Derailment with Airport Express train at Blackvreten

SUMMARY

On the morning of 27 May, 2023, Arlanda Express train 7900 was on route from Stockholm C to Arlanda Airport with 67 passengers on board. When the train passed Blackvreten station at 178 km/h, a welding joint in the movable crossing of switch number 106 ruptured. The switch rail in the crossing moved out of position under the train and the second to fourth wagons derailed. The derailed wagons followed the track and bounced over two following switches before coming to a stop after about 900 metres. One passenger was seriously injured and the damage to infrastructure and vehicles was extensive.

The investigations show that the welding joints in the drive connection plate that transmits power from the switch drive to the movable crossing had lack of fusion and fatigue cracks.

The direct cause of the derailment was that the movable crossing in switch 106 was moved out of position when the welding joint in the drive connection plate broke due to residual fracture.

Dynamic load from passing wheel axles had caused fatigue cracks in the drive connection plate welding joints, originating in lack of fusion in the butt welds.

At the system level, the drive connection plate was not designed for the load cases and conditions that existed in switch 106, furthermore the rules and routines for safety inspection and maintenance were not designed to identify and remedy cracking in the drive connection plate's weld joints.

Measures taken since the accident

A-Train AB:

A-Train has replaced the damaged switches 106 and 103 in Blackvreten. The new switches have the same dimensions and movable crossing, but slipper-integrated Easyswitch type drives with a different type of attachment and position indication for the movable crossing. Following the change of switches and drive type, A-Train no longer has any drive connection plates in its infrastructure.

A-Train has decided to double the number of safety inspections of switch 106 from six to twelve per year.

A-Train, aided by an external expert, has carried out an examination and welding quality measurement of the damaged drive connection plate for switch 106. The result of the examination was, among other things, that the welds did not meet the requirements of EN ISO 5817, acceptance class B.

A-Train's investigation also included a finite element simulation with varying boundary conditions. The simulations show that movements in the movable crossing can lead to high stresses in the butt welds of the drive connection plate. The calculated load cases in combination with the dimensioning and execution of the welds could lead to fatigue and failure.

The Swedish Transport Administration:

After the accident in Blackvreten, the Swedish Transport Administration has checked switches with the affected type of drive connection plate in its infrastructure. The check was carried out with the drive connection plates mounted under the crossing section. The welding joints were cleaned and treated with dye penetrant testing, see example in figure 25. None of the checked drive connection plates showed visible cracks in the welding joints. However, the inspection was not volumetric and could not detect any hidden cracks from the root side of the welds.

The Swedish Transport Administration's dispatch center in Stockholm has identified that it was the choice to use a prefix before dialing 112 that delayed the alarm call and has then informed the train dispatchers.

Safety recommendations

A-Train AB is recommended to:

• Due to previous high wear, maintenance and damage outcome in switch 106, follow up on wear, maintenance and other relevant indications to proactively identify any deficiencies in order to ensure safe operation of the new switch. In the event of any ambiguities regarding inspection and maintenance, A-Train should contact the manufacturer for an assessment of whether and, if so, how instructions and routines can be improved.
  

Vossloh Switch Systems AB is recommended to:

• Investigate whether welding joints in newly manufactured drive connection plates should be dimensioned for dynamic loads in order to minimize the risk of fatigue cracks and breakage.
  
  
• Follow up on rules and procedures to ensure that welding works meet requirements and standards.
  
  

The Swedish Transport Administration is recommended to:

• Examine drive connection plates with volumetric testing in order to ensure that the welding joints meet set requirements and to detect any hidden defects in load-bearing weldings.
  
  
• Review governing documents in order to ensure that welding joints in drive connection plates at movable crossings in the Swedish Transport Administration's infrastructure are inspected to the required extent to minimize the risks of fatigue cracks and breakage.
  
  
• In consultation with SOS Alarm Sverige AB, work out a way to quickly position a railway accident. The work should focus on the ability of the Swedish Transport Administration to, in connection with the first information about the accident, develop and convey a position to which SOS Alarm and rescue resources can relate.