Low-speed derailment at Bognor Regis (22/10)

[RichardKing]

As the title suggests, 313212 derailed as it was leaving Bognor this morning. RAIB are investigating and GTR and NR will be trying to re-rail the unit and repair the points in the meantime.

I believe the service involved was 2P03 Bognor Regis to Littlehampton. There were passengers onboard, but Southern state that no one was injured.

 

[2HAP]

RAIB Safety Digest published. Signalman's error:

https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/944586/D082020_201217_Bognor_Regis.pdf

During degraded operations (such as when providing verbal authority for a train to pass a signal at danger), it may not be appropriate to rely on the protection normally offered by the interlocking. It is therefore important that signallers use all available information, including points indicators, to ensure that a route is correctly set before giving permission for a train to pass over it.

It is important that signaller competence management systems impart and maintain required levels of knowledge and familiarity for signallers to operate all signalling locations for which they are authorised, especially where equipment may not operate in ways that signallers would normally expect.

When short-notice changes to working patterns are necessary to cover staff shortages, it is important that the risk of fatigue is managed appropriately. In accordance with Network Rail’s standard on fatigue risk management, roster amendments should be made to minimise the build-up of fatigue and, where resource shortages are likely to be prolonged, the actual hours worked should be reviewed and the roster amended. The amendments should be risk assessed, and control measures put in place to manage identified fatigue risks.

 

[ainsworth74]

I thought this was interesting:

An informal, locally-produced reference sheet in the signal box described all the lever movements that were necessary for a given train movement, and the signaller repeatedly consulted this sheet to check that he had carried out the correct actions. Because all the levers were in the correct positions according to the sheet, the signaller believed that the routes for each train were correctly set. However, the signaller did not recognise that, because the points at Bognor Regis involved in this accident are motorised, the position of the point levers only served as a reminder that he had commanded the points to move. The lever position does not necessarily reflect the actual position of the points on the ground, as it would if a mechanical linkage was in place and working correctly.

Perhaps I was being a bit naive but I was surprised that it seemed the signaller didn't realise the importance of confirming the the position of the points using the indicators rather than lever position. It seemed rather obvious to me that if your points are motorised you're going to need to use indicators as there is no mechanical linkage! Then again I wonder if that was where the fatigue (and fatigue under pressure at that) came in. Easy to fall into the usual habits and rely on your reference sheet if your feeling stressed and tired.

 

[alxndr]

Would a relief signaller such this the one involved have solely have worked this box or would there be any possibility that they would have worked boxes with points moved by traditional rodding runs as well as boxes with motorised points? If so, that may have added to the confusion and checking the indications.

Also, would there be any benefit in having the indications "flash" in a similar way to how they would in a power box to draw more attention to points that are not in correspondence? As I understand the report if they are not correctly detected either normal or reverse the indicator is simply blank. Should still be checked regardless, but it's not as eye-catching.

 

[Mcq]

For information - the batteries referred to for the point motors - are these rechargeable lead acid or alike - are they required to provide enough peak energy?

 

[broadgage]

For information - the batteries referred to for the point motors - are these rechargeable lead acid or alike - are they required to provide enough peak energy?

Yes, point motors need significant power, but only for a few seconds at a time, and this is commonly supplied by 24 volt lead acid batteries near the points. The batteries are generally trickle charged from the mains electricity supply. Wind or solar energy could be used in remote locations.

I recall an earlier incident, elsewhere, in severe snow. A signalman operated certain points frequently without any direct operational need, believing that so doing would help to avoid the points becoming frozen in one position. Unfortunately this depleted the batteries to the point where operation was unreliable.
The results were similar to this incident, points moved partially, points indicator not observed, train derailed, fortunately without serious consequences at low speed.

 

[Mcq]

Many thanks - very clear explanation

 

[MarkyT]

Yes, point motors need significant power, but only for a few seconds at a time, and this is commonly supplied by 24 volt lead acid batteries near the points. The batteries are generally trickle charged from the mains electricity supply. Wind or solar energy could be used in remote locations.

