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RAIB report - Near miss at Chalfont & Latimer 21/6/20

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Old 27th July 2021, 19:50
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RAIB report - Near miss at Chalfont & Latimer 21/6/20

The Rail Accident Investigation Branch (RAIB) has published it's report into a near miss at Chalfont & Latimer station which occurred on 21st June last year and it makes interesting, if not a little scary, reading.
Chalfont & Latimer station is a London Underground station, which is shared by Metropolitan Line (underground) & Chiltern Railways (overground) services.
The incident involved a Chiltern Railways train heading towards London Marylebone which passed a signal at danger (SPAD) which protected the junction for the Chesham Branch, triggering an automatic emergency brake application. The driver had missed the red signal and, thinking that the emergency brake application was "spurious", he reset the tripcock to release the brakes and carried on towards Chalfont & Latimer station, passing through (and damaging) the junction points, only realising that there was a problem when the train lurched to the right, taking the crossover at 10mph over the permitted speed. At this point he made a full emergency brake application, coming to a stand around 23 metres in front of a Chesham-bound Metropolitan Line train which was stationary in the platform.

https://assets.publishing.service.go...___Latimer.pdf

Tony



Last edited by TRP; 29th July 2021 at 10:26. Reason: spelling
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Old 29th July 2021, 12:07
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Thanks Tony.

Wow.

Three things spring to mind...

1) Unsolicited brake application - Driver must contact signaller, then establish cause before proceeding.

2) Operation of Emergency Brake system. Driver must call signaller and confirm that a SPAD has not occurred. Failure to do so is a 'Reset & Go'.

3) If you're resetting a tripcock in the vicinity of a signal, it's probably the arm which tripped it. At the very least you'd have to check it out then call it in as a signal fault.

I do have sympathy for the driver though - I used to drive Tripcock-fitted mainline trains trains (Class 313) on the Northern City Line, and the arrangement of having Mainline safety systems AND LU safety systems together in the same cab is an utter PITA, in my opinion. A typically British style lash-up.

Just reading through the RAIB report quickly, I was struck by the fact that the Chillout Lines train was only equipped with a GSMR radio. No LU radio, so there's no way of communicating with signaller controlling the route you're working over. Bearing in mind that there's many places where you can't get out and walk to a Signal Post Phone (because of Limited Clearances and Conductor Rail Equipment), that puts you out of contact. And if I understood the report correctly, it suggests that the TOC didn't provide drivers with phone numbers for their mobiles to contact signallers with. If this IS the case, that's very naughty.

Perhaps a silver lining to this safety incident is that maybe Chiltern/LU will have to sort this apparent Comms issue out?

Time will tell, as always.

Cheers, John.

Last edited by Beeyar Wunby; 14th August 2021 at 07:33.
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Old 15th August 2021, 03:18
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G'day BW,
Can you explain the procedure for the Trip Test, as in the situation applied to the double yellow signal in this incident.
We have the Train Stop (train trip) system in smog hollow.
It works VERY effectively, especially when combined with the double overlap.
If this junction existed in smog hollow, there would be TWO RED sticks protecting the junction points.
Our Train Stop lever only raising at signals displaying STOP, plus those displaying a restrictive subsidiary indication (slow speed or calling on).
The Slow Speed situation is train speed orientated, and the trip will drop when train speed is below that set (normally 25 kph).
In the actual smog hollow underground sections, the trip lever remains raised on sticks displaying Green over Red.
That again being train speed determined, and will drop when train speed on approach is below that stipulated (again usually 25 kph).
Sticks in our underground sections are virtually 8 car train length separation.
So, many more sticks existing than up in the atmosphere.
Steve.
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Old 15th August 2021, 19:34
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Yo Steve.

The Tripcock Test is simply a kind of treadle that the train's tripcock arm depresses as it goes over it. We had them at Finsbury Park on platforms 7 & 8, which was where the entry to the old London Underground tunnels to Moorgate was. On our system, the platform starter was held at danger as you approached at 25mph or less. On the way down the platform you could see the white proving light illuminated under the red. If you were successful, the light went out and the signal cleared if you had the road. However if you failed the tripcock test the light stayed on, the signal stayed on, and a dinky little bell half way up the platform rang - which in turn caused a lethargic platform person to slowly womble over to you and tell you what you already knew.

