Ormond Beach, FL, USA
N550XL
Liberty Aerospace, Inc. XL-2
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.
On February 21, 2007, about 1057 eastern standard time, a Liberty Aerospace, Inc., XL-2, N550XL, registered to Laft Asset Management, Inc., operated by Ormond Beach Aviation, Inc., experienced failure of the nose undercarriage leg during landing at Ormond Beach Municipal Airport (OMN), Ormond Beach, Florida. Visual meteorological conditions prevailed at the time and no flight plan was filed for the 14 Code of Federal Regulations (CFR) Part 91 personal local flight that departed at 0950. The airplane sustained minor damage and the certificated private pilot and the passenger were not injured. The pilot stated that he established contact with OMN air traffic control tower, and was cleared to join the downwind leg for runway 26. He reduced speed to 80 knots, extended 20 degrees of flaps, and turned onto base leg were the flight was cleared to land. He extended full flaps, and maintained 70 knots approach speed. The initial touchdown speed was 55 knots, and he may have heard the stall warning annunciation, but could not be sure of this. Upon touchdown just beyond the threshold, the aircraft veered to the right and became airborne approximately 3 to 4 feet. He allowed the airspeed to bleed off and reported hearing the stall warning annunciation during this time. He stated he tried to flare for the next touchdown, which was reported to be "heavy" and "... a harder than usual." The airplane settled, "... flat and hard on the nose." He felt a "thud" at this time and applied braking. The airplane did not porpoise after the second touchdown, and the nose did not immediately settle. The propeller contacted the runway later during the landing roll, and he applied differential braking in an effort to maintain runway alignment. The passenger (student pilot) verbally reported to a Federal Aviation Administration (FAA) inspector that he estimated the airspeed on final approach was between 70 and 80 knots, and both lights of the precision approach path indicator (PAPI) were white, then changed to red over white. The pilot was "in complete control," and the winds were a little gusty. He did not hear the stall warning annunciation, nor did he think the pilot forced the aircraft onto the runway. The first touchdown resulted in the airplane veering to the right. He recalled the airplane bounced two times, but in his opinion the first bounce left the pilot with insufficient time and speed to react. On the second touchdown, there was noticeably more "noise" and he thinks the third touchdown is when the nose wheel failed and propeller to runway contact occurred. The airplane slid approximately 400 yards; and the pilot maintained directional control while sliding. A surface weather observation report, taken at OMN at 1050, or approximately 7 minutes before the accident, indicates the wind was from 210 degrees at 10 knots with gusts to 15 knots. Examination of the airplane by the FAA inspector revealed the nose undercarriage leg was fractured. The airplane total time was approximately 65.9 hours since manufacture. The nose undercarriage leg P/N 135A-40-511, S/N NL A03680, was manufactured on September 10, 2006, in accordance with revision M of the engineering drawing dated June 22, 2006. The nose undercarriage leg was retained by the National Transportation Safety Board for further examination. Examination of the nose undercarriage leg was performed by the Safety Board Materials Laboratory located in Washington, D.C. The result of the examination revealed it was transversely fractured in the 2.0 inch radius bend, just above the axle area for the caster assembly. The upper fracture face was obliterated due to runway contact, while the lower fracture face was in generally good condition. Scanning electron microscope (SEM) inspection at high magnifications of the lower fracture surface revealed ductile dimples throughout the fracture surface consistent with ductile 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. A representative of the airplane manufacturer reported that the vendor is responsible for testing, and sample testing of the nose undercarriage leg prior to painting. They do not perform any testing or sample testing after the nose undercarriage legs are received. A representative of the airplane manufacturer also reported that 15 days before the incident date, a failure of the nose undercarriage leg occurred on an airplane (N554XL) that the manufacturer owned. The Safety Board classified the damage as minor for that incident and did not investigate. As a result of the occurrence 15 days earlier, the airplane manufacturer submitted the failed nose undercarriage leg from that airplane to two separate facilities for examination. In addition, the manufacturer began discussions with the nose undercarriage leg vendor. It was determined that the lower bend was manually formed by torch heating the bend area. The airplane manufacturer reported that the nose undercarriage leg drawing did not specify the forming procedure; however, the vendor represented expertise in metal work which met aerospace industry standards. As a result of the findings of the occurrence 15 days earlier and the Safety Board incident investigation results, 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 improper manufacturing of the nose undercarriage leg by the vendor, and the inadequate surveillance of the vendor by the airplane manufacturer.
Source: NTSB Aviation Accident Database
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