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Post by Deleted on Aug 15, 2017 18:38:19 GMT
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Post by Deleted on Aug 15, 2017 19:16:06 GMT
I do hope that South West Trains declares it a Void Day for Today and Tomorrow.
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Chris M
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Post by Chris M on Aug 15, 2017 20:13:38 GMT
The last time we had a thread with this title, the incident was rather messier and the resolution was almost certainly sweeter. |
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Post by Deleted on Aug 16, 2017 19:43:24 GMT
Changed  |
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Chris M
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Post by Chris M on Dec 20, 2017 14:50:57 GMT
The RAIB have released an interim report into the derailment. www.gov.uk/government/news/interim-report-collision-near-london-waterloo-stationIt seems that there was a change to the wiring of the points detection that necessitated a modification to the signal testing desk so that all three involved point ends could be simulated. The need for this modification was seemingly not anticipated in advance, and it was not approved or formally recorded. Even though it was intended to be in place only during testing, it was not removed before trains ran. The effect of this was that instead, per the design, the route being detected as secure and the signal clearing only when all three point ends were detected in the correct position, the route was detected secure and the signal was able to clear when any one of the three were detected secure. It was therefore a wrong-side failure caused by incorrect wiring in the signalling system - the cause of the Clapham Junction crash. |
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Post by superteacher on Dec 20, 2017 16:15:39 GMT
Wrong side failure - not good at all.
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Tom
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Post by Tom on Dec 21, 2017 21:37:38 GMT
What shocks me is that the person who made the modification didn't think about how it would work without the desk connected. That demonstrates a dangerously limited amount of understanding. I've tested with a test desk (though it was removed, including all the temporary wiring before trains started running again) and the golden rule for managing the temporary wiring is very straightforward: Each function to be simulated MUST have it's own switch. Here's the largest one I've ever used - this was during the King's Cross remodelling:  |
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rincew1nd
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Post by rincew1nd on Dec 21, 2017 21:41:52 GMT
The effect of this was that instead, per the design, the route being detected as secure and the signal clearing only when all three point ends were detected in the correct position, the route was detected secure and the signal was able to clear when any one of the three were detected secure. Also, the points stopped motoring once they had been (erroneously) detected; they were only part way across when the train arrived at them. |
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Chris M
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Post by Chris M on Dec 21, 2017 22:32:37 GMT
I wasn't sure on that point. The points stopped moving (if they had started*) when the power was cut, which seems fair enough. The power was cut when detection was achieved but it wasn't clear to me whether the power being cut was an automatic (and normal) consequence of detection being achieved or whether the testers cut the power manually after observing a successful (believed simulated) detection?
*Because the points weren't being detected it was not possible to know if they were set reverse before the run through or whether they were between reverse and normal.
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