I recall an earlier incident, elsewhere, in severe snow. A signalman operated certain points frequently without any direct operational need, believing that so doing would help to avoid the points becoming frozen in one position. Unfortunately this depleted the batteries to the point where operation was unreliable.
The results were similar to this incident, points moved partially, points indicator not observed, train derailed, fortunately without serious consequences at low speed.

Point batteries are typically 110V in UK to suit the standard range of point machines used, although different motor voltages can be provided by manufacturers. The charger is supposed to alarm if the mains input fails, so batteries should not become critically discharged unexpectedly. The battery should provide significant standby capacity in the event of charger failure, appropriate for many hours operation at typical duty cycle of the site concerned. Bognor is a major overnight rolling stock site, working closely with nearby Littlehampton to service and stable a large number of Southern units.

 

[alxndr]

For information - the batteries referred to for the point motors - are these rechargeable lead acid or alike - are they required to provide enough peak energy?

Typically they would be these where multiple point ends are fed from the same supply:

Cyclon 57 cell 25Ah battery pack, for Multiple Point Switching

If you watch Paddington 24/7 one of the episodes this year very briefly showed a point fault involving faulty batteries, although they didn't go into any great detail and I can't recall which episode it was in.
The issue is when they start to fail it may look as though there is sufficient voltage but they will no longer have enough "oomph" left to drive the points fully over, especially if multiple points are called in quick succession, or they are long points. There might be enough left to nearly make it, but not entirely.

 

[MarkyT]

Typically they would be these where multiple point ends are fed from the same supply:

Cyclon 57 cell 25Ah battery pack, for Multiple Point Switching

If you watch Paddington 24/7 one of the episodes this year very briefly showed a point fault involving faulty batteries, although they didn't go into any great detail and I can't recall which episode it was in.
The issue is when they start to fail it may look as though there is sufficient voltage but they will no longer have enough "oomph" left to drive the points fully over, especially if multiple points are called in quick succession, or they are long points. There might be enough left to nearly make it, but not entirely.

Do you recall where the failure was in the TV programme? While the early 1960s and 70s signalling schemes had point batteries at big junctions, later colour light schemes, especially SSI projects from the mid/late 1980s I think, specced the main signalling power supplies, and their central back-ups, able to power all the points that could be expected to move simultaneously without a local battery. Bognor Regis is not such a site, being a modernised traditional installation. For very modern schemes, the paradigm has shifted once again, with distributed batteries once again more in favour. For a 110V point battery set-up, a bank of these would be connected up in series. The Cyclon brand of sealed lead-acid cells has been used in signalling for decades, with small very low maintenance installations like these able to replace huge wet lead-acid batteries of old made up of multiple individual glass tank cells that needed periodic testing and top up.

 

[alxndr]

Do you recall where the failure was in the TV programme? While the early 1960s and 70s signalling schemes had point batteries at big junctions, later colour light schemes, especially SSI projects from the mid/late 1980s I think, specced the main signalling power supplies, and their central back-ups, able to power all the points that could be expected to move simultaneously without a local battery. Bognor Regis is not such a site, being a modernised traditional installation. For very modern schemes, the paradigm has shifted once again, with distributed batteries once again more in favour. For a 110V point battery set-up, a bank of these would be connected up in series. The Cyclon brand of sealed lead-acid cells has been used in signalling for decades, with small very low maintenance installations like these able to replace huge wet lead-acid batteries of old made up of multiple individual glass tank cells that needed periodic testing and top up.

The failure shown in the program was in Westbury, which is RRI from I think the mid-80s.

 

[Crossover]

Out of interest, why are the points fed off batteries rather than directly off mains? Is it common to all points or just in certain areas?

 

[MarkyT]

Out of interest, why are the points fed off batteries rather than directly off mains? Is it common to all points or just in certain areas?

It's a high but fairly brief intermittent load moving those heavy switch rails. In a mechanical box the maximum load is self managed though as only one lever can be moved at a time by the signaller, although the battery may also provide the standby as often there is only a single low grade mains supply on site. For large colour light schemes from the 1960s onwards the power supplies were much higher capacity and more resilient, often duplicated or with generator back up. However new interlocking techniques meant many points could be automatically set to move simultaneously on setting a single route on a control panel using the entrance-exit method, so a battery was often used to cope with the large spike in demand. If this still drew too much current for the supply in a particularly complex junction, engineers might artificially limit how many points could motor at the same time by arranging to move them sequentially in groups, although that would clearly extend the overall route setting time.

