MD Helicopters MD902, Salinas, Calif., July 21, 2008–The NTSB has determined that the pilot’s inability to maintain directional control of the helicopter stemmed from the fatigue failure of the threaded portion of the forward directional-control cable, resulting from an improperly installed lock washer. The medevac helicopter was operating under Part 91 on a positioning flight to its home base at Salinas Municipal Airport and was beginning its final approach when the pilot noticed he was using more left pedal than he thought necessary for the flight profile.
As the pilot established a hover over the ramp, the helicopter’s nose broke to the right and it entered an uncommanded rotation to the right. Applying full left pedal had no effect on stopping the rotation, the pilot told investigators, so he performed
a hovering autorotation and landed hard, damaging the skids.
Examination of the aft threaded end of the control cable showed it had been mechanically damaged and was too short to engage with the rotating cone control rod in the helicopter’s Notar system. An NTSB specialist deemed it probable that the offset between the grooves in the threaded portion of the control cable is indicative of a torsional force being imparted during assembly, which rotated