NTSB Identification: SEA01LA023.
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Accident occurred Friday, November 17, 2000 in STEVENSVILLE, MT
Probable Cause Approval Date: 07/02/2001
Aircraft: Piper PA-30, registration: N7062Y
Injuries: 5 Uninjured.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

During a descent, and while passing through approximately 8,000 feet mean sea level, a sudden, violent airframe vibration developed in the twin engine Piper PA-30, and the pilot shut down the right engine. He then noticed a portion of the one of the propeller's tips missing. Metallurgical examination of the blade revealed a fatigue fracture initiating from a dent about 0.2 inch from the leading edge of the blade. The dent measured approximately 0.07 inch wide in the chordwise direction and about 0.03 inch deep and was covered with flat black paint. The propeller log indicated repeated historical occasions whereby the propeller had been dressed and painted. FAA Advisory Circular 43.13-1B/2A, 'Aircraft Inspection, Repair & Alterations' states in Section 4. 'Repair of Metal Propellers,' paragraph 8-73(a) 'Flaws in Edges,' that the mechanic should '...Exercise care to remove the deepest point of the injury and also remove any raised metal around the edges of the injury....'

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

Fatigue of the right propeller blade resulting in an in-flight separation of the blade tip. A contributing factor was the improper maintenance procedure.

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