Cirrus Design Corp SR22 N101CD incident near Lakeland, Florida

Probable cause

A failure of the flap actuator rod end due to low stress, high cycle fatigue, and subsequent overstress failure.

NTSB analysis

While approaching the destination airport, the pilot attempted to extend the flaps to the 50-precent position. After moving the selector, the pilot heard a "bang" and the airplane rolled right. The pilot maintained control of the airplane, and after landing noted that the flaps were extended asymmetrically. Post-incident examination of the flap system revealed that flap actuator rod end was bent 90 degrees, and broken. No other anomalies of the flap system were found. The condition of the flap actuator rod end suggested that the rod end was bent initially while retracting the flaps, an action associated with extension of the flap actuator. This resulted in cracks forming at the thread roots along the outer bend. Subsequent attempts to extend the flaps placed the rod end under a reverse bending moment that acted to straighten the rod end. The manufacturer's assessment of the situation in a service bulletin concluded that the flaps could have been retracted beyond the full up position, possibly due to a sensor failure, initially bending the rod end. During a subsequent deployment, during the incident flight, the flaps over-deployed and allowed the flap actuator linkages to over-center. The rod end subsequently failed, and allowed the asymmetric flap condition.

Text from the NTSB. Open the NTSB docket for ERA09IA009 for the full record.