How do I use the FMC in X-Plane Mobile?

To use the FMC in X-Plane Mobile, power the aircraft, open the airliner’s CDU, enter the origin and destination, add the route and departure/arrival procedures, resolve route discontinuities, then activate and execute the flight plan. Use LNAV to follow it; VNAV also needs valid performance and altitude data.

What does the FMC control in X-Plane Mobile?

The FMC stores the programmed route and, where modelled, calculates lateral and vertical guidance for the autopilot. Strictly speaking, the keypad and screen are the CDU, while the FMC is the computer behind it, though simmers commonly call the whole unit the FMC.

Only suitably equipped aircraft have one. If the cockpit has a GPS or glass flight deck instead of a CDU keypad, use that system or X-Plane Mobile’s flight-planning interface. FMC pages and the depth of their simulation also vary between aircraft.

How do you programme an FMC route?

The usual workflow is route first, procedures second, performance data third, followed by a careful check of the LEGS page. The labels below are typical of a Boeing-style FMC; another aircraft may use different page names or commands.

1. Supply electrical and avionics power. A black CDU often means the aircraft is unpowered rather than that the FMC is broken. Start from a powered state while learning, or complete the aircraft’s normal electrical start-up.
2. Open the CDU. Move close enough to operate the keypad and screen, or use an enlarged panel if that aircraft provides one. If tapping and cockpit movement are the problem, our guide to using X-Plane Mobile’s touch controls explains the basic gestures.
3. Initialise the FMC. Complete any position-initialisation page presented by the aircraft. On most units, type an entry with the keypad so that it appears in the scratchpad, then press the line-select key beside the destination field.
4. Enter the route endpoints. Open the RTE or FPLN page and enter the origin and destination using their ICAO airport codes. Add a flight number and departure runway if the FMC requests them.
5. Add the en-route portion. Enter individual fixes or use the VIA/TO columns for airways and their exit fixes. If a route is already present from the mobile flight planner, inspect it instead of entering a second copy.
6. Select the departure and arrival. On the DEP/ARR pages, choose the runway, SID and transition, followed by the destination’s STAR, transition and approach. Changing the runway later can remove or alter associated procedures, so review them again after any runway change.
7. Check every leg. Open LEGS and work from top to bottom, looking for duplicated fixes, unexpected turns and ROUTE DISCONTINUITY entries. To close a genuine gap on a Boeing-style unit, copy the first wanted waypoint below the gap and place it over the discontinuity. Do not remove an intentional vector leg unless you have decided how the route should continue.
8. Enter performance data. Complete the available PERF INIT, take-off and climb pages using the aircraft’s weights, reserves, cost index, cruise altitude and required speed data. Mobile aircraft differ in how much of this is simulated, but missing cruise or performance information is a common reason VNAV remains unavailable.
9. Activate and execute the route. Press ACTIVATE and then EXEC, or the aircraft’s equivalent commands. Confirm that the navigation display shows a continuous route and that the active leg begins ahead of the aircraft rather than behind it.

The crucial detail is the scratchpad-and-line-select workflow; tapping a displayed field usually does not let you type directly into it. For more detail on route pages, airway entries and direct-to operations, see our full explanation of X-Plane FMS programming.

Why does the FMC show INVALID ENTRY or NOT IN DATABASE?

These messages usually mean the entry is in the wrong format, is being placed in an incompatible field, or is absent from the aircraft’s navigation database.

• Use the airport’s four-letter ICAO code rather than a city name or informal abbreviation.
• Clear an old scratchpad message before typing the replacement.
• Check waypoint spelling carefully; similar identifiers can exist in different regions.
• Confirm that an airway actually connects to the preceding fix.
• If a SID, STAR or approach is missing, the procedure may not exist in the installed navigation data. Repeatedly re-entering it will not make it appear.

Why won’t LNAV follow the FMC route?

LNAV will not follow a route unless that route is executed, continuous and associated with a valid active leg.

• Check that no unexecuted modification remains in the FMC.
• Remove unintended route discontinuities and duplicate waypoints.
• Use a direct-to function if the active waypoint is behind the aircraft.
• Intercept the first leg at a sensible angle; LNAV may not capture a distant course from an unsuitable position.
• Verify on the flight-mode annunciator that LNAV is active, not merely armed, and that HDG mode has not retained control.

A magenta line on the map does not by itself prove that the autopilot is following it. Our X-Plane Mobile autopilot instructions cover flight-director use, altitude selection and mode engagement once the FMC route is ready.

VNAV is a separate problem: it normally needs valid performance entries, altitude constraints and an appropriate selected altitude. Some mobile aircraft model less VNAV functionality than their desktop counterparts, so an active LNAV route does not guarantee full vertical guidance.

Can the FMC fly the approach and landing?

The FMC can guide the aircraft along a programmed arrival or approach, but it does not automatically guarantee approach capture or landing.

For an ILS, verify the selected runway and transition, tune or confirm the ILS data where required, establish the aircraft at a suitable intercept, and select the correct approach mode. Automatic landing works only in aircraft that model it and only when all required systems are configured; simply selecting an approach in the FMC is not enough.