Harvard, IL, USA
N2766D
CESSNA 170B
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.
On November 8, 2017, about 1630 central standard time, a Cessna 170B airplane, N2766D, experienced a flight control failure while landing at Dacy Airport (0C0), Harvard, Illinois. The private pilot was not injured. The personal flight was conducted under the provisions of 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed and no Federal Aviation Administration (FAA) flight plan had been filed for the flight. The flight departed Poplar Grove Airport (C77), Poplar Grove, Illinois, about 1615 and was en route to 0C0. According to the pilot, during the landing flare to runway 27 (3,589 ft. by 105 ft., turf), about 6 to 12 inches above the runway, he experienced a "complete loss of flight controls," and the nose of the airplane dropped. The main landing gear settled to the runway; during the landing roll the pilot was able to reach the copilot control yoke and completed the landing roll without further incident. An examination of the airplane revealed that the rivet in the universal joint (u-joint) for the pilot-side control tee (flight control yoke) had failed. The u-joint assembly was sent to the National Transportation Safety Board Materials Laboratory in Washington, D.C., for further examination and testing. As received, the swivel block on half of the u-joint could be rotated. However, hand-applied torque of the close-fitting gage pin installed in the cross-drilled hole in the center pin revealed that the center pin could not be rotated about its main axis. Galling and material transfer wear scars were observed on the mating surfaces of the swivel block. The center pin exhibited wear scars and accumulated particulate debris consistent with adhesive wear. The outside diameter of the half pins exhibited material loss and wear debris deposits. The ends of the half pins that contacted the center pin exhibited adhesive wear. The rivet shank fractured due to fatigue crack propagation consistent with reversed bending. The vertical and horizontal yoke ears exhibited galling and adhesive wear signatures. Similar wear signatures were observed on the mating portions of the center pin. No lubricant was visible during the examination. According to engineering data provided by McFarlane Aviation and confirmed during the examination, the block was manufactured out of 17-4PH stainless steel alloy. The rivet was manufactured from 300-series stainless steel with a nominal diameter of 3/32. According to the airplane maintenance records, the universal joint had been replaced with a McFarlane Aviation, Inc. universal joint (part number MC6183) on April 1, 2016. The airplane had accumulated 119.1 hours of flight time between the time of replacement and the failure. Additionally, the airplane was sold in October of 2017 and the new owners had flown the airplane approximately 6 hours prior to the failure. The new owners did not detect any change in the control characteristics during that time. According to the Cessna Service Manual, the joint should be inspected at every annual/100-hour inspection, for "…security, binding, cracks, looseness, and restricted travel…" The lubrication requirements according to the Cessna 170B owner's manual are as required or every 1,000 hours. McFarlane Aviation, Inc., reported 500 u-joints were manufactured in a batch that could potentially experience this seizure and subsequent failure. On December 11, 2017, McFarlane Aviation, Inc., issued Service Bulletin SB-9, Revision A. This service bulletin called for the "mandatory and immediate" inspection of the u-joint, and replacement within 100 flight hours (or 1 calendar year) after the initial inspection, if the u-joint passed the initial inspection requirements. Immediate replacement was required for u-joints that did not pass the inspection. The SB-9 also recommended the use of a rubber boot or sleeve to prevent debris from entering the joint and to maintain the level of lubrication. The rubber boot or sleeve was not a part of the original design from Cessna for this year, make, or model, and was not required to be installed.
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.
Source: NTSB Aviation Accident Database
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