Let’s say you’re an engineer on a long train, 2 locomotives and 130 cars. You’re running along and you’ve opened the throttle up to 5, 6 or even 8 as you’re climbing a slight grade. There isn’t much to do…no signals or crossing coming up… so you use the opportunity to get out of the seat, perhaps to go to the bathroom. But oh my gosh…all hell breaks loose as soon as you’re indisposed. There’s a sudden break in the brake pipe, and the brakes apply HARD. What happens now? You’re indisposed and out of the seat…does an application of the brakes automatically disengage the throttle?..or does a tug of war ensue?
The PCS (Pneumatic Control Switch) will drop the diesel engines back to idle.
Different scenario: Going downgrade at 20 - 30 MPH, with the dynamic brakes fully engaged and the engine in Run 5 or 6 to fully excite the motor fields and run the cooling blowers over the dynamic brake grids - otherwise the same. What result ?
I believe the engine stays running, to maintain the dynamic braking. There’ve been some NTSB (US) or TSB (Canada) accident investigations which involved that not happening, and which in turn led to the disaster without the DB to prevent a runaway. But I can’t put my finger on the titles or links for those reports right now.
- Paul North.
P.S. - Here’s one, though with a very complicated set of facts:
http://www.tsb.gc.ca/eng/rapports-reports/rail/1997/r97c0147/r97c0147.asp
With any luck, your conductor is also a qualified engineer (seniority, you know) and can handle the situation.
Somebody has to deal with the alerter while you’re out of the seat, or you’re gonna stop anyhow…
Even if he/she isn’t a qualified engineer, there’s a pretty good chance they may be able to keep things under control until you finish your business.
I was going to say, unless you are really fast, the alerter is going to go off and stop the train while you are missing in action.
HERE IS ONE OF THE LINKS YOU ARE REFERING TO WHERE LOSS OF DB CAUSED
A WRECK
True - but in that one, the engineer apparently inadvertently hit the “MU Shutdown” switch, which did just that - it was ‘self-inflicted’:
DERAILMENT OF UNION PACIFIC RAILROAD UNIT FREIGHT TRAIN 6205 WEST NEAR KELSO, CALIFORNIA - JANUARY 12, 1997
NTSB Report No. RAR-98/01= “Railroad Accident Report 98-01”, NTIS Report/ Publication No. PB98-916301, adopted Feb. 6, 1998.
I was thinking more of one where when the brakes went into emergency not initiated by the crew, and then the PCS shut down the prime mover, the locomotives also lost dynamic brakes. There might also be some where an override to keep the DB working in such a situation was installed, but didn’t function properly for some reason, which then caused the wreck. But thanks anyway for the link. [tup]
- Paul North.
Paul, the answer you are looking for is, maybe. It used to be that an emergency application would nullify the dynamic brake. Some engines have been modified to provide continuous dynamic braking, even during an emergency application from any source. My info says all UP engines with DB are so equipped, but many foreign (non-UP) line engines aren’t.
Regarding the PCS opening, some engines are set up so that there is a 20 second delay before power is cut off when the emergency application comes from the train line. This is to give the front end the chance to pull away from the back end during a break in two.
Jeff
Jeff, and others - The TSB report linked below is likely one that I had in mind. As you noted, evidently not all Dynamic Brake-equipped locomotives have the feature to keep the DB on even when the train is placed into emergency braking mode. See footnote 4 and the text just around it, which is as follows: [emphasis added - PDN]
“Soon after starting down the steepest section of the grade, the locomotive engineer placed the train into emergency. The dynamic brake 4 (DB) cut out and the locomotive engineer increased the locomotive independent brake to the fully‑applied position; however, the train speed continued to increase.”
From FN 4: “Unless equipped with a dynamic brake holding feature, the dynamic brake cuts out when the air brake system is in emergency.”
Railway Investigation Report
Non-Main-Track Train Derailment
Kootenay Valley Railway (KVR)
0700 Trail Yard Assignment
Mile 19.0, Rossland Subdivision
Trail, British Columbia
23 April 2007
Report Number R07V0109
http://www.tsb.gc.ca/eng/rapports-reports/rail/2007/r07v0109/r07v0109.asp
Two crewmen - the foreman [conductor] and helper [brakeman] - jumped and sustained only minor injuries; tragically, the engineer stayed with the locomotives, and was killed in the ensuing wreck of the runaway.
Dynamic Brake is a non-vital system that is very useful in modulating retardation up and down, something that the air brake can not do withouit a total release. (non vital means that the failure mode is to "Off: position.) In an emergemcy, however, the PCS switch will kill the engines in either power or brake mode. (I’ve been out of the brake business for 25 years but I’m certain this is mandated.) It behooves the enginman to maintain.a downhill speed that will permit an all friction stop.
A condr I worked with a while back told me this story. It was a situation kind of like Ulrich described. I don’t know how fast they were going, throttle notch etc. Anyway, the engr gets up to use the “facilities.” The cab signal changes from clear to restricting and the audible warning goes off. That means the engr (who’s indisposed in this case) has 6 seconds to either acknowledge the change and start slowing if under 40 MPH or initiate a brake application above 40 to keep a penalty application from happening. I think, but don’t remember, they were under 40 and all that need be done immediately was acknowledge the change. (The engr would’ve had time to finish his business and start slowing the train.)
The condr unsure of what needed to be done (pushing a button in this case) did nothing. The warning timed out and gave them a penalty brake application. It’s not an emergency application, but a full service application that also allows the PCS to open up, reducing the power to idle. Because of where they were, they got a knuckle and broke in two.
Later when the MOP (road foreman) was downloading the engine, he asked what happened. They told him the truth. The engineer was admoni
The alerter isn’t an issue. Just do what Homer Simpson did with the Y key on his keyboard in that episode where he gets to work from home. The one with the drinking bird toy. Just use that on the alerter. Problem solved.
Back to the initial question, you have to remember that if the brakes go into emergency, “all hell” doesn’t break out. It takes significant time to get the full application of the brakes and the momentum of the train causes it to slow gradually. If you are going up hill and there is break away, the train will go a few car lengths and stop with the break only a few car lengths. If you are going down hill, the train may stay together since the locomotive brakes are usually more effective than the freight car brakes. If the train breaks apart the cars will normally catch the train once the locomotive brakes apply.
One wouldn’t expect a break apart going down hill unless the locomotive is pulling deliberately to keep the train stretched (which is often done, but done gently).
Even a moderately sized train of a few cars will go about a train length after the thing goes into emergency from 30 mph for example. Things happen slowly on a big heavy train.
Brakibg ratios on locomotives are generally lower than on freight cars because of the lomotive’s greater weight. While the emergency is transmitted at about 900 ft/sec, the air brake control valves are designed to get the shoes against the wheels before the full application takes effect. Slack run-jn or pull-out is better controlled in emergency braking than in some service brake applications in conjunction wirh dynamic brake…