A LOOSE metal bolt was the likely cause of a Mass Transit Railway train coming off the rails outside Kowloon Bay station, the MTR said yesterday.
The MTR has checked all its trains and passed them safe, but it will be carrying out a full review of how it inspects and maintains its trains to make sure there are no other hidden defects.
One carriage in the eight-car train derailed 300 metres from the station at 8.31 pm on January 28. Although no one was injured, the accident brought chaos to passengers on the Kwun Tong line and sparked serious concern at the MTR's headquarters, barely 100 metres from where the incident happened.
The MTR's chief engineer (operations) Phil Gaffney told Legislative Councillors it seemed a bolt in the rear emergency suspension system of the carriage had worked itself loose, causing an emergency spring to extend.
This had displaced the carriage. With all the weight on the back wheels, one of the front wheels had lifted off the tracks.
''There is a weakness in the design. A simple defect such as a bolt becoming loose should not result in a derailment,'' Mr Gaffney said.
The emergency spring assembly was housed in a sealed unit which was maintenance free, he said. But the MTR would now review its equipment to see if there were other sealed units that should be checked more carefully.