A CESSNA CARAVAN IMMEDIATELY AFTER TKOF DECLARED AN EMER AND DIVERTED DUE TO PROP VIBRATION CAUSED BY INCORRECT COUNTERWT BOLT INSTALLATION.

Narrative

ON MAR/XA/01; A CESSNA CARAVAN; EQUIPPED WITH A MCCAULEY 3GFR34C703 PROP DEPARTED ZZZ AT XA47 ON A ROUTINE SCHEDULED FLT. UPON TKOF; THE PLT NOTICED AN UNUSUAL VIBRATION FROM THE PROP. THE PLT DECLARED AN EMER AND SAFELY RETURNED THE ACFT WITHOUT FURTHER INCIDENT. UPON INSPECTION; IT WAS DISCOVERED THAT ONE COUNTERWT HAD SEPARATED FROM ITS CORRESPONDING BLADE CAUSING DAMAGE TO THE SPINNER AND BLADE. THE PROP AND SPINNER WERE EXCHANGED AND THE FLT WAS CONTINUED. INSPECTION OF THE COUNTERWT BOLT REVEALED THAT THE BOLT HAD 'STRIPPED' OUT OF THE BLADE. THIS BOLT WAS COMPARED TO A TYPICAL BOLT THAT WOULD OTHERWISE CONNECT THE COUNTERWT TO THE BLADE. THESE BOLTS WERE FOUND TO BE IDENTICAL IN ALL RESPECTS EXCEPT IN LENGTH; WHICH DEVIATED BY 3/8 INCH. THIS IS THE ALLEGED CAUSE OF THE FAILURE. THE PROP IS CURRENTLY AT THE MANUFACTURER FOR EVALUATION. THIS CAN BE AVOIDED IN THE FUTURE BY PROPER PART IDENT. EMPLOYING A COLOR MARKING TO DIFFERENTIATE BTWN BOLTS SHOULD ALSO BE IMPLEMENTED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE BOLT THAT WAS INSTALLED IN A BLADE COUNTERWT AND WAS FOUND TO BE TOO SHORT BY .375 INCHES. THE RPTR SAID IT WAS AN APPROVED BOLT BY THE MANUFACTURER OF THE PROP; BUT NOT IN THIS TYPE PROP. THE RPTR STATED THE PROB WAS CAUSED BY IMPROPER PART IDENT.