Page:NTSB - Railroad Accident Report - Derailment on May 25, 1989.djvu/54

From Wikisource
Jump to navigation Jump to search
This page has been proofread, but needs to be validated.


Each of the SP cars was equipped with an "empty load" (EL) device. When the car is empty, this device reduces the brake cylinder pressure to prevent the wheels from sliding. According to timetable instructions in effect at the time of the derailment, loaded cars with empty load devices were to be considered the equivalent of one and one-half cars in determining tons per operative brakes (see Southern Pacific’s Method of Operation). The chief mechanical officer for SP testified that the SP cars with empty load devices, had a "normal braking ratio of 1." He further testified that at the time of the train derailment, the operating rules had not been changed to reflect this. The DRGW cars were not equipped with EL devices. All 69 hopper cars were equipped with composition brake shoes.

Following the derailment, many wheels and brake heads were inspected. This was a random inspection of available parts because many parts were buried and almost none of the parts could be identified as belonging to any particular car or part of the train. Of a possible 552 brake heads on the train, 160 were examined with the following conditions noted: 36 had been burned away, 102 showed signs of heavy heat and excessive braking, and 22 showed light or no signs of excessive braking although most of these showed signs of service wear. According to SP’s chief mechanical officer, some showed no signs of heavy braking because of "…the variation in the brake shoe thickness, the thickness of the wheels…and braking forces. They are not exactly the same on all cars." He further testified that braking forces are not evenly distributed even on one car. Of a possible 276 wheel sets, 142 were inspected of which 109 showed obvious evidence of overheating from heat buildup by excessive or heaving braking. The chief mechanical officer testified that based on SP’s postaccident inspection of the wheels and brake heads, he believed that the brakes on Extra 7551 East were effective and that the brake pipe was intact.

Locomotive wheels and brake shoes showed heaving braking and heat on every unit. Some brake shoes had been burned away and the backing plate had begun to melt.

Mechanical Information

Use of Dynamic Brakes.—According to the Associirtion of American Railroads’ Director of Safety and Operating Rules, many Class I railroads emphasize the use of dynamic brakes to control a train, thereby conserving fuel and minimizing brake shoe wear. Rule 58F of the SP Air Brake Rules and Train Handling Instructions states, "The dynamic brake must be used whenever practicable in reducing and controlling train speed.…" Rule 58I further states, "Where the available dynamic brake will not properly control the speed of the train, the automatic air brakes must (then) be used to an extent which will allow the dynamic brakes to be reduced to a value where it will be flexible enough to control changes made in speed due to physical characteristics of the road." The Safety Board is aware that similar rules exist on other railroads. Rule 501B of the Burlington Northern Air Brake and Train Handling Rules states:

Train handling must be performed in a manner that will be most fuel efficient consistent with good train handling. Therefore, maximum