US Airways Boeing 737 3B7 incident
Boeing 737 3B7 · Incident: aircraft structural failure during pushback
Event
- NTSB case
- ENG08IA051
- Event typeAccident: someone killed or seriously injured, or the aircraft substantially damaged (NTSB definition). Incident: an occurrence that affected or could have affected safety, short of that. Glossary
- Incident
- InvestigationHow far the investigation had got when the record was published: preliminary, ongoing, final or completed. Unknown where the source does not say. Glossary
- Completed
- API-reported fatalities
- 0 · all aircraft and ground
- Ground fatalities
- 0
- OperationWhat kind of flying it was, grouped by the rules it flew under: airline (US Part 121), air taxi and commuter (Part 135), general aviation (Part 91 and similar), military or government. Glossary
- Airline
- WeatherVisual meteorological conditions (VMC): good enough to fly by looking outside. Instrument conditions (IMC): cloud or low visibility, flying by instruments. Glossary
- Not recorded
Boeing 737 3B7
- Aircraft type
- Boeing 737
- Category
- Airplane
- RegistrationThe aircraft's tail number, such as N12345 or G-ABCD. Registrations are reissued, so the same one years apart can be a different aircraft. Glossary
- N514AU
- Operator
- US Airways
- Onboard fatalities
- Unknown
- Route
- From not recordedTo not recorded
- Aircraft age
- Not recorded
- Flight rulesThe regulations the flight operated under: in the US, Part 91 (general aviation), Part 121 (airlines), Part 135 (air taxi and commuter) and others; for flights abroad, the NTSB's coarser commercial or non-commercial code. Glossary
- Part 121: Air Carrier
- Phase of flightThe stage of the flight when things started to go wrong: standing, taxi, takeoff, initial climb, en route, maneuvering, approach or landing. Glossary
- Pushback/towing · engine not operating
- Defining eventThe single coded event the NTSB judges best describes what happened (records from 2008 on). Older records name the first occurrence in the sequence instead. Glossary
- Aircraft structural failure
- DamageDestroyed: beyond practical repair. Substantial: damage that affects the structure, performance or handling and normally needs major repair. Minor: less than that. Glossary
- Minor
Cause areas
- Aircraft › Aircraft systems
Approximate · Coordinates as recorded by the NTSB; no uncertainty radius is established.
NTSB narrative
In June 2008, after the incident airplane was towed, ground personnel noted that the left hand (LH) main landing gear (MLG) was leaking shock strut fluid from a crack in the wall of the outer cylinder. A visual examination of the outer cylinder revealed a crack located approximately 26” below the shock strut air valve. The outer cylinder had accomplished 3 ground air ground (GAG) cycles after completion of the December 2007 overhaul, and approximately 5836 cycles since the prior overhaul in 2004.
The subject outer cylinder developed fatigue cracking in the wall which resulted in leakage of shock strut fluid. The fatigue cracking initiated at and near the ID surface, and propagated through the wall toward to OD until the leakage was detected and the cylinder was removed from service. Crack initiation was due to base metal damage which took the form of over tempered martensite and chemical attack/pitting. The over tempering reduced the strength of the material and caused reduction of shot peen induced residual compressive stresses. The combination of these factors results in the affected material having reduced resistance to fatigue cracking. The ID surface displayed base metal chemical attack which most likely developed during a plating operation on the sealing surface during the 2004 overhaul. The pitting features act as stress raisers, thereby serving as favorable crack initiation sites. The observed ID surface conditions appear to have been created during the overhaul in 2004, with the fatigue cracking occurring once the cylinder was returned to service. The cracking in the cylinder wall was not detected during the 2007 overhaul. Spectrochemical analysis and hardness testing confirmed that the cylinder was fabricated from the specified material, in the required heat treat condition. The cylinder exhibited slightly elevated bulk hydrogen levels, likely caused by the multiple plating and stripping operations during the 2004 overhaul. The condition may have provided a minor contribution to the propagation of the fatigue crack after initiation had occurred.
Probable cause
The failure of the MLG was due to cracking in the cylinder wall resulting from a fatigue mechanism which initiated at, and near the inner diameter (ID) surface, with propagation through the wall toward the outer diameter(OD) surface. Crack initiation was due to base metal damage which took the form of over tempered martensite (OTM) and chemical attack/pitting of the base metal.
Verbatim NTSB analysis and probable cause from the NTSB dataset
Sources
NTSB record ENG08IA051
- Event ID
- 20100608X35931
- Case number
- ENG08IA051
- Dataset
- full-current
- Source SHA-256
- 5cf380f0061817c0331a6b2d8cc7e0ee3a79bea469a1001dc5c10e56f35f5ab3
Source notes (4)
- Unreviewed is an editorial label, not an investigation status. API-sourced is not report-checked or human-reviewed. Explicit event totals are used without summing aircraft injury tables; onboard allocation is withheld. Unknown values remain unknown. The operation category is mapped from the NTSB-reported FAR part and has not been reviewed.
- Filled from the NTSB case API where the bulk record had no value: investigation status. Values present in the bulk record are kept.
- The date is the local date, which is the same as the UTC date the NTSB stores.
- API snapshot SHA-256: bec1ddbfef2cb4225c08e8536688837d0d88c4566ebffedacbe059eab2e11e41; retrieved 2026-09-15T14:24:14.095Z.