Piper PA-28-181 N3060B accident near Winston Salem, North Carolina

Probable cause

Fatigue failure of the right main landing gear attach bolts due to an unreported hard landing at an unknown time, and subsequent collapse of the landing gear.

NTSB analysis

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.

Text from the NTSB. Open the NTSB docket for ERA13LA197 for the full record.