Incident Overview
During a personal flight, the airplane landed and veered right, bouncing 3 to 4 feet. The pilot-in-command allowed airspeed to decrease and heard the stall warning. The airplane then touched down hard, and the nose undercarriage leg failed near the 2-inch bend radius.
NTSB Examination
National Transportation Safety Board examination of the nose undercarriage leg determined that the failure was due to overstress separation. Transverse parallel crack-like features were observed on the forward surface below the fracture. These features were identified as local transverse regions of oxidation, many containing a transverse crack. A meandering crack network was present on the aft side adjacent to the fracture, intersecting the fracture at several locations, with oxidation accompanying the cracks.
A polished cross-section intersecting the cracks revealed at least eight cracks on the forward surface and one on the aft surface. Heavy oxidation of the crack surfaces and adjacent material indicated high-temperature exposure after crack formation. Hardness testing at several locations was within limits, and no fatigue cracks were found.
Root Cause
The cracks in the nose undercarriage leg were caused by improper forming of the bend by the vendor. Additionally, the airplane manufacturer did not specify forming procedures for the vendor to follow, nor did they perform sample testing. The vendor was responsible for sample testing.
Prior Occurrence
A failure of a nose undercarriage leg owned by the airplane manufacturer occurred 15 days before the incident. Testing of that failed leg revealed similar cracks to the ones in the incident case.
Manufacturing Process
Investigation of the manufacturing process showed that the 2-inch bend radius was torch heated and then manually bent. The torch heating caused the cracking observed.
Corrective Actions
As a result of the two failures, the airplane manufacturer changed vendors, modified the nose undercarriage leg drawing, wrote a specific technical document for future vendors regarding forming procedures, prepared Service Information Letter SIL-07-006, and inspected the nose undercarriage legs of 60 aircraft. Among those, 29 were found to be defective with cracks similar to those in the nose undercarriage leg of N550XL.