London Waterloo - station, services, facilities, incidents - and some quirks / odd facts (merged posts)

[whole diary]

[paul7575]

Thanks.   In the conversation about four positions, of course what we a looking at is analogous to a binary truth table, where Normal and Reverse are the equivalent of 0 and 1.  So two 'mechanisms' each with 2 conditions gives you four results?

N N
N R
R N
R R

...sort of thing?

Paul

[SandTEngineer]

Thanks.   In the conversation about four positions, of course what we a looking at is analogous to a binary truth table, where Normal and Reverse are the equivalent of 0 and 1.  So two 'mechanisms' each with 2 conditions gives you four results?

N N
N R
R N
R R

...sort of thing?

Paul

Correct again (I'll make a signal engineer out of you yet ).  In the incident the train was signalled through the points concerned NN, but they were actually set RN.  On clamplock operated double slips each end of a pair is individually driven by separate hydraulic rams but they are connected to the same single electro-hydraulic pump unit so 2 per double slip arrangement (there is a design version that has 2 separate electro-hydraulic pump units per pair - 4 in total for a set of double slips; but for reasons of economy in design, installation and ongoing maintenance, that configuration is rarely used).

[Chris from Nailsea]

Well, I'm glad to see that you two apparently understand it ... 

[eightf48544]

Still doesn't answer why weren't the points clipped N N. If RN and RR would cause a collison

[SandTEngineer]

Still doesn't answer why weren't the points clipped N N. If RN and RR would cause a collison

Its not for us to speculate why.  Its for RAIB^▸ (Rail Accident Investigation Branch) to determine that.

[SandTEngineer]

Well, I'm glad to see that you two apparently understand it ... 

I have tried to explain it in 'simple' non-technical terms but a double slip is probably the most complex set of points that exist so......

I have decided that I need to do you a drawing.  Watch this space 

[paul7575]

Still doesn't answer why weren't the points clipped N N. If RN and RR would cause a collison

Because if clipped to straight through i.e. "NN" there would have been no access to P13?

Paul

[paul7575]

Roger Ford's monthly preview of his next Modern Railways article again quotes an unnamed source who says that the points simply "should have been clipped" so I still await the RAIB^▸ (Rail Accident Investigation Branch) detailed explanation.   

Paul

[paul7575]

RAIB^▸ (Rail Accident Investigation Branch) interim report.  I'm no expert - it is as expected all to do with stage works and testing, is very detailed and I'm hoping someone can follow it through and come up with a short precise.  Seems the point ends the train approached were physically 'mid position' as seen from the FFCCTV.

As was postulated in various forums at the time, the driver and signallers cannot be considered responsible in any way.

https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/669469/IR022017_171220_Waterloo.pdf

Paul

[Oxonhutch]

Primarily points 1524A and 1524B should have been clipped in their normal position (as per plan) but were not.

Secondarily, a test wire was left connected which shorted out the electrical detectors to 1524A&B and fooled the signalling system into believing the point blades were correctly set and locked normal.

If only one of the above had happened the accident would not have occurred - it required the combination of the two. Holes in the cheese.

Had unclipped point blades moved without the testing wire being present, detection would have been lost and the starting signal would not have cleared.

[IndustryInsider]

Along with the incident at Cardiff, these are gentle reminders to NR^» (Network Rail - home page) and it’s contractors that although the recent safety record is incredibly good, a major incident could still easily happen if safety procedures are allowed to slip.

[SandTEngineer]

Primarily points 1524A and 1524B should have been clipped in their normal position (as per plan) but were not.

Secondarily, a test wire was left connected which shorted out the electrical detectors to 1524A&B and fooled the signalling system into believing the point blades were correctly set and locked normal.

If only one of the above had happened the accident would not have occurred - it required the combination of the two. Holes in the cheese.

Had unclipped point blades moved without the testing wire being present, detection would have been lost and the starting signal would not have cleared.

10 out of 10 for that summary.  As a practicing signal engineer for nearly 50 years now, I am bitterly disappointed to have to read that the lessons learnt from the Clapham accident have not been followed through.  I know that the pressure to complete things to time is greater than ever, but when safety of the travelling public is concerned, we need to remember not to be frightend and to stand up when required and say NO.

[paul7575]

With points 1524A and 1524B (and 1524C) all clipped normal, how would they achieve a route into P13/14?

Am I missing something obvious here?   Or did I misread something earlier that implied that 1524 and 1525 operated together?

Paul

[Oxonhutch]

With points 1524A and 1524B (and 1524C) all clipped normal, how would they achieve a route into P13/14?

Through Points 1525A which were free to move independently of points 1524A or B.  Points 1525B were also free to move but were located on a locked-out route.

[SandTEngineer]

With points 1524A and 1524B (and 1524C) all clipped normal, how would they achieve a route into P13/14?

Am I missing something obvious here?

Paul

Paul,  if you look at Figure 2 in the report you will see that it is 1525AB points that direct trains into/out of Platforms 12/13/14/15.  1524ABC points are only required normal for those movements.