SAIB CE-17-25 issued by FAA on cracks and corrosion in elevator torque tubes on Cessna 172, 175, 180, 182, 185, 188, and 208 airplanes.
An elevator torque tube removed from a Cessna Model 172C airplane during an annual inspection for cracks, corrosion and improper repairs. The airplane had spent 24 years in Florida (a high corrosion area). During the annual inspection, a blind rivet installation (not approved) was found. The date of this blind rivet installation could not be determined.
The Cessna 100 Series Service Manual, 1962 and Prior, in Section 2, Airframe Inspection item 34 states “Elevators for security of attachment, smooth operation, security of balance weights, cracks, corrosion, and skin or structural damage.
These elevator torque tubes have been installed on Cessna 100 airplanes since the 1950s and continue to be installed on production Cessna 172 and 182 airplanes. The tubes are made of aluminum. They are exposed to wheel spray during landings or spray from floats during water landings. The tube is oriented horizontally so it tends to retain water. Exposure to moisture over many years leads to corrosion damage. Airplanes used in coastal areas are especially prone to corrosion.
The SIDs state: “Visually inspect the torque tube for corrosion and rivet security. Pay particular attention to the flange riveted onto the torque tube near the airplane centerline for corrosion.
(1) Clean area before inspecting if grime or debris is present.”
For the 180/185 and 100 airplanes built between 1953 and 1968: Initial inspection compliance is recommended at 5,000 hours or 20 years. Repeat inspection intervals are recommended at 2,000 hours or 5 years.
For the 172, 182, and 188 airplanes built after 1968: Initial inspection compliance is recommended at 10,000 hours or 20 years. Repeat inspection intervals are recommended at 3,000 hours or 5 years.
Recommendations – For Cessna 100 airplanes and Cessna 208/208B airplanes, FAA recommend adherence to the applicable SIDs and maintenance manuals for corrosion inspections. Airplanes based or operated in high corrosion areas are recommended to be inspected more frequently. Pilots should check this area for corrosion or obvious damage during preflight inspections. If minor surface corrosion is found, remove the corrosion in accordance with Textron Aviation procedures. If cracks or severe corrosion is found, replace the affected parts.