Scotrail 334 becomes uncoupled near Uphall (26/11)

[Tomnick]

I thought the point of automatic brakes was that if a train divided, all the brakes come on.
if that isnt the case then thats a serious concern IMHO.
when you couple up 2 MU's dont they do a brake continuity test any more?

Yes, but the act of electrically coupling means that you won't get the brakes off unless you have brake continuity anyway. You should lose brake continuity if they come apart - unless the uncouple button has been pressed or false fed somehow.

 

[theironroad]

I thought the point of automatic brakes was that if a train divided, all the brakes come on.
if that isnt the case then thats a serious concern IMHO.
when you couple up 2 MU's dont they do a brake continuity test any more?

A brake continuity test isn't require in stock that a a brake continuity wire system unlike older stock with manual main Res and brake pipes that had to be manually connected where it was required in certain situations.

 

[Belperpete]

The rear unit of the train was in no more danger of being struck in the rear by a following train than any other train on that line. The wheels of the rear unit would have been detected by the track-circuit or axle-counter, and the signal behind the train would have been held at red.

There is nothing in the signalling system that prevents or holds a train that is split. Trains are often deliberately split, usually for the two halves to take different routes. Sometimes if a train fails, it may be decided to send the working front half on with the passengers, and leave the failed rear half behind.

Trains are displayed on the signalling panel or screen using a 4 digit train description, e.g. 1A23. When trying to contact a train, signallers will therefore usually use this code, not the unit number. There is a link between the train describer and the GSMR that allows the GSMR to correlate the train description number with the unit number when the driver initialises the train, or if the train description is changed. If the train splits, and the signaller tries to contact the train using its train description number, then he will get the unit that has been correlated with that train description (i.e. in this case, the front unit). I understand that signallers can contact trains by using the unit number, but of course they first have to find out what the unit number is.

If the rear unit was "dead" (lights out etc) then I very much doubt that the PA was switched on, so even if the signaller did try to contact the unit, I doubt that he would be able to make an announcement.

It does seem significant to me that the front unit experienced a "lights out" before departing. This suggests to me that something was reset, either automatically, perhaps as the result of a fault, or manually by the driver, for some reason.

I always understood that it was usual for locos to run with only one pantograph raised, because with both raised it could cause a standing wave in the overhead line between the two pantographs, that could causing arcing and damage the rear pantograph. Does this not also apply to multiple units, or is the pantograph separation great enough that it is not a problem?

 

[scotraildriver]

This is what happened. After station duties were completed the driver was undertaking a "pan drill/battery reset" (basically a reboot/switch off and on again) as a result of spurious faults on the train, very common on 334's. This is why there were reports of a "power outage." For some reason (and which is the focus of the investigation) the units detached themselves during this process. As a result the front unit rebooted as expected so the driver continued unaware, leaving the rear unit detached and dead in the platform.

 

[VioletEclipse]

This is what happened. After station duties were completed the driver was undertaking a "pan drill/battery reset" (basically a reboot/switch off and on again) as a result of spurious faults on the train, very common on 334's. This is why there were reports of a "power outage." For some reason (and which is the focus if the investigation) the units detached themselves during this process. As a result the front unit rebooted as expected so the driver continued unaware, leaving the rear unit detached and dead in the platform.

That would clarify a lot of things.

 

[Ken H]

.

I always understood that it was usual for locos to run with only one pantograph raised, because with both raised it could cause a standing wave in the overhead line between the two pantographs, that could causing arcing and damage the rear pantograph. Does this not also apply to multiple units, or is the pantograph separation great enough that it is not a problem?

Multiple pans on a train do cause problems with pans running into the disturbed wire caused by the first pan. And the 'dirty' air too. Tho the Japanese seem to manage with their bullet trains. But they have a heavy compound catenery.
Which is why TGV was designed with a 25Kv line down the train.
getting the 350's to be passed for 110 when in multiple was problematic because of 2 pans being raised at over 100mph. Were they not passed for 110 but not when in multiple at first?
I dont think we ever did double headers with 86 or 87's on passenger trains so no problem there.
i think 100mph is where the trouble starts.

 

[ComUtoR]

For some reason (and which is the focus if the investigation) the units detached themselves during this process.

Because the uncouple button was pressed

 

[scotraildriver]

Because the uncouple button was pressed

Not unless the driver shut down his desk, walked to the intermediate cab, somehow energised the desk during a reboot, pressed the uncouple button then returned to the front cab and drove off. If that actually happened the driver would be looking at a P45. At least.

 

[a_c_skinner]

The wheels of the rear unit would have been detected by the track-circuit or axle-counter

I did ask a while ago if a unit that was dead (electrically) would have working track circuit actuators, assuming these units have them, but they do need electricity.

 

[JN114]

I did ask a while ago if a unit that was dead (electrically) would have working track circuit actuators, assuming these units have them, but they do need electricity.

