Cessna and Reims Aviation 172, 180 and 185 series aircraft with S/N listed in Cessna Service Bulletin (SB) No. SEB01-3.
This Continuing Airworthiness Notice (CAN) alerts operators of the possibility of control yoke assembly failure due to internal corrosion. This failure could result in loss of elevator control and loss of aileron control if the control yoke assembly fails above the pivot point. The Cessna Aircraft Company has issued SB No. SEB01-3 with a corrosion inspection instruction to establish whether the yoke assembly is serviceable.
This CAN is prompted by a report of a control yoke assembly failure on a Cessna 172M manufactured in 1974 due to corrosion. The failure occurred under normal pilot loads while taxing. The corroded yoke failed below the pivot point at the lower elevator control lug. The design of the yoke leaves a closed tube section below the pivot point in which moisture can collect. In certain circumstances this moisture could lead to corrosion and failure of the control yoke assembly which could result in loss of primary pitch control. Furthermore, failure of the yoke above the pivot point could result in loss of aileron control. The control yoke assembly has been redesigned in production to eliminate the potential for moisture collection.
As a result of defect reports received by the manufacturer and the FAA, Cessna have issued SB No. SEB01-3 which requires an in situ ultrasonic inspection of the lower section of the yoke assembly. The yoke assembly should be replaced if the tube wall thickness is less than 0.037 inches. The SB contains a detailed list of affected aircraft, instructions for performing corrosion treatment and recommends an annual external visual inspection of the yoke assembly.
The CAA strongly recommends that aircraft operators/maintainers accomplishment the instructions in SB No. SEB01-3. The control yoke should be treated with corrosion preventative at the earliest opportunity. AD action is not considered necessary at this time. However, we highly recommend compliance with the instructions specified in SB SEB01-3.
Report all findings to the CAA by completing a defect report form CAA005D. Describe the findings in as much detail as possible and retain the defective part for further investigation.
