The manual (Starship 1 Avionics System) describes this process in two distinct situations (create new waypoint using joystick): During the insertion of a new waypoint into the flight plan and during the selection of a direct-to (DIRECT TO) destination.

Technical Mechanism and Procedure (Literal Basis from real manual).

1. Inserting a Custom Waypoint into the Flight Plan (FLT PLAN)

In the context of flight plan editing, the procedure is described on page 3-27 (Table 3-5, subitem INSERT WPT AFTER):

"The CHP joystick and the MFD map display may also be used to add a waypoint. Position the joystick symbol on the desired waypoint location; then press the ENT line key on the MFD. The waypoint ident (if a navaid) or @JOY then appears on the CDU; press the ENTER and OK line keys to complete the operation."

Technical flow breakdown:

The pilot positions the joystick symbol (a crosshair cursor with a circle) over the desired geographic location on the MFD's position or plan map.

By pressing the ENT (Enter) key on the MFD's bottom line, the geographic coordinates (latitude/longitude) of the point under the cursor are transferred to the FMS.

The FMS then checks whether those coordinates correspond to an existing navaid (VOR, NDB, airport, etc.) in the database.

If it does match, the standard navaid identifier (e.g., CID) appears on the CDU scratchpad.

If it does not match any database navaid (i.e., it is an arbitrary point on the map), the CDU displays the identifier @JOY on the scratchpad.

The pilot then presses the ENTER and OK line keys on the CDU to confirm the creation of the new waypoint.

The manual also notes (on the same page) that if the identifier is user-defined (not found in the database), a "boxed-x" (an X inside a square) is displayed next to the new ident, and additional prompts are shown to define the location or add a radial/distance offset, if desired.

2. Direct-To (DIRECT TO) Selection Using the Joystick

The same mechanism is described on page 3-37 (Table 3-5, subitem DIRECT TO page):

"The CHP joystick and the MFD map display may be used to select a destination waypoint. Position the joystick symbol on the desired direct-to location; then press the ENT line key on the MFD. The waypoint ident (if a navaid) or JOY appears on the scratch pad line of the CDU. Press the WPT, ENTER, and OK line keys to complete the operation."

Important note: In this context, the identifier displayed is JOY (without the @), but the logic is identical: the FMS recognizes that the point is not in the database and treats it as a user-defined waypoint.

Management and Persistence of Custom Waypoints

Once created, this custom waypoint (identified as @JOY or JOY) is stored in the FMS volatile memory as part of the active flight plan. It is not permanently added to the navaid database (which is read-only and updated via DBU), but it can be:

Reused within the current flight plan.

Inspected and deleted via the INSPECT WPTS page (page 3-34), which allows the operator to view and remove user-defined waypoints that are no longer in use on any route or flight plan.

Saved to a route (ROUTE LIBRARY) for future use, provided the route is stored in the FMS non-volatile memory.

So I ran a test to see if I could create a new custom waypoint, but instead of creating a new one at the desired location, it seems to insert whatever is closest to it. I recorded a video to show what happens. CHP-850: Waypoints

Is this a real feature that wasn't modeled, or am I doing something wrong?

Best regards!

Alan / From Brazil.