Track Circuit Actuators only aid train detection; they’re not the primary means of completing the track circuit.

 

[ainsworth74]

This is what happened. After station duties were completed the driver was undertaking a "pan drill/battery reset" (basically a reboot/switch off and on again) as a result of spurious faults on the train, very common on 334's. This is why there were reports of a "power outage." For some reason (and which is the focus if the investigation) the units detached themselves during this process. As a result the front unit rebooted as expected so the driver continued unaware, leaving the rear unit detached and dead in the platform.

Thank you for this contribution. I think that clears an awful lot of the confusion around this incident!

 

[ainsworth74]

I do wonder if people are perhaps a little confused by how track circuits actually operate. There is a very clear explanation provided by this old BR training video starting from 7:32 (though the whole video is worth a watch if you've got the time!).

 

[a_c_skinner]

Track Circuit Actuators only aid train detection; they’re not the primary means

Yes, but actuators were introduced because modern lighter weight stock didn't always activate track circuits, is my question not pertient?

 

[380101]

Because the uncouple button was pressed

Nope. All investigstions so far point to it being a false feed of some sort to the uncouple circuit which caused the units to uncouple as if the standard uncouple procedure was being carried out ie; intermediate cab desk open and uncouple button pressed. There was also no persons in either of the intermediate cabs at the time. What Scotraildriver details is pretty much what has happened. The engineers at Shields road EMU depot are working on trying to replicate the fault, but so far have had no luck. Both units remain out of service as you'd expect after this type of incident. The biggest issue that may arise once they find the cause of the false feed is that 334s may be barred from running coupled up unless there is an extremely easy and quick solution to prevent it from happening again. Not being able to run 6 car 334s would cause chaos as they pretty much run as a 6 all the time on the Airdrie - Bathgate line.

 

[Belperpete]

The biggest issue that may arise once they find the cause of the false feed is that 334s may be barred from running coupled up unless there is an extremely easy and quick solution to prevent it from happening again. Not being able to run 6 car 334s would cause chaos as they pretty much run as a 6 all the time on the Airdrie - Bathgate line.

Assuming that they do find the cause. Intermittent faults can be difficult to find at the best of times, almost impossible unless you can get it to happen again.

 

[380101]

Assuming that they do find the cause. Intermittent faults can be difficult to find at the best of times, almost impossible unless you can get it to happen again.

Yes, this is the big problem in this case. After 5 days of investigating, they have so far not been able to recreate the fault. The question I'd now be asking if I was still involved in engineering and not a train driver is "do we think it will or could happen again? and if we do, what will we do?". The company will have to either ground the entire 334 fleet until such time as they find the cause OR immediately ban 334 units from operating in multiple OR come up with a solution that completely isolates the couple/uncouple circuit, thus allowing them to keep multiple units already coupled in service. Its a tough decision to make, especially if grounding an entire fleet of 40 units has to be done. This could seriously harm the December timetable change.

 

[alangla]

Its a tough decision to make, especially if grounding an entire fleet of 40 units has to be done. This could seriously harm the December timetable change.

As I said upthread, grounding would be the ultimate nightmare for the Airdrie to Edinburgh section of the line- there is literally nothing available as a practical replacement. Locking the couplers for depot coupling only would probably be the best option, running as all 3 cars would make for some grim peak hours east of Bathgate, unless some paths & drivers could be found to operate extra services. All in all it’s a horrible situation & good luck to all at ScotRail & Alstom trying to fix it.

 

[Belperpete]

Yes, but actuators were introduced because modern lighter weight stock didn't always activate track circuits, is my question not pertient?

Without re-opening the whole argument about whether they are actuators or assistors or assisters, the suppliers' (Unipart) web-site states that they are for light-weight DMUs:
https://www.unipartrail.com/assets/j2540-tca-brochure-st3.pdf
So no, your question is not pertinent to this incident, as the units were not DMUs. EMUs probably don't need them because the high-current traction return through the wheels has pretty much the same effect. I also think that the problem was with low-voltage (usually battery-fed) track-circuits, that you don't get on electrified lines.

I seem to recall that they are permanently switched on, but can't off-hand find anything that says so. You certainly wouldn't want a train to suddenly "disappear" just because the driver has left it. The Railway Group Standard for configuration of Track Circuit Assisters states that they must be effective on both the leading and trailing vehicles:
https://docplayer.net/51036039-Track-circuit-assister-configuration-for-rail-vehicles.html
This suggests to me that the assister on a given vehicle isn't simply controlled by the cab on that vehicle being switched in.

