First sign of fault surfaced almost two hours before train stalled

The train that crippled East-West Line services for six days in 2024 had displayed potential signs of a fault in one of its axle boxes, close to two hours before the train stalled on Sept 25, 2024.

- Esther Loi

An axle box holds the train's wheels to the axle, which is a rod connecting a pair of wheels.

According to findings from an investigation report published by the Transport Safety Investigation Bureau (TSIB), a sensor on the tracks near Lavender station had detected that one of the axle boxes on the affected train reached a temperature of 118 deg C at 7.23am on Sept 25, 2024.

This was above the typical operating temperature that usually ranged from 30 deg C to 65 deg C, said TSIB on June 3.

But due to system issues, the heat detection tool that SMRT put in place in 2014 on its own initiative could not identify the affected train that experienced the temperature increase.

As a result, the rolling stock controller who received a warning for this anomaly believed it was a "false warning" and did not take any follow-up action, noted TSIB. Rolling stock refers to vehicles used on a railway.

This was then followed by reports of smoke and a burning smell inside the affected train from various staff from about 8.30am, which led to the withdrawal of the train from service to Ulu Pandan Depot near Clementi station.

Eventually, the train stalled on the tracks leading to Ulu Pandan Depot after the traction power tripped at 9.20am. The operations control centre could not restore the power.

TSIB's findings show that the wheels of the front bogie, or undercarriage, beneath the third train carriage of the six-car train had derailed.

This was after a faulty axle box on the same carriage — as well as chevron springs that hold the box in place — had dropped onto the tracks.

On SMRT's heat detection system for axle boxes, the rolling stock controller is supposed to inform the operations control centre after receiving a warning when the temperature of an axle box exceeds 90 deg C.

The control centre will then call for the train to be withdrawn immediately to a depot, and a maintenance team will be alerted.