NTSB Identification: CHI01IA016.
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Incident occurred Tuesday, October 17, 2000 in WOOD DALE, IL
Probable Cause Approval Date: 09/10/2002
Aircraft: Boeing B-727-61, registration: N530KF
Injuries: 108 Uninjured.

NTSB investigators used data provided by various sources and may have traveled in support of this investigation to prepare this aircraft incident report.

A U. S. Marshals Service employee, who was seated on the left side, middle section of the airplane's passenger cabin, said, "I was observing the ground area looking down and aft across the wing. The wing flaps were partially deployed when I observed a large piece of the flap area to rise and leave the a/c and disappear. The flaps continued down and I could not see the particular area the piece left from, from my position any longer." On landing, it was discovered that a 6-foot long, 16-inch wide outboard section of the aft segment of the left inboard, segmented fowler flap was missing. The segment was located at a residence 2 miles west of the airport. An examination of the flap segment revealed that the anodized layer was incomplete on the segment spar and a required oxide layer was not present. The area showed corrosion and the degrading of the bond resulting in separation between the honeycomb and the aft side of the segment spar. The flap segment had been in service since its overhaul in October 1993 and had approximately 5,000 hours. Overhaul facility instructions did not specify a maximum area of the flap segment's honeycomb core that could be debonded during the overhaul. Manufacturer's repair manuals did specify a maximum size for repair of the honeycomb core in the inboard and outboard trailing edge fore flap, but none of the figures in the manual that was in effect at the time of the overhaul covered repair to the honeycomb core for the aft flap segment. A current version of the manufacturer's repair manuals specifies the maximum size for the repair of the trailing edge aft flap segment that includes the honeycomb core.

The National Transportation Safety Board determines the probable cause(s) of this incident to be:

Inadequate overhaul of the flap segment that allowed for corrosion and debonding that resulted in the flap segment departing the airplane during the approach. Factors relating to this incident were insufficient information provided to the overhaul facility by the airplane manufacturer.

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