Learn how to use an airliner FMC in Microsoft Flight Simulator: enter routes, set performance data, engage LNAV/VNAV and fix common errors.
To use an FMC in Microsoft Flight Simulator, load or enter the route, set the aircraft’s position and flight data, choose the departure and arrival procedures, initialise performance and take-off values, then activate and execute the plan. Engage LNAV and VNAV only after checking the route for gaps and errors.
What do the FMC, CDU and MCDU actually do?
The FMC is the computer that calculates the flight path and performance, while the CDU is the keypad and display used to control it. Airbus aircraft normally call the interface an MCDU, which provides access to the wider flight management and guidance system.
Boeing tutorials commonly refer to RTE, LEGS, DEP/ARR, PERF INIT and TAKEOFF REF pages. Airbus equivalents include INIT, F-PLN and PERF. The principles are similar, but the buttons, terminology and order of entry are not interchangeable.
The FMC also does not fly the aircraft by itself. It supplies guidance that the flight director and autopilot can follow when the correct modes are selected. How completely this is modelled depends on the aircraft; our explanation of where Microsoft Flight Simulator matches real aviation and where it simplifies it covers that distinction in more detail.
How do I programme an FMC before departure?
Programme the FMC in a fixed sequence: aircraft position, route, route check, performance data, take-off data and guidance modes.
- Identify the exact aircraft and avionics. A Boeing 737 CDU does not operate like a 747 or 787 CDU, and an Airbus MCDU uses different terminology. Power the avionics and complete any required IRS or ADIRS alignment. Ready-to-fly departures may complete some of this automatically.
- Load fuel and payload first. Use the aircraft’s loading page or EFB where provided. The FMC needs the resulting weight and centre-of-gravity data; changing the load afterwards can invalidate performance figures.
- Initialise the aircraft position. Enter the origin airport and, where requested, the gate or stand. Copy or enter the present position on the position-initialisation page. Some aircraft automate this step, while others require it before navigation becomes available.
- Build or import the route. Enter the origin, destination, runway, departure procedure, en-route waypoints, arrival procedure and approach. On airway pages, the usual pattern is entry waypoint, airway and exit waypoint. Avoid adding both a manually entered procedure and an imported copy of the same procedure.
- Inspect every leg. Work through the LEGS or F-PLN pages and compare them with the navigation display. Check waypoint order, altitude and speed constraints, sharp turns, duplicate fixes and route discontinuities. A discontinuity before a vectors leg may be intentional, so deleting every gap blindly is a common mistake.
- Enter performance data. Typical entries include zero-fuel weight, reserves, cost index and cruise altitude. Some aircraft can pull weight figures from the EFB; others require manual entry. Missing or inconsistent values often prevent VNAV or managed climb from becoming available.
- Complete the take-off page. Confirm the runway, flap setting, centre of gravity or trim, and V1, VR and V2. Use the aircraft’s own performance calculator when supplied. Do not guess an assumed-temperature or FLEX value simply to obtain lower take-off thrust.
- Activate and execute the plan. Boeing systems normally require ACTIVATE followed by EXEC; Airbus systems commonly display a temporary revision that must be inserted. Until that confirmation is made, the edited route may appear on screen without becoming active.
- Set the guidance panel. Select the cleared initial altitude on the MCP or FCU, switch on the flight directors and set the appropriate lateral and vertical modes. Boeing aircraft normally use LNAV and VNAV; Airbus aircraft use managed NAV, climb and descent modes. The flight-mode annunciator is the authoritative indication of what the aircraft is actually doing.
Can I import a route from the World Map or EFB?
You can often import a route, but the amount transferred depends on the aircraft, avionics and whether you are using Microsoft Flight Simulator 2020 or 2024. Some aircraft receive the complete simulator flight plan, while others import only the origin, destination and en-route fixes.
Choose one route-building method as the master. Building part of the route on the World Map and then adding the same SID, STAR or approach in the FMC frequently creates duplicate waypoints and unexpected turns.
