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16Emergency Brake Fails To Engage - Off Highway Dump Truck

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Brief Description of Incident/Accident & Description of Consequences/Outcomes:

The service/retarder brake system of a 35 tonne payload dump truck failed while it was descending along a quarry haul road. The driver operated the emergency/secondary brake lever but failed to stop the truck. He eventually stopped the truck by steering into a stockpile. The incident was potentially fatal. Extensive investigation after the incident revealed no defects in the emergency/secondary brake system.

Identified Root Causes:

The failure of the emergency/secondary brake was likely to have been caused by incorrect operation of the actuating lever. During the run-away, the driver was trying to keep the vehicle on track while at the same time using the left hand to operate the actuating lever. The lever needs to be moved completely to the down position and HELD in that position to effectively engage the control valve and thus operate the brakes. When the lever is released it springs back to its normal position bringing the brake control valve to the OFF position. It is a distinct possibility that the emergency/secondary brakes failed to come on because the lever was either not fully engaged or not held down.

Energy Type(s) Involved:

Imprecise information on operation of critical operator controls for emergency situations

Equipment Type(s):

CAT 769D Off-Highway Trucks

Root & Contributing Cause(s):

LTA competency

Stated or Potential Consequence(s):

Potential Fatality

Preventative/Recommended/Accepted Steps of Risk Mitigation, Points of Interest:

  • Make truck drivers fully aware of the correct method of operation and limitations of the braking system.
  • The Operating Manual states "should a service/retarder air system failure occurs, pull the red lever on the left hand side (emergency/secondary brake lever) all the way back for emergency application of all four wheel brakes". It does not say that the lever must be HELD down.
  • Investigate and pursue design improvements because of the high likelihood of operator error in this system coupled with the need to steer with one hand during emergency braking.
  • In an emergency situation, drivers may not HOLD the emergency/secondary brake lever down.
  • It is more difficult for the driver to control the steering with one hand in an emergency while holding down the brake lever for the emergency stop.
  • In later model trucks, a foot-actuated pedal mounted on the floor has replaced this lever. This allows the driver to steer with both hands while braking. Presently, there is insufficient information in Caterpillar literature about this improvement.
  • There is no information at this stage on any manufacturer's retrofits or modifications to the method of brake operation.
  • Check for previously published unrelated problem with brake levers
  • Manufacturer's had issued information in 1997 about an unrelated problem in CAT 769D and several other models of CAT quarry and off-highway trucks, where the set screws on retarder and the secondary brake levers could break off and disable the levers (Caterpillar Service Magazine Media Number SEPD0369-00 dated 4 July 1997). Users must check whether this has been addressed and if necessary, should contact Caterpillar or their agents for more information and advice.


Queensland Government Department of Employment, Economic Development and Innovation (DEEDI)


Here are the results.


Reference Type:

Safety Alert #47

Mine Type:

Any Mine Type


Potential & Kinetic - Mechanical





Australia, Queensland

ICAM Categories

Organisational Factors

• LTA training

Task or Environmental Conditions


Individual or Team Actions

• LTA competency

• LTA emergency response

• LTA work method

Failed or Absent Defences


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