FMS/GPS data models used in the aircraft

Starting with Plane Maker 10.30, authors can select the type of GPS/FMS they would like to use in their plane. The possible selections are:

  1. Old, simplified FMS/GPS which is compatible with older panels and plugins.
    This type of FMS uses a list of waypoints, which can be airports, navaids, intersections or lat-lon-defined geographical locations, and uses great-circle courses to go from one waypoint to the next.
  2. Modern, ARINC424 capable FMS.
    This type of FMS uses a list of legs, each of which can be one of 23 different path-terminator combinations as defined in the ARINC424 standard, and navigates to each terminator along the defined path.

For each plane, there exist two slots for FMS/GPS, one that works on the pilot side instruments and sources, and one that works on the copilot side instruments and sources. Using HSI selectors, either can be switched to the respective side HSI or CDI, and using the autopilot source selector instrument, each side can be fed into the autopilot.

This settings defines the underlying logic used by X-Plane to manage the flight plan, and create the necessary output for the instruments and autopilot. This is independant of which instruments are installed in the panel, thus the logic can be selected on panel-less aircraft that might be used in professional, multi-machine setups.

Note that the plugin interface that is used by XPLMNavigation only works on the pilot-side FMS/GPS. Also, no advanced functionality of the new FMS is exposed through the plugin interface. From an external view, the “modern” FMS will appear “old” for compatiblity reasons. Exposing some of the advanced functionality to plugins, and making also the copilot side accesible, is subject to a new XPLMNavigation API which will be part of a future XPLM version, whith the particular design yet to be determined.

GPS/FMS panel instruments

Several instruments can be placed in the panel to give the pilot a user-interface to the underlying FMS in the aircraft. The combination of instrument and system define what functionality is available to the pilot. The instrument options are:

  1. GPS_GA, GPS_BC, GPS_HM, FMS and FMS_small.
    These instruments have been available since early versions of X-Plane and provide a very easy-to-use interface to the old, simple FMS. If one of this instruments is in the pilot or copilot slot of the panel, the aircraft must use the compatible, simplified FMS in the respective FMS slot (pilot or copilot).
  2. GPS_430_screen and GPS_530_screen.
    These instruments are new as of Plane-Maker 10.30. They are screen-only instruments for use by designers who create their own bezels, especially for use in 3d-cockpits. They provide access to popup window-style instruments, and can be used by commands that can be triggered from 3d-cockpit elements. They work on the new, advanced FMS, so to use them, the respective pilot or copilot slot must be equipped with the new, advanced FMS.
  3. GPS_430.
    This instrument has been available since X-Plane 9 and consists of a small screen and a bezel with controls around it. It has been used by designers to model various GPS navigators, both panel-mounted and handheld types. By default, it uses the old, simplified FMS/GPS logic and can only be used for direct-to navigation. As of X-Plane 10.30 however, it can also be driven by the new logic and support complex flightplans. So whether this instrument behaves old-style or new-style is determined by which FMS system is installed in the plane in the respective slot. In case the new system is used and the screen is too small to accomodate all UI elements, a simplified UI the old-style default nav page is displayed unless the instrument is installed with a larger scaling providing more screen estate. Because the simplified UI doesn’t play well with some custom-designed aircraft, it is not enabled by default. To make the GPS_430 instrument work on the new logic, the designer must enable the new FMS system for it.

Pilot and Co-Pilot GPS/FMS

Until X-Plane 10.25, the order in which GPS instruments were dropped into the panel in Plane-Maker’s panel editor determined which would work on COM/NAV/GPS1 and COM/NAV/GPS2. This is actually not desireable, since the first one you dropped into the panel would always work on the pilot side, no matter where you placed it. As of X-Plane 10.30, the unit for the copilot must be explicitly flagged to work on COM/NAV/GPS 2. This is done by selecting the “copilot” checkbox in the bottom bar of the panel editor for the instrument. In order to have one panel instrument work on the FMS installed in the copilot slot, you have to check the copilot box on the instrument.



  • Aircraft Development

Article type:

  • Reference