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ABOUT 3:25 P.M. A 1988 MACK TRUCK WITH A CONCRETE MIXER BODY WAS UNABLE TO STOP AS IT APPROACHED A "T" INTERSECTION AT THE BOTTOM OF AN EXIT RAMP IN PLYMOUTH MEETING, PENNSYLVANIA. AS THE TRUCK PROCEEDED THROUGH THE INTERSECTION, IT COLLIDED WITH & OVERRODE A 1985 SUBARU PASSENGER CAR. THE SUBARU DRIVER WAS KILLED; THE TRUCKDRIVER SUSTAINED MINOR INJURIES. THE TRUCKDRIVER WAS UNRESTRAINED; THE SUBARU DRIVER WAS FOUND RESTRAINED IN HER VEHICLE. THE WEATHER WAS CLEAR & DRY. NO FIRE ENSUED, & NO OTHER VEHICLE OCCUPANTS WERE INVOLVED IN THE ACCIDENT.
THE NTSB RECOMMENDS THAT THE AMERICAN TRUCKING ASSOCIATIONS, INC.: NOTIFY YOUR MEMBERS THROUGH SOURCES, SUCH AS THE TRANSPORT TOPICES MAGAZINE, OF THE FACTS & CIRCUMSTANCES OF THIS ACCIDENT & IN COOPERATION WITH THE AMERICAN TRUCKING ASSOCIATIONS' MAINTENANCE COUNCIL, URGE YOUR MEMBERSHIP TO IMPLEMENT PROCEDURES THAT WILL ENSURE THAT AIR BRAKE MANUFACTURERS' SUGGESTED INSTALLATION, INSPECTION, & FUNCTIONAL TEST PROCEDURES ARE ADHERED TO DURING & AFTER MAINTENANCE ON TRUCK AIR BRAKE SYSTEMS.
Original recommendation transmittal letter:
Closed - Acceptable Action
Plymouth Meeting, PA, United States
Truck Loss of Braking Contol on Steep Downgrade and Collision with a Vehicle
Addressee(s) and Addressee Status:
American Trucking Associations, Inc. (Closed - Acceptable Action)
Safety Recommendation History
American Trucking Associations, Inc.
Thank you for Mr. Larry Strawhorn’s November 25, 1997, letter in response to the National Transportation Safety Board’s Safety Recommendation H-97-33. This recommendation was issued to the American Trucking Associations, Inc. (ATA) as a result of the Safety Board’s investigation of a concrete mixer truck’s loss of braking control on a steep downgrade and collision with a passenger car near Plymouth Meeting, Pennsylvania, on April 25, 1996. Safety Recommendation H-97-33 asked the ATA to notify its members through sources, such as Transport Topics magazine, of the facts and circumstances of this accident and, in cooperation with the American Trucking Associations’ Maintenance Council, urge its membership to implement procedures that will ensure that air brake manufacturers’ suggested installation, inspection, and functional test procedures are adhered to during and after maintenance on truck air brake systems. The Safety Board is pleased to learn that an article about the accident near Plymouth Meeting, Pennsylvania, and Safety Recommendation H-97-33 was published in the November 24, 1997, edition of Transport Topics magazine. We understand, furthermore, that the ATA has developed Recommended Practice 423 that designates colors for the air lines for each vehicle subsystem. Because of these actions and the commitment to publish additional articles concerning this accident in future issues of the ATA Maintenance Council’s newsletter and other ATA publications, the Safety Board has classified Safety Recommendation H-97-33 “Closed--Acceptable Action.” In regard to Mr. Strawhorn’s comments about ensuring the durability, reliability, and maintainability of split braking systems, the Safety Board will continue to stress the importance of improved technological development.
American Trucking Associations, Inc.
