Tshirt said... "Do you go round, over or through all the "sub-sonic" clutter??"
Answer would appear to be 'over'... Boeing say this will cruise at FL400+
Not quite sure what to make of this... part of me wonders if this isn't an attempt by Boeing engineers to build an SST by the back door, without frightening the shareholders by using the word 'SST'... if this thing gets off the ground they're close to halfway there...