Aircraft Accident/Incident Report

Yuba City, California 95993
Saturday, November 4, 2006 11:39 PST

Recorded radar data showed that the airplane was at 2,600 feet mean sea level cruising on course. It entered a gradual climb to 2,800 feet, leveled off, and then entered a 2,000-foot-per-minute rate of descent, which was followed by a profusion of primary radar targets around the secondary target. The wreckage was found within 1/2 mile of the last radar return with signatures consistent with an in-flight breakup. Several witnesses were found and none saw any adverse weather conditions in the area. One witness said the airplane had been in straight and level flight just prior to the breakup. The airframe was examined by Safety Board engineering and metallurgical specialists. Other than some assembly anomalies unrelated to the breakup, no evidence of any assembly contrary to design plans or material deficiency was found that related to the integrity of wings, stabilizer, or flight control surfaces. No evidence of fatigue, corrosion, or previous damage was found. The separation of the wings and horizontal stabilizer was in a downward direction. All observed fracture surfaces were overload, and no oscillatory loading of the control surfaces was apparent. Analysis of the radar data revealed that the climb and descent that occurred before the breakup did not require aggressive control inputs. The pitch angle would have changed about 0.4 degrees per second during the climb, and would have decreased about 0.75 degrees per second in the descent, with generated load factors ranging between 1.04 G and 0.88 G. A radar return is only received once every 4.5 seconds and contains uncertainties in both altitude and position measurements. Consequently, the radar may not have detected an abrupt control input that would overload the aircraft structure before the airplane position and altitude changed significantly. While there is no evidence of an abrupt control input or aggressive maneuvering in the available radar data, because of the limitations in the data, the possibility of an abrupt control input cannot be excluded. This airplane is very responsive in pitch control. One of the handling quality characteristics designed by the airplane's manufacturer is that movement of the control stick produces large and rapid changes in pitch attitude.

In-flight structural failure of the horizontal stabilizer and wings for undetermined reasons.