First sign of fault that sparked MRT disruption surfaced almost 2 hours before train stalled

SMRT employees directing commuters away from Clementi MRT station after a train fault between Boon Lay and Queenstown on Sept 25, 2024. ST PHOTO: MARK CHEONG

Esther Loi

UPDATED Jun 04, 2025, 12:16 AM

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SINGAPORE – 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 .

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

According to 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 , damaging 2.55km of track and trackside equipment .

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The control centre will then call for the train to be withdrawn immediately to a depot, and a maintenance team will be alerted.

TSIB, a department of the Ministry of Transport, noted that controllers were not trained on what to do if they encountered cases where the system was unable to identify specific trains with axle boxes of higher temperatures.

It added that there were previous instances of the system’s inability to identify trains with overheated axle boxes, and SMRT staff had been giving feedback to the operator. However, the issue remained unresolved, pointing to procedures then being “not robust enough”, TSIB said.

TSIB is of the view that these controllers were repeatedly exposed to false warnings, which could have desensitised them and caused them to not follow up on such alerts .

It added that if controllers did not regard such alerts as false warnings, it would have been likely that the train would have been withdrawn to the depot earlier.

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SMRT said it has since rectified the issues with the system, which can now identify the trains.

The Land Transport Authority (LTA) and SMRT are also planning to have more trackside infrared sensors to improve the system.

Noting that the temperatures of axle boxes on trains are being measured only once during each round trip on the East-West Line lasting about two hours, TSIB said the frequency of temperature measurement could be increased with the roll-out of more sensors.

It added this would support early detection of abnormal temperatures and encourage proactive maintenance measures.

In its investigation report, TSIB said it could not determine the cause of the axle box’s failure, owing to the severity of damage to the box and its chevron springs.

It, however, pointed to two possible scenarios that caused the overheating of the faulty axle box.

In the first scenario, it suggested that the axle bearings had failed first, generating friction and heat that spread to the springs.

The affected train had operated beyond the stipulated 500,000km interval without undergoing additional maintenance, so the degradation of grease in the axle bearings was unknown. The bearings allow the smooth rotation of the wheels when the train is running.

The bureau said the grease in the faulty axle box had been burned off, so it was not possible to ascertain the quality of the grease. However, the bearings of other axle boxes on the affected train revealed certain levels of grease degradation.

In the second scenario, the bureau suggested that the rubber of the chevron springs had failed first, causing the bogie frame to fall onto the faulty axle box.

As such, the axle box and bearings had to withstand vibrational and horizontal forces from the train’s movement, generating heat within the axle box and damaging the springs.

This scenario was put forward because it is possible for the rubber in the springs to deteriorate over time.

Gap checks for chevron springs, which determine whether the springs have weakened to the extent that the train car droops, do not ascertain the quality of these springs. This is because the train car may not necessarily droop significantly even if a spring has weakened.

TSIB noted the last gap check for the springs – which SMRT typically conducts every three weeks – on the affected train took place on Sept 10, 2024 , about two weeks before the incident. The recorded gap was within the acceptable range of 27mm to 30mm .

SMRT also performed these gap checks more frequently than what is recommended by the train manufacturer Kawasaki Heavy Industries (KHI), which is every six months.

On overhauls, SMRT carries them out once its trains hit a mileage of 500,000km – estimated to be once every 3 ⅓ years – despite KHI’s proposal for overhauls to be done once every two years .

The rail operator told TSIB it had not encountered problems with axle boxes, including axle bearings, thus far, and it had been satisfied with the reliability performance of these components.

It also extended the interval between overhauls for the affected train beyond the mandated 500,000km interval to 750,000km, after assessing the reliability and condition of the train.

The train had logged a mileage of 690,000km since its last overhaul in 2018.

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However, TSIB said SMRT could not provide documentation of assessments for such extensions, which would require evaluation and approval from the operator’s senior management.

The bureau noted that the quality of axle boxes and chevron springs was no longer assured once the overhaul interval went beyond 500,000km.

Additionally, KHI recommends a grease leakage check via a visual inspection once every week , but SMRT does it once every three weeks.

When asked why SMRT did not follow KHI’s recommendation for these checks, the operator said this maintenance regime has been in place since the trains started service in 1987.

SMRT also performs a visual check of axle boxes once every three weeks , although KHI does not mandate such checks.

However, KHI proposes detailed visual checks of axle boxes once every three months, but SMRT does it once every six months instead.

These checks include detailed inspections of various parts, such as the hexagon bolts that fasten components to one another, which are not covered in SMRT’s visual check done once every three weeks. 

TSIB suggested that the authorities, manufacturers and operators in the rail industry here can work together more closely to share information.

It added that this could promote open and constructive dialogue, raise awareness of potential failures, and support the roll-out of preventive measures.

Associate Professor Walter Theseira, a transport economist at the Singapore University of Social Sciences, said there is a need to review how rail maintenance decisions are taken.

He said LTA needs more oversight of the maintenance regime, and that operators, which are responsible for maintenance, work within tight financial constraints to achieve the targeted service reliability. 

He said LTA should consider standards laid out by equipment manufacturers and global best practices, as well as have discussions with operators to better understand their maintenance needs. 

While Singapore’s rail network has been reliable overall, the East-West Line disruption reveals how complex railway systems are, said Associate Professor Raymond Ong, a transport infrastructure researcher at the National University of Singapore.

“Even a small thing like grease can cause the system to fail,” he said.

Prof Ong said LTA and operators have to look at how to maintain rail assets effectively without “overburdening” workers by increasing their workload.

It is also important to understand the risks and costs involved when adjusting maintenance procedures, he added. 

Additional reporting by Lee Nian Tjoe

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