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Reply to "Sad news from Canada"

Dynamic braking after the runaway began was mentioned.  Here's a little more uncertainty to those of us speculating from the warmth of our homes and not directly involved in the investigation.

When an emergency air brake application occurs, the pneumatic control switch (PC Switch) opens a circuit and interrupts the ability of the locomotive to produce power.  Virtually all large locomotives are equipped with the PC Switch feature.

Here's where the uncertainty enters:  It is entirely up to the individual railroad's Mechanical Department whether or not the opening of the PC Switch will also interrupt dynamic braking if the emergency air brake application occurs while the locomotive is in dynamic braking rather than pulling.  There are two trains of thought.

The reason for the open PC Switch to interrupt dynamic braking is to avoid slid flat wheels if the Engineer does not quickly bail off (using the independent brake handle) any buildup of locomotive air braking that would -- when combined with dynamic braking -- exceed the ability of the wheels to maintain traction.  Then the locomotives have no braking at all, when being pushed by a train.  To further complicate things, some railroads also equip their locomotives with dynamic brake interlock, which prevents any locomotive brake buildup from train brake applications, including emergency braking.  Again, some have it, and some don't.

The reason for not having the PC Switch interrupt dynamic braking is that dynamic braking is much more powerful than locomotive air brakes, and is more useful in stopping a heavy train.  If the couplers are compressed by dynamic braking throughout the train, and an emergency brake application occurs, you do not want slack to run out while the train is stopping, as other problems can result.

So, you can see that there are two valid ways to do it, and railroads are divided as to their choices.

So, we do not know whether dynamic braking was available to the second crew.  If the PC Switch had to be re-set in order to get dynamic braking working, then the only way to do it is to move the automatic brake valve to Release*, and that would also release whatever brake cylinder pressure remained on the cars.  That would have been a suicidal decision, but sometimes it's difficult to clearly think out the best decision, and this would have been a bell that could not be un-rung.

*  Older, non-electronic, 26-C automatic brake valves could re-set the PC Switch by being placed in the Suppression or Handle-Off positions on some railroads' locomotives, but, on others Release was required.  This whole thing about whether dynamic braking was available to the second crew comes down to this:

Maybe they had available dynamic braking, and maybe they did not.  But, either way, without adequate air braking, they were not going to make it to the bottom of the grade without a derailment or collision.

Last edited by Number 90

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