On 25 September 2024, train services on the Singapore Mass Rapid Transit (MRT) East–West line (EWL) were disrupted when an axle box of a Kawasaki C151 train dislodged, damaging the track and equipment along the stretch between the Clementi and Dover stations. This resulted in the suspension of regular services between the Boon Lay and Queenstown stations, affecting more than 2.6 million commuters.

Described by experts as a "rare" incident, the damage was reported to be extensive, and services was expected to be restored only some days after. During restoration works by engineers from the Land Transport Authority and SMRT Corporation, shuttle train services were restored for the stretches between the Queenstown and Buona Vista stations, and between the Jurong East and Boon Lay stations. Bus bridging services were provided for the closed segment between the Buona Vista and Jurong East stations.

Services resumed on 1 October. This was one of the longest train disruptions on the MRT network in Singapore's history, as well as the longest since 2017. Investigations into the incident are ongoing.

At about 9 am local time on 25 September 2024, a faulty eastbound Kawasaki C151 train was pulled out of service at Clementi station. Eyewitnesses said there was smoke emitting from the train as it arrived into Clementi station. The 850 passengers on the train disembarked and SMRT staff guided the passengers to Clementi station. To return to Ulu Pandan Depot, it had to switchover at Queenstown station. Near Dover station, a defective axle box dropped on the tracks, causing the bogie frame to be dislodged from the third car of the six-car train. The bogie damaged the third rail (exposing its cables), power cables, point machines (which enabled trains to change tracks), and rail fasteners as well as causing rail breaks across 2.55 km (1.58 mi) of track, triggering a power trip at 9:25am, which stalled the train.

This also stalled four other trains between Clementi and Buona Vista, including a train 40 metres (130 ft) near Clementi station, and the affected passengers from that stalled train also disembarked and walked to Clementi station with SMRT staff guidance. The train operator SMRT Trains first reported the incident at 9:52 am and suspended train services between the Queenstown and Boon Lay stations. The Land Transport Authority (LTA) later announced at 2:45 pm that there would not be train services between Boon Lay and Queenstown for the rest of that day because of the extensive damage.

The disruption caused "extensive damage" to the affected track stretch. The damages include 46 rail cracks, exposure of the third rail's cables, three point machines, power cables, and rail fasteners. A point machine between Jurong East and Clementi station was so badly damaged that it could not be salvaged and needed to be replaced. All of the equipment aforementioned needed replacement, with the point machines requiring realignment and careful recalibration. Emergency repair works have been underway since 25 September, with over 300 engineers involved in rectification and replacement works. There are also investigations currently ongoing.

Free regular bus services were offered between Queenstown and Boon Lay stations, while bridging buses started running between Buona Vista and Jurong East in 9:58 am by SMRT Buses, SBS Transit, Tower Transit and Go-Ahead Singapore. Police officers, LTA ground staff, and personnel from the bridging bus operators were deployed to manage the crowds at the affected stations. Shuttle train services between Queenstown and Buona Vista stations, as well as between Jurong East and Boon Lay stations, were activated at 3:56 pm and later 4:11 pm, respectively. By 26 September, the shuttle train services were running at 10-minute intervals. While the authorities initially hoped to restore partial services between Jurong East and Buona Vista by 27 September, this was ruled out in favour of minimizing delays in restoring full services with the new deadline set for 30 September. Transport Minister Chee Hong Tat issued an apology for the disruptions in a Facebook post.

The engineers managed to move the train back to Ulu Pandan Depot by attaching a temporary axle box to the train before using a hydraulic system to move the wheel back on the rail and pulled the train back to the depot. The power cables and two of the three point machines were replaced on 27 September, with repairs on the third rail expected to be completed on the same day. During maintenance, the engineers had to use mechanical jigs instead of rail vehicles due to the broken rails. The next day, SMRT and LTA reported that their engineers made "significant progress" with the maintenance as well as completion of heavy rail delivery work. The track point machines and associated trackside equipment were replaced and tested, while the power rail was restored. Once repairs were finished, systematic and functional tests were planned for 29 September 2024, including checks on tracks, power supply, and train signalling as well as running trains in different speeds to ensure smooth operations.

