Rockwell 690B N9KG accident near Baker City, Oregon

Probable cause

The landing gear collapse during the landing roll due to the fracture of the inboard hydraulic cylinder clevis pin housing boss for undetermined reasons.

NTSB analysis

The airplane sustained substantial damage following a right main landing gear collapse on its first landing after a 150-hour maintenance inspection. The collapse was due to a fracture and separation of the right main landing gear's housing boss from the inboard hydraulic cylinder clevis. The 150-hour inspection included the installation of a new clevis on the right main landing gear's inboard hydraulic actuator. A postaccident examination by a Federal Aviation Administration inspector revealed that the inboard hydraulic rod bearing attach bolt was screwed all the way in, which was contrary to instructions specified in the maintenance manual. While the manual states that the attach bolt should be backed off three complete turns in order to maintain proper rigging, the manufacturer reported that improper preload adjustment of the right main landing gear actuator cylinder could not create a large enough force to induce the failure of the right main landing gear outer body boss and clevis fitting. A metallurgical examination of the inboard hydraulic cylinder clevis and associated clevis pin housing boss showed that the housing boss had fractured from the main body of the strut and that the fracture was consistent with overstress. There was no evidence of wear or fatigue cracking on either the clevis or the housing boss. The postaccident examination of the airplane, the landing gear system, and its associated components failed to reveal the initiating event that subsequently resulted in the overstress failure and landing gear collapse.

Text from the NTSB. Open the NTSB docket for SEA08LA157 for the full record.