As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
REMOVED 2-BLADED PROPELLER. INSTALLED 3-BLADED HARTZELL PROPELLER UNDER STC SA090015. SPENT HUNDREDS OF MAN HOURS TROUBLESHOOTING EXTREME VIBRATION IN AIRFRAME. INSTALLED SAME 3-BLADED PROP ON DIFFERENT AIRCRAFT SAME VIBRATION (BAD). REMOVED PROP, RETURNED TO STC HOLDER. SUBMITTER RECOMMENDED REMOVING THE O470U ENGINE FROM THIS STC.