Man in fatal crash off bridge probably fell asleep - coroner

File photo / NZ Herald

A distinguished mathematician who died when his car crashed off a bridge in south Westland probably fell asleep at the wheel, a coroner has found.

Charles Edward Miller Pearce, died on June 8, 2012, after his rental car drove through a wooden bridge railing on the Manakaiaua River, about 20km south of Fox Glacier.

The 72-year-old, originally from New Zealand but a resident in Adelaide since the 1960s, had flown into Christchurch Airport and then on to Hokitika Airport, where he picked up a rental car and drove towards Haast.

The University of Adelaide mathematician, who had also published a book with his wife, Frances Pearce, on Pacific pre-history, was on his way to Mahitaki (Bruce Bay) to speak to Maori about a survey of the bay to find evidence of early settlements. He was also due to give a talk in Christchurch four days later.

His car was found upside down in the river by a passing motorist about 12.20am.

Mr Pearce was belted into the driver's seat upside down, with his head immersed in water.

A post-mortem examination found he had suffered only minor external injuries, and died from immersion and probable drowning.

No mechanical problems were found with the vehicle.

Coroner Ron McElrea found the circumstances of the crash were consistent with Mr Pearce having fallen asleep at the wheel and losing control of the vehicle.

He could have also suffered a medical event, but there was no evidence of this in the post-mortem examination finding, despite a finding of hypertensive heart disease.