NTSB Identification: BFO96LA015.
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Accident occurred Monday, October 30, 1995 in LEBANON, VA
Probable Cause Approval Date: 03/31/1997
Aircraft: Piper PA-28-180, registration: N477SP
Injuries: 1 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.

The pilot reported that the airplane was in cruise flight at 5,500 feet when it began to vibrate severely. He stated that the subsequent oscillations in the pitch and yaw axis were so severe that he shut off the engine. The pilot made a forced landing in a soft field. During the landing roll, the nose gear and left main landing gear separated. Postaccident examination revealed that the outboard portion of a propeller blade had separated in flight. Metallurgical examination of the remaining propeller blade revealed a fracture with features indicative of fatigue cracking. The fatigue cracking features extended through about 80% of the cross section of the blade. The origin area of the fatigue cracking showed presence of corrosion damage. The airplane was in storage about 22 years. AD69-09-03 required all 76EM series propellers to be modified and a 'K' stamped after the serial number. The 'K' modification thinned and retuned the entire blade for improved vibratory characteristics. This modification lowered the stresses in the minimum power operating range. The AD also required that the tachometer be placarded to avoid continuous operation between 2150-2350 RPM. The propeller showed no 'K' stamp afer the serial number, and the pilot stated that he knew of no placard that existed in the airplane.

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

failure of the propeller blade due to fatigue cracking originating from corrosion damage. A related factor was the soft terrain encountered during the forced landing.

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