Introduction
On September 6, 2008, at about 1600 central daylight time, a Bellanca 17-30A, registration N9792E, sustained substantial damage when its nose landing gear partially collapsed during the landing roll at Upper Cumberland Regional Airport (SRB) in Sparta, Tennessee. The private pilot, the sole occupant, was not injured. The flight originated from York Airport (THV) in York, Pennsylvania, at approximately 1230 eastern daylight time under an instrument flight rules (IFR) flight plan. Visual meteorological conditions prevailed at the time of the accident.
Accident Sequence
The pilot reported that on approach to runway 4 for a full-stop landing, the wind was from 010 degrees at less than 5 knots. He did not apply any crosswind correction and landed first on the main landing gears. The airplane bounced a few feet then settled back on the main landing gears. As soon as the nose landing gear contacted the runway, the airplane jerked sharply to the left. The pilot applied full right rudder but could not correct. The airplane departed the runway, continued turning left. The pilot applied aft elevator input to clear a ditch but subsequently collided with a fence.
Aircraft and Examination Findings
The airplane was manufactured in 1976. An FAA inspector examined the aircraft and found the nose landing gear partially collapsed. Further inspection revealed the engine mount assembly (part number 191898) was fractured in two locations near the right side of the nose landing gear attach point. Sections of the engine mount were sent to the NTSB Materials Laboratory for analysis.
Laboratory examination showed that one tube (P/N 191902-8) exhibited overstress fracture near its juncture with the right hand bed rail and the front bed rail. No preexisting cracking or corrosion was visible. The second tube (vertically oriented) was separated at the upper weld bead near the right bed rail. Overstress fracture features were noted on only a thin band of the weld bead. Approximately 80 percent of the weld bead remained attached to the vertical tube while a small portion remained on the right bed rail. Magnified inspection revealed gaps, lack of weld penetration, and regions without fusion. Additionally, energy dispersive x-ray spectra (EDS) of the weld fusion zone showed no chromium, indicating an inappropriate filler rod was used.
Maintenance History
On September 21, 1977, FAA Approved Bellanca Service Letter B-96 was disseminated, informing owner/operators of reports of cracks in the nose landing gear mount. It specified that if cracks or damage were found, the mount should be repaired per Service Kit (SK1267-4019), which installed vertical oriented tubes on either side of the engine mount. Installation of the kit eliminated repetitive inspections required by FAA Airworthiness Directive (AD) 77-22-02 (November 2, 1977).
Review of maintenance records showed the engine mount was modified per SK1267-4019 on February 1, 1990, signed off by an airframe and powerplant mechanic with inspection authorization. The mount was removed and inspected in December 2003 following propeller contact. Extensive airframe work was completed on August 21, 2008, and the airplane had operated 7 hours since that work.
Conclusion
The accident occurred due to the partial collapse of the nose landing gear, resulting from fractures in the engine mount assembly. The fractures were attributed to overstress and weld deficiencies, including lack of penetration and use of inappropriate filler rod.