I don't understand why the Sea World spokesperson I can see here in the UK on TV broadcasts appears to be saying that 'we have never experienced anything like this before'. I am sure that there has been numerous accidents and incidents, and Sea World should have been well aware of Tilikum's past history in which two people died. There have also been numerous near misses as Youtube would testify too.
There are a lot more details here
With such amazing but essentially wild social animals confined in small tanks that are completely unrelated to their natural environments away from family and social groups, no wonder these 'accidents' are always lurking as possibilities.
Time to let the orcas go free, -that's not just the best for the orcas, but its the best way to avoid any accidents, and definitely avoid such a tragedy like this from happening again.