Daytona Beach, FL, USA
N938ER
Piper PA-44-180
The landing gear was confirmed to be down and locked, three green annunciator lights were noted, and the nose landing gear was visually seen to be down and locked. The airplane touched down, veered sharply to the left and departed the runway. It collided with a runway distance remaining sign, damaging the right wing. Post-accident examination revealed the nose landing gear had collapsed. The upper drag brace (that connects the nose gear to the fuselage) was fractured, and the pivot lug (that connects the upper brace to the lower brace) was fractured in two places. The pivot lug fractures were consistent with overload stress separations. At least 13 internal horizontal and parallel cracks were uncovered near the vertical centerline of the brace. The cracks followed the grain flow lines resulting from forging. Flow lines were longitudinal in the arm portion of the brace with a smooth, gently curving transition into the thicker portion of the lug. However, flow lines in the upper fracture were convoluted and tightly twisted. A laboratory-induced fracture of the brace revealed an irregular boundary with ductile overstress features interspersed along the edge of the crack. Low magnification revealed a smooth, undulating surface. High magnification revealed a fine granular texture. Energy dispersive x-ray spectra revealed an increased oxygen level on the crack surface.
On March 29, 2006, at 1042 eastern standard time, a Piper PA-44-180, N938ER, registered to Wells Fargo Bank Northwest and operated by Embry-Riddle Aeronautical University, was substantially damaged when the nose landing gear collapsed and the airplane went off the side of the runway during landing roll at Daytona Beach International Airport, Daytona Beach, Florida. Visual meteorological conditions prevailed at the time of the accident, and no flight plan had been filed for the local instructional flight was being conducted under the provisions of Title 14 Code of Federal Regulations (CFR) Part 91. The commercial-certificated flight instructor and commercial-certificated dual student were not injured. The flight originated approximately 0855 from Daytona Beach. The flight instructor and pilot trainee stated that while they were on final approach to runway 25 for a full-stop landing, they both confirmed the landing gear was down and locked by noting three green annunciator lights and looking at the engine nacelle mirrors to verify that the nose landing gear was down and locked. The airplane touched down on the main landing gear, followed by the nose landing gear. The airplane then veered sharply to the left. Both pilots applied right rudder and brake to correct the veer but to no avail. The airplane departed the runway and collided with a runway distance remaining sign, damaging the right wing, and came to rest on grass median. A flight instructor-witness, waiting to cross the runway, observed the aircraft's approach and landing. He stated (in part): "As the aircraft descended near the runway, almost into ground effect, it appeared to point directly at us. Something just wasn't right with the approach. The aircraft appeared to touch down pointed left of centerline." Post-accident examination revealed the nose landing gear had collapsed. The upper drag brace, part number 67146-004, that connects the nose gear to the fuselage was fractured, and the pivot lug, that connects the upper brace to the lower brace, was fractured in two places. These parts were sent to NTSB's Materials Laboratory for analysis. According to the laboratory's factual report, the lower fracture in the pivot lug "was matte gray in appearance with a rough surface texture consistent with an overstress separation [with] bulk yielding and deformation." The upper fracture in the pivot lug "had a dull metallic sheen with…a smooth, multi-planar texture. Small regions of matte gray overstress fracture were uncovered [along] the edges of the fracture...accompanied by local yielding [but] no plastic deformation." At low scanning electron microscope (SEM) magnification of the shiny portions of the fracture "displayed a finely textured granular surface consistent with an oxidized surface...in contrast to the sharp well-defined overstress features from the lower fracture." No progressive cracking was seen. At least 13 internal horizontal and parallel cracks were uncovered near the vertical centerline of the brace. The cracks followed "the grain flow lines resulting from forging." The microstructure was relatively uniform throughout the metallurgical section with no changes in structure near the centerline cracks. Flow lines were longitudinal in the arm portion of the brace with a smooth, gently curving transition into the thicker portion of the lug. However, flow lines in the upper fracture were convoluted and tightly twisted. A laboratory-induced fracture of the brace revealed an irregular boundary. Ductile overstress features were interspersed along the edge of the crack. Low magnification revealed a smooth, undulating surface. High magnification revealed a fine granular texture. Energy dispersive x-ray spectra revealed an increased oxygen level on the crack surface.
Failure of the nose landing gear upper drag brace assembly due to overload acting on an undetected forging defect formed during the initial forging of the brace. A contributing factor in this accident was the runway distance remaining sign.
Source: NTSB Aviation Accident Database
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