capture zone.
• Autopilot not engaged: The flight director may show APP commands while the aircraft remains under manual control.
• Aircraft-specific modelling: Some simulated avionics require a particular FMC setup, navigation-source change or separate LOC selection.

Why does the localiser capture but the glideslope does not?

A localiser-only capture normally means the aircraft is above the glideslope, has not reached it yet, APP was armed too late, or the procedure has no usable vertical signal. Check that GS is armed, remain at the intercept altitude, and verify that the glideslope indicator is moving down towards the centre.

Does APP mode land the aircraft automatically?

APP mode does not normally land the aircraft; it tracks approach guidance towards the runway until the pilot disconnects or another mode takes over.

Autoland requires a suitably equipped and correctly modelled aircraft, an appropriate ILS, the required autopilot channels and proper aircraft configuration. APP alone also does not automatically manage power, flaps, landing gear, minima or the missed approach. Unless the aircraft explicitly indicates an armed autoland system, plan to disconnect and land manually.