It started with a faulty train, and quickly escalated into Singapore’s second-longest rail disruption.

On Sept 25, a train - which has been in operation for more than 35 years - encountered a fault near Clementi station on the East-West Line (EWL) and was withdrawn from service. On its way back to the depot, it unexpectedly left a trail of destruction, causing extensive damage to tracks and trackside equipment.

The incident disrupted train services between Boon Lay and Queenstown stations.

By 5pm on Sept 25, SMRT started to run shuttle train services between Buona Vista and Queenstown, and between Boon Lay and Jurong East. But the four-station stretch between Jurong East and Buona Vista has remained closed.

Rail operator SMRT said it aims to restore services fully by Sept 30. The date was pushed back to Oct 1 after new cracks were discovered during stress tests on Sept 28.

This is Singapore’s second-longest rail disruption, after a five-day halt in train services between Joo Koon and Tuas Link in November 2017, following a train collision caused by a software glitch in the signalling system. The suspension of services between Joo Koon and Gul Circle stations was later extended till mid-2018, when the East-West Line switched to a new signalling system.

Here’s how the latest incident happened.

A first-generation Kawasaki Heavy Industries train encountered a fault near Clementi station on the EWL at about 9am on Sept 25. A power trip occurred and smoke was emitted. All passengers on the eastbound train disembarked at the station. SMRT withdrew the train from service by turning it around onto the westbound track.

While travelling back to Ulu Pandan Depot, the third carriage of the six-carriage train was damaged.

A defective component of the train’s wheel set - known as an axle box - dropped onto the tracks near Dover station.

This caused the bogie frame - a structure below the train carriage with two sets of wheels - to drop down…

… and caused the wheels to shift.

As the train travelled with one bogie derailed, it caused extensive damage to the tracks and trackside equipment.

With one bogie derailed, the damage wrought by the train caused a power trip at about 9.25am. This caused other trains to stall, and crippled services across nine stations between Boon Lay and Queenstown.

One train that stalled near Clementi was carrying about 850 passengers, who had to disembark on the tracks and were guided back to the station platform.

The train put three point machines, that are used to divert trains to different tracks, out of operation and dislodged rail fasteners. One of the point machines, located between Jurong and Clementi stations, was so badly damaged that it cannot be salvaged and must be replaced.

Stretches of the third rail, which supplies power to trains, along the eastbound track were also damaged.

The third rail serving the track into Ulu Pandan Depot is linked to the same power supply that serves the third rail on the eastbound track. Hence, when the defective train damaged the third rail while entering the depot, it also tripped the power supply to the eastbound track.

Engineers later found 34 rail fractures, such as cracks or chips, with most of them at the time believed to be along 1.6km of tracks between Clementi and Dover stations.

On Sept 29, it was clarified that the fractures were actually across a distance of 2.55km of tracks.

12 cracks that were previously not visible were found during stress tests conducted on Sept 28

The additional 12 cracks – found on unreplaced segments of the rails between Clementi MRT station and the track crossover towards Ulu Pandan Depot – meant that another 10 rail segments had to be replaced.

As a result, full restoration of train services was pushed back by a day to Oct 1.

Transport Minister Chee Hong Tat said late on Sept 26 that engineers and technicians from LTA and SMRT have been working day and night to carry out repairs and checks on the damaged tracks and equipment.

“As the damage is very extensive, they have to do this carefully, and it requires a lot of time,” he said during a visit to the tracks leading to Ulu Pandan Depot.

Trains cannot safely operate until the damaged segments are replaced.

SMRT and the Land Transport Authority had initially planned to partially restore services on Sept 27 by running a shuttle train service that would go up and down the affected four-station stretch - between Jurong East and Buona Vista - every 20 minutes.

But the authorities later shelved the plan as it would mean slowing down the repairs on the parallel damaged rail, which could delay the full restoration of services. This is because repairs cannot be done when the shuttle train service is in operation.

SMRT said it aims to restore services fully on Sept 30.

Until then, it will continue to operate shuttle train services between Buona Vista and Queenstown stations, and between Jurong East and Boon Lay stations. There will also be free bridging bus services between Jurong East and Buona Vista. Free regular bus services are also available between Boon Lay and Queenstown stations.