Pilot Debrief

BOEING 737 near Chicago, IL — 2008-10-01

Final reportENG08IA042
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Date
2008-10-01
Location
Chicago, IL, USA
Airport
MDW
Aircraft
BOEING 737
Registration
N551WN
Category
Airplane
Highest injury
None
Fatalities
0
Phase of flight
Landing

Probable cause

The right nose landing gear axle's failure from intergranular and fatigue cracking due to an earlier bearing failure.

NTSB narrative

The airplane experienced separation of the right nose landing gear (NLG)wheel assembly as it exited runway after landing. Metallurgical examination revealed that the NLG axle fractured in a transverse plane, and that the failure of the axle was due to intergranular cracking that acted as stress concentrators from which fatigue cracks emanated. The fracture of the right side inboard journal on the NLG inner cylinder assembly was most likely due to the failure of a prior tapered roller bearing. Eventually the size of the fatigue crack and the forces generated during landing were sufficient to drive the crack in overstress, leading to fracture of the inboard journal. The change in ownership of the plane and the monthly swapping of bearings and wheels make it difficult to determine when the bearing failure occurred or why.

Analysis

Primary failure mode
Mechanical failure
First missed decision gate
Inspection of landing gear prior to flight could have identified potential issues.

NTSB coding

  • Landing gear collapse · Taxi-from runway

Evidence available

  • FDR / data
  • 3 docket documents
View NTSB final reportView NTSB docket

Docket documents3

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