The route was set up in readiness for the slot being given and on this occasion it avoided a serious derailment. The photo in question is an evidential photograph showing things in the exact position as it was at the time of the incident.
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Chiltern parliamentary - RAIB investigation
- Thread starter cjohnson
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The route was set up in readiness for the slot being given and on this occasion it avoided a serious derailment. The photo in question is an evidential photograph showing things in the exact position as it was at the time of the incident.
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I have no problem whatsoever with informed speculation, or with discussion around the underlying principles, but - as Greenback suggests - it's a fine line between that and jumping to uninformed conclusions, as has already happened early on in this thread.
Well I await to see if that's the standard procedure in place, let alone permitted by the locking, with the previous movement still foul of the single line, because if so it shows that the concept of Flank Protection which stood the railways in good stead for 100 years continues to be forgotten by signalling designers. Given that the site of the Ladbroke Grove accident is just down the road from here, which would have been prevented if the same longstanding principle had been in place, you would have hoped for better. Over to you, RAIB.
carriageline
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I imagine the catch/trap points are more to do with stoping a train enter the single line when a train is entering in the other direction (ie, wouldn't be able to clear the signal going the otherway until the catch/trap points are normalised (to divert a 'runaway'), this has nothing to do with flank protection mate, something different.
Indeed, it's not flank protection at all. Both ends of the crossover would need to be normal for a move off the single line (at least one going direct towards Paddington) thus protecting against a head-on collision. Certainly for passenger trains, though, there's no need to use any sort of trap points in these circumstances, because there'll always be a requirement to provide a suitable overlap in advance of the protecting signal (as there must have been here) - passenger trains approaching 'open' trap points within the overlap is, quite rightly, seen as a Bad Thing. In this case, the points in question will have been beyond the overlap of the first signal to be SPAD-ed. Since they're not really protecting anything, no sensible signalman is going to work them back normal knowing that they're going to have to be reversed again in a couple of minutes - and it's far better to have a train wrongly entering a section behind a train moving in the same direction than it is to run one against a set of stops and have it off the road.
moggie
Member
You've obviously made your mind up though.
Yeah, the two red signals is a little thing really lol, the fact the TPWS failed to stop the train is the monumental balls up.
Cobblers. Even if you are being facetious the introduction of TPWS in no way absolves the driver from the fundamental requirement to observe signals and control the train accordingly, as you well know. As i'm sure you also well know TPWS when operational does not prevent SPADS. A TPWS intervention will merely seek to limit the consequence of a SPAD - i.e. to prevent collision with a conflicting movement. TPWS is not fitted to signals which merely protect against rear end collisions. That is why this particular incident is concerning due to the extent of the overrun.
What additional requirements of the TPWS system are identified if any will no doubt form a recommendation of the investigation.
One other point to note; TPWS as a system is not fail safe in that power is required to make an intervention when a train is about to pass a signal at red. i.e. loss of power renders TPWS ineffective. The mitigation against this was to include proving of the TPWS loop energised in controls of signals on the approach (with some exceptions) thereby providing a form of protection against failure of a protecting system. Railtrack initially thought the latter feature was unnecessary but were persuaded from their ill thought through early views.
As for the onboard kit. I'll leave that for others to debate.
So you are complaining about other people posting inaccuracies and then you come out with the highlighted bit! :roll:
Thye TPWs was not isolated it was in a fault state, a very well known fault state, I have had it in that condition dozens of times on a 458.
(Apologies for going a little off-topic...)
There was plenty of flank protection at Ladbroke Grove. The fact is, though, you can't flank protect against everything: the designers of the signalling were forced to choose where a train overrunning SN109 would go. The first set of points after SN109 took trains over to the Down Relief, and then there was a long gap to the second set of points connecting to the Up Main. Trains had to end up on one or the other after passing SN109, because line 3 ends at that point.
The general principle they abided by is that trains aren't very likely to SPAD by a long distance - short-distance SPADs of a few metres are quite common; long SPADs like SN109 remain quite rare. So in choosing the flank locking for SN109, the designers chose to protect against the more likely risk of a glancing collision with a train on the Down Relief, rather than the less likely (but more serious) risk of a head-on collision on the Up Main. Unfortunately, the latter is what happened in 1999.
In short, the signal designers at Ladbroke Grove couldn't prevent every possible collision with flank locking: the fact that they lost a 60-40 bet doesn't mean they were wrong to design it the way they did.
