What had happened: The aft pressure bulkhead was ruptured and the pressurized air in the cabin blew out into the aft fuselage, blowing off the Auxiliary Power Unit (APU) and portions of the tail cone, forcing considerable part of the vertical stabilizer to break off.
I don't know how four of then can survive. They are lucky! But the 520 died... The heavy turbulance (if you saw) is when the tail broke off)
