Accident Sequence
The airplane was on final approach to land at Hilton Head Airport when, according to witnesses, it suddenly rolled to the right and descended. It initially impacted trees at about the 70-foot level, then struck the ground. A fire ensued upon ground impact, and the debris field spanned approximately 370 feet along an azimuth of about 082 degrees.
Examination Findings
Examination of the wreckage revealed that the left wing flap actuator and jack nut measurements were consistent with the wing flaps being extended to 40 degrees. In contrast, the right wing flap jack nut and actuator measurements were consistent with the right flap being extended to about 20 degrees. Additionally, the right flap torque tube assembly between the flap motor and the flap stop assembly had disconnected. The female coupler of the flap torque tube assembly, which attaches to the male spline end of the flap motor and flap stop assembly, was found with a cotter pin installed through the female coupler of the flap stop assembly. However, the cotter pin had not been placed through the spline and the coupler consistent with normal installation as per Mitsubishi's maintenance manual or as specified in Airworthiness Directive 88-23-01. Instead, the cotter pin had missed the male spline on the flap motor. Furthermore, the flap coupler on the opposite side of the flap motor was also found without a cotter pin installed.
Maintenance Records
Company maintenance records showed that on April 3, 2001, about 87 flight hours before the accident, the airplane was inspected per Airworthiness Directive (AD) 88-23-01, which required the disassembly, inspection, and reassembly of the flap torque tube joints. On July 9, 2001, the airplane was given a phase 1 inspection, and Bankair records showed that a company authorized maintenance person performed the applicable maintenance items and certified the airplane for return to service.
Probable Cause
The official probable cause was improper maintenance/installation and inadequate inspection of the airplane's flap torque tube joints during routine maintenance by company maintenance personnel, which resulted in the right flap torque tube assembly coupler becoming detached and the flaps developing asymmetrical lift when extended, which resulted in an uncontrolled roll, a descent, and an impact with a tree during approach to land.