The cracks, which were found on the undercarriage of the trains, do not compromise their ability to bear passenger weight, according to a joint statement by operator SBS Transit and the Land Transport Authority (LTA). The trains were manufactured by Japan's Mitsubishi Heavy Industries.

The joint statement said a fleet-wide inspection was carried out in July - the month when cracks on 26 new MRT trains on the North-South and East-West lines came to light. SBS Transit said the defects were on 11 of its first generation Sengkang-Punggol LRT trains. The 11 were immediately withdrawn from passenger service for replacement of their bogie frames - a part of the undercarriage - 'as a precautionary measure'.

Six of the 11 have since been restored and returned to service, and the remaining five are expected to be reinstated by the middle of next month. The joint statement said LRT services have not been affected as there are 57 trains in the Sengkang-Punggol fleet, and a maximum of 36 trains are deployed at any one time. SBS Transit has also been inspecting all trains on a weekly basis for any new defects.

To determine the cause, a sample of the affected bogie frame was sent to Mitsubishi Heavy Industries' R&D Centre in Japan for a detailed analysis. "LTA and SBS Transit are working with the manufacturer to redesign, strengthen and replace the bogie frame structures on all 57 trains," the joint statement said, adding that Mitsubishi will bear the replacement costs. In July, 19 trains on the Bukit Panjang LRT were also found to have cracks on their undercarriage.