The movements were found on several Caterpillar 988G.H model wheel loaders. The specific unit involved in the accident, when tested at about 25 degrees Fahrenheit, had abnormal operation.

“During raising of the loader arms, the arms would continue to rise after the lift control was released,” the US Mine Safety and Health Administration (MSHA) said.

“When the operator tried to feather the arms down, the bucket would drop several feet.”

The agency said Caterpillar had developed new machine warm-up procedures to address the problem and was asking operators to contact their local Cat service dealer immediately for more information.

MSHA reminded mines of the risk to personnel when lifting or lowering objects with anyone in the immediate area, as it posed a risk that the bucket would drop the object and injure personnel.

Also, when loading trucks, MSHA said, the bucket dropping might cause significant equipment damage and could jolt or injure the truck driver.

Until a fix is determined, officials urged the implementation of administrative controls to address the hazards, which included:

• ensuring the hydraulic fluid is warm per CAT’s operating manual
• ensuring the operation of the bucket is checked before the machine is put into production work
• ensuring all personnel are clear of the machine when it is operating
• truck operators must remain in the truck cab or a safe distance away while it is being loaded
• ensure equipment operators are fully trained in the equipment they operate.

Also, MSHA said, if any machine, equipment or tool did not function as designed, it should immediately be removed from service and the manufacturer contacted.