How do I program the FMC in a Boeing 737 flight simulator?
To program a Boeing 737 FMC in a flight simulator, we enter the aircraft position and route, load the departure and arrival procedures, remove any route discontinuities, then add performance, fuel and take-off data before activating the route. The exact page names and prompts vary a little between 737 add-ons.
What does the 737 FMC do in a flight simulator?
The Flight Management Computer, usually accessed through the 737 CDU, builds the route the aircraft will follow and calculates speeds, fuel and vertical guidance. In practical sim terms, it is what feeds the autopilot and flight director for LNAV and VNAV.
On some aircraft it is labelled FMC, on others FMS, but in a Boeing 737 cockpit most simmers still call it the FMC or CDU. The workflow is broadly the same whether you are flying a study-level NG, a simpler default 737 or a freeware variant: initialise, enter route, select procedures, verify the legs, enter performance, then execute.
What do you enter in the 737 FMC first?
First, make sure the aircraft is actually ready for FMC entry. On many 737 simulations, especially the more detailed ones, the inertial reference system must be aligned or at least powered before the position pages will behave normally.
Then work through the basic setup in this order:
| FMC area | What we enter | Why it matters |
|---|---|---|
| Initialisation | Present position and basic aircraft state | Gives the FMC a valid starting point |
| Route | Origin, destination and route or company route | Creates the lateral flight plan |
| Departure/arrival | Runway, SID, STAR and approach | Connects the route to real procedures |
| Legs review | Discontinuities, vectors and waypoint order | Prevents surprises after take-off |
| Performance | Weight, reserves, cost index, cruise altitude | Lets VNAV calculate correctly |
| Take-off setup | Flaps, assumed temperature if used, V-speeds, trim | Prepares the aircraft for departure |
Step-by-step: how to program a 737 FMC
Power the aircraft and prepare the CDU. With electrical power established, bring up the CDU or FMC screen. If your 737 simulation models IRS alignment, set that up first and confirm the FMC can accept a present position.
Set the present position. On the position initialisation page, copy the aircraft’s current GPS or reference position into the present position field if your add-on requires it. Some simpler simulators fill this automatically; the more realistic ones often expect a manual confirmation.
Enter the origin and destination airports. On the route page, enter the departure and arrival ICAO codes. This tells the FMC which two aerodromes define the flight.
Enter the flight number if required. This is not essential for the aircraft to fly, but many add-ons include the field and some airline-style procedures expect it to be filled in.
Load the route. You can either type the route manually waypoint by waypoint, enter airways with entry and exit fixes, or load a saved company route if your aircraft supports that. In most study-level 737s, airways entry is quicker and less error-prone than typing a long string of fixes individually.
Select the departure runway and SID. Go to the departures page for the origin airport and choose the active runway and standard instrument departure. Be careful here: choosing the wrong runway often creates an odd first turn or an impossible intercept after take-off.
Select the arrival, STAR and approach. On the arrival page, choose the expected STAR, arrival runway and instrument approach if you already know it. If the destination weather is uncertain, you can leave the approach until later and just select the arrival.
Check the legs page carefully. This is the bit many simmers rush. Step through the legs page and look for route discontinuities, duplicated fixes, vectors legs and any obvious detours. If there is a discontinuity that should not be there, close it only after confirming the next fix is correct.
Activate and execute the route. In most 737 FMCs, changes sit in a modified state until you press the execute key. If you do not execute, the route may look entered but LNAV will not use the amended path.
Enter performance data. On the performance initialisation pages, add zero fuel weight or gross weight as required, fuel reserves, cruise altitude and cost index if your aircraft models it. VNAV needs sensible data here; otherwise the speed and descent calculations may be wrong or unavailable.
Set take-off data. Enter the planned flap setting, centre of gravity if required, and calculate or accept V1, VR and V2 if your simulation supports them. Put the trim value from the FMC into the aircraft’s trim wheel or trim control.
Brief the route on the navigation display. Use the ND map and range controls to make sure the path out of the airport and into the en-route structure looks sensible. We always recommend zooming in after procedure changes, because the map often reveals bad route joins faster than the CDU text does.
How do I enter a route manually in the 737 FMC?
Manual entry normally means typing a waypoint into the CDU scratchpad and placing it on the correct line with the line select key. For airways, you usually enter the airway on one side and the exit fix on the other. The FMC then fills in the intermediate points from the nav database.
This is much cleaner than entering every fix one by one, but only if the airway and exit fix actually match the published route. If the FMC rejects an airway or waypoint, check the spelling first. Then check whether your nav data recognises that fix in the region you are flying.
Why is my 737 FMC route not working?
Most FMC problems in flight simulators come down to a handful of issues rather than a broken add-on.
No EXEC pressed after making route or procedure changes.
Route discontinuity still present, so LNAV has nowhere to go after a certain waypoint.
Wrong runway or SID, creating a path that does not match the departure.
Aircraft not in the correct mode, so the autopilot is not actually following FMC lateral or vertical guidance.
Insufficient performance data, which can stop VNAV from arming or calculating properly.
Out-of-date or mismatched nav data, especially when flying current charts against older simulator data.
Flying too far off the programmed path when trying to engage LNAV, so the aircraft cannot sensibly capture it.
If LNAV refuses to engage after take-off, the usual cause is simple: the aircraft is not close enough to the FMC path, or the route begins with a leg type your particular add-on does not like from the runway threshold. Heading select is often the safe fallback until you are established and can re-intercept the route.
Do all 737 flight simulator FMCs work the same way?
No. The logic is broadly similar, but the depth varies a lot. A simple built-in 737 may let you enter a route with only basic performance data, while a higher-fidelity add-on may expect proper position initialisation, detailed weights, realistic route modifications and strict execution logic.
That is why the sequence matters more than the exact button label. If you know the order of work, you can move between different 737 simulations without getting lost.
Common mistakes when programming a 737 FMC
Entering the full route but forgetting the departure and arrival procedures.
Selecting a runway based on guesswork rather than the actual departure you plan to use.
Deleting a discontinuity without checking whether the next leg really belongs there.
Relying on the FMC map alone and never checking the legs page line by line.
Trying to fly VNAV with missing cruise altitude or weight data.
Assuming the imported route is correct without verifying every procedure transition.
A practical 737 FMC workflow we recommend
If you want a clean habit pattern, keep it simple: position, route, departure, arrival, legs, execute, performance, take-off. That sequence works across most Boeing 737 simulations and catches the errors that usually ruin a departure.
Once you are comfortable, you can start using route uplinks, company routes and more detailed performance entries. But for day-to-day sim flying, getting the basics right matters far more than using every advanced page the FMC offers.
If you are building out your simulator setup or looking for more aircraft and utility downloads, our library at Fly Away Simulation downloads is a good place to start.