'Really sad situation': Hire firm's trailer modification led to fatal crash

She was the aunt who organised everything, the much-loved mum and family matriarch who kept everyone in line and always had advice when needed.

When 35-year-old Mandy Rita Mackenzie’s life was cut short in a head-on crash, it appeared to be another devastating road tragedy.

But investigators would trace the disaster back years, uncovering a modification to a hired trailer that altered its balance and set in motion the events that killed the beloved mother, friend and nurse who touched many lives.

Kerikeri Tool Hire 2015 has now been ordered to pay more than $470,000 in fines and reparation to the loved ones Mackenzie left behind.

“This is a really sad situation,” Judge Brandt Shortland said at the start of the company’s sentencing on Monday at the Kaikohe District Court.

On December 28, 2024, Mane Adams hired a trailer and mini loader from the company for work at his property.

After finishing, he loaded the machine onto the trailer and began the 8km trip to Kerikeri Tool Hire.

Travelling at 70km/h in a 100km/h zone, he headed south towards Waipapa Stream bridge around a sweeping left-hand bend.

The trailer began to fishtail, crossing the centre-line and colliding head-on with the vehicle driven by Mackenzie.

Her husband and four other passengers were also in the car.

Mackenzie, a mother of three boys, died at the scene. Several passengers sustained injuries, including one who needed multiple surgeries.

Adams suffered minor injuries.

WorkSafe launched an investigation after the Serious Crash Unit conducted a re-enactment of the crash and noticed irregularities in a comparison.

The investigation found the trailer had been modified about five years earlier, with ramp-locking bars extended to allow the mini loader to sit further back on the deck.

WorkSafe said the changes affected the trailer’s balance and load distribution, preventing the loader from being positioned in a way that achieved adequate tow-ball downforce.

The result was a shifted centre of gravity that left the trailer unstable under normal driving conditions and more prone to fishtailing.

Kerikeri Tool Hire told WorkSafe the work was carried out by an on-site mechanic whose background was in welding.

Underinflated tyres were identified as a secondary factor, however, WorkSafe said even if they were inflated correctly the downforce pull would have remained.

Mandy Mackenzie was described as a warm wife, mother, friend and aunt who always organised family events.

Kerikeri Tool Hire was charged in 2025 with exposing individuals to risk of harm and pleaded guilty this year.

“It was reasonably practicable for Kerikeri Tool Hire to have ensured that the trailer hired to tow the mini loader was safe or safe to use,” WorkSafe lawyer Alexandra Simpson said.

Kerikeri Tool Hire’s lawyer Ellie Harrison began by acknowledging Mackenzie and the loss to her family and community.

She said her client had no intention to operate unsafely but the accident highlighted a bigger issue.

“No particular qualification is required to hire or tow a trailer and heavy machinery; anyone with a driver’s licence can do so,” Harrison said.

“The tragedy partly demonstrates that failure to regulate.

“When Kerikeri Hire was reflecting on their legal responsibilities, some further guidance from NZTA would have been helpful and it may be time for NZTA to act whether through licencing or mandatory checks.”

Harrison suggested the issue could be considered further by the coroner.

Judge Shortland said the impact on all victims could never be measured in human form, something highlighted in the victim impact statements he had read.

“Whenever there is a death involved it is tragic for all involved from the family and the knock-on effect can never be measured,” the judge said.

“In the same token, it is also very difficult to try and measure that harm in any way in a form that is acceptable to all and the court’s required to find that balancing act as best as possible.”

Judge Shortland acknowledged the company had fully co-operated from the beginning and entered a guilty plea early.

“I say that as there are often many cases where WorkSafe are prosecuting potential cases that they do not get the co-operation and compliance from those who are being investigated that’s not uncommon in many respects.

“This is a company that is prepared to pay reparation.

“There is genuine remorse that has been expressed through everything that’s been provided to the court from this company and they have a previous good record, they have not been in the courts before.”

Kerikeri Tool Hire was fined $140,000 and ordered to pay $333,833 in consequential and emotional loss reparation.

WorkSafe regional manager Brad Duggan said there were lessons to be learned following the tragedy.

He urged businesses that hire out equipment to look at what was being supplied, how it has been modified, and to act before someone is hurt.

“A family has lost a mother and a wife, and another has been left with serious injuries, in a tragedy that could have been prevented.

“When a business changes a piece of equipment and then hires it out, it takes on responsibility for making sure it is safe for the people who use it and everyone else they encounter while it’s being used.”

Shannon Pitman is a Whangārei-based reporter for Open Justice covering courts in the Te Tai Tokerau region. She is of Ngāpuhi/Ngāti Pūkenga descent and has worked in digital media for the past five years. She joined NZME in 2023.