Commercial Vehicle Investigation Unit officer Jeff Fleury, of Dunedin, said he expected to finish an inspection of the braking system and mechanical components of the 1986 Volvo bus by last night.
"We're lucky everything is intact. It's usually fairly straightforward to see where something has gone wrong once the inspection is carried out," he said.
The crash endangered the lives of about 40 University of Otago Selwyn College hostel students who were on a weekend skiing trip.
The Otago Daily Times understands brake failure was not the cause of the accident.
Eight people, including the driver, were taken by ambulance to medical centres in Wanaka and Queenstown for treatment to their injuries, described as moderate to minor.
Passenger Transport's Dunedin fleet maintenance manager, Kayne Baas, has declined to speculate on the likely cause of the Cardrona crash, but said he did not believe a mechanical fault was to blame as the bus had recently been serviced.
Mr Fleury, a non-sworn police officer, said a vehicle crash was typically the result of one of three causes.
"Every crash has three elements: A driver, a vehicle, and the environment."
Driving conditions on the 14km descent of Cardrona skifield's twisting, gravel road were fine, dry, and sunny at the time of the accident.
Mechanical component inspections typically focused on braking systems, which in this case was an air brake system.
The bus had an up-to-date certificate of fitness, he said.
Land Transport New Zealand officer Warrick Andrews, of Invercargill, is helping Mr Fleury with the investigation.
His focus is on ensuring vehicles were appropriately maintained before the incident.
Mr Fleury said he expected to be able to present a report to Wanaka police in the next couple of days.
The CVIU might then decide to interview the driver, he said.
