It has been downgraded from 10.7 million tonnes to 9.8-10Mt.

Changing conditions have led to a revision of a recovery plan timetable, which now envisages a return to longwall production in two to three weeks.

Whitehaven CEO Paul Flynn said: “We are confident that the recovery plan currently being executed will deliver a return to production in the indicated timeframe.

“All necessary resources have been committed to resolving the issue expeditiously and the Narrabri team is being supported by the appropriate external service providers.”

Mining in the third longwall panel at Narrabri started on schedule early last month and was ramped up to full production.

The configuration of longwall panel three installation differed to that of longwall panels one and two, in that two additional roof supports were added to the tailgate end of the longwall.

This modification was made to improve safety and reduce costs by eliminating the need to install additional secondary support in the tailgate roadway as had been installed in longwall panels one and two.

As the longwall retreat progressed with this revised configuration, the floor horizon control at the tailgate end of the longwall face-line was “lost”, resulting in a difference between the floor levels of the longwall face-line and the tailgate development roadway.

At this point, management decided to stop production.

Following an evaluation of the status of the longwall by management, external advisers and OEM support, a recovery plan was developed and implemented.

It was expected that the recovery plan would be completed safely within a timeframe so as not to impact the company’s ability to meet forecast ROM production of 5.5Mt (100% basis) from the Narrabri mine. However, with the revised recovery plan, Narrabri’s ROM coal production on a 100% basis for FY2014 has been reforecast to be in the range of 4.8-5Mt.

The costs of the recovery plan are not expected to be material, the company said.

“Appropriate controls to mitigate a recurrence of this event have been implemented and discussions are continuing with the longwall supplier about control systems for consistent horizon control when cutting the tailgate end of the longwall face.”