Originally Posted by
etudiant
The type was not grounded, nor was there any immediate service bulletin, as would have been expected had there been an obvious issue.
The cause, a duplex bearing failure, did get a service bulletin as noted by Jahn R81, as a result of the investigation.
The current situation is that the actuator has been modified by replacing the right hand thread at the input end of the control shaft with a left hand thread.
This removes the repetetive inspection on the nut for loss of torque.
The 10 hour inspection on the duplex bearing remains. As does the rotational force check at 100(?) hours.
A number of duplex bearings have been replaced on a precautionary basis, I believe so far they have all been found to be serviceable.
My guess is a one off failure, either a manufacturing fault on the bearing or maybe it just didn't get greased.