Train detached near Twinbrook station

[YOLO]

https://twitter.com/AdamTuss/status/808319183096266752" onclick="window.open(this.href);return false;

https://twitter.com/RailTransitOPS/stat ... 6605990913" onclick="window.open(this.href);return false;

It looks like a 7K train detached but can't confirm, no direct report saying so

[MCL1981]

Yep. There's video of passenger's being offloaded through the bulkhead door down to the roadbed and walking back to the station. Definitely a 7000 set. Looks like two A ends, so a coupling released/broke. Not a B end with drawbars.

Dan Stessel, Metro's Minister of Information and chief smoke blower, will claim this isn't a problem with the new cars. They're just offloading people in the middle of the right of way for enhanced customer service.

[JDC]

https://twitter.com/AdamTuss/status/808319183096266752

https://twitter.com/RailTransitOPS/stat ... 6605990913" onclick="window.open(this.href);return false;

It looks like a 7K train detached but can't confirm, no direct report saying so

http://www.nbcwashington.com/traffic/tr ... 22525.html

[srepetsk]

Lead deuce separated from the trailing 6 cars. Seems the separation was between 7135 and 7219 in the middle of Twinbrook interlocking towards Shady Grove.

[Backshophoss]

To seperate this type of coupler,there's a two step routine,Key inserted and pushing a button in the cab to start a release
sequence that results in the cars cut off go into Emergency braking(air dumps in the brake pipe trainline )
Somehow a seperation sequence was started by a false signal from 1 of the cabs involved.

[Chris Brown]

Didn't this just happen in January with a 3k series train?

Seems Metro (as usual) is not doing proper maintenance and (as usual) has lots of under-trained incompetent staff behind the wheel.

[MCL1981]

To seperate this type of coupler,there's a two step routine,Key inserted and pushing a button in the cab to start a release
sequence that results in the cars cut off go into Emergency braking(air dumps in the brake pipe trainline )
Somehow a seperation sequence was started by a false signal from 1 of the cabs involved.

Would this not have to take place from the cab at the coupling? Or can you release any coupling in the train from the lead cab?

[Sand Box John]

"MCL1981"

Would this not have to take place from the cab at the coupling? Or can you release any cupling in the train from the lead cab?

It can only be done in one of the two cabs where the uncoupling is being done. The brake pipe will not dump if the valves behind the couplers are closed.

Me thinks this was a mechanical malfunction in one of the couplers.

[MCL1981]

OK. That's what I thought. I'd also like to think that the commands for decoupling cars are inhibited when the brakes aren't applied?

[mmi16]

Not knowing WMATA's coupling system - is it possible that there was something analogous to a 'broken knuckle' in a Class 1 carriers couplings

[Sand Box John]

"mmi16"
Not knowing WMATA's coupling system - is it possible that there was something analogous to a 'broken knuckle' in a Class 1 carriers couplings

If memory serves, the coupler hooks pivot on a vertical pin to the left to open. A pneumatic piston is used to uncouple. The hooks are held against their mates by a spring. I'm not sure, but I believe the mating surfaces on the hooks are angled like a J to to hold them closed when being puled.

[Backshophoss]

Reported to be that the "reason" was the manual uncoupling pin was "played with"
This was buried in the WTOP report about the "Track Inspector" firings.
This normally done with wrenches at the coupler,between cars in the Yard or in emergency at wrecks on the road,
when the electronics are dead or no power avaible.

[MCL1981]

Is it the kind of thing that could have been partially loosened (are not tightened) and over time it backed out enough to release? Or is it an all or nothing kind of thing? Basically what I'm getting at is how did it stay put and just all of a sudden release at Twinbrook?

[dcmike]

Didn't this just happen in January with a 3k series train?

Yes, and vehicle engineering has yet to determine a root cause for that particular incident.

Or can you release any coupling in the train from the lead cab?

The early cars were delivered with this functionality but it was removed fairly quickly. Automatic uncoupling is restricted to the coupler adjacent to the operating cab only on all fleets.

I'd also like to think that the commands for decoupling cars are inhibited when the brakes aren't applied?

No, quite the opposite. It would impossible to break the coupling without relieving the pressure on the coupler hooks, which requires releasing the brakes.

is it possible that there was something analogous to a 'broken knuckle' in a Class 1 carriers couplings

Yeah, we had one of these as recently as 2014. The hook snapped and through metallurgical testing we determined a small batch of hooks was not properly heat treated by the vendor.

Reported to be that the "reason" was the manual uncoupling pin was "played with"

I received the same information.

Is it the kind of thing that could have been partially loosened (are not tightened) and over time it backed out enough to release?

No, my understanding is the manual uncoupling mechanism was found affirmatively latched in the uncouple position. Here's a few pics to help understand:

First, a coupler hook in it's normal resting state, ready to couple and hold:



As stated earlier, the hook pivots on a pin and is normally retained in position by a heavy spring. When an automatic uncoupling is requested, a pneumatic cylinder pushes against the hook to compress the spring and release the hook from the other coupler.

In an emergency situation where power and/or pneumatics are unavailable, the hook can be pivoted manually using a special tool. The coupler has a receiver for this tool as pictured here (note the orange backwards "L" shaped piece at the bottom for later):



Here is the mechanism with the tool installed:



Using the tool as a lever to overcome the spring force, the "L" shaped piece is pushed up to latch the mechanism in the uncoupled position and the tool can be removed, allowing personnel to stand clear while the cars are uncoupled:



Here's a shot of the hook in the retracted or uncoupling position:



From what I understand, car 7219 was found latched in the uncoupled position.

Basically what I'm getting at is how did it stay put and just all of a sudden release at Twinbrook?

Good question. It likely took more than just the hook being latched in the uncoupled position. I would hazard a guess that one or both of the car end brake pipe cutout cocks was in the wrong position, and/or one or both of the automatic coupler brake pipe valves failed to operate correctly. It's difficult to imagine the propulsive and braking forces were matched so perfectly as to prevent enough air escaping at the brake pipe interface (the black donut) to dump. As to why it happened at an interlocking, I would speculate that the combination of dynamic forces transmitted to the coupler as the cars pass through switches and the third rail gap causing mismatched propulsive effort triggering the event.

[MCL1981]

OMG. So you're saying this thing was likely driving around on the mainline without the coupling engaged at all. And by sheer luck, it just kinda stuck together until the interlocking jostled it and it separated.

Lets say some moron left the air cut outs closed, which prevented the air from leaking out and dumping the brakes. Are the electrical connectors on spring loaded terminals (for lack of a better description) that would allow them some forgiveness in the coupler moving around in such a case as this? If so, when the electrical connection is broken, would that also trigger the brakes into emergency? They're saying the brakes dumped. So I'm guessing if the air was cut out, it did so once the electrical was disconnected?

I wonder if this consist just came out of maintenance and someone forgot a few steps when putting it back together? But then how the hell would it get out of a yard in such a state without separating.