The failure shown in the program was in Westbury, which is RRI from I think the mid-80s.

Yes I was a drawing office trainee at the time and Westbury was definitely early/mid 80s, although I never worked on that particular scheme as it was essentially already designed and being built. I did visit some of the installations though and assisted on commissioning weekends, and I'm sure both Westbury and similar vintage Exeter had point batteries where neccessary at each of their many relay rooms. At a training course for designing newly developed SSI schemes a few years later, I was surprised to be told there would be no point batteries provided in SSI schemes, at least in standard equipment cabinet designs. That's not to say a battery would be impossible clearly, and I'm sure some custom designs may have used them over the years, especially in later so called 'interfaced SSI' schemes where SSI logic replaces a troublesome relay interlocking suffering from degraded wiring, but all the legacy outside trackside cabling and equipment remains unchanged.

 

[LAX54]

I thought this was interesting:



Perhaps I was being a bit naive but I was surprised that it seemed the signaller didn't realise the importance of confirming the the position of the points using the indicators rather than lever position. It seemed rather obvious to me that if your points are motorised you're going to need to use indicators as there is no mechanical linkage! Then again I wonder if that was where the fatigue (and fatigue under pressure at that) came in. Easy to fall into the usual habits and rely on your reference sheet if your feeling stressed and tired.

Have to say I read the report, then had to read it again, to make sure I had read it right ! personally think the fatigue mention is a little bit of red herrring.

 

[WL113]

I must admit to being somewhat surprised on reading this report. Correct detection on points is the first thing to look for if a signal wont clear.

Nobody sets out to have an incident though, and this has strong similarities to the derailment at Knaresborough in 2015. In that case the box was being operated by a Mobile Ops Manager and also had motor operated points controlled by a lever frame. The MOM took the fact that the lever being in the correct position meant that the points must be fitting correctly as they would be if operated mechanically.

Good shout by Alxndr. Some form of alarm to attract the signallers notice that the points have failed would be a good idea. Both ends and the correspondance light flashing on an NX panel do that job well, as does the points indication flashing with an audible alarm sounding on Westcad workstations. A bulb not being lit can be missed it seems.

Knaresborough report here..Report 16/2016: Derailment at Knaresborough - GOV.UK (www.gov.uk)

 

[MarkyT]

I must admit to being somewhat surprised on reading this report. Correct detection on points is the first thing to look for if a signal wont clear.

Nobody sets out to have an incident though, and this has strong similarities to the derailment at Knaresborough in 2015. In that case the box was being operated by a Mobile Ops Manager and also had motor operated points controlled by a lever frame. The MOM took the fact that the lever being in the correct position meant that the points must be fitting correctly as they would be if operated mechanically.

Good shout by Alxndr. Some form of alarm to attract the signallers notice that the points have failed would be a good idea. Both ends and the correspondance light flashing on an NX panel do that job well, as does the points indication flashing with an audible alarm sounding on Westcad workstations. A bulb not being lit can be missed it seems.

Superficially, the idea to flash the existing N and R lamps when there's no detection seems attractive, but that introduces more complexity and failure modes into the circuits, including a flasher unit to go wrong. A separate out of correspondence bell/lamp might be better, perhaps a general alarm for any set of electric points in the box, activated after a short time, although you might imagine that being a complete PITA with an ongoing known failure awaiting attention and then masking any further failures. All additional complexity as well. Even with purely mechanical point actuation, it could be possible to insert an FPL bolt with no detection, and that, plausibly, could be due to some broken part of the mechanism leaving a switch improperly positioned. An FPL should not be considered a detector. There was electric detection here. The signaller should have referred to it before authorising the movement.

The signalling diagram in the RAIB report is out of date (not in any respect important to the incident). The engine release ground frame crossover near the buffer stops between pl. #3 and the middle siding was removed as part of the point motor job, as was the peculiar semaphore shown on the up line near the signal box, combined with a colour light distant for an intermediate block home. The former IB home and its distant were moved north towards Barnham for sighting reasons.