I think that they work on the same kind of principle as the RELCO units that were used with model railways (and may still be available, I don't know). If they detect that no circuit is made, they apply a burst of high frequency current to break through the dirt, rust or whatever. Once the circuit has been established, they then switch themselves off. So for a train stopping where there is contamination on the rails, the assister will burn through the rust, dirt etc, and so enable the track-circuit current to flow, in the first few milliseconds of the train coming to a stand. It is highly unlikely that contamination will then form between the wheel/rail interface, as the two are in immediate, stationary contact. So even if this incident had occurred on a non-electrified line with DMUs, and even if the TCAs had been disabled on the rear unit by the train splitting, the track-circuits should by then be detecting the unit.

 

[JN114]

Yes, but actuators were introduced because modern lighter weight stock didn't always activate track circuits, is my question not pertient?

With all due - none of the what-if isms are particularly pertinent. It’s mountains from molehills. Members come here for facts about the incident, not speculation on what could have made it worse if there were 5 Mondays in the month.

There is nothing to suggest the TCA was faulty.
Even if the TCA was faulty, it’s highly unlikely all 12 wheel sets were insulated from the rails.
Even if the train was fully insulated from the rails; while the passengers were stuck for a while the driver and signaller both became aware of the issue within a few minutes - long before another train was due, and plenty of opportunity for appropriate protections to be applied by the signaller.

Credit to @scotraildriver for his candid account of what actually happened.

 

[Larry Trapp]

Reading this thread got me thinking about a brake failure incident on a 319 at Haywards Heath in 2006.

In that case a washer had found its way into one of the drumswitches on the train and shorted out wiring causing a false feed to be sent to the brakes.

I wonder if something similar could have happened here?

Here's the link to the report incase anybody wants a look:

http://www.railwaysarchive.co.uk/eventsummary.php?eventID=1514

 

[Chuggington21]

Not sure if it's been mentioned but now someone else has given most of the details anyways. These units had been running about for days together over a week I'm told.

But scotrail driver has told most of the story as it is at the min

 

[Belperpete]

This is what happened. After station duties were completed the driver was undertaking a "pan drill/battery reset" (basically a reboot/switch off and on again) as a result of spurious faults on the train, very common on 334's.

Thanks to you and 380101 for your insights.

Does a "pan drill/battery reset" involve lowering and raising the pantograph? If so, raising the pan may have caused a brief power surge when contact was made again with the OLE. Power surges and their attendant electro-magnetic interference are notorious for causing unexpected things to happen in low-voltage circuits. Replicating exactly the same power surge will be impossible unless they can recreate exactly the same OLE conditions (impedance, loading, effect of adjacent trains, etc.) as existed on site at the time the fault occurred.

Do the units concerned have "black boxes"? And if so, would they be functional on both units, or just the leading (driving) unit? A black-box would at least give some clue as to what might have happened, and equally importantly what couldn't possibly have happened.

 

[Chuggington21]

Yeah a pan drill you drop the pan and switch off the batteries. Wait a min, switch bats back on, then pan up.

OTMR (black boxes) would have recorded in both units until the point of the bats being tripped

 

[scotraildriver]

Just to add, despite the rear unit being "dead", it was operating track circuits normally so there was no danger to the public, apart from maybe egressing on the wrong side(which no one did)

 

[whoosh]

It seems the units 'uncoupled', rather than 'divided'. Divided would of meant the front section came to a stand with the braking continuity wire broken.

Someone mentioned a false feed to the uncouple button. Maybe that's a possibility - I remember prepping a HST on a depot, and you could dial in a number on the NRN radio to leave yourself a message. This would test the microphone and the earpiece and loudspeaker. When I pressed the 'push to talk' button on the NRN radio handset the brake released!! A false feed to brake system.

So false feeds can happen.

 

[bengley]

There's also a way on 319s of pressing the signal buzzer and another button while the doors are open and the interlock circuit becoming energised.

 

[snookertam]

This is what happened. After station duties were completed the driver was undertaking a "pan drill/battery reset" (basically a reboot/switch off and on again) as a result of spurious faults on the train, very common on 334's. This is why there were reports of a "power outage." For some reason (and which is the focus of the investigation) the units detached themselves during this process. As a result the front unit rebooted as expected so the driver continued unaware, leaving the rear unit detached and dead in the platform.

Pan drills aren't supposed to be done on the main line if the train is still capable of proceeding in service. Making sure that instruction is adhered to might be a way of mitigate risk of a repeat whilst the investigations are ongoing.

 

[Macwomble]

Thank you @scotraildriver & @380101 for their input.

It's always good the get the real answers rather than a lot of (usually unfounded) speculation.

 

[theironroad]

Thank you @scotraildriver & @380101 for their input.

It's always good the get the real answers rather than a lot of (usually unfounded) speculation.

+1
...

 

[Bletchleyite]

Does this not also apply to multiple units, or is the pantograph separation great enough that it is not a problem?

More that an autocoupler doesn't provide a good enough electrical connection to be putting traction power down it.