Whakapapa ski field is defending its maintenance processes after a woman was badly hurt when a T-bar broke this week.
The woman was riding the Valley T-bar lift on Tuesday when her seat separated suddenly from the overhead cable, causing her to fall and slide five metres across the snow.
She suffered a broken leg.
A T-bar is a surface lift that can tow one or two people up a slope.
A spokeswoman for ski area operator Ruapehu Alpine Lifts (RAL) said the connection between the T-bar seat and the grip on the overhead cable had disengaged as a result of a worn thread.
She said an investigation into the incident had been launched and all three T-bars operating at Whakapapa had been immediately checked.
"This included reviewing the daily pre-checks done by both maintenance staff and lift operations staff on all T-bars," the spokeswoman said.
She said the investigation was ongoing.
"However, in the interim we have introduced a stronger test and inspection process to ensure that any worn components are replaced before the unit is available for public use."
RAL wouldn't release any other details about the woman, including her age and nationality, citing privacy concerns.
Sam Clarkson, owner of the Edge to Edge ski rental shop in Whakapapa Village, said the T-bar failure was the result of a lack of maintenance resources on the mountain.
"We're not blaming the maintenance department for it, because those boys are under-resourced ... and under-paid and under-appreciated," said Clarkson, who is one of RAL's more than 4000 shareholders and vocal critic of the company.
"It's a system that's running backwards or barely maintaining itself because of budget constraints."
He said T-bar failures like Tuesday's were not uncommon.
"If they had a proper maintenance programme then that wouldn't happen at all," Clarkson said.
The RAL spokeswoman confirmed that T-bars had broken in a similar manner on other occasions.
But the company's long-serving chief executive, Dave Mazey, had no recollection of anyone being injured before, she said.
The spokeswoman said the failures were not the result of poor maintenance resources.
"Safety of our customers is paramount."
RAL chairman Murray Gribben told shareholders at the firm's annual meeting last month
that a lack of infrastructure investment had been impacting the performance of the company, which also operates Turoa ski field.
"We are now at the point where it is proving difficult to source some parts for our older lifts and when we do they take some time to get to the mountain," he said.
"The board realises that the current operating model is not sustainable. The financial results over the past few years are a key indicator of that."
The Valley T-bar was installed in 1981.
"The age of the lift did not contribute to the accident," the spokeswoman said.
A new express quad chairlift at Whakapapa, which runs from the base area up to Hut Flat, began operating this winter.
RAL is also planning to install another quad chairlift on the upper mountain this summer, which will replace one of its ageing T-bars.