NTSB Identification: FTW97IA144.
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Scheduled 14 CFR DELTA AIR LINES, INC.
Incident occurred Thursday, March 27, 1997 in DFW AIRPORT, TX
Probable Cause Approval Date: 11/10/1998
Aircraft: Boeing 767-232, registration: N105DA
Injuries: 198 Uninjured.
NTSB investigators used data provided by various sources and may not have traveled in support of this investigation to prepare this aircraft incident report.
During the landing approach, with the flaps extended to 15 degrees and the spoilers deployed, an 18-foot section of the right outboard flap separated from the trailing edge of the right wing. After making a flyby of the tower to allow controllers to view the extent of the damage, the flightcrew landed the airplane without further incident. The flap separation resulted from fatigue cracking of the four aft bolts fastening the flap to the inboard flap carriage support beam. The relief shoulders on three of the bolts exhibited thread contact marks which indicated that the attachment nuts were inserted all the way down to the relief shoulders. Either the bolt grip lengths were longer than necessary for this installation, or not enough shims were installed under the heads of the bolts or attachment nuts. Under these circumstances, the bolts most likely did not receive sufficient preload in tension, since the nuts probably bottomed onto the relief shoulders before the preload could be produced. Maintenance records indicated that the flap had not been removed from the wing since manufacture of the airplane in 1982 and had accumulated 45,577 flight hours and 22,155 flight cycles.
The National Transportation Safety Board determines the probable cause(s) of this incident to be: The manufacturer's improper installation of the flap, which resulted in fatigue cracking of the flap attach bolts and separation of the flap. Full narrative available
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