Oliver,
The actual "passing score" for a professional exam is closely guarded secret. The answer to your question then is "we don't know."
With that, I've seen posts on the Lessons Learned board and there have been reports that people have passed with a single BT score. This is what I conclude. "It depends."
The PMP as it sits today is essentially 5 rubric areas (Domains) corresponding to the Process Groups (Initiating, Planning, Executing., etc.). Each group is given a weight on the exam. That information is published in the PMP Exam Content Guide. Both Initiating and Closing are listed at 13% and 7% respectively. So, I suspect that you could get a BT in one of low-weighted domains and still pass the exam.
Of course, that is all just speculation.
Harry