BOEING 737 near Los Angeles, CA — 2009-09-08

Probable cause

The failure of the right main landing gear inboard axle due to fatigue cracking as a result of fretting damage in one of the brake mounting bolt holes.

NTSB narrative

During landing, the inboard axle of the right main landing gear separated from the airplane. The crew taxied the airplane off the runway and the passengers and crew deplaned with no injuries. Examination of the axle revealed an area of fatigue cracking emanating from the brake mounting bolt hole at the 12:00 position. The fatigue crack likely initiated in an area where there was scoring and fretting damage to the Sermetal coating. In-service examination of brake mounting bolt torque indicated that over time, the brake mounting bolts may loosen allowing the bolts to spin in the holes.

Analysis

Primary failure mode

Mechanical failure

First missed decision gate

Inspection of the RMLG axle flange for fatigue prior to the incident.

NTSB coding

• Aircraft structural failure · Landing-landing roll

Evidence available

• 8 docket documents

Docket documents8

• Other Pertinent Forms and Reports - Boeing AMM 32-41-41form
• Other Pertinent Forms and Reports - SWA Brake Torque Dataform
• Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1form
• Release of Aircraft Wreckage, NTSB Form 6120.15form
• Statement of Party Representatives to NTSB Investigationinterview
• Meteorology 5 - Attachment 1other
• Reports from Parties to the Investigation - Boeing EQA Reportreport
• Reports from Parties to the Investigation - Boeing M&PT Reportreport

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