ERA13LA197

While landing in gusty wind conditions, the fixed right main landing gear collapsed during rollout. Metallurgical examination of the right main landing gear trunion revealed extensive wear, fretting, hole elongation, and disturbed metal around the holes of the lower trunion flange. Additionally, two bolt heads were recovered from the lower flange holes and exhibited fatigue at their respective fracture surfaces. The bolt fatigue, in conjunction with the excessive wear and damage at the lower flange, was consistent with bolt looseness and wear over a period of time. According to the airplane manufacturer, similar events involved airplanes used for student pilot training, such as the accident airplane, which experienced a previous hard landing that went unreported. The damage could then propagate over time, but it was difficult to tell if the initiating hard landing occurred months or years before the actual landing gear failure. However, mechanics commonly check the bolts during annual and 100-hour inspections. Specifically, they check the condition and security by verifying the proper exposed thread count and that the cotter pins were in place. The accident airplane's most recent annual inspection was completed about 3 months before the accident and the airplane had flown about 51 hours since that inspection. The two mechanics who performed the most recent annual inspection reported that the bolts were visually inspected and attempts were made to check retention and security of the hardware with tools; however, the nuts were in an area that was difficult to access with tools. It could not be determined if the wear began before or after the most recent annual inspection.

On April 7, 2013, about 1540 eastern daylight time, a Piper PA-28-181, N3060B, operated by Piedmont Flight Training, was substantially damaged when the right main landing gear collapsed during rollout at Smith Reynolds Airport (INT), Winston Salem, North Carolina. The private pilot and flight instructor were not injured. The instructional flight was conducted under the provisions of 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed and no flight plan was filed for the flight that departed Asheville Regional Airport (AVL), Asheville, North Carolina, about 1430. The private pilot reported that after an uneventful cross-country flight, the airplane was landing on runway 22 at INT. The touchdown was normal; however, the right main landing gear collapsed during rollout and the airplane came to rest on the runway. The operator reported that during the accident landing, the airplane left approximately 850 feet of skid marks on the runway from the right main landing gear tire, with no corresponding skid marks from the left main landing gear tire. An additional 435 feet of scrape marks continued beyond the 850-foot skid marks, consistent with the collapse of the right main landing gear. Examination of the airplane by a Federal Aviation Administration (FAA) inspector revealed substantial damage to the right wing. The right main landing gear trunion was forwarded to the NTSB Materials Laboratory, Washington, DC, for further examination. The trunion attached to the wing via four bolts through an upper flange and four bolts through a lower flange. Metallurgical examination revealed extensive wear, fretting, hole elongation, and disturbed metal around the holes of the lower flange. The wear was more pronounced at the two most outboard holes of the lower flange. Additionally, two bolt heads were recovered and exhibited white paint, consistent with their preimpact location being from the lower flange. The fracture surfaces of both bolt heads exhibited fatigue. The bolt fatigue in conjunction with the excessive wear and damage at the lower flange attachment bolt holes was consistent with bolt looseness and wear over a period of time. Review of NTSB Materials Laboratory records did not reveal any similar events within the past 10 years. According to a representative from the airplane manufacturer, he had seen similar events in the past and such wear usually involved airplanes used for student pilot training. The airplanes would suffer an initiating hard landing that was not reported by the student pilot. The damage could then propagate over time, but it was difficult to tell if the initiating hard landing occurred months or years prior to the actual landing gear failure; however, it was also common practice for mechanics to check the bolts during annual and 100-hour inspections. Specifically, they usually checked for condition and security by verifying the proper exposed thread count and that the cotter pins were in place. Reviewof the make and model airplane maintenance manual for 100-hour inspections revealed, "16. Inspect gear struts and mounting bolts for condition and security." The airplane's most recent annual inspection was completed on January 11, 2013. At that time, the airplane had accrued 6,762 total hours of operation. The airplane accumulated an additional 51 hours of operation, from the time of the most recent annual inspection, until the accident. According to an FAA inspector, the operator did not employ mechanics, but rather contracted mechanics when maintenance was required. During interviews, the two mechanics that performed the most recent annual inspection stated that the bolts were visually inspected and attempts were made to check retention and security of the hardware with tools; however, the nuts were in an area that was difficult to access with tools. The recorded wind at INT, at 1554, was from 200 degrees at 10 knots, gusting to 17 knots, and varying between 150 degrees and 230 degrees.