The Civil Aviation Authority says it could take up to a year to determine the cause of a light plane crash that killed the chief executive of mobile company 2degrees and his wife off the coast of Raglan.
Navy divers recovered the bodies of Eric and Kathy Hertz, aged 58 and 64, and most of the wreckage of their twin-engine plane at the weekend.
The couple took off from Auckland and were travelling to Timaru when their twin-engined Beechcraft Baron crashed into the sea on 30 March.
CAA spokesperson Mike Richards said on Monday the investigation may involve sending parts of the wreckage overseas or calling in specialists, and it is unlikely to find quick answers.
Mr Richards said that if investigators find anything alarming they will let the aviation industry know straight away.
Police said the wreckage is being taken to Auckland for the CAA investigation.
Meanwhile, a private memorial service for Mr and Mrs Hertz's family, friends and work colleagues will be held at the Auckland University of Technology on Thursday.