How do I program an Airbus or Boeing FMC/MCDU?

In a general flight simulator, program an Airbus MCDU or Boeing CDU by initialising position, entering or importing the route, selecting runways and procedures, clearing only genuine route gaps, adding performance and take-off data, then committing the plan. Engage managed navigation or LNAV/VNAV only after checking every leg against the clearance and charts.

What is the difference between an FMC, CDU and MCDU?

The FMS or FMC is the system that calculates the route and performance; the CDU is the Boeing-style keypad and display used to control it. Airbus calls its interface the MCDU, which also provides access to some systems outside the flight-management function.

Simmers often use FMC to mean the entire Boeing unit. That shorthand is harmless, but understanding the distinction helps when an aircraft manual refers separately to the FMC, CDU, flight plan and autopilot.

Page names, calculations and simulated failures depend on the aircraft. A default airliner may model only part of the system, while a detailed add-on can require electrical power, IRS alignment and complete performance entries. This is especially relevant in older simulators; our guide to FMS/CDU support in FSX aircraft explains why some cockpits have only a decorative or simplified unit.

What information do I need before programming the FMC?

Prepare the route and operational data before entering anything. At minimum, you will normally need:

• Departure and destination airport identifiers.
• The planned runway, SID, en-route fixes or airways, STAR and approach.
• Cruising altitude and, where used, a cost index.
• Aircraft weight, fuel quantity and reserves.
• Departure weather, runway condition and take-off configuration.
• Calculated V-speeds, assumed temperature or thrust setting where the simulated aircraft requires them.

Do not guess take-off speeds or copy them from another flight. They depend on weight, runway, weather, flap setting and aircraft model. Some add-ons calculate them through an onboard performance tool; others expect the pilot to enter externally calculated values.

Airbus MCDU and Boeing CDU page equivalents

Both systems require broadly the same information, but organise it differently.

These are common labels rather than a guarantee for every aircraft. Regional jets, business aircraft and simplified airliners may arrange the same functions differently.

How do I enter and activate the flight plan?

1. Power and initialise the system. Supply the required electrical power and allow any simulated IRS alignment to finish. Enter the aircraft position if the model does not do so automatically.
2. Enter the origin and destination. Use the Airbus INIT page or the Boeing RTE page. Add the flight number and company route only if the aircraft supports them.
3. Build the en-route section. Enter fixes directly or use airway-and-exit pairs. Verify each identifier because the database may contain several waypoints with the same name in different regions.
4. Select departure and arrival procedures. Choose the runway, SID, transition, STAR and approach that match the clearance or intended flight. Adding a procedure already contained in an imported plan can create duplicate fixes.
5. Inspect every leg. Compare the CDU sequence with the navigation display and charts. Check for duplicate waypoints, impossible turns, unexpected altitude constraints and route discontinuities.
6. Enter performance data. Add cruising altitude, cost index, weights, fuel and reserves. On Airbus aircraft this is usually spread across INIT and performance-related pages; Boeing aircraft normally use PERF INIT followed by thrust and take-off pages.
7. Complete take-off entries. Enter the flap or configuration setting, centre of gravity or trim where required, thrust data and valid V-speeds. Confirm that the speeds appear on the primary flight display if the aircraft models that function.
8. Commit the plan and configure guidance. Insert any Airbus temporary revision or press Boeing ACTIVATE and EXEC when prompted. Set the cleared altitude on the FCU or MCP before selecting the appropriate lateral and vertical modes.

For aircraft-specific control sequences, use our detailed Airbus A320 MCDU programming workflow or the Boeing 737 CDU programming walkthrough.

Should I remove every route discontinuity?

No. Remove a discontinuity only when the chart and clearance require the two surrounding legs to connect directly.

A discontinuity between a STAR and approach may represent radar vectors or a deliberate break between procedures. Deleting it blindly can produce a sharp turn back to an earlier fix, bypass an expected vector or join legs that were never intended to connect. After closing any gap, inspect both the waypoint order and the drawn path.

How do I use the FMC during flight?

Use the FMC to manage and monitor the planned path, but use the flight mode annunciator to confirm what the aircraft is actually doing.

• For lateral guidance, select Airbus managed NAV or Boeing LNAV only when the active leg is correct and the aircraft can intercept it. Use selected heading or heading select to establish a sensible intercept if necessary.
• For vertical guidance, managed climb/descent or VNAV needs complete performance data and a suitable altitude selected on the FCU or MCP. The selected altitude can prevent the aircraft climbing or descending even when the calculated profile continues beyond it.
• For route changes, revise the arrival, approach or active leg, review the resulting temporary modification and then commit it. Never execute a change merely because the EXEC light has illuminated.
• For monitoring, compare the active waypoint, distance, altitude constraints and mode annunciations with the expected flight path. The magenta line alone does not prove that the autopilot is following it.

On many Airbus simulations, pushing an FCU knob commands a managed target and pulling it selects a pilot-entered target. Mouse gestures vary between simulators and aircraft. Boeing aircraft use MCP modes such as LNAV, VNAV, heading select, level change and vertical speed; selecting one of those modes can override FMC guidance.

Why will the aircraft not follow the FMC route?

The usual cause is an inactive mode, an uncommitted route or unsuitable intercept geometry rather than a broken FMC.

• Route displayed but not followed: check the flight mode annunciator. LNAV or managed NAV may be armed rather than active, or selected heading may still be controlling the aircraft.
• EXEC light still illuminated: the Boeing modification has not been committed. Review it before pressing EXEC.
• Temporary flight plan remains: an Airbus revision is waiting to be inserted or erased.
• Aircraft turns towards the wrong fix: confirm the active waypoint and use a direct-to function or a heading intercept when appropriate.
• Aircraft stops at a waypoint: the next item may be a discontinuity, manual leg or vectors instruction.
• VNAV will not engage: complete the cruise altitude, weight, fuel and performance entries, then check whether the particular aircraft actually models VNAV.
• Descent does not begin: lower the selected altitude when cleared and use the required descent command. Many aircraft will not descend solely because they have reached the calculated top-of-descent point.
• Waypoint or airway rejected: the plan and aircraft may use different navigation-data cycles. Rebuild the affected section with fixes available in the aircraft database.

Can I import a flight plan instead of entering it manually?

Yes, if the simulator and aircraft support route import, but an imported plan rarely completes the whole setup.

Imports may omit runway procedures, transitions, weights, fuel, cost index, winds and take-off data. They can also duplicate a SID or STAR if you import one version and then select the same procedure in the CDU. Follow our route-import steps for Airbus and Boeing systems, then inspect the route leg by leg before using managed guidance or LNAV/VNAV.