There was plenty of flank protection at Ladbroke Grove. The fact is, though, you can't flank protect against everything: the designers of the signalling were forced to choose where a train overrunning SN109 would go. The first set of points after SN109 took trains over to the Down Relief, and then there was a long gap to the second set of points connecting to the Up Main. Trains had to end up on one or the other after passing SN109, because line 3 ends at that point.
The general principle they abided by is that trains aren't very likely to SPAD by a long distance - short-distance SPADs of a few metres are quite common; long SPADs like SN109 remain quite rare. So in choosing the flank locking for SN109, the designers chose to protect against the more likely risk of a glancing collision with a train on the Down Relief, rather than the less likely (but more serious) risk of a head-on collision on the Up Main. Unfortunately, the latter is what happened in 1999.
In short, the signal designers at Ladbroke Grove couldn't prevent every possible collision with flank locking: the fact that they lost a 60-40 bet doesn't mean they were wrong to design it the way they did.
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That crossover is almost always left in the reverse position unless required for an up movement. We cannot accept a train from Ruislip until it is normalised. Once a train is on the single line, the crossover cannot be reversed until the up train has been on the berth track circuit at the signal for approx 45 seconds.
In the old days, as an old school signalman, I would have dropped the train down to the first signal that was SPADed cleared it and then held a red flag out from the box to chat to the driver. It wouldn't have helped here as, as the first signal passed was only 55 yards or so from the box so time was very much against the signalman. The second one being not far either.
With regards to the emergency call issues, I don't know what happened there so will wait for the RAIB report, or a local interim report about that.
In the old days, as an old school signalman, I would have dropped the train down to the first signal that was SPADed cleared it and then held a red flag out from the box to chat to the driver. It wouldn't have helped here as, as the first signal passed was only 55 yards or so from the box so time was very much against the signalman. The second one being not far either.
With regards to the emergency call issues, I don't know what happened there so will wait for the RAIB report, or a local interim report about that.
I think you will find it was 1 poster. 1.
And why can they not have a comment about it? Yes there was a fault with the TPWS as has been aired but also the driver, according to the report, went through 2 red signals. If he was concentrating then why did he not see the signals at red?
I dont want to berate the driver too much because I am unaware of the full facts apart from what is in the report, as you are, so dont deride others for wanting to discuss the fact that 2 signals were passed at danger.
Precisely. Discussion is fine, but know the limits!
carriageline
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No, I agree, and this very situation highlights the need for drivers to concentrate, and the safety critical role they are in.
What I meant was, spads happen a lot, for a huge variety of reasons (even if they are not called spads any more
), what doesn't happen often is TPWS failing to stop a train after it has had a SPAD (I imagine?). The reason for the SPAD will be highlighted quickly, with possibly a small recommendation to chiltern. The TPWS situation will be, again i imagine, looked at in a lot of detail, and with a huge nationwide recommendation to all TOC/FOCs and network rail.I may be wrong, but that's how I see it
Apologies, I was just copying what the RAIB had said, saying it had "self isolated", and what was said on the 'other forum', I don't care about inaccuracies, I care about jumping to conclusions, which you have said plenty of times your self! We all can't be perfect
As I have said plenty of times, I like discussion (why would I be here otherwise!
), and with some of the minds on this place brings out some interesting views, and also brings out the technical nitty gritty stuff that wouldn't normally be discussed. Heck, we can talk why the signals were passed at danger, he might of not been concentrating/micro sleep/fatigued/not very competent, but I just don't agree with people stating things as if they know what happened (as a solid fact), that is all. Again, talking about topics such as micro sleep interests me, definitely from a drivers point of view.
Sometimes I just think it's the way things are worded which causes misunderstanding, I for one often post things and it comes out in a way I wouldn't of said it in real life, apologies all!
MichaelAMW
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It might be worth pointing out, given your remark about there being no requirement for a trap point in most double-to-single passenger situations, that the "trap point" in question is only there as a left over from the singling of the line to Northolt Junction: when it was still double track the facing crossover was part of the single-lead junction round to the Ealing line. I hazard a guess that it was left as it was to avoid needing to change much in the interlocking and detection.
