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NTSB Propeller Warning Becomes an AD

Reprinted with permission from FAA Aviation News

The FAA is adopting a new airworthiness directive (AD) for certain Hartzell Propeller, Inc, McCauley Propeller Systems, Sensenich Propeller Manufacturing Company, Inc., and Raytheon Aircraft Company (formerly Beech Aircraft Corporation) propellers returned to service by T & W Propellers, Inc. of Chino, CA. The AD requires maintenance actions amounting to an overhaul of the affected propellers. This AD is prompted by the results of a National Transportation Safety Board (NTSB) investigation of a failed propeller blade and subsequent inspections of various propeller models returned to service by T & W Propellers, Inc. The FAA is issuing this AD to detect unsafe conditions that could result in separation of a failed propeller blade and loss of control of the airplane.

This AD results from an NTSB Safety Recommendation issued after the investigation of a January 24, 2003, accident in which a two and a half section of a blade separated from a Hartzell model HC-92ZK-2 propeller installed on the NO. 2 (right) engine of a Beech 95 (Travelair), N2733Y. This happened shortly after takeoff from Cable Airport, Upland, California. The separated section of the Hartzell 8447-12A (Z-shank) blade was recovered about one mile from the accident site and examined by the NTSB Materials Laboratory. The examination of the fracture surfaces revealed that the failure was due to fatigue cracking that had initiated at corrosion pits on the internal surface of the blade's pilot tube hole. The cracking had progressed through about 60 percent of the blade cross section and around more than half of the pilot tube bore before final over-stress separation. According to Maintenance records, T & W Propellers, LLC, Chino, California, performed the overhauls for both propeller assemblies. The overhaul entries, dated January 11, 2000, indicated that the overhauls were completed in accordance with Hartzell Manuals 105A (Propeller Model HC-92ZK-2 Overhaul Manual), 133C (Aluminum Propeller Blade Overhaul Manual), and 202A (Hartzell Standard Practices Manual), and all applicable service bulletins, service letters, and airworthiness directives to date. The propellers were installed on the accident airplane on May 16, 2002, and failed on their initial flight after several ground tests.

The Safety Board also learned during investigation that, on March 7, 2003, personnel at a repair facility in Redding, California, notified the propeller manufacturer that they had received a Z-shank propeller that had been overhauled six years earlier but had not been operated in service since the time of overhaul. The serviceable tag attached to this propeller indicated that T & W Propellers had overhauled it on December 29, 1997. The repair shop observed that the propeller was not in compliance with overhaul requirements for inspection, rework, and finishing. Specifically, the shop reported that both blades exhibited severe corrosion pitting in the same bore area and a lack of chemical conversion coating and required paint in specified areas. The shop also noted that a substance that appeared to be wash primer had been painted over areas of significant corrosion.

As a result of the investigation, the NTSB published Safety Recommendation A-03-13 and-14 on April 29, 2003, which recommends that the FAA:

Requires the immediate inspection of all propeller parts and propeller assemblies overhauled or inspected by T & W Propellers, Chino, California, to determine if they are airworthy. (A-03-13) The Board is concerned that other propeller blades and components overhauled by T & W Propellers may contain similar unconnected defects.

Require that all Hartzell Z-shank propellers be overhauled every 2,000 hours or five years; whichever comes first, as recommended by the manufacture. (A-03-14) Because the corrosion that was observed on these blades has been found primarily in areas that the manufacturer has designated as safety critical, the NTSB is concerned that, without immediate action, a similar accident could occur.

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