FENZ began an investigation after the truck - which had been on its way to the garage for checks after failing the night before at the station, but was called to the fire instead - froze up for 5-10 minutes, forcing firefighters to change tactics.
The fleet manager said the truck did not create "a serious risk" to operators.
Investigator Joe Stanley, who worked on the Newtown truck that broke down at Kilbirnie for several years till shifting to Christchurch, said the opposite.
"It was terrible," he said.
Firefighters had nicknamed the truck 'Christine', after the killer car in a Stephen King horror novel.
"I can't in good conscience be an investigator on an appliance failure of this nature, knowing that this appliance has failed many times in the past and then have all the information that we've provided FENZ just swept under the carpet," he told RNZ last night.
It is highly unusual to have an investigator speak up this way, and Stanley said he did fear it would hurt his career, but added:
"It's the public that's at risk, but it's also my friends, my colleagues, my mates who are operating this appliance who could be put in danger.
"So I feel like I'm compelled to, to bring this information out."
FENZ said in a statement the investigator should not be speculating while the draft report is going through the usual internal review and consultation.
"Fire and Emergency New Zealand takes the safety of our firefighters very seriously," it said.
"It is inappropriate for any party to speculate about the investigation or the draft report while that process is ongoing.
"It is disappointing to hear a member of that investigation team is doing just that through the media."
Stanley is on a three-person investigation team that includes other qualified investigators from FENZ management and an independent.
They had all signed off on the damning final report in April, he said.
He was then told by one of them, that FENZ had asked the other two investigators to rewrite the report without him.
"There was going to be a meeting held with those two investigators, without me, to talk about what the report should look like. And then to compel them to change the report.
"And that was going to exclude me specifically."
He had not heard from FENZ and did not know if the rewrite was going ahead.
"They want to hide the issues that we've raised with the systemic failures within our fleet management system that have allowed this particular accident to happen, and have been ongoing for a period of time that have allowed previous accidents to happen as well."
FENZ also wanted the report split in two, to keep wider fleet management issues separate from the Kilbirnie analysis, he claimed.
"So that the fleet management team can rewrite their side of the report, and then for a very brief outline of the health and safety issues.
"My fear is that they'll try and blame the firefighters again."
The original terms of reference did just that, Stanley, an investigator of seven years, said.
"The initial Terms of Reference was an attempt to put the blame of the appliance not working properly, squarely on the operators who attended ... to assert that they had put the appliance in the wrong place, or they had undertaken the wrong actions when they first saw the fault occurring in the appliance."
In fact, the final report found they took care to park farther from the fire, in case the truck broke down - which it did.
The report found real weaknesses in how the country's firetruck fleet is managed - but did not lay blame, he said.
One recommendation in it was for proper, joined-up breakdown and repair logs that, he said - for a fleet worth hundreds of millions of dollars.
"The report talks about issues with fault-logging for firefighters, operators and officers ... and the inability for there to be transparent access.
"There is no way for firefighters to tell whether any of the faults that they've logged have been fixed or not."
Similar recommendations arose from a 2017 investigation into a cage failure on the same Newtown truck. The email trail showed FENZ had trouble locating that report.
Other recommendations from Kilbirnie covered:
- Better training because some firefighter traning on big ladder trucks is out of date
- Getting the latest training material from manufacturers when new trucks come in
- Better manufacturer training of the service agents to keep the trucks running
Stanley speculated that the "serious fiscal implications" of bringing the firetruck fleet up to standard was behind the pushback which was unlike anything he had experienced.
"There may be reputational issues for many of the people have been involved in the purchase, maintenance and the continuing operation of this, from a fleet perspective," he added.
"And at the moment, those within the organisation who are responsible for ensuring we have fit-for-purpose vehicles ... are trying to cover themselves from accountability."
