On June 26, 2011, about 0930 mountain standard time, a Piper PA-46-350P, N9246M, sustained substantial damage when the nose wheel landing gear collapsed during landing roll at the Flagstaff Pulliam Airport (FLG), Flagstaff, Arizona. The airplane was registered to N9246M LLC, Las Vegas, Nevada, and operated by the pilot under the provisions of Title 14 Code of Federal Regulations Part 91. The airline transport rated pilot and two passengers were not injured. Visual meteorological conditions prevailed, and no flight plan was filed for the personal flight. The cross-country flight originated from Las Vegas, Nevada, about 0810 with an intended destination of FLG.
In a written statement to the National Transportation Safety Board investigator-in-charge, the pilot reported that following a normal landing on runway 21, the nose began to lower. As the nose wheel landing gear touched the runway surface, the airplane suddenly swerved to the left. Despite her control inputs, the airplane exited the left side of the runway, and the nose wheel landing gear collapsed. Subsequently, the airplane came to rest nose low about 150 feet left of the runway surface.
Examination of the airplane by a Federal Aviation Administration (FAA) inspector revealed that the engine firewall was bent. Further examination of the nose gear revealed that the attachment components between the nose landing gear actuator and the engine mount were fractured.
The engine mount assembly was sent to the NTSB Materials Laboratory, Washington, DC, for further examination.
An NTSB metallurgist reported that the engine mount was of a welded tubular construction. The aft end of the nose landing gear actuator was bolted between two attachment feet (left and right) at the aft end of the engine mount structure. Each attachment foot was painted black, machined from a single solid piece, and welded to three support tubes. The right attachment foot was fractured in the circumferential direction inboard of the support tubes. A longitudinal fracture that extended from the circumferential fracture to the outboard end of the attachment foot was also observed.
The right attachment foot was cut from the rest of the engine mount so that the fractures could be examined using an optical microscope. The longitudinal fracture was inclined at 45 degrees to the inner and outer surfaces of the tube, consistent with a ductile overstress fracture. The circumferential fracture, viewed looking generally outboard along the attachment foot, exhibited multiple cracks with smooth features and curved crack arrest marks, consistent with fatigue. The largest of these cracks initiated at the “T-shaped” intersection of two of the support tube welds. The fatigue cracks then continued to propagate along the toe of the weld that joins the forward support tubes to the attachment foot.
A factual report describing the detailed examination of the engine mount components is available in the public docket.
Service Bulletin / Engine Mount Design Information:
Piper Aircraft Inc. Service Bulletin 1103D mandates an inspection of the left and right attachment feet for PA-46-350P Mirage serial numbers between 4622001 and 4622200 as follows:
“Upon reaching 290 hours time in service on the currently installed engine mount, initial inspection to coincide with the next regularly scheduled maintenance event.
Thereafter, compliance to be accomplished on a recurring basis, at a frequency interval not to exceed one hundred (100) hours time in service.”
As part of the inspection procedure, the paint is removed prior to fluorescent penetrant inspection. After inspection, the area where the paint was removed is to be coated with a corrosion prevention compound consisting of a layer of Dinitrol/Ardrox AV8 and a layer of Dinitrol/Ardrox AV30.
If a crack is found during the inspection, a new engine mount, part number 89137-042, is to be installed. However, the service bulletin notes that installing a new engine mount does not relieve the recurring inspection requirement.
Beginning in April 2002, Piper issued a series of mandatory Service Bulletins (SB 1103, with subsequent revisions A, B, C and D) 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.
Review of supplied copies of airframe and engine logbooks, which were from July 20, 2007 (airframe total time of 1,965 hours) through November 4, 2010 (airframe total time of 2,237.6 hours), revealed no entries that pertained to compliance with SB1103 revisions A, B, C, or D.