As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHILE PERFORMING A PART 91 FLIGHT TRAINING, PILOTS EXPERIENCED CONTROL YOKE OSCILLATION. RETURNED TO AIRPORT WITHOUT INCIDENT. DURING INSPECTION, FOUND TRIM TAB TUBE BROKEN AS SECONDARY DAMAGE. BELIEVE PRIMARY FAILURE OF ELEVATOR COUNTER BALANCE WEIGHT ATTACH RIB.