John Beckenridge, a Swedish-born helicopter pilot, breached a court order when he picked up his 11-year-old son Mike Zhao-Beckenridge from James Hargest College on March 13, 2015.
Six weeks later police dragged the wrecked vehicle from the water.
The bodies were never found and rumours that Mr Beckenridge staged their deaths have swirled ever since.
Police have failed to solve the mystery and it has been confirmed that it will be the subject of a coronial inquiry at the Christchurch District Court in May and June.
It is scheduled to run for two weeks.
Five years after the disappearance of the duo, Mike’s mother Fiona Lu told The New Zealand Herald she was convinced her boy was still alive.
“I miss him deeply and I am hopeful he will return. I love him,’’ she said at the time.
The couple later moved to Queenstown but their relationship broke down in 2014, shortly after Ms Lu moved to Invercargill to begin a hairdressing course.
While police had followed up on potential sightings of Mr Beckenridge and his son in New Zealand and overseas, their inquiries proved fruitless.
In 2017, international child-abduction expert Col Chapman said the evidence led him to strongly believe they had fled the country.
