One of the 13 defendants accused of health and safety breaches in the lead up to the deadly Whakaari eruption has pleaded guilty and been ordered to pay more than a quarter of a million dollars.

Inflite, a scenic flight operator based in Auckland, changed its plea to guilty today.

Judge Evangelos Thomas fined the company $227,500 and ordered it to pay prosecution costs of $40,000.

There were 47 people on the volcano when it erupted in December 2019, most of them international tourists.

Twenty-two people were killed and many others were seriously injured.

The others charged were: the island's owner Whakaari Management Limited and its directors Andrew, James and Peter Buttle; GNS Science; the National Emergency Management Agency; White Island Tours Limited; Volcanic Air Safaris Limited; Aerius Limited; Kahu NZ Limited; I D Tours New Zealand Limited; and Tauranga Tourism Services Limited.

The remaining 12 defendants have all pleaded not guilty and a four-month trial has been set to start in July 2023.

Inflite did not operate the tours itself, but promoted and sold tour packages to the island off the Whakatāne coastline.

The day of the eruption, Inflite operated a tour to Whakaari using Kahu as the tour provider. However, no Inflite tourists were on the island when it erupted as they returned shortly after midday.

Judge Thomas told the court at an earlier sentence indication hearing it was only "luck" that Inflite did not have customers on the island at the time of the eruption.

WorkSafe lawyer Steve Symon told the court that at the time Inflite failed in its obligation to ensure adequate risk assessment and provide clear communication on the risks to its customers when booking.

Inflite's lawyer Alistair Darroch argues its role was as a "ticketing agency" and the obligation fell on those contracted to do the tour.

He maintained the company was entitled to rely on GeoNet's risk assessments.

However, today Darroch said the guilty plea was in recognition of the business's shortcomings.

"It is appropriate for all those involved in the island to reflect on what happened and look at what might have been done better.

"Inflite had a limited and specific role in the island. It acknowledges it did not do all it should have done and its guilty plea is a recognition of that.

"It regrets it did not achieve the high standard it attempts to in all its operations."

Judge Thomas said today, Inflite failed to ensure reasonably practical steps were taken.

"The failures it has pleaded guilty to are that it failed to undertake an adequate risk assessment, or implement itself, appropriate controls to ensure the health and safety of tourists to Whakaari.

"This includes a failure to ensure that its subcontractors were ensuring the health and safety of its customers."

He said Inflite failed to monitor and review known hazards after the changes in volcanic alert levels.

"Thirdly it failed to ensure there was adequate risk information was available to its customers so that its customers could make an informed decision, whether or not, to go on the island."

The charge carried a maximum penalty of $1.5 million.

The summary of facts

The summary of facts said Inflite did not have a safety management system or any safe operating procedures for conducting guided tours on Whakaari.

The summary also said Inflite did not provide adequate safety information to tourists, at any stage of the booking and tour process.

It said Inflite's PPE for tourists, including gas masks, was "inadequate".

"They did not provide adequate protection against the high concentrations of hydrogen sulphide and sulphur dioxide on Whakaari. The masks were also 'one size fits all' yet did not fit all face shapes, people with small faces or those with beards."

Just before the volcanic eruption on December 9 2019, Inflite operated a tour to Whakaari using the helicopter business Kahu NZ as the provider.

The group spent an hour and a half on the tour and returned to Whakatāne shortly after midday.

-RNZ/Leah Tebbutt.