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QUOTE: Originally posted by M.W. Hemphill Most locomotives no longer have a PC switch, which disable the dynamic brake and return the prime mover to idle when an emergency brake application ismade. Control systems have been redesigned to use vastly more sophisticated methods to avoid the wheel-slip condition that the PC switch prevented. (PC stands for Pneumatic Control, by the way.) There's nothing necessarily "wrong" or "unsafe" about a lead locomotive equipped with a PC switch so long as the operating rules for mountain-grade operation are written in such a way that dynamic braking is not being counted on for a safe descent. SP's rules were so written. (There were some other problems with the rules, but they were not major factors in this runaway.) These were the pertinent questions in this runaway: 1. Were the operating rules of the Southern Pacific written in such a manner that a train that cannot be controlled on a descent is prohibited from initiating that descent? 2. Were the conditions assumed by the rules in fact "true conditions" -- that is, was the crew properly trained, the equipment said to be in working order truly in working order, and was the weight of the train known accurately? In this case, the rules could have been written better. The crew was inexperienced. Some of the equipment reported to be in working order was not in working order. Most important, the weight of the train was undereported by 45%! A railroad's operating rules for mountain-grade operation recognize that trains come in all tonnages and lengths, with few locomotives or many, with all of the locomotives on the head end or interspersed in other locations in the train, with or without locomotives equipped with working dynamic brakes, and outside in a broad temperature range. Thus the rules present a flow-chart that enables a crewman to insert the train's trailing tonnage, its number of operative air brakes (one per car except for cars such as articulated double-stack cars), number of axles of effective dynamic braking, and in some cases the temperature. The train is inspected at its initial terminal and at required intervals en route to ensure that brake-cylinder piston travel is within limits, brakes shoes are present and within wear limits, and that the brake line is competent and that the brakes can be set and released. The train crew is given a trainlist that reports the tonnage. Before beginning the descent of the mountain grade, the train crew inserts their train data into the flow chart, and follows its decision path to determine (1) if their train is legal to descend that hill, (2) what speed is permitted for the descent, and (3) if retainers are required. If they do this correctly, the inspections have been done correctly, and the information reported to the train crew is correct, and the rules are correct, the descent will be made safely. At the time, SP's rules (as well as most railroads' operating rules) contemplated that a train could have a complete dynamic brake failure after departing the top of the hill -- which is the condition, of course, that a train encounters with an emergency brake application when the PC switch cuts them out, and there are many reasons to initiate an emergency brake application (or have one initiated unexpectedly), not just to stop a runaway. Therefore, SP's rules prohibited a train from descending from Hiland to West Colton that could not be controlled by air brakes alone. However, SP had gotten into the habit, as kenneo explains cogently, of underestimating weights. To quote the NTSB: "The accepted practice of estimating weights at the time cars were released, coupled with the belief that these weights would be changed at a later time, created a potentially hazardous situation in which yard clerks were merely satisfying a requirement of the Southern Pacific computer system." An additional error arose in that SP operating rules stated that SP cars equipped with empty-load sensing devices had a braking capacity of 1.5 times normal, but in reality they had a braking capacity of 1.0 times normal. An experienced and attentive crew, in my opinion, would have known something was up within moments after releasing the air at Mojave Yard and beginning their trip. A train so far over its reported tonnage will accelerate and decelerate noticeably differently than a train of that true tonnage. However, neither the road engineer or helper engineer observed that brake applications to control speeds on previous descents were excessively heavy, nor that the train was excessively sluggish under power. Nor did they seem to be aware that a heavy tonnage train coming over the top and beginning the descent of a mountain grade must "balance the grade" immediately, and if it cannot be balanced, an emergency brake application must be made at once. (Balancing the grade means that the train remains at a constant speed that is a safe speed at a constant braking effort without additional control input.) Thus the engineer let the train accelerate toward its 30 mph authorized speed (based on the wrong weights) and then looked to see if he could balance the grade, and when he couldn't, he did not dump the air immediately. In making numerous trips over Soldier Summit, Utah, with experienced Utah Railway and Rio Grande engineers on 15,000-ton coal trains, they emphasized to me the crucial importance of balancing the grade immediately after leaving the summit. As one said to me, if he did not have the train balanced by a certain landmark after beginning the 2.0% descent (which I later determined was 4,500 feet beyond the summit), he would dump the air at once, and if the train did not promptly begin to decelerate, he and his conductor were leaving the train for the bushes while they still could. Another trip, the same engineer and conductor later told me that one winter night they came off the summit in heavy snow. They were the first train down the westward main in about eight hours. They were plowing over a foot of fresh snow with the train, and apparently so much snow had built up on the trucks that the braking effort was very poor. He couldn't balance the hill, so he dumped the air. The train refused to decelerate so he and the conductor took their grips out on the front platform and started looking for a good place to jump off. While they dithered looking for a good snowbank, the brakes finally burned off enough snow buildup to take effect, and because there wasn't any wheel heating to speak of, they got a good solid brake application, and despite the speed having gone to 45 mph the train began to slow and stopped. Then the conductor tied handbrakes so the engineer could get a release and recharge, and their were able to come off the mountain safely. Since that time, he said, when there was a possibility of snow or ice buildup he made enough of a brake application at the summit to burn off anything that was there, then a full release and recharge using the power to hold the train on the grade while the helper cut out, and only then did he leave.
QUOTE: Originally posted by M.W. Hemphill Eric: I saw the Discovery Channel show. The video was interesting and useful. The narration was pretty breathless and silly.
USAF TSgt C-17 Aircraft Maintenance Flying Crew Chief & Flightline Avionics Craftsman
"No soup for you!" - Yev Kassem (from Seinfeld)
QUOTE: Originally posted by M.W. Hemphill Vsmith: I think an experienced, smart, and attentive engineer would have sensed that something was wrong the moment the train didn't sit down as expected with a 10-12 lb. reduction, and dumped the air right then. It's been my fortune to ride with some very good engineers, and I think they would have figured out the train was way overweight long before that point from the way it pulled.
Have fun with your trains
QUOTE: Originally posted by M.W. Hemphill 7. Because the mine and the railroad estimated the lading weights, rather than scaling the cars at the mine, the train was waybilled at 6,151 tons or 89 tons per operative brake but was actually 8900 tons and 128 tons per operative brake. By SP rules, a train exceeding 125 TPOB and 18 axles of operative dynamic braking would not have been permitted to descend the hill eastward from Hiland to West Colton. 8. Computer simulations found with 6,151 trailing tons and 24 axles of dynamics -- the amount the train crew believed they had -- the train was controllable and the descent was made at 30 mph. At 8,900 tons and 18 axles of dynamic braking, and including the efficiency losses of the brake shoes as they heated, the train exceeded 105 mph. Summary: Had the engineer gone straight to a full-service brake application at the time he increased the reduction to 13 lbs., while the train was still in the curves at the top of the hill, he would have been able to stop the train. One the train had reached MP 469 and gone to 21 lb. reduction, the train was no longer controllable.
QUOTE: Originally posted by M.W. Hemphill Mud: To quote the NTSB: "The NTSB determined that the probable cause of the pipeline rupture on May 25, 1989, was the inadequate testing and inspection of the pipeline following the derailment that failed to detect damage to the pipe by earth-moving equipment."
QUOTE: Originally posted by Clemente If I remember it correctly, wasn't there some interfacing feature of the dynamic brakes that was preventing them from making an emergency air application? Some kind of cut-out or override? If the helper crew had cut off as mentioned above, and they left the rear car's angle **** open, would that have been enough to trigger an emergency application, or was their air already pissed away by then?
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