Check your B777 manual under Flight Management, Navigation -
FMC Cruise.
There is no position updating (or need for position updating) of a FIX when identified/inserted on the FIX page. It
is where it
is on the surface of the planet and as such is contained in the database as a Lat/Long and Elevation. It doesn't move but its' Lat/Long are influenced by magnet variation from time to time. Your aircrafts' position relative to it, moves and it is your aircraft position which needs updating, not the FIXs.
When you think about DME and its use for aircraft position updating it would make sense the DME signal should eminate from a fixed object.
Typically, DME is a position reference used with IRS and GPS to generate a blended aircraft position.
Hope this helps?
Willie
