Witness Account
A U.S. Marshals Service employee seated on the left side of the passenger cabin observed the wing flaps partially deployed. The employee reported seeing a large piece of the flap area rise, detach from the aircraft, and disappear. The flaps continued to deploy, and the witness could no longer see the area where the piece had separated.
Discovery of Missing Segment
After landing, inspection revealed that a 6-foot-long, 16-inch-wide outboard section of the aft segment of the left inboard segmented fowler flap was missing. The missing segment was subsequently located at a residence approximately 2 miles west of the airport.
Examination Findings
Examination of the recovered flap segment showed that the anodized layer on the segment spar was incomplete, and a required oxide layer was absent. The area exhibited corrosion and degradation of the bond, resulting in separation between the honeycomb core and the aft side of the segment spar. The flap segment had been in service since its overhaul in October 1993 and had accumulated approximately 5,000 flight hours.
Maintenance Manual Guidance
Instructions from the overhaul facility did not specify a maximum area of honeycomb core that could be debonded during overhaul. Manufacturer's repair manuals at the time of the overhaul specified a maximum size for repair of the honeycomb core in the inboard and outboard trailing edge fore flap, but none of the figures covered repair to the honeycomb core for the aft flap segment. A current version of the manufacturer's repair manuals now specifies the maximum size for repair of the trailing edge aft flap segment, including the honeycomb core.