Iakklat
This was covered in a recent thread but I don't know how to link to that!
Reason for no T/O in Flap 1+F with ADIRU u/s is that if there were another problem with one of the other ADIRUs on departure the flap could autoretract to flap 1. This I believe happened in the early days of the a/c.
By selecting Flap 2 we get around the problem,
idg
