Incident Summary
While performing a steep turn maneuver, the pilot of an airplane noticed a loss of altitude and applied increased elevator pressure to correct. Upon recovery, the control yoke began to vibrate and the rudder pedals moved rapidly back and forth. The pilot released backpressure and landed without further incident. The airplane sustained substantial damage to the left stabilator spar.
Inspection Findings
Review of the airplane's maintenance logbooks revealed that both ruddervators had recently been reskinned, painted, and balanced. An examination of the aircraft showed that the ruddervator trim tabs had been installed upside down, and the trim tab wire was threaded improperly. Additionally, the left ruddervator was found to be 19.86 inch-pounds underbalanced, exceeding the allowed underbalance range of 16.80 to 19.80 inch-pounds.
Metallurgical Examination
An on-site inspection identified a crack in the left stabilator spar. The fracture initiated at the top of the spar where it attaches to the bulkhead, migrated through the top outboard bolt hole, and progressed to the bottom outboard bolt hole. Metallurgical analysis determined that the fracture was consistent with a tension overload along the entire length of the fracture zone.