BOEING COMPANY, LONG BEACH DIV BOEING MD-11 near Aguadilla, PR — 2013-08-31

Probable cause

an insufficiently robust flange attachment hardware design, which failed to contain engine components that were liberated during an LPT mechanical failure, resulting in engine/nacelle uncontainment. A factor in the incident was the lack of a module-level LPT inspection and the lack of an inspection requirement to detect/monitor the LPT S4 for advanced sulfidation attack.

NTSB narrative

Four LPT stage 4 (S4) vane clusters weakened by an undetected sulfidation/corrosion attack disengaged at their inner attachment. The disengaged clusters displaced aft and contacted the S4 blades during operation. The contact machined a groove into the blade leading edges near the platforms. High cycle fatigue cracks initiating in the machined area of several blades propagated to overload separation. The blade liberation led to the separation of the remaining S4 blades and extensive downstream LPT blade and vane cluster damage. A large amount of metal debris was released into the gas path, loading the engine casings. The P-flange attachment hardware separated in overload, resulting in engine uncontainment.

Analysis

Primary failure mode

Mechanical failure

First missed decision gate

Inspection of engine components prior to takeoff could have identified issues.

NTSB coding

• Uncontained engine failure · Takeoff-rejected takeoff

Evidence available

• FDR / data
• 4 docket documents

Docket documents4

• Flight Data Recorder 10 - Attachment 1fdr
• Flight Data Recorder 10 - Factual Reportfdr
• AD 2012-14-09other
• Powerplants Group Chairman's Factual Reportreport

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