From X-Plane SDK
XPLM_API void XPLMGetFMSEntryInfo( int inIndex, XPLMNavType * outType, /* Can be NULL */ char * outID, /* Can be NULL */ XPLMNavRef * outRef, /* Can be NULL */ int * outAltitude, /* Can be NULL */ float * outLat, /* Can be NULL */ float * outLon); /* Can be NULL */This routine returns information about a given FMS entry. A reference to a navaid can be returned allowing you to find additional information (such as a frequency, ILS heading, name, etc.). Some information is available immediately. For a lat/lon entry, the lat/lon is returned by this routine but the navaid cannot be looked up (and the reference will be XPLM_NAV_NOT_FOUND. FMS name entry buffers should be at least 256 chars in length.