A fault in the tram control valve of the machines has been known to cause the machines to continue travelling forward or in reverse after the lever has been reversed.

The fault seems to occur when tramming the machine, where one of the levers does not return to centre after being released causing the machine to move forward or pivot without activation by the operator.

While the cause of the fault is being investigated, JH Fletcher's risk management department has urged anybody using the machines to thoroughly check its hydraulic levers at the tram deck, positioning and drilling controls to ensure they are in the neutral position before energising the hydraulic system.

Operators are then to inspect the valve bank assembly, check oil levels and change oil filters regularly, alert all staff to the potential problem and ensure that no personnel are standing between the machine and rib during tramming.

While the occurrences of the sticking lever are not common and have not resulted in injury or death, JH Fletcher is urging all operators of the potentially faulty machines to be cautious and said a recall of the machines will be decided once the cause of the fault has been determined.