Incident Description
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. The flightcrew performed a flyby of the tower to allow controllers to assess the damage, then landed the airplane without further incident.
Investigation Findings
Examination revealed that the flap separation resulted from fatigue cracking of the four aft bolts that fastened the flap to the inboard flap carriage support beam. The relief shoulders on three of the bolts exhibited thread contact marks, indicating that the attachment nuts were inserted fully down to the relief shoulders. This condition suggested that either the bolt grip lengths were longer than necessary for the installation or insufficient shims were installed under the heads of the bolts or attachment nuts. Consequently, the bolts most likely did not receive sufficient preload in tension, as the nuts probably bottomed onto the relief shoulders before preload could be produced.
Maintenance History
Maintenance records showed that the flap had not been removed from the wing since the airplane's manufacture in 1982 and had accumulated 45,577 flight hours and 22,155 flight cycles.