The signaller would tell you to crawl under the cab and visually check that the tripcock arm was in the set (down) position. If you were happy they'd clear the starter, then get you to pass the next siganal at danger. If doing this fired off the tripcock, you'd have to reset it, and then were 'good to go' into the Underground system. If it didn't fire, you'd go to the next station, change ends, and go empties to the shed for repairs
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Old 15th August 2021, 19:43
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I'm guessing that the double yellow in the Chalfont & Latimer photograph is only cleared due to the white light being out. I would expect the signal to be at danger if there were a problem, because a driver is never going to see a little pidldy white light when approaching a signal - we're trained to 'target fix' on the aspect - and 'watch it through' until you're past it, in case the sigggy 'puts back' in an emergency.

Could be wrong though.

Cheers, John
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Last edited by Beeyar Wunby; 15th August 2021 at 19:54.
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Old 15th August 2021, 19:53
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The slow speed release of tripcocks you mention is known in the UK as Moorgate Release - after the terrible collision at Plat 9 in Moorgate, when the London Underground operated it.

I used to drive into Plats 9 & 10 when I worked for Great Northen. You had speed boards bringing you down from 30, to 20, to 10 on the approach to both dead_end plats. As you rolled down the platform a timer counted down, and you watched nervously for the trip arm half way down the platform to drop. I never did more than 8mph myself, because you just don't need the crap that goes with a stopped train in the rush hour, OR a safety incident on your licence.

Cheers, John
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Old 16th August 2021, 03:50
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Ah ok BW, thanx for that detailed description.
I had thought that the test would result in an emergency application by tripping the bogie lever.
And, I thought that such testing might create an AUTOMATED response by the driver.
Loose the air, shove it into emergency until air flow stopped, and then release to reset the trip lever.
So, the test dingus gets depressed, and does not possess the rigidity to cause the trip lever (pendulum as we calls it here) to go off vertical and dump the air.
No such digus here.
Though, there are portable trip blocks that can be plonked down beside the track for emergency purposes, and also for train brake response testing.
I was sent down to perform some union train brake testing back in the early 1990s.
Belt the empty car train along a section of closed to traffic track and hit the temporary trip block.
Sand bags plonked on seats to replicate cattle weight.
Then measuring the distance from the trip block to where the train finally stopped.
Various set types possessing differing braking systems and abilities.
It was real fun when squirting water on the track.
WOOHOOO, I'll finally stop after crossing the state border.
Smog hollow emu and now dmu trains must have the trip apparatus in operation at each end of the set, but not within the set.
The trip lever locked up after amalgamation, that pair of cabs being now in the middle of the train.
Should the trip not be locked up, then it will hit the first signal passed by the train.
That signal going to STOP as the front passes it, and the trip raising.
And, after uncoupling to create two shorter trains, trip lever locked into active position.
The train safety apparatus will not provide power when the specific cab trip lever is locked up.
The rear trip pendulum naturally being on the opposite side of the track to signalling and trips would ONLY go off if hitting something laying near to the track.
The trip remaining set at the rear to facilitate quick turnaround at terminus stations.
But, the front trip can also hit materials laying near to the track.
I was travelling home pas one time from smog hollow riding up front with the Lithgow Daddy (senior driver having transferred to the interurban roster, aka partially retired).
Slamming down through the ten tunnels we espied a wild goat trot in ahead of us.
Sure enough, the front trip went off hitting the body of the snotted goat.
I was out the cab door and down on the bottom step holding onto the handrails attempting to reset the trip pendulum before we lost all of the air and forced to stop.
After a number of thumps with me boot, I got the pendulum reset and the air dump stopped.
We could keep rattling down the hill.
We were very late due to other dramas.
How stupid was I.
But, I was younger and invincible back then.
The tunnel wall whisking past me earlobes as I held on outside the cab.
Yes, intermediate trips exist at various locations on the underground and in the atmosphere sections for terminus and locations where quad track converges into double track.
Riding around with smog hollow hoggers I did get stunned by their approach to these dingi.
Having FAITH that the trip would drop, they just let the train roll.
You would not see that trip drop, even when standing up to squiz out the cab windscreen.
It is a bozner safety system and has saved numerous serious incidents in smog hollow.
Especially when combined with the double overlap.
Though, has never been fitted to locomotives for pas or freight.
The XPT (pseudo HST) power cars are now fitted, but regarded as a dmu.
Steve.
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