As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ATB - DURING CLIMB OUT THE LEFT ENGINE VIBRATION WAS INDICATING 4.3. CREW COMPLIED WITH QRH AND AIRCRAFT RETURNED TO JFK. CORRECTIVE ACTION: MAINTENANCE REPLACED AVM AND NUMBER ONE ENGINE FAN BLADES PER B737 AMM. ALL VIBES NORMAL ON HIGH POWER RUN, AIRCRAFT RETURNED TO SERVICE.