Unless there has been a change at Greenford very recently, the previous signal to the one shown is fairly close, perhaps only 50 odd yards behind the photographer - the two signals are only 142 yards apart according to the RAIB summary - so the first signal passed at danger is somewhat less than the usual 440 yard overlap distance from those points. On the other hand, the outermost home signal, which is the signal where the overlap is relevant, is a lot further away, beyond the other side of the triangle. The train must have passed that signal, 57, and the following one at the east end of the triangle, 56, both showing proceed aspects before this incident occurred.
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Does that mean that you can't set the route for a train coming from South Ruislip round to the West Ealing line until it's basically at the up home signal?
(P.S. My other post was just intended to add a bit of detail to what you said - you obviously know more first-hand about the place than I do!)
It is quite an interesting question, I've noticed it happening to myself a few times when walking around. Not seeing a flashing bike light or a cars indicator. (Fortunately I always look into incoming traffic when I cross a road, so didnt get hit by the cyclist.)
I wonder if instead of On/Off Flashing, it should go Bright/Dim, to make it more obvious if you look when the warning light is off
It is an unintentional flaw Mr Leigh and if they knew this would happen it would have been designed differently. The difference between the AWS magnet and the TPWS grid is quite a major one in that with the TPWS fault, and it is a fault you get a brake release and can continue your journey. I cannot see your view in that it is a feature of the TPWS system, it is poor design and needs rectifying as there has now been an incident that in other circumstances could have been a lot worse than it was.
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You also have to remember that this is absolute block and the distant signal must have been at caution. As most of us know if a distant signal is at caution a driver must assume all associated signals are at danger.
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I don't know about other drivers on this forum but I had never been told by any of the four TOC's I have worked for, by any DM, any trainer or any driver that if the yellow light is flashing when setting up the cab the TPWS is not operational. I have been told in the past to continue to the next stopping point and then reboot the cab to get rid of the flashing light.
I HAVE been told in the past that it isn't a fault but it only flashed because you are over a grid.
I think that no body actually realised that if you set up a cab over a grid the TPWS will self isolate and not be operational.
Have any other drivers been told any different? I don't think the RIAB, the RSSB or any other body knew this flaw up until this incident.
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MichaelAMW
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As it happens it's TCB, but the point you're making is still exactly the same of course. An extra factor at Greenford is that the outer home is a 3-aspect colour light, rather severely approach released if I recall correctly a conversation I had with a relief signalman many years ago, and so that would have only cleared to a single yellow, offering another caution signal on top of that at the distant.
O L Leigh
Established Member
OK, perhaps to use the word "feature" was unclear or wrong. However, what I mean by that is that it is simply the way the system operates. You can argue that it is a "flaw", but briefing out details about this to drivers is the best way to deal with it rather than by having to re-equip the entire fleet. I've only ever had this happen to me twice and know that it can be dealt with relatively quickly and easily.
How do you know you have a TPWS fault? Because you get a flashing yellow light. Do you know what the fault is and whether or not it will affect the safe and correct operation of the TPWS? No you don't, and so you have to assume that whatever the fault is that is causing the flashing yellow light is serious enough that it will prevent it from working. In the absence of any definitive information you have to assume the worst.
O L Leigh
Does that mean that you can't set the route for a train coming from South Ruislip round to the West Ealing line until it's basically at the up home signal?
Yep that's correct.
As it happens it's TCB, but the point you're making is still exactly the same of course. An extra factor at Greenford is that the outer home is a 3-aspect colour light, rather severely approach released if I recall correctly a conversation I had with a relief signalman many years ago, and so that would have only cleared to a single yellow, offering another caution signal on top of that at the distant.
Yes, there is no distant signal. The signals are all stop signals on the down although GE.57 works a bit like a distant, if all associated stop signals are cleared then there is no approach release, if the route is set towards Ruislip you get a green at GE57, 56, 55 and 50, if the route is set via the East Curve towards West Ealing you get a proceed aspect at GE.57 (can't recall if green or yellow), green at GE68, and 67. If, however all other signals are not cleared then as stated above GE57 is approach released and it is a heavy one, the train has to be almost at the signal before it clears.
Yep that's correct.
As it happens it's TCB, but the point you're making is still exactly the same of course. An extra factor at Greenford is that the outer home is a 3-aspect colour light, rather severely approach released if I recall correctly a conversation I had with a relief signalman many years ago, and so that would have only cleared to a single yellow, offering another caution signal on top of that at the distant.