After any import, verify:
- the origin, destination and selected runways;
- the SID, STAR, transitions and approach;
- every discontinuity and vectors leg;
- altitude and speed constraints;
- the active first leg and its direction; and
- fuel, weight, cruise and take-off data, which usually require separate initialisation.
Why does ATC show a different route?
Built-in ATC can retain the simulator’s original flight plan even after the route is changed inside an aircraft-specific FMC. An internal direct-to, different arrival or new approach therefore may not update ATC.
If following built-in ATC matters, keep the simulator flight plan and FMC route aligned. Otherwise, expect ATC to issue instructions based on the older plan rather than the magenta route displayed in the cockpit.
Why will LNAV or VNAV not follow the FMC?
LNAV and VNAV usually fail because the route was not executed, the wrong guidance mode is active, required performance data is missing or the aircraft has not intercepted the active leg.
| Symptom | Likely cause | What to check |
|---|---|---|
| The edited route is visible but ignored | The modification is still temporary | Press EXEC or insert the temporary flight plan, then confirm that the route is active. |
| LNAV or managed NAV will not engage | No valid active leg, a route gap, or the aircraft is too far from the leg | Check the first active waypoint and intercept the route using heading mode if necessary. |
| The aircraft continues on a heading | HDG or selected heading remains active | Read the flight-mode annunciator rather than relying on the illuminated button alone. |
| VNAV or managed climb is unavailable | Missing weight, cruise altitude, cost index or take-off data | Complete the performance pages and check for an invalid altitude constraint. |
| The aircraft stops climbing or descending | The MCP or FCU altitude prevents further movement, or a constraint is active | Set the cleared altitude and confirm the active vertical mode before changing the route. |
| The route doubles back or makes a sharp turn | Duplicate waypoints, the wrong transition or an incorrect active leg | Review the LEGS or F-PLN sequence and rebuild the affected procedure rather than applying random direct-to commands. |
NOT IN DATABASE appears | The waypoint is misspelt or absent from the installed navigation-data cycle | Check the identifier and use a route compatible with the aircraft’s installed data. |
A magenta line only shows the planned path. The mode annunciator tells you whether the aircraft is following that path, and it should be checked after every mode selection or autopilot change.
How do I update the FMC for arrival and approach?
Update the arrival once the expected runway, STAR, transition and approach are known, then inspect the revised legs before executing them.
Remove or replace the old arrival rather than stacking a second procedure on top of it. Check for duplicate runway fixes, unreasonable altitude constraints and discontinuities. A vectors segment normally requires heading guidance until ATC clears the aircraft to intercept or proceed directly to a fix.
The FMC may tune an ILS frequency and course automatically, but this varies by aircraft. Confirm the radio setup, approach mode, decision height or minimum descent altitude, landing configuration and missed-approach altitude separately.
Does the FMC land the airliner automatically?
No, an FMC route alone does not provide an automatic landing. Autoland requires a suitably equipped and correctly configured aircraft, an appropriate instrument approach, the required autopilot channels or landing modes, and correct runway and weather conditions.
For an ordinary ILS or RNAV approach, the FMC can provide lateral and sometimes vertical guidance, but the pilot must still arm the correct approach mode, monitor the annunciations and disconnect or continue according to the aircraft’s procedure.
Which FMC tutorial should I follow?
Follow a tutorial for the exact aircraft model and avionics version installed in your simulator. A generic Boeing or Airbus video can explain the sequence, but copying button presses from another aircraft is a reliable way to encounter missing pages, rejected entries or different mode behaviour.
Microsoft Flight Simulator 2020 and 2024 may also load routes differently, and default aircraft can behave differently from community aircraft. If the aircraft came from our Microsoft Flight Simulator aircraft and mods library, confirm that the package supports your simulator generation and read any included manual or checklist before applying instructions written for another version.