Because the penalty for that speed is higher fuel burn. That's why Boeing is having trouble selling the 747-8, and why four-engine airliners in general are gett

Because the penalty for that speed is higher fuel burn. That's why Boeing is having trouble selling the 747-8, and why four-engine airliners in general are getting phased out. My source for the wing sweep thing is also Joe Sutter, in his wonderful book. Also highly recommend Widebody, by Clive Irving, which is sadly out of print.