What triggered the six-day East-West Line MRT disruption in September 2024

SINGAPORE – Degraded grease in a component of an MRT train’s undercarriage was likely to have caused the six-day disruption to services on the East-West Line in September 2024, according to

investigation findings that the authorities released

on June 3.

Investigations by the Land Transport Authority (LTA) and the Transport Safety Investigation Bureau (TSIB) under the Ministry of Transport found that an axle box – part of the train’s undercarriage that holds the train wheels to the axle, a rod connecting a pair of wheels – became dislodged likely because of degraded grease that led to increased wear and tear on the axle bearings.

Extreme heat was generated due to the degraded grease, burning off the rubber layers of the chevron springs that supported the axle box, which was on the third carriage of the six-carriage train.

Each train carriage has two undercarriage bogies, and each bogie holds four wheels. An axle box and two sets of chevron springs are attached to each wheel.

Chevron springs absorb shock and vibration from the train’s movement and connect the axle box to the bogie frame.

Without the support of the chevron springs, the axle box fell off the affected train near Dover station as it was returning to Ulu Pandan Depot.

This dislodgement caused the wheels on the front undercarriage of the third train car to derail.

The train then severely damaged the running rails, the third rail supplying power to the trains and trackside equipment along 2.55km of tracks on the East-West Line as it headed back to the depot.

Here is a timeline of what happened on the morning of the incident:

6.58am: The affected train started to travel westwards from Pasir Ris station to Tuas Link station.

7.23am: A sensor on the track near Lavender station detected that one of the axle boxes on the affected train had clocked a temperature of 118 deg C, above its typical range of 30 deg C to 65 deg C. But due to system issues, SMRT staff could not identify the train that was producing excess heat. The staff also thought it was a false warning and did not take further action.

8.22am: The affected train arrived at Tuas Link station.

8.25am: The train departed Tuas Link station to travel towards Pasir Ris station. About five minutes later, operations staff reported that there was a burning smell.

8.34am: The station manager of Tuas Link station checked the track of the westbound platform and reported that there was no burning smell there.

8.50am-8.52am: The station manager of Clementi station boarded the affected train to carry out an inspection and reported that there was a burning smell inside.

8.53am: The operations control centre requested

that

passengers disembark the affected train

so that it can return to Ulu Pandan Depot. To return to the depot from Clementi station, the train had to travel eastwards to a crossover track located between Queenstown and Redhill stations to turn around. 

9.04am: When the train arrived at Dover station, the station manager boarded the affected train to conduct checks. He reported a burning smell inside the train, but did not notice any smoke. At the same time, the train driver did not notice any signs of a train fault.

9.08am: The train turned around from the eastbound track to the westbound track near Queenstown station.

9.16am: A power trip occurred when the train was travelling westwards between Dover and Clementi stations, but it was able to move into Clementi station. The train driver and station manager of Dover station – who was still on board – did not notice any burning smell or smoke.

9.19am: Traction power was restored. The Dover station manager alighted at Clementi station and the train continued moving towards Ulu Pandan Depot.

9.20am: Another power trip happened and the affected train stalled on the track leading to Ulu Pandan Depot. The operations control centre could not restore traction power.

9.28am: The operations control centre sent a recovery team to rescue the train. They found that four wheels of the train’s front undercarriage had come off the rails, and the axle box on the third train car had fallen off near Dover station.

9.52am: SMRT alerted the public to the disruption between Boon Lay and Queenstown stations on its Facebook page.