In a joint statement by SMRT and LTA on 29 September, it was announced that engineers had found 12 more cracks through stress and loading tests which were previously not visible during the replacement of other damaged parts of the track. As such, the expected reopening of the segment was further delayed to 1 October after more tests were being carried out on 30 September. On the next day, the LTA announced the restoration of the third rail and the completion of locomotive stress tests and other tests for electric meggering and track circuiting and they were still performing loaded train endurance tests. They also carried out ultrasound tests on the welds of the tracks.

The LTA and SMRT announced that train services would resume on 1 October, though with temporary speed restrictions on westbound tracks for safety. Train speeds would be reduced from 60 to 80 kilometres per hour (50 mph) to 40 kilometres per hour (25 mph) for safety. With that, only C151, C151A, C151B, C151C, and R151 are allowed to operate, while all C651 and C751B are permanently withdrawn from service ahead of the deadline. C151s are only running on weekdays.

The disruption caused significant increases in travel times, with The Straits Times reporting that a typical journey from Jurong East to Redhill took approximately 90 minutes instead of the usual 21 minutes. Queues at bus stops serving the affected stations were as long as 100 metres (330 ft). Many commuters were also confused with the transport arrangements, such as the location of free bridging bus stops for closed stations. Some voiced their frustration regarding the disruption and its spillover effects, including the longer travel time and the long walking distance between Jurong East station and its free bridging bus stop.

It is estimated that the disruption affected more than 2.1 million commuters as of 30 September, with 358,000 passengers on the first day, 516,000 passengers on the second day, and 500,000 passengers on the third day of the disruption. Some commuters avoided the affected section of the MRT system from Queenstown to Jurong East due to lack of safe distancing in all public bus services, and some of the elderly struggled with route changes on all days.

The incident occurred during the Primary School Leaving Examination (PSLE). In response to the disruption, the Ministry of Education (MOE) announced that students taking the PSLE on 26 September were granted the full allocated time to sit their paper as long as they turned up before the end of the exam. Free taxi services were offered to ferry students to their examination venues from affected stations, though according to The Straits Times, the taxis were not used by the students. According to MOE, five students were late to the English and foundation English examination (four of which were N-level candidates and one was a PSLE candidate) on 26 September due to the disruption, of which one student took the examination in another examination centre. All of them were given the full duration of the paper. Additionally, according to the Singapore Examinations and Assessment Board (SEAB), no candidates were affected by the disruption for the Mathematics exam on 27 September.

It is the second longest MRT disruption in Singapore's history, as well as the longest one since 2017. The incident has been described by experts as "rare", with Dubai Road and Transport Authority's chief specialist of rail operations Jumadi Husani stating that "Under normal circumstances, the axle box, bogie... and train wheels do not come off from the train", adding that if it does, it was "mainly due to improper installation of parts after maintenance or testing activities or if defective components... are not replaced". Similarly, electrical engineer Teo Chok Kok said "it's very rare for [axle boxes] to drop... it's a very rare case".

On 2 October, the LTA established an Expert Advisory Panel (EAP) to investigate the cause of the incident. Malcolm Dobell, who was the former Head of Train Systems for London Underground, has been appointed as the EAP Chairman. He would also be assisted by five other local and overseas experts. The investigation would involve finding the root cause of the axle box failure and the fault detection and incident handling procedures. The investigation would be held over a few months with the findings released to the public. In addition, the LTA and representatives from public bus operators met on 2 October to discuss their management of the bridging bus services during the breakdown to examine improvements needed for such incident management plans. On 1 November, SMRT announced the establishment of a tripartite workgroup – comprising representatives from LTA, SMRT and the National Transport Workers’ Union (NTWU) – that would oversee the reliability and safety of the rail network.

A total of thirty one Parliamentary Questions have been filed against Minister of Transport Chee Hong Tat, with nineteen questions answered on 14 October.

• Media related to 2024 East–West MRT line disruption at Wikimedia Commons