Air Brake Accidents

Deadly accidents caused by defective truck brakes are preventable.  Maryland class A commercial driver’s licenses require drivers to demonstrate that they know the safety rules for air brakes.  Many trucks use air brakes. A typical passenger car uses hydraulic fluid to activate disc brakes. A car’s braking system uses hydraulic fluid in a chamber. Pressing the brake pedal pumps the hydraulic fluid through hoses into a piston that presses two brake shoes against a brake pad or rotor. If a brake hose develops a leak the hydraulic system will fail. Most large commercial trucks and buses use air brakes to avoid this type of failure.

Most large commercial trucks and buses use the foundation air brake system. Unlike a car’s braking system, the starting position or resting position for truck brakes is that they are activated. The truck uses air lines or brake pipes to build up air pressure. This built-up air pressure causes the brakes to release. If the tubes develop a leak the brakes activate and that is safer than the brakes failing. The air that feeds the brake lines is stored in a compressor tank. When the brake pedal is pressed compressed air is released from the tank causing the brakes to return to their activated position.  The release of this air produces the sound that trucks make while braking.

Pre-trip inspections require drivers to perform an airbrake test to ensure that the system will operate safely. A typical airbrake test involves the driver building the pressure to 120 psi in the air tanks. Once 120 psi is reached, a governor cut-off will release air so that there is not too much pressure in the system. Following that, drivers perform a leak test which involves holding down the brake to ensure that no more than 3 psi is lost per minute. The next step involves fanning the brakes to 55 psi to ensure that the low-pressure warning on the dash is working properly. A driver must then continue to fan the brakes until the valves inside of the cab pop out, locking the brakes to the cab, as well as the trailer. Finally, once completed and the pressure is built back up, a driver accelerates the truck to 5mph applies the brakes and listens for any sounds consistent with a defect, and to verify that braking does not pull the vehicle to a side.

AIR BRAKES MUST BE PROPERLY CALIBRATED

The mechanism used by air brakes involves compressed air causing the brakes to release. When the compressed air is released, a pushrod pushes a brake s-cam. The s-cam pushes the brake shoes outward inside of a brake drum. The brake drum is a hollow drum inside the wheel. As the brake pads are pressed against the drum, the truck slows to a stop. 

The air brake system must be properly adjusted and have adequate air pressure. If the push rod and s-cam are out of adjustment the brake pads may not fully engage against the brake drum. Brake pads that are lightly pressing against a brake drum produces very little stopping power but a lot of heat. A truck tire on fire is a sign of an improperly adjusted braking system. Improperly adjusted brakes press against a brake drum with enough force to create to friction and heat but braking force is decreased.  This results in the brake drum becoming hotter and hotter, particularly with heavy trucks descending steep mountains.  In some cases the brake drum becomes hot enough to result in the tire failing and catching fire.

The proper application of brakes is a driving skill. Drivers are taught methods to avoid overheating their brakes. When descending steep mountains, there are often lower speed limit signs for trucks. A driver is taught to drive at 5mph below the lower speed limit. Once the driver hits the safe speed, they are supposed to let off the brake until they reach the speed limit again. Once they hit the speed limit, they can apply the brakes again. This method of fanning the brakes helps to control the speed and temperature to avoid brake failure. Failure to do so, could lead to the brakes overheating and failing.

Similar problems occur if the air pressure system has leaks or is improperly calibrated. If an air compressor can’t keep up with leaks in the system, the brakes will not fully disengage. This generates heat as described above. A tire that catches fire is a symptom of this problem, but the real danger is insufficient braking power. A poorly maintained braking system may work fine while driving on level roads, but problems arise when trucks require greater stopping power as they descend steep hills or mountains.

Section 393.40 of the Federal Motor Carrier Act Regulations requires brakes to be properly adjusted.

STANDARD VEHICLE INSPECTION REPORTS REQUIRE BRAKE ADJUSTMENT MEASUREMENTS

Vehicle Inspection Reports Record Brake Adjustments

A Department of Transportation approved vehicle inspection report for a truck with air brakes has a brake adjustment section. The brake adjustment section documents how far out of adjustment each push rod stroke is per brake chamber.  There are different types of brake chambers that have different acceptable measurements that are contained in the Federal Motor Safety Carrier Act regulations.  Some trucks have devices to minimize the braking force on the front brakes. This prevents the front brakes from engaging with greater force and effectiveness than the rear brakes. This prevents the tractor stopping or slowing more abruptly than the trailer a frequent cause of jackknifing.

Under current regulations most commercial vehicles must be equipped with a warning signal to alert the driver when a failure occurs in the truck’s braking system.  These warnings apply to commercial vehicles with hydraulic brakes, air brakes, vacuum brakes and hydraulic hybrid braking systems.  Performance standards for brakes are detailed in the regulations.  In serious truck accidents involving a brake failure or lack of braking performance it is important to reach out to a Board-Certified truck accident lawyer before valuable evidence is lost.  A truck accident lawyer can secure the involved truck for an inspection.  In addition, a lawyer can identify the records that should be preserved while you are recovering from your injuries.  If steps are not taken to preserve these records, they may be destroyed by the trucking company.