This bulletin is issued as the result of two recent incidents reported to the factory, of in flight separation of the propellor reduction unit driven pulley from the propellor shaft. In one of these incidents, the propellor and hub assembly completely separated from the aircraft and struck the vertical fin and rudder, resulting in moderate damage to the aircraft. In the second case, all the drive belts were broken, but the propellor did not separate from the aircraft.
In both of the cases, the left hand threaded stud and nut which retain the reduction unit driven pulley, had worked loose and unscrewed.
A third incident also occured involving a factory aircraft. In this case, the snap ring which retains the front bearing and thus, the reduction unit driven pulley, un- seated with the same result as mentioned above.
All three of these aircraft were successfully landed with no further damage to the aircraft and no injury to the pilots.
Before further ground run or flight, disassemble the propellor reduction unit and safety both the retaining stud and nut per the attached diagram. Upon re-assembly, be certain the front bearing snap ring is firmly seated.
Please address any further questions to me personally.
Gene C. Head