Kiwirail says Aratere's auto-pilot button should never have been pressed.

The ferry ran aground  in June as it headed out from Picton.

An interim report from the Transport Accident Investigation Commission details how the crew didn't know how to turn off the auto-pilot as it steered the ferry towards land.

InterIslander Executive General Manager Duncan Roy says it was pressed in error, then no one could flick it off.

"They didn't know on the bridge, we didn't know on Interislander - working with the people that provided us this service right now, as we speak, to work out why we didn't know."

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