Sultan,
You must be very new to the game.
Bell Helicopters had a very long learning curve with the Huey series.
Tail booms fell off those machines with disgusting regularity. We lost two aircraft in one day at Fort Rucker due to that killing six people.
The problem started at the four bolt attach point, and with modifications worked its way to the 90 degree gearbox attach points along the way. The Cobra was notorius for shedding gear boxes from the tail boom.
It was not without basis it was said Bell Helicopters killed more troops than did the NVA....althought not exactly true in actual numbers but enough to have some weight.