BOEING 747 near Atlanta, GA — 2013-05-19

Probable cause

Failure of the right inboard foreflap outboard fitting due to fatigue and bearing anomalies on the sequence carriages which resulted in the partial separation of the right inboard foreflap. Contributing to the incident was the failure of maintenance personnel to detect the fatigue cracking and bearing anomalies during dedicated inspections.

Contributing factors

Contributing to the incident was the failure of maintenance personnel to detect the fatigue cracking and bearing anomalies during dedicated inspections.

NTSB narrative

The airplane experienced a partial separation of the right inboard foreflap during approach to the airport after the crew selected flaps 30. The crew performed a go-around and landed uneventfully. Examination of the outboard fitting that attaches the right inboard foreflap to the sequence carriage revealed a fracture in the lug. A portion of the fracture had a slow growth region consistent with fatigue that caused the lug to fail under normal flight conditions. The failure of the lug resulted in a skewed condition of the right inboard foreflap and subsequent partial separation of the foreflap. Examination of the sequence carriages for both the right and left inboard foreflaps revealed several discrepancies with the bearings including incompatible parts, flat spots, play, binding, and roughness of operation. Due to several other prior events, the manufacturer previously recommended specific maintenance tasks on the foreflaps and the FAA issued an airworthiness directive for mandatory inspections. A review of the airplane's maintenance records revealed that the foreflap components had been inspected or lubricated three times in the preceding six months, the most recent occurring two weeks prior to the incident. The records showed that the airplane was in compliance with all required and recommended maintenance practices for the flaps. However, maintenance personnel failed to notice the fatigue cracking in the lug and the anomalies with the bearings on the sequence carriages during the dedicated foreflap maintenance tasks.

Analysis

Primary failure mode

Mechanical failure

First missed decision gate

Inspection of the foreflap mechanisms prior to the flight could have prevented the failure.

NTSB coding

• Aircraft structural failure · Approach
• Maintenance

Evidence available

• CVR
• 10 docket documents

Docket documents10

• CVR Event Timeline provided by ASCcvr
• Evidence Control Formsform
• Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1form
• Release of Aircraft Wreckage, NTSB Form 6120.15form
• Statement of Party Representatives to NTSB Investigationinterview
• Airworthiness Attachment 2 – Maintenance Recordsother
• Airworthiness Attachment 1 – Boeing Reportsreport
• Airworthiness Group Chairman’s Factual Reportreport
• Airworthiness Group Chairman’s Factual Report – Appendix A - Figuresreport
• CAA Taiwan Summary Reportreport

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