For a discussion of the problems with the CH-46 Phrog where the aft pylon, aft transmission, and aft rotorhead and blades departed the aircraft in flight....and the subsequent fix with questions about the actual cause of the problem...hit this link.
CH-46As Breaking up in Flight!!! - NOTAM Board
On the CH-47A in Vietnam, we had two significant problems....one being an "incidence bolt" on the rotor blades failing....with catastrophic results, and flight control push-pull tubes coming apart at the riveted ends also resulting in the loss of the aircraft. The CH-47C model went through a phase where Power Turbines shattered and tried to cut the aircraft in half...always causing a hell of an inflight fire and loss of the aircraft.