On July 6, 2002, a Grumman-schweizer G-164B (registration N3631B) was involved in an aviation accident near Sacramento, CA. Investigators recorded the probable cause as: Fatigue initiation at a mechanical dent on the camber surface near midspan of the propeller blade. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A propeller blade fractured due to fatigue from a mechanical dent, causing vibration and engine failure. The pilot attempted an emergency landing on a road, but the aircraft struck a levee and flipped over.
Accident Sequence
Shortly after takeoff, while initiating a left turn at approximately 15 feet above ground level, the pilot heard a loud bang and felt a sharp jolt, followed by violent shaking of the airplane. The pilot leveled the wings and reduced power, but the vibration persisted. He then executed a shallow right turn to attempt a landing on a nearby road. As he maneuvered, a burst of flame was seen from the exhaust, the engine quit, and the aircraft began to settle. The airplane subsequently impacted a levee, flipped over, and came to rest inverted.
Post-Accident Investigation
Examination of the wreckage revealed that the outboard section of one propeller blade was missing. The remaining inboard section of the Hamilton Standard propeller blade was sent to the National Transportation Safety Board Materials Laboratory for detailed analysis. The blade was found to be fractured approximately 26 to 27 inches from the butt end. Optical examination of the fracture surface showed features consistent with fatigue progression over the majority of the fracture. Closer inspection revealed beach marks and other progression features indicating that the fatigue crack initiated at a mechanical dent located on the camber surface near midspan. Fatigue progression accounted for approximately 70% of the total fracture area.
Probable cause
Fatigue initiation at a mechanical dent on the camber surface near midspan of the propeller blade.