What happened
On August 25, 2018, a Bell 212 helicopter, registration N512TA, was performing external load operations for the US Forest Service near Dardanelle, California. While conducting water bucket operations at a dip site approximately 35-40 miles from the helibase, the pilot heard an unusual "one per revolution" whispering sound.
The pilot elected to return to the helibase and was escorted by an Air Attack controller flying in an A-Star helicopter. During the return flight, at an airspeed of approximately 60 knots, the noise transitioned into a physical vibration and shuddering. The pilot attempted to land at the nearest available site.
Just before reaching the landing area, the vibration momentarily ceased, followed by a loud bang, intense vertical vibration, and a significant nose-down pitch. The pilot reported that despite having engine power, he could not maintain control. The helicopter struck the steep, mountainous terrain, rolled once, and came to rest on its left side. The pilot sustained one serious injury and was able to exit the aircraft unassisted. The engine continued to run for approximately 1.5 hours after the impact.
The investigation
Investigators from the NTSB, FAA, and the helicopter manufacturer examined the wreckage and the rotor system. The investigation revealed that the swashplate had separated from the swashplate support, with significant metal deformation at the mounting points.
Examination of the main rotor blades showed that one blade (serial number A-7774) had an overload fracture, while the other (serial number A-7749) exhibited spanwise bending and wrinkling.
Detailed analysis of the control system found that a swashplate drive link (serial number HE-017) had fractured at the lower lug. The inner race of the trunnion bearing had separated from the rotating swashplate, and the outer sleeve of that bearing showed evidence of brinelling caused by axial impacts. The investigation determined that the failure of the drive link's lower lug and the trunnion bearing led to the swashplate assembly separating from its support.