An article covering the accident and NTSB’s recommendation was carried in Transport Topics (copy enclosed). Additional articles will be run in forthcoming issues of The Maintenance Council’s newsletter and in other ATA publications. Further, in cooperation with The Maintenance Council of ATA, we have developed a Recommended Practice (RP 423) which designates colors for the air lines for each vehicle subsystem (copy enclosed). Because of maintenance problems and the fact air lines have been reverse-connected at the factory, RP 423 was written to help both motor carriers and vehicle manufacturers. The practice endorses using green lines for the primary brake system and orange for the secondary. It also makes recommendations for the color of the lines in the charging, parking brake supply, parking brake control, trailer supply, trailer control, and accessory systems. Further, the RP provides a numeric identification to be used for banding or marking line ends, thereby revealing their function (supply, delivery, exhaust, and control). The problems which led to the accident stem in part from the truck using a split brake system and two low air pressure sensors. This illustrates that redundancy can be dangerous. If the truck had been furnished with a single low pressure sensor connected to its wet tank, its failure would have been detected during vehicle inspections conducted before the accident. Either sensor in a system with two can cause the warning buzzer to sound during the standard test and by doing so hide the fact the other is inoperative. If, however, there is only one, its loss will not be masked since there is only one electrical path to the buzzer. The fact that the complexity of a system created to improve safety actually lead to an accident was not discussed in NTSB’s report of this accident. We believe the Board has missed an opportunity to discuss an important topic. Technologically new systems are appearing at an ever increasing rate and it is important that there be guidelines to assure their safe operation and repair. Many innovations show promise. However, unless new designs can be appropriately handled in the field, the tragic consequences of this accident are likely to be repeated. To be acceptable, any system must be maintainable with as low a degree of sophistication as possible. Because there are so many trucks, there is much safety to be gained in having them easy to fix and maintain. More complex and harder to repair components may ultimately not be “better” because proper rejuvenation is uncertain in an environment composed of persons with a variety of skill levels. Adding complexity (more pieces and parts) decreases system reliability. Also, the history of technological development indicates that introducing innovative systems breeds a plethora of misunderstood, unproven products in the market place. As the accident explored in this investigation shows, making a relatively simple arrangement complex can have serious consequences. Before split braking systems, with primary and secondary reservoirs and alternate air path plumbing, it was virtually impossible to miss-connect air lines and retain braking. Now, with the redundancy afforded by the split system, such mistakes can be made. We do not mean to imply that going to split braking systems was a mistake. Our point is that there were safety trade-offs in doing so. New technology should not be adopted without understanding its total impact on safety. From the consumer’s standpoint, we believe there are major flaws in the Federal Motor Vehicle Safety Standards (FMVSS). They require neither that systems function beyond what is necessary to show new vehicle certification nor that they be easily maintained.The Environmental Protection Agency (EPA) regulations for exhaust missions from heavy truck engines require manufacturers to certify that, with the maintenance specified, engines will meet the standards for 290,000 miles. DOT should adopt a similar approach with its rules, to assure that durability, reliability, and maintainability are paramount design considerations during development of the systems needed for compliance. Motor carriers believe that both the National Highway Traffic Safety Administration and the Federal Highway Administration Office of Motor Carriers should place a significant focus on maintenance difficulties in their safety regulations. Wear markers, indicators to facilitate proper reassembly, component identification in terms of both operational limits and parts numbers and access for inspection are all things which often get ignored and yet they play a major role in both how well equipment operates and how easy it is to quickly and accurately inspect and repair. Ignoring durability, reliability and maintainability can have tragic consequences as this accident demonstrated. We ask that NTSB raise these important considerations at every opportunity. This was a unique collision resulting from three unusual events: an airline drain valve was broken while the truck was being operated, one of two low-air pressure switches was inoperable, and the treadle valve air lines were reverse-connected. NTSB’s conclusion, that the vehicle operated safely for quite some time with the reversed air brake lines, indicates it took this special combination of circumstances to kindle the catastrophe. CVSA employs the North American Uniform Out-Of-Service Criteria for its inspections. Using the current document, the missing drain valve would have been discovered under item 1.h. Air Loss Rate. The faulty low air buzzer may have been detected during the examination for a Low Pressure Warning Device based on item 1 .g. While the Board contends that inspectors may have missed a single inoperable low air pressure warning switch, this conclusion is at best uncertain and complicated by the system complexities which we have already mentioned. In any event the inspections CVSA now conducts involve checking for two of the three failures that occurred prior to this accident. One method of testing a truck without a front axle relay valve for miss-connected primary and secondary brake lines at the treadle valve is to: 0 stop the engine, 0 close the tractor protection valve (if so equipped), l release the parking brakes, l drain air from the wet tank and check for backflow from the service reservoirs, 0 if no backflow, make a series of brake applications and observe the pressure gauge(s). 0 if the green pointer (primary pressure) falls much faster than the orange pointer (secondary pressure) the primary/ secondary lines are probably crossed. Performing such tests at the roadside will take a great deal of time, during which vehicles which might otherwise have been inspected will be turned away. It is our belief that having on-highway inspectors look for more common and easily detectable problems on more trucks is a better use of their time. It is hoped that the information provided will help you to understand ATA’s view on the issue at hand. Please feel free to contact me if you have further questions.
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