Yes, there is no distant signal. The signals are all stop signals on the down although GE.57 works a bit like a distant, if all associated stop signals are cleared then there is no approach release, if the route is set towards Ruislip you get a green at GE57, 56, 55 and 50, if the route is set via the East Curve towards West Ealing you get a proceed aspect at GE.57 (can't recall if green or yellow), green at GE68, and 67. If, however all other signals are not cleared then as stated above GE57 is approach released and it is a heavy one, the train has to be almost at the signal before it clears.
440 yards is only required beyond the home signal on an AB line with a semaphore distant though - the standard overlap on a TCB line is only 200 yards. The latter can be reduced further in some cases (including where there's a delayed yellow in the signal in rear!) and - not sure whether it's required here, but I'd be surprised if not - there's usually a requirement to bring a train nearly to a stand at a semaphore stop signal if the next one can't be cleared. Incidentally, failing to apply that rule is a very good way to mislead a driver into passing a subsequent signal at danger, though of course there's no suggestion that that happened here.
The latter can be reduced further in some cases (including where there's a delayed yellow in the signal in rear!) and - not sure whether it's required here, but I'd be surprised if not - there's usually a requirement to bring a train nearly to a stand at a semaphore stop signal if the next one can't be cleared.
That's how I would work it, the bloke on shift has been at Greenford for a long long time though so I would hope he did the same. I don't actually know though, but I do know the forward CCTV has been viewed, so it will be fairly easy to see what signals the driver saw.
That's how I would work it, the bloke on shift has been at Greenford for a long long time though so I would hope he did the same. I don't actually know though, but I do know the forward CCTV has been viewed, so it will be fairly easy to see what signals the driver saw.
DaveHarries
Established Member
All,
After a PM from 'yorkie' regarding my earlier post on this I have removed the said comment as I gather it caused outrage. Apologies for any annoyance / offence / etc. caused.
Dave
After a PM from 'yorkie' regarding my earlier post on this I have removed the said comment as I gather it caused outrage. Apologies for any annoyance / offence / etc. caused.
Dave
Mr. Leigh you use the word assume and it was a driver assuming. I have never been told that if the yellow light flashes over a grid the TPWS self isolates itself and does not work have you?
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So it is TCB with 2 semaphore stop signals one following the other? How does this work then?
I certainly have, I thought it was well known that the flashing fault/isolate light indicates the system is isolated and needs resetting? Part of setting up the desk is checking the AWS/TPWS and if any of the tpws lights remain on after cancelling the AWS you would certainly look into it before departing.
It's a common problem at kings x platforms 9,10&11 with single 313s as the country end is right on the grid. That is why 313s stop half a coach short of the stops at kings x.
PermitToTravel
Established Member
Is the tiny distance in between a block in its own right?
BravoGolfMike
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And me! I'm actually surprised that there are drivers who hadn't been told this, I had assumed, because of how often it had been drilled into us, that it was common knowledge industry wide. Obviously not! Some of ours have got themselves into bother for waiting until the first station and resetting there to save time, as they 'know' it's displaying a fault because they reversed over some grids.
MichaelAMW
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TCB applies to the method of working between signals in a MAS area and between *signal boxes* where they are operating the signals. From the outer home to the starter at Greenford is within station limits so are not covered by block regulations, at least not as far as we're thinking about them here. The same would apply in an absolute block area - that's similarly the method for working between the boxes but not within the area controlled by the box. So it's TCB from the last down signal, somewhere near Park Royal, operated by Slough New and the Greenford outer home; and it's TCB again from the Greenford down starter to the first signal, approaching Northolt Junction, operated by Marylebone.
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TCB throughout, surely? Station limits was an AB term, but even that's been done away with in the quest to dumb the regs down even further. It's a pedantic point though, and I'd agree that it doesn't differ much in practice. Either way, it'll be worked no differently to a sequence of semaphores in an AB area - if one can't be cleared, each signal in rear should be kept at danger until the approaching train is quite or nearly at a stand (though specific exemptions do exist) and the distant signal in rear (whether an isolated distant or a stop signal in rear acting as the distant, as is the case here and at plenty of AB locations) won't come off, or clear to a green, until all the semaphores are off.
O L Leigh
Established Member
Not wishing to be inflammatory, but perhaps I should ask what you understand by a flashing Isolation/Fault light if not that the system is not working.
O L Leigh
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