As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) AIRCRAFT DEPARTED AIRPORT AND UPON CLIMBOUT THE RT ENGINE RPM INDICATION BEGAN TO FLUCTUATE. ALL OTHER PARAMETERS REMAINED NORMAL. AIRCRAFT RETURNED AND UPON INVESTIGATION FOUND DRIVE SHAFT INTACT YET SLIPPING INTERNALLY. TACH GENERATOR REPLACED, RUNUP COMPLETED AND AIRCRAFT RETURNED TO SERVICE. (TC NR 20060920008)