Parkersburg, WV, USA
N779MA
PIPER PA 46-350P
During landing, the airplane veered hard to the right when the nose gear was lowered to the runway after touchdown. The pilot attempted to maintain directional control with rudder input, but the airplane veered to the right and departed the runway. Initial examination of the airplane at the site revealed that the nose landing gear had collapsed and the attachment components between the nose landing gear actuator and the engine mount were fractured. Each of the right and left two-piece attachment feet were fractured at the nose landing gear actuator attach location. Detailed examination of the right foot showed evidence of fatigue, which covered a 0.75-inch arc and approximately 0.04 inches of the 0.06-inch wall thickness of the foot. The left foot also showed evidence of fatigue, which covered a 0.35-inch arc and was approximately 0.03 inches deep. The manufacturer had issued a series of Service Bulletins (SB 1103, with subsequent revisions A, B, and C) for PA-46-350P models that required inspections for cracks in the engine mounts in the areas of the nose landing gear actuator attachment feet. Inspections were to take place at the next regularly scheduled maintenance event, and at each 100 hours time in service or annual inspection, whichever occurred first. Records showed that SB 1103B was accomplished on the accident airplane during an annual inspection in 2007, but records of subsequent annual inspections in 2008 and 2009 showed that SB1103 was not accomplished. Previous nose gear failures and runway excursions resulted in the redesign of the original engine mount due to compliance (flexibility) in the engine mount actuator attach feet structure. This compliance issue was sometimes exasperated at various speeds, resulting in a high speed shimmy effect and subsequent uncommanded left or right turn of the nose wheel during takeoff and/or landing. The new engine mount incorporates a one piece design at the actuator attach point, eliminating the two piece feet design. The one piece design provides a less compliant structure, which prevents relative motion between the two feet in the original engine mount design. The Federal Aviation Administration did not mandate the actions outlined in SB 1103B, but compliance could have alerted the operator of any problems because the SB inspection criteria called for examinations of the engine mount in the areas where the fatigue cracks were located. Replacement of the engine mount with the new design that had one-piece nose landing gear actuator attachment feet would have relieved the operator of the manufacturer's repetitive inspection requirement, but because the accident airplane still had the welded two-piece attachment feet it was subject to the repetitive inspection per the service bulletin.
On April 16, 2010, about 1520 eastern daylight time, a Piper PA 46-350P, N779MA, was substantially damaged when the nose landing gear collapsed upon landing at Parkersburg, West Virginia (PKB). The airplane was operated by P & C Aviation LLC. The commercial pilot and one passenger were not injured. Visual meteorological conditions prevailed, and an instrument flight rules (IFR) flight plan was filed for the business flight conducted under the provisions of 14 Code of Federal Regulations Part 91. The pilot reported that he was landing on runway 21 at PKB. The main landing gear touched down normally and as the nose gear was lowered to the runway, the airplane veered hard to the right. The pilot attempted to maintain directional control with full left rudder, but as the airplane slowed and rudder authority became less effective, the airplane departed the right side of the runway into the grass. An inspector from the Federal Aviation Administration (FAA) responded to the accident site and examined the wreckage. The structure surrounding the nose gear and engine mount was substantially damaged. A cursory examination of the nose gear revealed that the attachment components between the nose landing gear actuator and the engine mount were fractured. Photographs were taken of the affected components and the airplane was moved to a hangar and secured. The engine mount was subsequently disassembled and the fractured sections were removed and sent to the NTSB Materials Laboratory for examination and analysis. NTSB Materials Laboratory Examination / Findings: The engine mount was of a welded tubular construction, and the attachment feet were positioned at the aft end of the engine mount. Each attachment foot was constructed by welding a tube to a disk. The welded attachment feet on the airplane were of an older design (Newer attachment feet have since been redesigned to be machined from a single solid piece.). Each attachment foot was welded to three support tubes that extended forward and down and were welded to the engine mount. The right attachment foot was completely separated from the support tubes by fractures. The left attachment foot was separated from two of the support tubes by fractures, and one of the tubes supporting the left attachment foot was bent. Along the inner edge of the right attachment foot where the foot was welded to its center support tube, the fracture surface was smooth and retained curving crack arrest markings consistent with fatigue cracking emanating from multiple origins along the toe of the weld joining the foot and the support tube. The fatigue cracking propagated primarily through the parent metal of the attachment foot. The fatigue cracking extended over an arc length of approximately 0.75 inch, and penetrated at least 0.04 inch through the estimated 0.06-inch wall thickness of the foot. There was significant oxidation of the fracture surface in the area of fatigue cracking on the right attachment foot. No welding deficiencies (such as incomplete penetration or incomplete fusion) were observed in the welds joining the right attachment foot to the support tubes. Along the lower inner edge of the left attachment foot where the foot was welded to its center support tube, the fracture surface retained several regions that were smooth and had curving crack arrest markings consistent with fatigue cracking emanating from multiple origins along the weld joining the foot and the support tube. The fatigue cracking propagated through the parent metal of the center support tube and in the weld metal between the center and bottom support tubes. The area of fatigue cracking extended over a length of approximately 0.35 inch, and penetrated a maximum of approximately 0.03 inch deep. There was very little oxidation of the fracture surfaces in the area of fatigue cracking on the left attachment foot. No welding deficiencies (such as incomplete penetration or incomplete fusion) were observed in the welds joining the left attachment foot to the support tubes. A factual report (Materials Laboratory Factual Report No. 10-102) describing the detailed examination of the engine mount components is available in the public docket of supporting documentation for this accident investigation. Service Bulletin / Engine Mount Design Information: Beginning in April 2002, Piper issued a series of mandatory Service Bulletins (SB 1103, with subsequent revisions A, B and C) for PA-46-350P models, requiring inspections for cracks in the engine mounts in the areas of the nose landing gear actuator attachment feet. Inspections were to take place at the next regularly scheduled maintenance event, and at each 100 hours time in service or annual inspection, whichever occurred first. Replacement of the engine mount with the new design that had one-piece nose landing gear actuator attachment feet would have relieved the repetitive inspection requirement, but since the accident airplane still had the welded two-piece attachment feet, it was subject to repetitive inspection per the service bulletins. Maintenance Information: An examination of the airplane maintenance logbooks revealed that Piper SB 1103B was accomplished during an annual inspection on May 4, 2007. An examination of the logbook entries for the subsequent annual inspections accomplished on May 1, 2008 and June 5, 2009 revealed that Piper SB1103 was not accomplished. The operator did not provide a reason for why the inspections were not accomplished after May 4, 2007.
The inadequate design of the engine mount by the manufacturer, resulting in collapse of the nose landing gear. Contributing to the accident was the failure of the operator to adhere to the manufacturer's suggested engine mount inspection schedule.
Source: NTSB Aviation Accident Database
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