maxmobil- You have some good points and some stupid ones. The upper deck of a 747 has only about 20 people at most on it. Not 300+ like the A380. The 747 passed 90 second evac by a mere .5 second with 550 for Japan Airlines. How do you think they are going to another 300 off in that .5 second and not pile people up at the bottom of the slides??? From 6 stories up, how fast do you think they will be moving at the bottom??? If they lengthen them to cut the angle they will blow all over the place.
The A320 has high airframe noise and I can fix that, but it is proprietary so you won't see it here.
So is the landing gear configuration of the PD Supersonic airliners. But I can tell you that they have parachutes for emergencies on RTO and landing.