One would assume that it would be Mast bumping/MR connection with tail boom. .but you would also state a commercial pilot knows of these dangers, unless inflicted by other means. . . or maybe it's as simple as a maintenance fault from the factory...and the tail boom just held in for the 4 hours..then seperated..who knows... condolences to the families. sad.
I'm interested to know the investigation result or other ppruners comments ?