Brétigny-sur-Orge english summary

On 12 July 2013 at 17.11, the four rear coaches of Intercités train No 3657 heading to Limoges on track 1 of the Paris-Orléans line derailed in the points area located at the northern entrance to Brétigny-sur-Orge station.
The first two derailed coaches remained on track 1 and ended up lying on their right-hand side. The third derailed coach crossed over between tracks 1 and 3 and swept along platform No 3 over a distance of about 100 metres. The last coach came to a halt on track, without keeling over.
This accident’s human toll was particularly heavy. Seven lives were lost : 3 passengers on the train concerned and 4 people who were on platform No 3. Thirty-two other people were injured, eleven of whom seriously.

This interim report provides a summary, five months after this derailment, of the findings and of the investigations carried out during that period by BEA-TT’s technical investigators. The analysis it provides gives a first evidence-based approach to the causes of this accident. They must still be confirmed, examined in greater depth and completed, in particular using the information that will be provided by the ongoing metallurgical analysis.
The derailment occurred about 150 metres upline of platform No 3, on double slip crossing 6/7/8/9, specifically at the frog located on the right track of the crossing. It was caused by the obstruction of the crossing’s flangeway by the inner plate of the joint linking it to a set of points. In order to become jammed in the flangeway, this inner plate pivoted as train No 3657 passed around the headless body of the fourth bolt on the joint.
In order for this to happen, the three other bolts must have had to come out of their housings. This disassembly was, in all likelihood, the result of cracking that had developed over several months in the core of the rail end of the incriminated frog crossing, until a piece broke off, generating abnormal forces on the third bolt of the splice bar 1. These forces caused this bolt’s head to break. The other three bolts then gave way, one by coming unscrewed and the other two by breakage of their heads.
In theory, at the time of the inspection round carried out on 4 July 2013, only the failure of the splice bar’s third bolt could be detected. The lesser amount of attention paid to problems affecting the bolts – compared with other equipment defects that are considered to be more critical, added to the limits inherent to any visual inspection, notably when carried out on tracks that are in service – may have contributed to this defect not being detected.

At this stage of the investigation, BEA-TT has already sent SNCF three recommendations respectively concerning :

  • control of the bolted assemblies in order to increase their robustness, particularly when they are installed on points that are placed under great strain in places where they are not particularly visible ;
  • clarification and strengthening of the instructions relating to the maintenance of bolts on points and crossings, in order to eliminate any ambiguities that could lead to deviations in their application ;
  • adaptability of the monitoring plan for points and crossings to ensure that, beyond the general instructions and criteria currently applied, the specific features such equipment may have are taken into account in a reliable and auditable way.

These recommendations are not exhaustive. More detailed investigations must still be carried out to ensure that the technical analysis of this accident is complete. In view of the information that will be provided by the ongoing metallurgical analysis, they must look in particular at the quality control of the maintenance operations carried out on points and crossings.

Notes et références

1A splice bar, also called a ‘joint’ in this report, is a bolted assembly that is used to attach two successive rails to each other. In this case, the assembly concerned comprised four bolts. The respective positions of these bolts are identified with respect to the trains’ running direction on track 1.

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