NTSB Identification: FTW00LA242.
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Nonscheduled 14 CFR
Accident occurred Thursday, August 24, 2000 in CORSICANA, TX
Probable Cause Approval Date: 07/17/2001
Aircraft: Mitsubishi MU-2B-35, registration: N770MA
Injuries: 2 Uninjured.
NTSB investigators may have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.
The twin-engine airplane was in cruise flight at 11,000 feet msl, when the pilot heard a loud bang and felt the airplane vibrate. The pilot shut down the right engine, feathered the propeller, and landed the airplane at an alternate airport. Examination of the right propeller revealed that one of its propeller blades separated approximately 8.5 inches from the hub. This blade was manufactured from 7076 aluminum alloy, which is referred to as a 'hard alloy.' Examination of the propeller blade's fracture surface revealed that it failed as a result of fatigue cracking, which originated from an area of intergranular corrosion. The propeller was overhauled 222 hours prior to the accident. According to the overhaul facility, they used a process of Alodining the blades for corrosion control, which is an approved method. According to the propeller manufacturer, the preferred method of corrosion control is anodizing due to its corrosion detection properties; however, it is a more expensive and time consuming corrosion control process. As a result of this accident, the propeller manufacturer issued a service bulletin indicating that 'hard alloy' blades should be removed from service due to their susceptibility to intergranular corrosion.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: the in-flight separation of the propeller blade, which resulted from intergranular corrosion and fatigue cracking. Full narrative available
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