How do I enter latitude/longitude waypoints in an FMC?

To enter a latitude/longitude waypoint in an aircraft FMC, convert the position to the format that unit accepts, type it in the scratchpad, and line-select it onto the RTE or LEGS page. A common Boeing-style entry is N5128.7W00027.7. Check both hemispheres and the plotted position before pressing EXEC.

In real-world aviation, no universal FMC coordinate syntax exists; simulated units usually reproduce the aircraft they model. Some require a slash between latitude and longitude, while others reject it. Airbus-style systems may require you to create a pilot-defined waypoint before inserting it into the flight plan.

What coordinate format does an FMC accept?

An FMC normally wants latitude first and longitude second, expressed as degrees and minutes with hemisphere letters rather than signed decimal degrees. A common Boeing-style pattern is NDDMM.MWDDDMM.M, where longitude always has three degree digits.

Some units instead expect N5128.7/W00027.7. Preserve leading zeros, do not type degree symbols, and never treat decimal degrees as decimal minutes: 51.4775° is 51°28.65′, not 51°47.75′. Our explanation of converting and checking latitude/longitude in a simulator covers the underlying coordinate conventions.

How do I insert the coordinate into the route?

Enter the coordinate in the scratchpad, insert it at the intended point in the route sequence, and verify the resulting modification before executing it.

1. Identify the insertion point. Note the waypoint immediately before and after the new coordinate. This prevents a valid position from being placed in the wrong leg.
2. Convert the coordinate. Use the exact hemisphere, degree width and minute precision accepted by that FMC. Latitude comes first.
3. Enter it in the scratchpad. For the example above, try N5128.7W00027.7 on a Boeing-style unit, adding the slash only if its documented format requires one.
4. Line-select the entry. Place it on the appropriate RTE or LEGS line. On many Boeing implementations, selecting an occupied LEGS line inserts the new point before that waypoint rather than replacing it.
5. Inspect the modified route. Check the generated waypoint name, track, leg distance and position on the navigation display. A coordinate can be accepted syntactically yet still be thousands of miles away because E/W was reversed.
6. Handle discontinuities deliberately. Remove a route discontinuity only when the intended path genuinely joins the surrounding legs. Do not delete one merely to make the page look tidy.
7. Execute the change. Press EXEC or the aircraft-specific equivalent only after the route and map checks agree.

For route-page selection, discontinuities and activation, see our complete Boeing FMC route-programming workflow. In an actual aircraft, use the operator-approved entry and cross-check procedure rather than relying on a generic format.

Can I enter an oceanic waypoint such as 5220N?

Yes, some FMCs recognise five-character ARINC shorthand for whole-degree latitude/longitude points. 5220N represents 52°N 020°W, but the final letter is a quadrant code rather than merely a latitude hemisphere.

• N means north latitude and west longitude.
• E means north latitude and east longitude.
• S means south latitude and east longitude.
• W means south latitude and west longitude.

For longitudes of 100° or more, the letter moves into the middle: 50N30 represents 50°N 130°W. Use this shorthand only when the FMC and operational procedure support it. Entering 5220N for 52°30′N 020°W would move the point about 30 NM south.

Why does the FMC reject my latitude/longitude entry?

Most rejected coordinates result from the wrong syntax, missing leading zeros or a format unsupported by that particular FMC.

• FORMAT ERROR or INVALID ENTRY: Remove degree symbols and spaces, check the number of digits, and try the documented slash convention. Minutes must be below 60.
• NOT IN DATABASE: The unit may be treating the text as a named fix rather than a raw coordinate, or it may require a pilot-defined waypoint page.
• Waypoint appears in the wrong place: Check N/S and E/W, longitude’s three-digit degree field, and any decimal-degree conversion.
• Nothing changes after entry: The coordinate may still be in the scratchpad, may have been inserted into an inactive route, or may be waiting for route execution.
• An unexpected discontinuity appears: Confirm that the coordinate was inserted between the intended surrounding fixes and that no original waypoint was accidentally replaced.

Does a coordinate waypoint require current navdata?

A raw pilot-defined latitude/longitude position normally does not depend on navdata, because the FMC stores the coordinates directly. Named fixes and some shorthand identifiers do depend on database support; if those are missing, our guide to checking and updating simulator navigation data explains what an update can—and cannot—fix.

Do Boeing, Airbus and simulator FMCs use the same syntax?

No. Boeing-style FMCs commonly accept coordinates directly through the scratchpad, while Airbus FMGS implementations often create them through a pilot-defined waypoint or LAT/LONG field before insertion into the flight plan.

Generic simulator FMS units and third-party aircraft can differ again, even within the same simulator. X-Plane users should follow the modelled unit’s procedure; our guide to route activation and waypoint entry in X-Plane explains how its FMS workflow differs from a Boeing CDU.