ERA13IA326

The pilot receiving instruction was recovering the airplane from a demonstrated minimum control airspeed condition. According to the flight instructor, the airplane was initially about 5,000 ft in a "clean" configuration. Both pilots then felt two "kicks" in the rudder system, which they then verbally confirmed to each other did not result from either of them making inputs. The pilot receiving instruction then heard a "snap," and the rudder pedals began to "pump" full deflection right and left. Subsequently, the flight instructor took control of the airplane and found that neither applying full rudder nor using both feet on the rudder neutralized the deflections. Even with both pilots trying to neutralize the rudders, the deflections continued. The flight instructor subsequently diverted the airplane to a nearby airport and landed it uneventfully. During the on-scene examination, the rudder trim tab control rod was found fractured near the trim tab end. The control rod was replaced, and, during subsequent flights, no further rudder anomalies occurred. Metallurgical examination of the rod revealed that it had failed in overload, and no evidence of fatigue or corrosion was found. Further examination revealed that the rudder trim control rod was composed of a low-alloy, 1000-series carbon steel. An airplane manufacturer representative indicated that the rod should have been composed of a higher grade, 4000-series steel. The airplane was manufactured in 1972, acquired by the current owner in 2005, and had 11,575 hours of operation at the time of the incident. It could not be determined when or by whom the rod was installed on the airplane; it was not installed during the airplane's current ownership.

On July 17, 2013, about 1300 eastern daylight time, a Piper PA-34-200, N767PE, operated by Phoenix East Aviation (PEA), experienced in-flight tail vibrations near Palm Coast, Florida. The airplane subsequently landed without structural damage at Flagler County Airport (XFL), Palm Coast, Florida. The flight instructor and the private pilot under multi-engine instruction were not injured. Visual meteorological conditions prevailed during the local instructional flight, which departed Daytona Beach International Airport (DAB), Daytona Beach, Florida, and was operating under the provisions of 14 Code of Federal Regulations Part 91. According to the flight instructor, the airplane was initially about 5,000 feet in a "clean" configuration with the pilot under instruction recovering from minimum control airspeed condition. There were then two "kicks" in the rudder system, which the pilots confirmed did not come from either of them. The pilot under instruction then heard a "snap", and the rudder pedals began to "pump" full deflection both right and left. The flight instructor took control of the airplane and found that neither the application of full rudder nor the use of both feet to neutralize the deflections had any effect. Even with both pilots trying to neutralize the rudders, they could not overcome the deflections. The flight instructor diverted the airplane to XFL, subsequently landing with 25-degree flaps without further incident. There was minimum rudder control during the approach, with the rudder pedals still pumping back and forth throughout the landing. Once on the ground, full rudder control was again available. On the ground, the rudder trim tab control rod was found to be fractured near the trim tab end. The control rod was replaced, and subsequent flights revealed no further rudder anomalies. Remnants of the control rod end were forwarded to the NTSB for further examination. According to the Materials Laboratory Factual Report, "the overall fracture morphology was cone-shaped, concave toward the bearing head. The thread adjacent the fracture surface exhibited some local deformation….The four thread roots adjacent the fracture surface exhibited cracking along the roots." In addition, "both halves of the fractured rod end exhibited smearing damage consistent with post-failure damage. The smearing damage on the bearing head portion was located on opposite sides of the part, evident as mirrored damage patterns positions 180° apart. Similar damage was noted on the fractured side of the threaded shaft….On the threaded shaft, most of the outer portions of the fracture surface had been obliterated." The bearing head portion of the fractured shaft was subsequently ultrasonically cleaned to remove surface oxidation (rust). The fracture surface was then inspected using a scanning electron microscope (SEM). The fracture surface was "rough and tortuous with high peaks and valleys," but "generally concave downward." The fracture morphology wasconsistent with "dimple rupture" with no other types of fractures noted. "The presence of only dimple rupture fracture morphology, the general cup-and-cone shape of the mating fracture surfaces and the secondary thread root cracks are consistent with failure from overstress. The dimple rupture shape and local deformation of the part are consistent with overstress in tension. No indications of other failure modes, such as fatigue or pre-fracture corrosion, were observed." The chemical composition of the part was inspected using energy dispersive x-ray spectroscopy (EDS) and found to be consistent with low-alloy carbon steel, a 1000-series steel. According to an air safety investigator with Piper Aircraft, the rod should have been "a 4130 gr1 type material," a 4000-series steel. According to the PEA Director of Safety, a review of aircraft logbooks confirmed that PEA had not changed the rod since acquiring the airplane, which Federal Aviation Administration records indicated occurred in 2005. The airplane was manufactured in 1972 and had a reported total time of 11,575 hours at the time of the incident.