Track Miles for the 777
Say I have been vectored on an imaginary line downwind.
I then call for PNF to "extend the centre-line from the course fix".
From this postion, how does the FMC calculated the track miles to touch down? Is it a an imaginary 90 degree line for base from where I am? Or is it a gentle curve for the base turn to join the final leg? Or it is a direct distance from where I am to the runway threshold?