WCML Signal 113 (near Primrose Hill tunnel) fault

[Railperf]

WM113 (and WM116) were reconnected on the 23rd.

Where was the problem in the end?

 

[Nippy]

I don’t actually know I’m afraid. We (signallers) were just told it could be booked back into use.

 

[Bald Rick]

Where was the problem in the end?

AIUI it was interference somewhere on the datalink affecting specific modules.

Somethign similar, but on a bigger scale, happened on the GWML a few months back.

 

[Tilting007]

Where was the problem in the end?

Still not fully resolved but approach control removed.

 

[Class 170101]

AIUI it was interference somewhere on the datalink affecting specific modules.

But when they were first installed they weren't a problem so whats changed since their installation?

 

[alxndr]

But when they were first installed they weren't a problem so whats changed since their installation?

I don’t know in this specific case, but components can degrade overtime and become less effective at filtering out interference or cables can be damaged. The level of interference can also increase beyond what can be filtered out, this has happened in a few different places where there has been issues with the overhead line switching equipment.

 

[Annetts key]

But when they were first installed they weren't a problem so whats changed since their installation?

The interference may have come from a faulty item of signalling equipment. Or other nearby equipment.

Or part of the datalink (cable or equipment module connected to it) have have degraded resulting in a worse signal to noise ratio. Like listening to an AM radio, then a car passes with an unsuppressed ignition system and the audio signal becomes hard to hear due to the interference.

The trouble is, with up to 63 Trackside Functional Modules (TFM) per data link, tracking down the source of the trouble is time consuming.

 

[Bald Rick]

But when they were first installed they weren't a problem so whats changed since their installation?

Lots of things, not necessarily to do with the railway.

 

[Tilting007]

The reason for the failure here is still under investigation.
The only change is approach control on Fast Lines has been removed.

 

[MarkyT]

The interference may have come from a faulty item of signalling equipment. Or other nearby equipment.

Or part of the datalink (cable or equipment module connected to it) have have degraded resulting in a worse signal to noise ratio. Like listening to an AM radio, then a car passes with an unsuppressed ignition system and the audio signal becomes hard to hear due to the interference.

The trouble is, with up to 63 Trackside Functional Modules (TFM) per data link, tracking down the source of the trouble is time consuming.

In addition to interference from railway sources such as traction, it's plausible third party activity near the railway can cause problems, say a really noisy electrical process under the line in a commercially leased arch, or a powerful new radio transmitter nearby. Unfortunately BR chose a copper datalink standard while Belgium specified fibre optics for the same job when they also adopted SSI technology through Alst(h)om (a little later than BR I think to be fair). While Belgium used the same central interlocking hardware, they had different custom TFMs, datalink modules and customised main programme and data config language that better matched their national standards. I think the field address space was larger, i.e. more modules per system, and the fibre datalink protocol was much faster and suitable for axle counter evaluation over the same link. Alstom developed a special TFM that, in addition to standard inputs and outputs, could directly connect the inductive sensors.

 

[alf]

The reason for the failure here is still under investigation.
The only change is approach control on Fast Lines has been removed.

This fault caused considerable disruption over many weeks.

If the approach control, which caused many down fast drivers to slow to 10mph from 55 mph, can be removed now with the ‘failure’ still under investigation why was approach control ordered in the first place.

For the signallers’ & the public’s benefit I hope this fault can be eliminated & publicly explained so lessons can be learnt.

 

[najaB]

If the approach control, which caused many down fast drivers to slow to 10mph from 55 mph, can be removed now with the ‘failure’ still under investigation why was approach control ordered in the first place.

I'm not in he industry so this is purely speculation, but my guess would be that they initially defaulted to the safest mode of operation per the rule book (approach control) until they were able to make the safety case for resuming normal operating procedures.

In other words, assume that it will kill you until you can prove that it won't. Don't forget that the rules are literally written in blood.

 

[Tilting007]

I'm not in he industry so this is purely speculation, but my guess would be that they initially defaulted to the safest mode of operation per the rule book (approach control) until they were able to make the safety case for resuming normal operating procedures.

In other words, assume that it will kill you until you can prove that it won't. Don't forget that the rules are literally written in blood.

This fault caused considerable disruption over many weeks.

If the approach control, which caused many down fast drivers to slow to 10mph from 55 mph, can be removed now with the ‘failure’ still under investigation why was approach control ordered in the first place.

For the signallers’ & the public’s benefit I hope this fault can be eliminated & publicly explained so lessons can be learnt.

To prevent a SPAD at line speed. It will not have been applied for the fun of it - and the delay will have caused significant financial penalty to NR.

Still in under investigation means the exact cause may not be known but there is enough data and enough has been done to stabilise the link enough to remove the approach control.

 

[Bald Rick]

It will not have been applied for the fun of it

Correct

and the delay will have caused significant financial penalty to NR.

Not correct, as the delays will largely be ‘sub threshold’ and not accounted for financially.

It has, however, completely screwed On Time and Time to 3 punctuality, which has caused much consternation.

 

[Annetts key]

Still in under investigation means the exact cause may not be known but there is enough data and enough has been done to stabilise the link enough to remove the approach control.

Or to put it another way, permission given for a return to normal working, but the fault is still open (also known as "left on test").

Or more than one actual faulty unit / cable or suspected unit / cable / cause may have been identified. With the most likely or worse having been dealt with. Leaving some other work remaining. Maybe due to having to wait for spares to arrive or for a suitable "wheels free" time slot.

The trouble is, with some intermittent faults, only the passage of time can reveal if the system will be reliable. And sometimes, it's hard to know for certain until normal working is back in operation. Been there, done that. If the desired outcome, everything is fine and stays that way, over 24 hours (or however long), book it back in working order. Or you may get a call five minutes, ten minutes or maybe an hour later "it's done it again!"...

 

[Tilting007]

Correct




Not correct, as the delays will largely be ‘sub threshold’ and not accounted for financially.

It has, however, completely screwed On Time and Time to 3 punctuality, which has caused much consternation.

Delay was around 3 mins per train with the delay totalling around 14k mins since the incident started late March.

 

[Bald Rick]

Delay was around 3 mins per train with the delay totalling around 14k mins since the incident started late March.

Thanks, that sort of demonstrates my point. Well over 300 trains a day use that stretch on the fasts, if they had all racked up 3 minutes attributed delay the incident over the almost 2 months it would have been a 50k mins+ incident.

Clearly a big incident, and one that needed resolving quickly.