NTSB Identification: MIA07IA052.
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Incident occurred Wednesday, February 21, 2007 in Ormond Beach, FL
Probable Cause Approval Date: 06/30/2008
Aircraft: Liberty Aerospace, Inc. XL-2, registration: N550XL
Injuries: 2 Uninjured.
NTSB investigators used data provided by various sources and may not have traveled in support of this investigation to prepare this aircraft incident report.
While landing during a personal flight, the airplane touched down, veered right, and bounced 3 to 4 feet. The pilot-in-command allowed the airspeed to bleed off, and heard the stall warning. The airplane landed hard, and the nose undercarriage leg failed near the 2 inch bend radius. National Transportation Safety Board examination of the nose undercarriage leg revealed overstress separation. Transverse parallel crack-like features were noted on the forward surface of the leg below the fracture. The crack-like features were established to be local transverse regions of oxidation, many of which also contained a transverse crack in the surface. A meandering crack network was also noted in the aft side of the leg adjacent to the fracture. The cracks intersected the fracture at several locations, and oxidation accompanied the cracks. A polished cross-section intersecting the cracks in the forward and aft surfaces revealed at least eight cracks in the forward surface, and one crack in the aft surface. Close examination revealed heavy oxidation of the crack surfaces and adjacent material consistent with high temperature exposure after crack formation. Hardness testing in several locations of the nose undercarriage leg was within limits. No fatigue cracks were noted. The cracks of the nose undercarriage leg were caused due to improper forming of the bend by the vendor. In addition, the airplane manufacturer did not specify forming procedures for the vendor to comply with, nor did they perform any sample testing. The vendor was responsible for performing sample testing. A failure of a nose undercarriage leg owned by the airplane manufacturer occurred 15 days before the incident date. Testing of the failed nose undercarriage leg from the occurrence 15 days earlier revealed it had similar cracks as the incident case investigated by the Safety Board. Further investigation of the manufacturing process of the nose undercarriage legs by the airplane manufacturer revealed the 2-inch bend radius was torch heated then manually bent; the torch heating caused the cracking noted. As a result of the 2 failed nose undercarriage legs, the airplane manufacturer changed vendors, modified the nose undercarriage leg drawing, wrote a specific technical document for future vendors pertaining to the forming procedure, prepared Service Information Letter SIL-07-006, and inspected the nose undercarriage legs of 60 aircraft. Of the 60 aircraft inspected, the nose undercarriage legs of 29 were found to be defective with cracks similar to cracks found in the nose undercarriage leg of N550XL.
The National Transportation Safety Board determines the probable cause(s) of this incident to be: The improper manufacturing of the nose undercarriage leg by the vendor, and the inadequate surveillance of the vendor by the airplane manufacturer. Full narrative available
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