Engineering news
A derailment at Paddington station in London last year was caused by maintenance shortcomings at Siemens, an inquiry by the Rail Accident Investigation Branch (RAIB) has found.
The third vehicle of an empty five-car Class 360/2 unit manufactured by Siemens and operated by Heathrow Express derailed in May 2014 while it was running along Platform 3 at Paddington. All four wheels on the leading bogie of the third vehicle became derailed on a track defect.
RAIB found that the derailment occurred because the bogies of the third vehicle had been set up incorrectly. This resulted in the left-hand wheels of the leading bogie being partially unloaded even when stationary. The track defect along Platform 3 exacerbated this unloading and contributed to the derailment.
RAIB also found that the incorrect set-up was the result of the repeated implementation by Siemens technicians of a procedure aimed at setting the vehicle ride heights following tyre turning or bogie replacement. This procedure did not clearly instruct the technicians on how to adjust one of the bogie components – the anti-roll bar – which resulted in the technicians setting it in such a way as to create the wheel load imbalance.
None of the checks in the procedure identified the incorrect setup because these checks were not monitoring parameters likely to provide a clear indication of a wheel load imbalance. An underlying factor was the lack of effective transfer of design information about the role and importance of the anti-roll bars between the vehicle designers Siemens Germany and the vehicle maintainers Siemens UK.
RAIB has made a series of recommendations following the incident. It said that Siemens’ procedure for setting the vehicle ride heights after tyre turning or bogie replacement should be revised to reflect the original design intent, including the function of the anti-roll bars and the risks associated with incorrectly setting the anti-roll bar links. The revised procedure should also include checks of the bogie setup post-intervention to ensure that the wheel load distribution is maintained within Siemens’ acceptable limit.
The company's training materials and competence assessments for technicians and supervisors should also be revised, said RAIB, to capture the function of anti-roll bars, their method of adjustment and the risks associated with incorrectly setting the anti-roll bar links. Siemens should also make this information available to maintenance and overhaul contractors working on its behalf.
The German company should also complete its review of the safety critical procedures used to maintain its vehicles operating in the UK to confirm that they meet the original design intent and are capable of being implemented by competent staff. Based on the findings of this review, Siemens should make any necessary changes to the procedures and re-brief its maintenance staff.
And the German company should review the effectiveness of its recently developed processes for ensuring that all necessary information from the design process is correctly incorporated in maintenance procedures and training materials. If found necessary, Siemens should update its processes and continue to monitor their effectiveness, said RAIB.
