KiwiRail has been charged over the loss of power incident involving an Interislander ferry last year.

As the Kaitaki approached Wellington Harbour on January 28 amid heavy seas it lost power and drifted near rocks southwest of Sinclair Head in Cook Strait.

A mayday was issued with over 800 passengers and 80 crew on board. After regaining limited power, the ferry made its way into port where passengers were able to safely disembark.

KiwiRail at the time said a faulty cooling system caused all of the ferry’s four engines to shut down.

The Transport Accident Investigation Commission had found KiwiRail had not followed the advice of the manufacturer of safety-critical rubber expansion joints. The failure of the part meant the engines were unable to be restarted safely after the ship lost power.

Following an investigation Maritime NZ laid one charge this week under the Health and Safety at Work Act 2015 against operator KiwiRail.

Maritime NZ director Kirstie Hewlett said the investigation involved reviewing the operator’s “organisational information” relevant to processes and procedures connected to safety and maintenance management, undertaking interviews and examining the Kaitaki after the incident occurred.

“Material was then comprehensively reviewed before the decision was made to prosecute.”

KiwiRail said it has been advised of the Maritime NZ decision to prosecute.

“We assure all our passengers and staff that their safety is and will always be our highest priority,” chief executive Peter Reidy said.

“The safe and reliable operation of the Interislander service is an absolutely non-negotiable requirement for KiwiRail Board and management. Following the Kaitaki incident, we conducted a full review of all of our asset management practices, using global experts to ensure we are running the Interislander to world’s best practice standards.”

The maximum penalty is $1.5m.