Originally Posted by
DaveReidUK
More typically that's done at the gate (most airports publish stand coordinates and/or display them where the crew can see them).
I guess that it's done more easily before you start moving, on the assumption that the IRS isn't going to drift too much on the taxy out.
The initial position is entered at the gate, true, but with some Airbus' and if GPS PRIMARY is not available, the FMS will update to the database threshold coordinates when takeoff thrust is applied - unless you get the gate position wrong, then all sorts of weird and wonderful things happen...Just ask AirAsia
what happened out of Sydney a few years ago!