CEN24LA162 · American Champion Aircraft 7ECA

The pilot and flight instructor were conducting an instructional flight during which the pilot performed upset recoveries and basic aerobatic maneuvers. During the flight and subsequent taxi, the pilot reported intermittent rudder resistance that he described as a “catch” and an audible “pop.” A post-flight inspection revealed that the lower rudder hinge had separated from the rudder post. Postaccident examination revealed that the rudder post had fractured along the weld toes that attached the middle knuckle of the lower rudder hinge to the post. Although the service manual required inspection of the rudder for damage and cracks, it is likely that the fatigue cracking was obscured by the fabric covering and was not readily apparent during routine visual inspection. Further inspection of the fracture surface revealed features consistent with fatigue cracking that initiated primarily from the exterior surface of the rudder post at the weld edge. Pits and branching microcracks near the crack origins were consistent with corrosion fatigue crack initiation and progression. Wear observed on the hinge knuckles and the vertical stabilizer hinge hardware, along with the measured offset of the upper hinge knuckle from the rudder centerline, was consistent with a misaligned hinge system that produced rubbing and binding during rudder movement. The misalignment was associated with the rudder’s previous damage history and subsequent repair activity. This binding would have increased localized stress at the lower hinge weld toes and contributed to the growth of the fatigue cracks. The rudder post had been finished with a protective coating; however, the presence of corrosion-related features at the crack origins indicated that the coating had been compromised at some time during the rudder’s life and was insufficient to prevent corrosion due to environmental exposure, which contributed to the acceleration of the fatigue cracking. As the fatigue cracks progressed, the remaining tube wall section was reduced until it could no longer sustain operational load applied during rudder movement. The pilot’s reported rudder resistance and audible “pop” were consistent with progressive binding and final separation of the lower rudder hinge from the rudder post. Although minor welding anomalies were identified, they were not located at the fatigue crack origins and did not contribute to the fatigue cracking. Hardness testing showed that the rudder post material met the required tensile strength specifications.

Verbatim NTSB analysis and probable cause from the NTSB dataset