Investigation brief · generated 2026-10-09 · source: NTSB public docket and accident database
BOEING 737 — Chicago, IL, USA, 2008-10-01
NTSB number
ENG08IA042
Operator
Southwest Airlines, Co.
Registration
N551WN
Highest injury
No injury
Regulation
Part 121
Damage
Minor
Cohort
Part 121 airline
Recorder data
Tier 1 — decoded recorder tables
Every sentence below is taken directly from NTSB records — the accident database, the docket's recorder reports and the Board's findings — with its source noted. Nothing is paraphrased or inferred.
NTSB summary
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.
The right nose landing gear axle's failure from intergranular and fatigue cracking due to an earlier bearing failure.
Verbatim, NTSB determination.
Flight data recorder
— 95,020 samples, 16 parameters, 00:00:00.0 to 26:23:39.0.
Parameter
Max
at
Min
at
Final
at
Pressure altitude ft
41,053.0
06:32:51.0
-179.0
02:16:41.0
604.0
26:23:39.0
Computed airspeed kts
324.2
16:32:46.0
45.0
00:17:58.0
45.0
26:23:39.0
Vertical acceleration g
1.3
03:57:46.0
0.7
00:36:10.0
1.0
26:23:39.0
Computed from the docket's tabular attachment; times as recorded (local or SRN as published).
Sequence of events (FDR factual report)
Time
Event
Page
1055 CDT
Southwest Airlines Boeing 737-700, registration N551WN, experienced a separation of the right nose landing wheel assembly as it exited runway 31C after landing at the Midway Airport, Chicago, Illinois.
1
N/A
The right nose landing wheel assembly separation event was recorded after the last recorded landing.
2
Extracted by claude-sonnet-5; 2 of 2 stated events verified against the raw recorder data.