Lexington, KY, USA
N391MC
BEECH 58
The pilots were practicing instrument approaches and performed a missed approach. At that time, the landing gear was retracted and the corresponding gear retracted cockpit indication was noted; however, the approach controller advised the pilots that the nose landing gear appeared to remain in the extended position. The pilots then selected the nose landing gear to the extended position and noted the corresponding gear extended cockpit indication. During a subsequent landing, the nose landing gear collapsed and the airplane slid to a stop on the runway. Examination of the airplane revealed that the right side of the nose landing gear aft drag brace had separated. Metallurgical examination revealed that the origin point of the fracture was consistent with overstress, and the fracture extended from the origin point over a significant period of time. The airplane had accumulated over 10,000 hours of flight time, and the initiation of the overstress event was most likely the result of a previous hard landing or landings. Review of the maintenance manual for the make and model airplane revealed that the nose gear was an "on condition" inspection item; however, the fracture was in an area that would not be easily visible or detected by a mechanic during an inspection.
On December 10, 2009, about 1205 eastern standard time, a Beech 58, N391MC, operated by Air Lexington Inc., incurred minor damage while landing at Blue Grass Airport (LEX), Lexington, Kentucky. The certificated airline transport pilot and certificated commercial pilot were not injured. Visual meteorological conditions prevailed and no flight plan was filed for the local flight, which originated from LEX about 1030. The personal flight was conducted under the provisions of 14 Code of Federal Regulations Part 91. The pilots reported that the commercial pilot was practicing instrument approaches, while the airline transport pilot acted as a safety pilot. During a go-around at LEX, the commercial pilot retracted the landing gear and noted the corresponding gear retracted cockpit indication; however, the LEX Approach controller advised the pilots that the nose landing gear appeared to be in the extended position. The pilots then selected the landing gear to the extended position and noted the corresponding gear extended cockpit indication. During a subsequent landing, after touchdown on runway 22, the nose landing gear collapsed and the airplane slid to a stop on the runway. Examination of the airplane by a Federal Aviation Administration (FAA) airworthiness inspector revealed damage to the nose gear area and both propellers. The examination also revealed that the right side of the nose landing gear aft drag brace had separated. The inspector also noted that the nose landing gear indicating system and linkage remained intact and undamaged. The right side nose landing gear aft drag brace was forwarded to the NTSB Materials Laboratory, Washington, DC. The FAA inspector also forwarded photographs of the damage to a representative of the aircraft manufacturer. The representative noted that review of the photographs revealed that a plug used to contain linoil within the drag brace appeared to be missing. Additionally, the component tubing appeared to be absent of linoil, which was required per Hawker Beechcraft Specification 455. The representative added that the incident airplane was manufactured in 1976 and the manufacturer redesigned the component in 1977 to reduce man-hours required to fabricate the component. The redesigned component was forged and not constructed of tubing, which also eliminated the need for a plug and linoil. The representative further stated that review of the manufacturer’s field condition reports did not reveal any record of similar failures to the same model nose landing gear aft drag brace. Examination of the component by an NTSB metallurgist revealed that the origin point of the fracture exhibited features consistent with overstress. Additionally, the metallurgist noted “crack arrest marks” along the fracture extension, consistent with an overstress failure over a period of time. The fracture initiated from a different area than that of the missing linoil plug. The investigation could not positively determine if the plug departed before or after the failure of the component. Review of the maintenance manual for the make and model airplane revealed that the nose gear was an "on condition" inspection item; however, the FAA airworthiness inspector noted that the fracture was in an area that would not be easily visible or detected by a mechanic during an annual or 100-hour inspection. The incident airplane was maintained under an FAA approved inspection program (AAIP). The airplane's most recent AAIP inspection was completed on November 9, 2009. The airplane had accumulated 20.2 hours of operation since that inspection and had accumulated 10,437.3 total hours of operation at the time of the incident.
The overstress failure of the nose landing gear aft drag brace.
Source: NTSB Aviation Accident Database
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