The failure of company maintenance personnel to replace the tail rotor drive shafts following tail rotor blade damage in 1999, the failure of maintenance personnel to replace the tail rotor drive shafts in 2004, following their knowledge that the tail rotor blades and hub were scrapped due to tail rotor blade damage, and improper inspection and return to service by an FAA approved repair station for their failure to condemn the tail rotor drive shafts in 2004, all of which resulted in failure of the No. 5 tail rotor drive shaft during approach for landing.