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NTSB warns about slack adjusters maintenance

The National Transportation Safety Board (NTSB) has adopted a final report of a runaway truck accident in Pennsylvania that has shown the consequences of improper maintenance on automatic slack adjusters for air brake systems.

"The warnings in existing materials available to owners, drivers, mechanics, and inspectors of air-braked vehicles equipped with automatic slack adjusters have not been successful in communicating the inherent dangers of manually adjusting automatic slack adjusters to correct out- of-adjustment brakes," the board said.

The board issued safety recommendations aimed at improving training for drivers and mechanics who work with air brakes.

The fatal accident in the Borough of Glen Rock PA occurred April 11, 2003, when the truck driver was unable to stop on a steep downgrade.

The NTSB determined that the probable cause of the accident was the lack of oversight by the truck's owner, which resulted in an untrained driver improperly operating an overloaded, air brake-equipped vehicle with inadequately maintained brakes.

Contributing to the accident was the misdiagnosis of the truck's underlying brake problems by mechanics involved with the truck's maintenance. Also contributing was a lack of readily available and accurate information about automatic slack adjusters and inadequate warnings about safety problems caused by manually adjusting them, the NTSB said.

The 21-year-old driver received no training on how to drive an air brake-equipped vehicle. This is important because air brakes on trucks operate differently from hydraulic brakes on passenger cars, NTSB said.

The board found that mechanics who worked on the truck and the driver who worked on a truck involved in a similar accident that occurred in California in 2003 did not look for underlying problems with the slack adjusters or other brake components; consequently, they misdiagnosed the brake problems, probably because they were not properly educated on the function and care of automatic slack adjusters and how they relate to foundation brake systems.

The safety recommendations by the NTSB address training or regulations concerning air brake-equipped vehicles, and were sent to the Federal Motor Carrier Safety Administration, state governments, the Commercial Vehicle Safety Alliance, automatic slack adjuster manufacturers, manufacturers of vehicles equipped with air brakes, the National Institute for Automotive Service Excellence, and several publishers of study guides.

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