FTW94IA321

The right hand inboard flap vane departed the airframe when the airplane was 500 feet above the ground on final approach to the runway. The vane to track support, aft adjustment eccentric, and the spring cartridge stop assembly separated due to tensile overload; however, the tensile properties did not appear to influence the failure of the vane. The support track, the roller support bolt, and the flap support bushing separated due to shear overload. Testing failed to determine the cause for the failure.

On September 28, 1994, at 2050 Alaska standard time, a McDonnell Douglas MD-11-F, N603FE, received minor damage during approach near Anchorage, Alaska. The crew of two were not injured. Visual meteorological conditions prevailed for Federal Express Flight 81, scheduled Title 14 CFR Part 121 cargo flight to Anchorage, Alaska.

Company personnel and Federal Aviation Administration inspectors reported that the right hand inboard wing flap vane departed the airframe when the airplane was 500 feet above the ground on final approach. The airplane landed without further incident and taxied to the gate.

The Federal Aviation Administration (FAA) inspector and the airplane manufacturer examined the components and found the right inboard flap vane components: #2 vane to track support (P/N ARC7481-1), aft adjustment eccentric (P/N 2941-503), and the spring cartridge stop assembly (P/N ARC2948- 2), separated due to tensile overload. The tensile properties "did not appear to influence the failure of the vane" (enclosed report). The support track (P/N ARC2700-501), the roller support bolt (P/N ARC3154-1), and the flap support bushing (P/N ARC7495-1) separated due to shear overload.

During flight testing the flap system was instrumented using strain gauges. During the testing the manufacturer isolated vibratory loads that were being imparted in a lateral motion on the failed part. They reported that no fatigue was evidenced in the failed parts. Additional testing concluded that part of the assembly (part numbers ARC7481-1 and ARC2941-503) were not manufactured in accordance with the current engineering drawings.

A review of these components by the manufacturer's Material Review Board subsequently declared them within the safety requirements. It was also determined that these components, although non-conforming, did not contribute to the failure of the system.