CARROLLTON, GA, USA
N256AS
Embraer EMB-120RT
Atlantic Southeast Airline Flight 529 was climbing through 18,000', when a blade from the left propeller separated. This resulted in distortion of the left engine nacelle, excessive drag, loss of wing lift, & reduced directional control. The degraded performance resulted in a forced landing. While landing, the airplane passed through trees, impacted the ground, & was further damaged by postimpact fire. An exam of the left propeller revealed the blade had failed due to a fatigue crack that originated from multiple corrosion pits in the taper bore surface of the blade spar. The crack had propagated toward the outside of the blade & around both sides of the taper bore. Due to 2 previous blade failures (separations), a borescope inspection procedure had been developed by Hamilton Standard to inspect returned blades (that had rejectable ultrasonic indications) for evidence of cracks, pits & corrosion. The accident blade was one of 490 rejected blades that had been sent to Hamilton Standard for further evaluation & possible repair. Maintenance technicians, who inspected the blade, lacked proper NDI familiarization training & specific equipment to identify the corrosion that resulted in fatigue. (See: NTSB/AAR-96/06 for additional information.)
Please See NTSB Bluecover Report of Aircraft Accident - NTSB AAR-96/06 for further information regarding this accident.
the in-flight fatigue fracture and separation of a propeller blade resulting in distortion of the left engine nacelle, causing excessive drag, loss of wing lift, and reduced directional control of the airplane. The fracture was caused by a fatigue crack from multiple corrosion pits that were not discovered by Hamilton Standard because of inadequate and ineffective corporate inspection and repair techniques, training, documentation, and communications. Contributing to the accident was Hamilton Standard's and FAA's failure to require recurrent on-wing ultrasonic inspections of the affected propellers. Contributing to the severity of the accident was the overcast cloud ceiling at the accident site.
Source: NTSB Aviation Accident Database
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