Cessna 170B N2766D accident near Harvard, Illinois

Probable cause

The failure of the universal joint in the pilot-side flight control yoke due to the fatigue fracture of a rivet within the universal joint. Contributing to the universal joint failure was the universal joint design, which was prone to galling wear and seizure.

NTSB analysis

The private pilot was conducting a personal flight. He reported that he experienced a "complete loss of flight controls" during the landing flare. The main landing gear settled to the runway; during the landing roll, the pilot was able to reach the copilot-side control yoke and completed the landing, but the airplane received substantial damage.

A postaccident examination of the airplane revealed that the rivet in the universal joint for the pilot-side control yoke had failed, causing the universal joint to disassemble. The examination of the universal joint also revealed that the assembly seized and would not articulate as designed. The assembly seized due to galling wear between the center pin and the yoke ear holes and between the swivel blocks and the yoke ears, resulting in high alternating stresses in the rivet that held the half pins in place. The high alternative stresses in the rivet caused the rivet to fail by low-cycle reversed-bending fatigue fracture. The universal joint design was prone to galling wear and seizure.

Maintenance records indicated the universal joint had been replaced 1.5 years before the accident and had acquired 199.1 hours of flight time since being installed. The component had been maintained in accordance with the requirements prescribed in the airframe manufacturer's service manual. No evidence suggested that the failure was related to improper maintenance or lubrication.

Text from the NTSB. Open the NTSB docket for CEN18LA044 for the full record.