Two months after hairline cracks on 26 MRT trains were made public, similar cracks have been found on 11 Sengkang-Punggol LRT trains.
The cracks, which were found on the undercarriage of the 13-year-old 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) yesterday. An independent assessor had also determined that the defects were not "safety-critical".
The trains were made by Mitsubishi Heavy Industries (MHI) in Japan.
The statement said a fleetwide 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.
When the cracks - measuring 15-90mm long and 1-2mm wide - were discovered, SBS Transit said the trains were withdrawn immediately from passenger service "for replacement of their bogie frames" - a part of the undercarriage - "as a precautionary measure".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, according to the operator.
The 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.
Meanwhile, a sample of the affected bogie frame was sent to MHI's R&D Centre in Japan for a detailed analysis. "LTA and SBST are working with MHI to redesign, strengthen and replace the bogie frame structures on all 57 trains," the statement said, adding that Mitsubishi will bear the replacement costs.
The 26 affected MRT trains are also being shipped back in batches to manufacturer Kawasaki- Sifang's plant in China to have their car-bodies replaced.
Since the discovery of the cracks, which were caused by impurities in the aluminium alloy, Kawasaki-Sifang has decided to cast the component in Japan instead of China.
Separately, 19 trains on the Bukit Panjang LRT were found to have cracks on their undercarriage last year. The US-made trains, in service since 1999, had their cracks welded and returned to service.
SIM University senior lecturer Park Byung Joon said cracks on metal are not uncommon. "Many people don't realise airplanes are flying full of cracks," he said. "As long as those are properly monitored, they do not pose a safety concern."