ERA13LA410 · Cessna 188B

While spraying a cotton field, the pilot completed a pass and, at the end of the field, pulled up to turn to the right. During the climb, he applied right rudder, but the right rudder pedal assembly broke off, allowing the pedal full travel to the back of the hopper tank. The pilot was able to return to the airfield and make an uneventful landing, but during the landing roll, the airplane began to turn left, and the pilot had no way to correct since the right rudder, right brake, and right tailwheel steering were not operable. The airplane then exited the left side of the runway and entered a soybean field, causing the right main landing gear to collapse and the right wing to impact the ground and sustain substantial damage.

Postaccident examination of the rudder pedal assembly revealed the right rudder pedal arm had separated from its mounting location on the right rudder bar. Both were constructed of steel tubing. The external surfaces of the right rudder pedal arm exhibited areas with disbonded topcoat paint and exposed steel with minor surface corrosion. Internally, the right rudder pedal arm exhibited heavy rust scaling over all surfaces and rust scale that had sloughed from the surfaces had collected at the base of the right rudder pedal arm, where it attached to the right rudder bar. Although measurements of the tube wall's thickness at the top of the rudder pedal arm appeared to be full thickness, with measurements of 0.054 inch, 0.053 inch, 0.056 inch, and 0.055 inch (measured at 90 degree intervals around the circumference), measurements of the tube wall's thickness at the point of the fracture were only 0.030 inch at the thickest point and 0.013 at the thinnest point.

The airplane was equipped with a liquid dispersal system, including a hopper tank located immediately forward of the cockpit. Remnants of corrosion product had adhered to silicone plugs that were at the top of the rudder pedal arm tubing, indicating that the corrosion product was present before the application of the silicone sealant. The plugs had likely been inserted in an attempt to keep contaminants (chemicals from the hopper tank and water from cleaning) out of the rudder pedal arms.

Review of the Service Manual and Illustrated Parts Catalog revealed that the manufacturer had published inspection criteria for the airplane based on operating usage and operating environment. The criteria provided mandatory inspection intervals for components and airplane structures. The manufacturer also offered a supplemental Corrosion Prevention and Control Program to help prevent or control corrosion in the airplane's primary structure so that it did not cause a risk to continued airworthiness as the airplane aged. A supplemental inspection document also included guidance regarding corrosion inspection and corrosion control of the rudder system. Review of the maintenance records revealed no record of the modifications and no record of an inspection of the rudder system per the supplemental inspection document.

Verbatim NTSB analysis and probable cause from the NTSB dataset