As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
APPROX 100 HRS AGO TRANSMISSION WAS O/H AND NEW PMA GEAR SET WAS INSTALLED S/N GR586A FROM HELICOPTER TECH DURING FLIGHT PILOT HEARD AND FELT NOISE AND MADE A PRECAUTIONARY LANDING AND FOUND COOLING FAN DRIVE PULLEY AND APPROX 1.25 INCHES OF THE DRIVE SHAFT WAS MISSING. WE ARE SENDING IN REMAINING SHAFT SEGMENT WHERE IT SHEARED FOR METALLURGICAL ANALYSIS.