Fractures of Urbos 3 LRV underframes — Sydney Inner West Light Rail Line - 27 October 2021

Read the Light Rail Safety Investigation Report

What happened

In late September 2021 fractures were identified in the underframe of Sydney Urbos 3 light rail vehicles (LRV) operating on the Inner West Light Rail (IWLR) line. The fractures were identified by maintenance staff in the underframe rotation bump stop (RBS) during a routine maintenance inspection.  

Additional inspections carried out in October 2021 identified multiple fractures on all LRV C modules within the underframe bogie box area, with the presence of those fractures representing a safety risk. Sydney Urbos 3 services were subsequently suspended in late October 2021 as a precautionary measure to eliminate the potential of a safety incident.

What we found

The investigation identified the following factors contributed to the incident:

• The 2013 Sydney Urbos 3 underframe design was not sufficient to last the required 30-year operation considering cyclic loading at key structural locations.
• The maintenance regime detected the presence of LRV underframe fractures. However, there was insufficient time to take any action that would have permitted the fleet to remain in service.
• The knowledge of similar factures identified in overseas Urbos 3 vehicles was not acted on by any of the parties in a timely fashion to permit some proactive action to take place.

Actions taken by directly involved parties during the investigation  

A significant number of post incident safety actions were undertaken and coordinated by TfNSW, CAF, ALTRAC, Transdev and Alstom in order to address the potential risks identified as a consequence of the Urbos 3 underframe fractures. These actions included:

• TfNSW made an amendment within their supply contract with CAF for the 4 new Urbos LRVs being procured to expand the Urbos 3 fleet operating on the IWLR line. The amendment included an obligation relating to ‘Notifiable Faults’. This obligation required CAF to provide notice within 20 business days of any defects (including design fault) or a material operational issue which occurred in any vehicle in the newly designed Urbos fleet anywhere in the world, and which may impact safety and reliability of any LRV.
• Extensive dynamic on-track testing was carried out by TfNSW and CAF to inform themselves of how the Urbos 3 original design performed on the IWLR line in compliance with the LRV design standard requirements.
• CAF and TfNSW carried out their respective technical investigations into the underframe fractures and provided the results of their investigations to OTSI.
• CAF prepared a modified bogie box design and repair procedure with that work being accepted by TfNSW as part of the Urbos 3 return to service program. CAF, TfNSW, ALTRAC, Transdev and Alstom then implemented the Urbos 3 repair program including refabrication of the bogie box.

Recommendations

Alstom – the contracted Urbos 3 maintainer

• Continue to progress and finalise improvements in the Urbos 3 training and competency assessment system in the conduct of underframe and bogie inspections.
• Consider a program to rotate technical staff across vehicles to provide an opportunity for staff to work on different vehicle types.

ALTRAC – the accredited Urbos 3 operator and maintainer

• Undertake audit activities to provide assurance that the Urbos 3 training and competency assessment system is in accordance with the ALTRAC Safety Management System.
• Review the ALTRAC Safety Management System to determine if further guidance is required to cover when proactive investigations of original equipment manufacturer reported light rail vehicle (LRV) component failures are undertaken. The decision to undertake proactive investigations should consider if it would be reasonable to expect similar LRV failures could be possible.  

Construcciones y Auxiliar de Ferrocarriles (CAF) – the Urbos 3 designer

• Review its light rail vehicle (LRV) structural design processes to consider improving validation practices in the areas of:
• Selection of appropriate weld categories to apply against welds identified in the finite element analysis to be on the boundary of compliance with the fatigue load design standard. The selection practice should consider the sensitivity of the weld assessment category chosen (in terms of stress direction) to meet the required design life. (see Finding 3.1)
• A focus on validating those areas of major principal stresses in the weld material, derived from fatigue load cases, in terms of both stress magnitude and direction. The validation of those principal stresses may consider assessment through either static or on-track strain gauge testing using a risk-based approach. (see Finding 3.1 and 3.6.)
• Sourcing its customers relevant track maintenance defect limit standards and measured track geometry data to verify LRV designs can cope with those variables over their required design life. (see Finding 3.1 and 3.6.)
• Review the CAF welding quality assurance process covering the selection of welds to consider including critical structural welds that would not be possible to review once assembly of the fabricated structure is complete. (see Finding 3.4)
• Review the CAF commissioning and acceptance certification process for LRVs of a similar bogie configuration to the Urbos 3 to consider recording of bogie drag link shimming and bogie rotation bump stop clearance shimming configurations. (see Finding 3.8 & 3.9)