Cessna 340A N346MC accident near Bakersfield, California

Probable cause

Maintenance personnel’s repeated failure to re-rig the main landing gear (MLG) in accordance with the airplane manufacturer's service manual requirements, which resulted in the collapse of the right MLG.

NTSB analysis

The airline transport pilot was conducting a personal cross-country flight. The pilot reported that he configured the airplane to land at his destination airport. However, during his instrument panel scan, he observed a warning light indicating that the right main landing gear (MLG) was not locked in the extended position. He then departed the traffic pattern and attempted to troubleshoot the indication by cycling the landing gear without success. He subsequently returned to the airport and used the hand crank to manually deploy the gear but continued to receive the "gear unlocked" indication. The airplane touched down normally, but as the pilot attempted a right turn to exit the runway, the right MLG collapsed, which resulted in substantial damage to the right aileron.

Postaccident examination of the landing gear revealed that the right MLG aft drive tube, which supplies overcenter tension to the aft bellcrank and side brace lock link when the MLG is in the extended position, failed in tensile overload. According to an airplane manufacturer representative, low overcenter tension, which is typically a result of improper rigging, will cause the MLG to collapse when it is under load in the extended position. If the MLG collapses while it is in the extended positon, the aft drive tube will fracture in tensile overload.

According to the airplane service manual, the landing gear must be re-rigged following any adjustment to the gear down-lock tension; however, a representative of the pilot's maintenance provider reported that maintenance personnel had not complied with this service manual requirement after adjusting the MLG down-lock tension in 2011, 2012, and 2013. Therefore, it is likely that maintenance personnel's failure to re-rig the MLG in accordance with the manual requirements led to its being improperly rigged and to the subsequent collapse of the right MLG.

Text from the NTSB. Open the NTSB docket for WPR16LA058 for the full record.