Page:NTSB - Railroad Accident Report - Derailment on May 25, 1989.djvu/56

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facility) foreman. He further testified that mechanical department personnel, if they become aware of any defects, will update the computer with information. According to the chief mechanical officer, the dispatcher, once he receives information from engineers regarding defects, has the responsibility to update the computer. The assistant chief dispatcher testified that he often updates the computer when he receives reports of defects, although he believed it was not his responsibility to do so, or he will give the information to a clerk who will then update the computer when time is available.

A review of maintenance records and failure reports by Safety Board investigators revealed that on May 4, an engineer had filed a failure report on unit 7549, the third unit in the head-end consist, noting that there were no dynamic brakes. According to the maintenance record, the motor braking switch was stuck and the repair was made. The chief mechanical officer testified it was not a major repair and that there was a possibility that a defect of that type could occur again. With respect to unit 9340, the fourth unit in the head-end consist and the one that the head-end engineer reported as "intermittent' in dynamic braking, maintenance records indicated that it had received extensive repairs to the dynamic brake on April 27 and 29, 1989. According to the chief mechanical officer, the extensive repairs would indicate to him that the dynamic brakes should have been working on the day of the accident. According to the failure reports, unit 8317, the lead unit in the helper consist, had been reported as having inoperative dynamic brakes on May 8, 1989, 4 days before the accident. The chief mechanical officer testified that it was not uncommon for a unit to continue to be used in helper service "until it worked its way" to the Los Angeles repair facilities. Testimony by the head-end engineer and the helper engineer indicated that it was not uncommon to have a unit in a locomotive consist with inoperative dynamic brakes. The chief mechanical officer testified that the number of units reported to have inoperative dynamic brakes varied on a daily basis from 3 to 35.

Recovering Dynamic Brakes.—According to the chief mechanical officer, an engineer can recover the dynamic brakes (after an emergency application of the train brakes has been made) by going to "a handle off position and recover[ing] the PC after about 70 seconds."[1] He stated that he believed the head-end engineer had sufficient time to recover his dynamic brakes. He also stated, "I suspect there could have been some slight benefit going back into dynamic brakes but at those speeds the dynamic braking effort is very, very low."

  1. When an emergency air brake application is made, the PC switch, an electropneumatic device (sometimes referred to in the industry as the power cut-off switch or the pneumatic control switch), trips the eletric current which causes the main generators to unload and the engines to return to idle. When the air brace handle is placed in the handle off position, the PC will automatically reset. After the pressure is restored ithin 20 to 30 seconds (which the engineer can observe in front of him), the engineer can then manually move the handle and go back into dynamic braking.