As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PILOT REPORTED ELEVATOR VIOLENT SHUDDER AND PITCH DOWN WITH THE AMOUNT OF NOSE DOWN REQUIRED FOR 500 FPM DESCENT AT CRUISE POWER. MAINTENANCE PERFORMED INSPECTION OF ELEVATOR SYSTEM AND FOUND THE ELEVATOR TRIM TAB BINDING AND APPEARED TO HAVE SIGNIFICANT AMOUNTS OF PLAY BETWEEN THE THREADED ROD AND ACTUATOR BUSHING. TEAR DOWN INSPECTION REVEALED THE ACTUATOR SCREW AND SHAFT WERE WORN BEYOND LIMITS.