The setback comes weeks after PPK declared that all safety issues with the machine’s throttle pedal were fully resolved by late March.

In an alert dated May 4 (reference document number SB15005), PPK said the Myuna mine reported an incident of a coal tram experiencing uninitiated engine response.

“A previous upgrade to the accelerator pedal position sensor (refer to SB15003) has been undertaken by PPK,” the original equipment manufacturer said.

“This is not within the scope of the current investigation.”

While the cause is not yet conclusively identified, PPK has identified a need to improve inspection and maintenance regimes and consequently reviewed the routine service sheets for the Coaltrams.

“Compromised connections, including missing Ingress Protection connector seals and weather boots, have been observed in multiple locations on the machine,” PPK said of the Coaltram which had the incident. “This may be a significant contributing factor.”

However, PPK said a random fault with an electronic control unit was the most likely cause of the symptoms reported.

PPK’s investigations are still ongoing. In relation to the previous issues with the Coaltrams, an industry source told ICN that the primary safety failure related to how the electronic throttle would get stuck on “full throttle” when it got wet.

The safety alert also listed what to do if an uninitiated engine response including high engine revs per minute occurred on a Coaltram, which mainly involves using braking and engine ceasing mechanisms, plus outlined the additional site risk assessment requirements in relation to the issue.