Collector shoes failed to detach as expected
Trains' shoes supposed to break off in abnormal conditions but instead damaged the third rail
By Royston Sim, The Straits Times, 1 May 2012
THE collector shoes were supposed to break off from the train when they were subject to abnormal operating conditions.
But in the first major disruption on Dec 15 last year, SMRT maintenance staff found the shoes - which draw power for the train from the third rail - were still attached to the trains.
Two officers told the Committee of Inquiry (COI) yesterday that the shoes on several trains had simply twisted after going past a sagged portion of the third rail.
Said assistant engineer Ibrahim Ismail, 43: 'My understanding is that once certain pressure is applied on the shoe, it should break so no more damage is done to the third rail.'
He added that the twisted shoes had ripped off parts of the third-rail cover, which were scattered beside the tracks.
During an earlier incident in January 2010 when the third rail sagged at a high-speed ramp between Paya Lebar and Aljunied stations on the East-West Line, staff had found one claw dislodged and five collector shoes strewn at that section.
While those shoes had broken off as they were supposed to, the same did not happen on Dec 15.
This issue was one of several raised in yesterday's hearing as four SMRT maintenance staff took the stand on week three of the public inquiry into two major disruptions last December that affected more than 220,000 commuters.
On both days, a section of the third rail had sagged and damaged the collector shoes of nine trains, which stalled.
Staff were queried on repairs conducted and their observations after the Dec 15 and 17 incidents as the inquiry moved from incident management to technical details.
Technical officer Adam Ismail, 45, said maintenance staff had raised the sagged third rail and mounted it back on Dec 15 after visually checking that it had no defects.
The committee also heard how staff had noticed a hairline crack on the third rail after it had been raised on Dec 17.
Chief District Judge Tan Siong Thye, who heads the three-man COI, asked Mr Adam why the third rail was not replaced after staff spotted the crack.
He replied that there was insufficient time to do so, and the crack had taken place at the top part of the rail where it would not affect the running of trains.
The hearing's focus then shifted to a cracked mirror on a Multi Function Vehicle (MFV), which measures whether the third rail is correctly aligned.
On Dec 17 before the second incident, the MFV was operated by assistant engineer Yew Kai Png, 49. It was unable to acquire third-rail readings twice while on the southbound track between Newton and Orchard stations that morning.
He later found a side mirror had cracked when he arrived at Dhoby Ghaut station. Staff were dispatched to check the sections between Newton and Orchard where the MFV had lost readings, but did not report any abnormalities.
Yesterday, the committee heard that Mr Yew's estimations were likely to be inaccurate as he had wrongly keyed in some information to the MFV.
This could have led to staff not spotting the cause behind the cracked mirror during their checks that night, which to date remains unknown.
Mr Yew had earlier said that two prior incidents of cracked MFV mirrors were caused by knocks against a slab rim along the track and a third-rail cable.
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