"....at this point the IRS will NOT further reduce errors in accelerometer alignment."
Thanks, mono.
From your description, there appears to be quite a few differences between the aircraft I work on and yours, but I can't see the basic operating principles varying too much.
Here are a few of the variations:
The T/O update is inhibited on our 744's because of the installation of GPS (not deemed necessary). Prior to the installation of GPS, the update was triggered by pushing the TOGA switches on the throttles. On our 767's, the T/O update is/was triggered by pushing the N1/EPR button on the A/P Mode Control Panel. To be honest, I would have thought an unsquat signal would have introduced larger errors than taxying from the gate to the T/O position(???). Unsquat can be half way down the runway.... or all the way down the runway (give or take a few meters). This would introduce errors measured in kilometers, wouldn't it?
VOR/VOR updating is not used on our aircraft (I didn't realize it was an option).
We do use Last Position to set up the IRS's. The interesting thing about GPS is that it updates the Last Position continuously. If the aircraft is towed to a different gate, even with the IRS's switched off, the Last Position changes (on the FMC CDU).
3T + T has now been replaced with a chart/graph (which varies from this formula).
Cheers.
Q.