Cessna 310Q N7770Q accident near St. George, Utah

Probable cause

Failure of the left main landing gear lower adjusting bolt due to overstress, which resulted in the left main landing gear collapse during landing.

NTSB analysis

The commercial pilot reported that he completed three takeoffs and landings before departing the area to practice in-flight maneuvers, after which he reentered the traffic pattern for landing. With normal landing gear indications in the cockpit, the pilot landed the airplane normally and uneventfully. During the landing roll, the left wing lowered more than normal, and the engine propellers and left wingtip impacted the runway surface; subsequently, the airplane slid to the left and exited the runway surface. The airplane sustained substantial damage to the left aileron. Postaccident examination revealed that the lower adjusting bolt on the left main landing gear was fracture separated. Both fracture surfaces exhibited fractographic features consistent with overstress fracture due to tensile and cantilever bending loads applied to the tie-rod end fitting. No indications of preexisting cracking were observed. The airplane's last annual inspection was completed on the day of the accident, during which the left and right main landing gear side brace bolts and bushings were replaced and a gear retraction test was satisfactory. According to the manufacturer, the area where the fracture occurred is where a mechanic would place a spring scale to measure the down lock force. This area is one of two main fracture locations when the down lock is improperly adjusted. The investigation could not determine if the bolt fractured as a result of overstress from the landing sequence, an improper adjustment of the bolt, or a combination of the two.

Text from the NTSB. Open the NTSB docket for WPR15LA129 for the full record.