A Pilot Instructor reports having to take control of a Storm Aircraft during student pilot training when the aircraft developed a severe shake in the tail section which could be felt in the stick. The elevator had fluttered severely and the trim tab had disconnected. Of the three hinges attaching the elevator; the outboard hinge had failed and the center hinge was near failure.

Narrative

While training a Student Pilot in a Storm aircraft; doing basic right and left turns at 85 KTS IAS; the plane developed a severe shake in the tail section which could be felt in the stick. I took over from the Student Pilot; reduced power and attempted to unload the tail to stop the vibration. I then looked back and observed the elevator to be fluttering severely. It appeared the trim tab was disconnected. I established a zero thrust glide at 45-50 KTS and made a successful precautionary landing. Upon landing I observed the actuator arm had pulled loose from the trim tab via failure of the two rivets which attached the arm to the trim tab. I was later informed by the owner of the plane that the outside elevator hinge attach point had failed and the middle hinge attach point was near failure. I believe the hinge failures are a result of the flutter. I believe the flutter was caused by the trim tab failure. In my opinion; the actuator attach point to the trim tab is a poor design and should be investigated.