I didn't say 1/15 the speed now did I? Force = MASS x velocity American Eagle 4184 was a ATR 72 with a max. take off weight of 48,400 lbs a less than 1/5 the MTW of a 757 (255,000 lbs). Impact angle also directly affects the force imparted on a crashing object and AE 4184 hit the ground at about a 52 degree angle (38 degree nose down) and about 450 mph, UA 93 at close to 90 degrees and about 580 mph. Do the math; this doesn't even take kinetic energy mass x velocity squared into account.