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On 25 July 2009, a Boeing 737-7Q8 aircraft, registered VH-VBA, was taxiing toward the runway for departure at Melbourne aerodrome, Victoria, when the crew reported hearing a loud thud from the airframe. The crew of a passing company aircraft advised the crew of VH-VBA that they had lost a nose wheel tyre. It was subsequently discovered that the right wheel had detached from the nose landing gear (NLG) as a result of a fracture of the axle.

An Australian Transport Safety Bureau investigation of the NLG failure determined that the nose wheel had separated as a result of the initiation and propagation of a fatigue crack through the right, inboard bearing journal. The fatigue crack had originated under the influence of residual stresses in the steel surface associated with grinding damage during manufacture, and its initiation was probably hydrogen-assisted from plating processes applied to the journal bearing surfaces.

As a result of the occurrence, the aircraft operator conducted an immediate, fleet-wide inspection of axles with similar service history. To reduce the likelihood of future possible axle failures, the aircraft manufacturer conducted an audit of the landing gear supplier's processes and production records, in an attempt to establish the extent of the grinding problem. The aircraft manufacturer also released a communication to 737 operators and maintenance providers, detailing enhanced inspection recommendations for the identification of grinding damage.

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Safety issue

AO-2009-047-SI-01 -  

Nose landing gear residual stress and hydrogen embrittlement

Fatigue cracking originated within the aircraft nose landing gear (NLG) right axle as the result of surface damage associated with grinding during manufacture, and was probably assisted in its initiation by hydrogen evolved during plating processes.

Safety issue details
Issue number:AO-2009-047-SI-01
Who it affects:Operators of Boeing 737 aircraft
Status:Adequately addressed

General details
Date: 25 July 2009 Investigation status: Completed 
Time: 0826 EST  
Location   (show map):Melbourne Aerodrome Investigation type: Occurrence Investigation 
State: Victoria Occurrence type: Landing gear/indication 
Release date: 30 July 2010 Occurrence class: Technical 
Report status: Final Occurrence category: Serious Incident 
 Highest injury level: None 
Aircraft details
Aircraft manufacturer: The Boeing Company 
Aircraft model: 737 
Aircraft registration: VH-VBA 
Serial number: 28238 
Type of operation: Air Transport High Capacity 
Damage to aircraft: Minor 
Departure point:Melbourne, Vic.
Destination:Sydney, NSW
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Last update 14 November 2018