"Out of the 324 people on board, there were 72 initial survivors (71 humans and 1 dog) spread across the three sections of the plane crash. The opening season featured 14 regular speaking roles, making it the second largest cast in American primetime television".
There were 324 passengers on the plane including crew. Since 71 people survived the crash (1 nose, 48 midsection, 22 tail), this puts the survival rate of the crash itself at 21.9%